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BRAlr:!' 


A  MANUAL 

OF   IHB 

ITOMY  OF  INVERTEBRATED. 
ANIMALS 

•H0MA8   H.  HUXLEY,  LL.D.,  F.K.S. 


LONBON 
fc  A.  CHURCHILL,  KEW  BUELINGION  STREET 


IS 


"7  ■  i  •   f -^ 


PBEFAOK 


Thb  pTMent  Tolnme  oa  the  Aaatoaj  of  Invertebnted 
AnimiJii  fnlflla  an  imdertakiiig  to  prodnM  a  IvwUm  on 
compantiTe  anatoiBf  for  itndemt^  into  whidi  I  entered 
tw>-aikd-tw«n^  jean  ago.  A  oonsideraUe  inatalment  of 
tlie  work,  rdating  lAoUj  to  the  Jawarfabrafa,  ^tpeared  in 
the 'Medical  Ttmea  and  Gaaette '  for  the  jrean  1866  and 
1857,  nnder  the  title  of  "Lectnrea  on  General  Natural 
Hiatorj."  Bnt  a  TSrietr  of  circimuUiioea  having  con- 
apired,  abont  that  time,  to  compel  me  to  direct  my  attention 
more  particnlarlj  to  the  Fertebrfita,  I  was  led  to  interrupt 
the  publication  of  the  "Lectures"  and  to  complete  the 
Vertebrate  half  of  the  propoaed  work  first.  This  appeared 
in  1871,  aa  a  'Uanoal  of  the  Anatomy  of  Tertebratod 


A  period  of  incapacity  for  any  aerious  toil  preveatad  me 
from  attempting,  b«£)re  1671,  to  grapple  with  the  immense 
mass  of  new  and  important  information  respecting  the 
atmcture,  and  especially  the  derelopment,  of  Invertebrated 
animala,  which  the  activi^  of  a  boat  of  inTestigators  has 
accnmolated  of  late  years. 

That  my  pn^neas  has  been  slow  will  not  surprise  any 
one  who  is  acquainted  with  the  growth  of  the  literature 
of  animal  morphology,  or  with  the  expenditure  of  time 
involved  in  the  attempt  to  veri^  for  onesdf  eren  the 
cardinal  facts  of  Uwt  science ;  bnt  I  ham  endeavonred,  in 
ibe  Uak  ohapter,  to  supply  the  moat  important  recent 


IT  PREFACE. 

additions  to  our  knowledge,  respecting  tbe  gronpe  treated 
of  in  those  wliich  have  long  been  printed. 

When  I  commenced  this  work,  it  was  mj  intention  t 
continue  the  plan  adopted  in  the  '  Manaal  of  the  Anatomy 
of  Yertebrated  Animals/  of  grring  a  summary  account  of 
what  appeared  to  me  to  be  ascertained  morphological  facts, 
without  referring  to  my  sources  of  information.  I  soon 
found,  howeyer,  that  it  would  be  incouYenient  to  carry  out 
this  scheme  consistently ;  and  some  of  my  pages  are,  I  am 
afraid,  somewhat  burdened  with  notes  and  references. 

I  am  the  more  careful  to  mention  this  circumstance  as, 
had  it  been  my  purpose  to  give  any  adequate  Bibliography, 
the  conspicuous  absence  of  the  titles  of  many  important 
books  and  memoirs  might  appear  onaccountable  and  indeed 
blameworthy. 

My  object,  in  writing  the  book,  has  been  to  make  it 
useful  to  those  who  wish  to  become  acquainted  with  the 
broad  outlines  of  what  is  at  present  known  of  the  morpho- 
logy of  the  Inveriehrata ;  though  I  have  not  avoided  the 
incidental  mention  of  facts  connected  with  their  physiology 
and  their  distribution.  On  the  other  hand,  I  have  abstained 
from  discussing  questions  of  etiology,  not  because  I  under- 
estimate their  importance,  or  am  insensible  to  the  interest 
of  the  great  problem  of  Erolution;  but  because,  to  my 
mind,  the  growing  tendency  to  mix  up  SBtiological  specula- 
tions with  morphological  generalisations  will,  if  unchecked, 
throw  Biology  into  confusion. 

For  the  student,  that  which  is  essential  is  a  knowledge 
of  the  facts  of  morphology ;  and  he  should  recollect  that 
generalisations  are  empty  formulas,  unless  there  is  some- 
thing in  his  personal  experience  whicH  gives  reality  and 
substance  io  the  tesmg  of  the  proporitCons  in  whioh  these 
generalisations  are  expressed. 


A 


CONTENTS. 


INTRODUCTION. 

PAOS 

The  General  Principles  of  Biology 1 

CHAPTER  I. 
The  Distinctive  Characters  of  Animals 42 

CHAPTER  II. 
The  Protozoa 76 

CHAPTER  III. 
The  Porifera  and  the  CoBlentcrata 110 

CHAPTER  IV. 
The  Turbellaria,  the  Rotifera,  the  Trcmatoda,  and  the  Cestoidea    176 

CHAPTER  V. 
The  Uirudinea,  the  Oligocheta,  the  Polychccta,  the  Gcphyrea   .    2U 

CHAPTER  VI. 
The  Arthropoda 200 

CHAPTER  VII. 
be  air-breathing  Arthropoda 371 

CHAPTER  VHI. 
The  Polysoa,  the  Brachiopoda,  and  the  Mollusca  .432 


Vm  CONTENTS. 

CHAPTER  IX. 

PAG] 

The  Echinodermata 54J 

CHAPTER  X. 
The  Tunicata  or  Asddioida 59! 

CHAPTER  XI. 

The  Peripatidea,  the  Myzostomata,  the  Enteropneusta,  the  Chse- 
tognatha,  the  Nematoidea,  the  Physemaria,  the  Acantho- 
cephala  and  the  Dicyemida    .        .  .        .  .    624 

CHAPTER  XII. 
The  Taxonomy  of  Invertebrated  Animals 056 

Index 689 


THE  ANATOMY 

or 

INVEETEBEATED   ANIMALS. 


INTRODUCTION. 

I. — THE  OKKSRAL  PRINCIPLES  OF  BIOLOOY. 

The  Biological  sciences  are  those  which  deal  with  the 
phenomena  manifested  by  living  matter;  and  though  it 
ii  customaiy  and  convenient  to  group  apart  such  of  these 
phenomena  as  are  termed  mental,  and  such  of  them  as  are 
exhibited  bj  men  in  society,  under  the  heads  of  Psychology 
and  Sociology,  yet  it  must  be  allowed  that  no  natural 
boundary  separates  the  subject  matter  of  the  latter  sciences 
from  that  of  Biology.  Psychology  is  inseparably  linked 
with  Physiology;  and  the  phases  of  social  life  exhibited 
by  animals  other  than  man,  which  sometimes  curiously 
foreshadow  humlkn  policy,  fall  strictly  within  the  province 
of  the  biologist. 

On  the  other  hand,  the  biological  sciences  are  sharply 
marked  off  from  the  abiological,  or  those  which  treat  of 
the  phenomena  manifested  by  not-living  matter,  in  so  far 
as  the  properties  of  living  matter  distinguish  it  absolutely 
from  all  other  kinds  of  things,  and  as  the  present  state  of 
knowledge  furnishes  us  with  no  link  between  the  living 
and  the  not-living. 
These  distinctive  properties  of  living  matter  are — 
1.  Its  ekemieal  eompontion — containing,  as  it  invariably 
does,  one  or  more  forms  of  a  complex  comx>ound  of  carbon, 
hydrogen,  oxygen,  and  nitrogen,  the  so-called  protein  (which 
lum  never  yet  been  obtained  except  as  a  product  of  living 

B 


2     THE  ANATOMY  OF  IKYEBTEBBATSD  ANIMALS. 

bodies)  united  with  a  large  proportion  of  water,  and  forming 
the  chief  constituent  of  a  substance  which,  in  its  primai} 
unmodified  state,  is  known  as  protoplasm, 

2.  Its  wniversal  dinntegration  and  toasie  hy  ooeidaHon, 
and  its  eoneomiiant  reinieffredion  hy  the  intus-suaception  oj 
new  matter. 

A  process  of  waste  resulting  from  the  decomposition  oi 
the  molecules  of  the  protoplasm,  in  virtue  of  which  thej 
break  up  into  more  highly  oxidated  products,  which  cease 
to  form  anj  part  of  the  living  bodj,  is  a  constant  con< 
comitant  of  life.  There  is  reason  to  believe  that  carbonic 
acid  is  always  one  of  these  waste  products,  while  the  othere 
contain  the  remainder  of  the  carbon,  the  nitrogen,  the 
hydrogen,  and  the  other  elements  which  may  enter  intc 
the  composition  of  the  protoplasm. 

The  new  matter  taken  in  to  make  good  this  constant 
loss  is  either  a  ready-formed  protoplasmic  material,  supplied 
by  some  other  living  being,  or  it  consists  of  the  elementa 
of  protoplasm,  united  together  in  simpler  combinations, 
which  consequently  have  to  be  built  up  into  protoplasm 
by  the  agency  of  the  living  matter  itself.  In  either  case, 
the  addition  of  molecules  to  those  which  already  existed 
takes  place,  not  at  the  surface  of  the  living  mass,  but  by 
interposition  between  the  existing  molecules  of  the  latter. 
If  the  processes  of  disintegration  and  of  reconstruction 
which  characterise  life  balance  one  another,  the  size  of  the 
mass  of  living  matter  remains  stationary,  while,  if  the  re- 
constructive process  is  the  more  rapid,  the  living  body  growM, 
But  the  increase  of  size  which  constitutes  growth  is  the 
result  of  a  process  of  molecular  intus-susception,  and  there- 
fore differs  altogether  from  the  process  of  growth  by  accre- 
tion, which  may  be  observed  in  crystals  and  is  effected 
purely  by  the  external  addition  of  new  matter — so  that,  in 
the  well-known  aphorism  of  LinnsBUs,*  the  word  "  grow," 
as  applied  to  stones,  signifies  a  totally  different  process  from 
what  is  called  "  growth  "  in  plants  and  animals. 

*  **  Lapidu  erescnnt:  vegettiriUa  ereseont  et  vivunt:  onimaHa  eres- 
eanti  vivoni  et  Mnttunt." 


CHASACTBB8  OV  LIVINO  MATTER.  3 

3.  Its  tendency  to  undergo  eyeUcal  changes. 

In  the  ordinary  course  of  nature,  all  living  matter  pro- 
ceeds from  pre-existing  living  matter,  a  portion  of  the  latter 
being  detached  and  acquiring  an  independent  existence. 
The  new  form  takes  on  the  characters  of  that  from  which 
it  arose;  exhibits  the  same  power  of  propagating  itself 
by  means  of  an  offshoot ;  and,  sooner  or  later,  like  its  pre- 
decessor, ceases  to  Uve,  and  is  resolved  into  more  highly 
oxidated  compounds  of  its  elements. 

Thus  an  individual  living  body  is  not  only  constantly 
changing  its  substance,  but  its  size  and  form  are  under- 
going continual  modifications,  the  end  of  which  is  the  death 
and  decay  of  that  individual ;  the  continuation  of  the  kind 
being  secured  by  the  detachment  of  portions  which  tend 
to  run  through  the  same  cycle  of  forms  as  the  parent.  No 
forms  of  matter  which  are  either  not  living,  or  have  not 
been  derived  from  living  matter,  exhibit  these  three  pro- 
perties, nor  any  approach  to  the  remarkable  phenomena 
defined  under  the  second  and  third  heads.  But  in  addi- 
tion to  these  distinctive  characters,  living  matter  has  some 
other  peculiarities,  the  chief  of  which  are  the  dependence 
of  all  its  activities  upon  moisture  and  upon  heat,  within 
a  limited  range  of  temperature,  together  with  the  fact  that 
it  usually  possesses  a  certain  structure,  or  organization. 

Ajb  has  been  said,  a  large  prox>ortion  of  water  enters  into 
the  composition  of  all  living  matter ;  a  certain  amount  of 
drying  arrests  vital  activity,  and  the  complete  abstraction 
of  this  water  is  absolutely  incompatible  with  either  actual 
or  potential  life.  But  many  of  the  simpler  forms  of  life 
may  undergo  desiccation  to  such  an  extent  as  to  arrest  their 
vital  manifestations  and  convert  them  into  the  semblance 
of  not-living  matter,  and  yet  remain  potentially  alive ;  that 
is  to  say,  on  being  duly  moistened  they  return  to  life  again. 
And  this  revivification  may  take  place  after  months,  or  even 
years,  of  arrested  life. 

The  propertieB  of  liriDg  matter  are  intimately  related  to 
tonpeimtiire.  Not  only  does  exposure  to  heat  sufi&cient  to 
deeompote  proton  matter  destroy  life,  by  demolishing  the 

B  2 


4  THE  AKATOMT  OF  IITVEBTBBBATBD  AKIMAL8. 

molecular  stmotnre  apon  which  life  depends ;  bat  all  vital 
activitj,  all  phenomena  of  nutritive  growth,  movement, 
and  reproduction  are  possible  only  between  certain  limits 
of  temperature.  As  the  temperature  approaches  these 
limits  the  manifestations  of  life  vanish,  though  thej  maj  be 
teoovered  bj  return  to  the  normal  conditions;  but  if  it 
pass  far  beyond  these  limits,  death  takes  place. 

This  much  is  clear ;  but  it  is  not  easy  to  say  exactly 
what  the  limits  of  temperature  are,  as  they  appear  to  vary 
in  part  with  the  kind  of  living  matter,  and  in  part  with 
the  conditions  of  moisture  which  obtain  along  with  the 
temperature.  The  conditions  of  life  are  so  complex  in 
the  higher  organisms,  that  the  experimental  investigation 
of  this  question  can  be  satisfactorily  attempted  only  in 
the  lowest  and  simplest  forms.  It  appears  that,  in 
the  dry  state,  these  are  able  to  bear  far  greater  ex- 
tremes both  of  heat  and  cold  than  in  the  moist  condition. 
Thus  Pasteur  found  that  the  spores  of  fungi,  when  dry, 
could  be  exposed  without  destruction  to  a  temperature  of 
120°-125°  0.  (248°-257°  Fahr.),  whHe  the  same  spores, 
when  moist,  were  all  killed  by  exposure  to  100^  G.  (212^ 
Fahr.)  On  the  other  hand,  Cagniard  de  la  Tour  found 
that  dry  yeast  might  be  exposed  to  the  extremely  low 
temperature  of  solid  carbonic  acid  (—60**  C.  or  —76°  Fahr.) 
without  being  killed.  In  the  moist  state  he  found  that  it 
might  be  frozen  and  cooled  to  —  5°  G.  (23°  Fahr.),  but  that 
it  was  killed  by  lower  temperatures.  However,  it  is  very 
desirable  that  these  experiments  should  be  repeated,  for 
Gohn's  careful  observations  on  Bcusteria  show  that,  though 
they  fall  into  a  state  of  torpidity,  and,  like  yeast,  lose  all 
their  powers  of  exciting  fermentation  at,  or  near,  the 
freezing-point  of  water,  they  are  not  killed  by  exposure 
for  five  hours  to  a  temperature  below  —10°  G.  (14°  Fahr.) 
and,  for  some  time,  sinking  to  —18°  0.  (— 0°*4  Fahr.)  Speci- 
mens of  Spirillum  vohUans,  which  had  been  cooled  to  this 
extent,  began  to  move  about  some  little  time  after  the  ice 
containing  them  thawed.  But  Gohn  remarks  that  EuglefUB, 
which  were  frozen  along  with  them,  were  all  killed  and 


BXSISTAKCX  TO  HXAT  AND  COLD.  5 

disorgasiBed,  and  that  the  same  fate  had  befallen  the 
higher  Infiuoria  and  Botifera,  with  the  exception  of  some 
encysted  VoHieelloR,  in  which  the  rhythmical  movements  of 
the  contractile  vesicle  showed  that  life  was  preserved. 

Thns  it  would  appear  that  the  resistance  of  living  matter 
to  cold  depends  greatly  on  the  special  form  of  that  matter, 
and  that  the  limit  of  the  Euglena,  simple  organism  as  it  is, 
is  mnch  higher  than  that  of  the  Bacterium. 

Considerations  of  this  kind  throw  some  light  upon  the 
apparently  anomalous  conditions  under  which  many  of  the 
lower  plants,  such  as  Prataeoccus  and  the  DiatomacecB,  and 
some  of  the  lower  animals,  such  as  the  Badiolariaf  are 
observed  to  flourish.  Protaeoccus  has  been  found,  not  only 
on  the  snows  of  great  heights  in  temperate  latitudes,  but 
covering  extensive  areas  of  ice  and  snow  in  the  Arctic 
T^ons,  where  it  must  be  exposed  to  extremely  low  tem- 
peratures,— in  the  latter  case  for  many  months  together; 
while  the  Arctic  and  Antarctic  seas  swarm  with  DiatomacecB 
and  Badiolaria.  It  is  on  the  DiatoTitacecB,  as  Hooker  has 
well  shown,  that  all  surface  life  in  these  regpions  ultimately 
depends ;  and  their  enormous  multitudes  prove  that  their 
rate  of  multiplication  is  adequate  to  meet  the  demands 
made  upon  them,  and  is  not  seriously  impeded  by  the  low 
temperature  of  the  waters,  never  much  above  the  freezing- 
point,  in  which  they  habitually  live. 

The  maximum  limit  of  heat  which  living  matter  can 
resist  is  no  less  variable  than  its  minimum  limit.  Kiihne 
found  that  marine  Amcebm  were  killed  when  the  tempera- 
ture reached  35°  0.  (95°  Fahr.),  while  this  was  not  the 
case  with  fresh-water  Amc^m,  which  survived  a  heat  of 
5°,  or  evea  10°,  C.  higher.  Aetinophrya  EichJiomii  was  not 
killed  until  the  temperature  rose  to  44°  or  45°  G.  Didymium 
aerjnda  is  killed  at  35°  0.;  while  another  Myxom/ycetef  JEthO' 
Hum  sepUcwn,  succumbs  only  at  40°  G. 

Cohn  ("  XJntersuchungen  iiber  Bacterien,"  Beiirdge  «ir 
Biologie  der  Pflanaen,  Heft  2, 1872)  has  given  the  results  of 
a  series  of  experiments  conducted  with  the  view  of  Ascer- 
taining  the  temperature  at  which  Bacteria  are  destroyed 


6  TBI  AKATOKT  OV  IimBTZBBA.TXD  A1TIMAI.S. 

Then  liring  m  a  fluid  of  definite  chemical  compocition,  Etnd 
free  from  all  snoh  compUcationa  as  most  arise  from  the 
inequslitieB  of  phjaical  condition  when  solid  particles  other 
than  the  Baeteria  co-exiet  with  them.  The  fiuid  employed 
oontAined  0*1  gramme  potasBiom  phosphate,  O'l  gr.  0170- 
tallised  magneainm  Balpfaat«,  O'l  gr.  tribasic  calcium 
phosphate,  and  0'2  gr.  ammoniom  torttate,  dissolved  in 
20  cnbic  centimeteee  of  distilled  water.  If  to  a  certain 
qoantitj  of  this  "normal  fluid"  a  email  proportion  of 
water  containing  Baeteria  was  added,  the  moltiplication  of 
the  Baetwia  went  on  with  rapidity,  whether  the  mouth  of 
the  containing  flask  was  open  or  hermeticallj  closed. 
Hermetically-sealed  flasks,  containing  portions  tA  the 
normal  fluid  infected  with  Baeieria,  were  submerged  in 
water  heated  to  various  temperatures,  the  flask  being  care- 
fully shaken,  without  being  raised  out  of  the  water,  during 
its  submergence. 

The  result  was,  that  in  those  flasks  which  were  thus 
aubjected.  for  an  hour,  to  a.  heat  of  60°-62°  0.  (140°-143= 
Fahr.),  the  Baeteria  noderwent  no  development,  and  the 
fluid  remained  perfectly  clear.  On  the  other  band,  in 
r  eiperimenta  in  which  the  flasks  were  heated  only 


BB8IBTAV0S  TO  HBAT  AND  GOLD.  7 

they  haye  been  heated  aboTe  the  boiling-point,  require 
renewed  inTeetigation. 

Both  in  Kiihne's  and  in  Cohn's  experiments,  which  last 
have  lately  been  confirmed  and  extended  by  Dr.  Boberts  of 
Manchester,  it  was  noted  that  long  exposure  to  a  lower 
temperature  than  that  which  brings  about  immediate 
destruction  of  life,  produces  the  same  effect  as  short  ex- 
posure to  the  latter  temperature.  Thus,  though  all  the 
Baderia  were  killed,  with  certainty,  in  the  normal  fluid,  by 
short  exposure  to  temperatures  at  or  above  60°  0.  (140° 
Efthr.),  Cohn  observed  that,  when  a  flask  containing  in- 
fected normal  fluid  was  heated  to  50°-52°  G.  (122°-125° 
Fahr.)  for  only  an  hour,  the  consequent  multiplication 
of  the  Baderia  was  manifested  much  earlier,  than  in  one 
which  had  been  exposed  for  two  hours  to  the  same  tempe- 
rature. 

It  appears  to  be  very  generally  h^d  that  the  simpler 
vegetable  organisms  are  deprived  of  life  at  temperatures  as 
high  as  60°  0.  (140°  Fahr,) ;  but,  it  ia  affirmed  by  competent 
observers,  that  AlgcR  have  been  found  living  in  hot  springs 
at  much  higher  temperatures,  namely,  from  168°  to  208° 
Fahr.,  for  which  latter  surprising  fact  we  have  the  high 
authority  of  Descloiseaux.  It  is  no  explanation  of  these 
phenomena,  but  only  another  mode  of  stating  them,  to  say 
that  these  organisms  have  become  "  accustomed  "  to  such 
temperatures.  If  this  degree  of  heat  were  absolutely 
incompatible  with  the  activity  of  living  matter,  the  plants 
could  no  more  resist  it  than  they  could  become  "accus- 
tomed *'  to  being  made  red  hot.  Habit  may  modify  sub- 
sidiary, but  cannot  affect  fundamental,  conditions. 

Recent  investigations  point  to  the  conclusion  that  the 
immediate  cause  of  the  arrest  of  vitality,  in  the  first  place, 
and  of  its  destruction,  in  the  second,  is  the  coagulation  of 
certain  substances  in  the  protoplasm,  and  that  the  latter 
€emkKBM  various  ooagukble  matters,  which  solidify  at  dif - 
ferent  temperatures.  And  it  remains  to  be  seen,  how  far  the 
death  of  any  form  of  living  matter,  at  a  given  temperature, 
depends  on  the  destaruction  of  its  fundamental  substance 


8 


THB  AVATOMT  OP  nrVX&TBBBATSD  AVIMALS. 


at  that  heat,  and  how  far  death  is  hronght  about  by  the 
coagalation  of  merely  accessory  compounds. 

It  may  be  safely  said  of  all  those  living  things  which 
are  large  enough  to  enable  us  to  trust  the  eyidenoe  of 
microscopes,*  that  they  are  heterogeneous  optically,  and 
that  their  different  parts,  and  especially  the  surface  layer, 
as  contrasted  with  the  interior,  differ  physically  and  chemi- 
cally ;  while,  in  most  living  things,  mere  heterogeneity  is 
exchanged  for  a  definite  structure,  whereby  the  body  is 
distinguished  into  visibly  diverse  parts,  which  possess  dif- 
ferent powers  or  functions.  Living  things  which  present 
this  visible  structure  are  said  to  be  organiaed;  and  so 
widely  does  organisation  obtain  among  living  beings,  that 
organised  and  living  are  not  unfrequently  used  as  if  they 
were  terms  of  co-extensive  applicability.  This,  however,  is 
not  exactly  accurate,  if  it  be  thereby  implied  that  all  living 
things  have  a  visible  organisation,  as  Uiere  are  numerous 
forms  of  living  matter  of  which  it  cannot  properly  be  said 
that  they  possess  either  a  definite  visible  structure  or  per- 
manently specialised  organs :  though  doubtless,  the  simplest 
particle  of  living  matter  must  possess  a  highly  complex 
molecular  structure,  which  is  far  beyond  the  reach  of 
vision. 

The  broad  distinctions  which,  as  a  matter  of  fact,  exist 
between  every  known  form  of  living  substance  and  every 
other  component  of  the  material  world,  justify  the  sepa- 
ration of  the  biological  sciences  from  all  others.  But  it 
must  not  be  supposed  that  the  differences  between  living 
and  not-living  matter  are  such  as  to  bear  out  the  assump- 
tion that  the  forces  at  work  in  the  one  are  different  from 


*  In  considering  the  question 
of  the  complication  of  molecalar 
Btructore  wliich  even  the  smallest 
and  simplest  of  living  beings  may 
possess,  it  is  well  to  recollect  that 
an  organic  particle  rgjon  of  an 
inch  in  diameter,  in  which  our 
best  microscopes  may  be  incom- 
petent   to   reveal   the   slightest 


differentiation  of  parts,  may  be 
made  up  of  1,000,000  particles 
Tgoiiwo  of  an  inch  in  diameter, 
wnile  the  molecules  of  matter  are 
probably  much  less  than  |(jooo<kj  of 
an  inch  in  diameter.  Hence  in 
such  a  body  there  is  ample  scope 
for  any  amount  of  complexity  of 
molecular  structure. 


MOBPHOLOGT.  9 

those  which  are  to  be  met  with  in  the  other.  Considered 
apart  from  the  phenomena  of  conscioasnees,  the  phenomena 
of  life  are  all  dependent  upon  the  working  of  the  same 
physical  and  chemical  forces  as  those  which  are  active 
in  the  rest  of  the  world.  It  maj  be  convenient  to  use 
the  terms  "  vitalitj  "  and  "  vital  force  "  to  denote  the  causes 
of  certain  great  groups  of  natural  operations,  as  we  employ 
the  names  of  '*  electricity  "  and  "  electrical  force  "  to  denote 
others ;  but  it  ceases  to  be  proper  to  do  so,  if  such  a  name 
implies  the  absurd  assumption  that  either  "  electricity  "  or 
''vitality"  are  entities  playing  the  part  of  efficient  causes 
of  electrical  or  vital  phenomena.  A  mass  of  living  proto- 
plasm is  simply  a  molecular  machine  of  great  complexity, 
the  total  results  of  the  working  of  which,  or  its  vital  pheno- 
mena, depend,  on  the  one  hand,  upon  its  construction,  and, 
on  the  other,  upon  the  energy  supplied  to  it ;  and  to  speak 
of  "  vitality  "  as  anything  but  the  name  of  a  series  of  opera- 
tions is  as  if  one  should  talk  of  the  "  horologity  "  of  a  clock. 

Living  matter,  or  protoplasm  and  the  products  of  its 
metamorphosis,  may  be  regarded  under  four  aspects : — 

(1.)  It  has  a  certain  external  and  internal  form,  the 
latter  being  more  usually  called  structure ; 

(2.)  It  occupies  a  certain  position  in  space  and  in  time ; 

(3.)  It  is  the  subject  of  the  operation  of  certain  forces, 
in  virtue  of  which  it  undergoes  internal  changes,  modifies 
external  objects,  and  is  modified  by  them ;  and 

(4.)  Its  form,  place,  and  powers  are  the  effects  of  certain 
causes. 

In  correspondence  with  these  four  aspects  of  its  subject. 
Biology  is  divisible  into  four  chief  subdivisions — I.  Mor- 
phology;   n.  DiSTsiBTjnoN ;    III.  Physiolooy;    rv. 

JSjT10JA>QY. 

I.  MOKPHOLOOY. 

So  far  as  living  beings  have  a  form  and  structure,  they 
faJH  within  the  province  of  AncUimiy  and  Histology,  the 
latter  being  merely  a  name  for  that  ultimate  optical  analysis 


10    THE  ANATOMY  OF  IKYBBTBBBATBD  AKIMAL8. 

of  living  Btmctnre  which  can  be  carried  out  only  by  the 
aid  of  the  microscope. 

And,  in  so  far  as  the  form  and  stractnre  of  anj  living 
being  are  not  constant  during  the  whole  of  its  existence, 
but  undergo  a  series  of  changes  from  the  commencement 
of  that  existence  to  its  end,  living  beings  have  a  Develop' 
ment.  The  history  of  development  is  an  account  of  the 
anatomy  of  a  living  being  at  the  successive  periods  of  its 
existence,  and  of  the  maimer  in  which  one  anatomical  stage 
passes  into  the  next. 

FmaUy.  the  syBtematic  statement  and  generalisation  of 
the  facts  of  Morphology,  in  such  a  maimer  as  to  arrange 
living  beings  in  groups,  according  to  their  degrees  of  like* 
ness,  is  Taaonomy, 

The  study  of  Anatomy  and  Development  has  brought  to 
light  certain  generalisations  of  wide  applicability  and  g^reat 
importance. 

1.  It  has  been  said  that  the  great  majority  of  living 
beings  present  a  very  definite  structure.  Unassisted  vision 
and  ordinary  dissection  suffice  to  separate  the  body  of  any 
of  the  higher  animals,  or  plants,  into  fabrics  of  different 
sorts,  which  always  present  the  same  general  arrangement 
in  the  same  organism,  but  are  combined  in  different  ways 
in  different  organisms.  The  discnmination  of  these  com- 
paratively few  fabrics,  or  tissues,  of  which  organisms  are 
composed,  was  the  first  step  towards  that  ultimate  analysis  of 
visible  structure  which  has  become  possible  only  by  the  recent 
perfection  of  microscopes  and  of  methods  of  preparation. 

Histology,  which  embodies  the  results  of  this  analysis, 
shows  that  every  tissue  of  a  plant  is  composed  of  more  or 
less  modified  structural  elements,  each  of  which  is  termed 
a  ceU;  which  cell,  in  its  simplest  condition,  is  merely  a 
spheroidal  mass  of  protoplasm,  surrounded  by  a  coat  or  sac 
— ^the  ceU-waU — ^which  contains  cellulose.  In  the  various 
tissues,  these  cells  may  undergo  innumerable  modificationa 
of  form — the  protoplasm  may  become  differentiated  into  a 
nucleus  with  its  nucleolus,  a  primordial  utricle,  and  a 


HI8TOLOOT.  11 

cafitj  filled  witli  a  waterj  fluid,  and  the  cell- wall  may  be 
Tarionaly  altered  in  composition  or  in  stmoture,  or  may 
coaleace  with  others.  But,  howerer  extensive  these  change 
may  be,  the  fact  that  the  tissaes  are  made  np  of  morpholo- 
gically distinct  nnits — the  ceUs — remains  patent.  And,  if 
any  dbonbt  could  exist  on  the  subject,  it  would  be  removed 
by  the  stady  of  development,  which  proves  that  every  plant 
commences  its  existence  as  a  simple  cell,  identical  in  its 
fondaznental  characters  with  the  less  modified  of  those 
odls  of  whidi  the  whole  body  is  composed. 

Bui  it  is  not  necessary  to  the  morphological  unit  of  the 
plant  that  it  should  be  always  provided  with  a  cell-walL 
Certain  plants,  sueh  as  Frotococcue,  spend  longer  or  shorter 
periods  of  their  existence  in  the  condition  of  a  mere  spheroid 
of  protoplasm,  devoid  of  any  cellulose  wall,  while,  at  other 
times,  the  protoplasmic  body  becomes  enclosed  within  a 
cell-wall,  fabricated  by  its  superficial  layer. 

Therefore,  just  as  the  nucleus,  the  primordial  utricle, 
and  the  central  fluid  are  no  essential  constituents  of  the 
morphological  unit  of  the  plant,  but  represent  results  of 
its  metamorphosis,  so  the  cell-wall  is  equally  unessential ; 
and  either  the  term  "  cell "  must  acquire  a  merely  technical 
significance  as  the  equivalent  of  morphological  unit,  or 
some  new  term  must  be  invented  to  describe  the  latter. 
On  the  whole,  it  is  probably  least  inconveuient  to  modify 
the  sense  of  the  word  "  cell." 

The  histological  analysis  of  animal  tissues  has  led  to 
snnilar  results  and  to  difficulties  of  terminology  of  precisely 
the  same  character.  In  the  higher  animals,  however,  the 
modifications  which  the  cells  undergo  are  so  extensive, 
thai  the  fact  that  the  tissues  are,  as  in  plants,  resolvable 
into  an  aggregation  of  morphological  units,  could  never 
hafie  been  established  without  the  aid  of  the  study  of  de- 
velopment, which  proves  that  the  animal,  no  less  than  the 
phuit,  commences  its  existence  as  a  simple  cell,  fundament- 
ally identical  with  the  less  modified  cells  which  are  found 
m  tbe  tissaes  of  the  adult. 

Thofogh  the  nnoleas  is  very  constant  among  animal  cells, 


12    THE  ANATOMY  OF  IKYBBTEBBATED  AKIMALS. 

it  is  not  uniyersall J  present ;  and  among  the  lowest  forms 
of  animal  life,  tlie  protoplasmic  mass  which  represents  the 
morphological  imit  maj  be,  as  in  the  lowest  plants,  devoid 
of  a  nucleus.  In  the  animal,  the  cell-wall  never  has  the 
chai*acter  of  a  shut  sac  containing  cellulose ;  and  it  is  not 
a  little  difficult,  in  manj  cases,  to  saj  how  much  of  the 
so-called  "cell-wall'*  of  the  animal  cell  answers  to  the 
"primordial  utricle  "and  how  much  to  the  proper  "  cellulose 
cell-wall "  of  the  vegetable  cell.  But  it  is  certain  that  in 
the  animal,  as  in  the  plant,  neither  ceU-wall  nor  nucleus 
are  essential  constituents  of  the  cell,  inasmuch  as  bodies 
which  are  unquestionablj  the  equivalents  of  cells — true 
morphological  units — ^maj  be  mere  masses  of  protoplasm, 
devoid  alike  of  cell- wall  and  nucleus. 

For  the  whole  living  world,  then,  it  results: — ^that  the 
morphological  unit — the  primary  and  fundamental  form  of 
life — is  merely  an  individual  mass  of  protoplasm,  in  which 
no  fui*ther  structure  is  discernible ;  that  independent  living 
forms  may  present  but  little  advance  on  this  structure; 
and  that  slII  the  higher  forms  of  life  are  aggp*egates  of  such 
morphologpLcal  units  or  cells,  variously  modified. 

Moreover,  all  that  is  at  present  known  tends  to  the  con- 
clusion, that,  in  the  complex  aggregates  of  such  imits  of 
which  all  the  higher  animals  and  plants  consist,  no  cell  has 
arisen  otherwise  than  by  becoming  separated  from  the  pro- 
toplasm of  a  pre-existing  cell ;  whence  the  aphorism  "  Omnit 
eellula  e  cellvld." 

It  may  further  be  added,  as  a  general  truth  applicable 
to  nucleated  cells,  that  the  nucleus  rarely  undergoes  any 
considerable  modification,  the  structures  characteristic  of 
the  tissues  being  formed  at  the  expense  of  the  more  super- 
ficial protoplasm  of  the  cells;  and  that,  when  nucleated 
cells  divide,  the  division  of  the  nucleus,  as  a  rule,  precedes 
that  of  the  whole  celL 

2.  In  the  course  of  its  development  every  cell  proceeds 
from  a  condition  in  which  it  closely  resembles  every  other 
cell,  through  a  series  of  stages  of  gradually  increasing 
divergence,  until  it  reaches  that  condition  in  which  it 


DBTSLOPMBITT.  13 

presents  the  characteristic  features  of  the  elements  of  a 
special  tissae.  The  development  of  the  cell  is  therefore  a 
gradual  progress  from  the  general  to  the  special  state. 

The  like  holds  good  of  the  development  of  the  body  as  a 
whole.  However  complicated  one  of  the  higher  animals  or 
plants  may  be,  it  begins  its  separate  existence  under  the 
form,  of  a  nucleated  cell.  This,  by  division,  becomes  con- 
verted into  an  aggregate  of  nucleated  cells:  the  parts  of 
tills  aggregate,  following  different  laws  of  growth  and 
multiplication,  give  rise  to  the  rudiments  of  the  organs ; 
and  the  parts  of  these  rudiments  again  take  on  those  modes 
of  growth  multiplication  and  metamorphosis  which  are 
needful  to  convert  the  rudiment  into  the  perfect  structure. 

The  development  of  the  organism  as  a  whole,  therefore, 
repeats  in  principle  the  development  of  the  celL  It  is  a 
progress  from  a  general  to  a  special  form,  resulting  from 
the  gradual  differentiation  of  the  primitively  similar  mor- 
phological units  of  which  the  body  is  composed. 

Moreover,  when  the  stages  of  development  of  two 
Mtiimala  are  compared,  the  number  of  these  stages  which 
are  similar  to  one  another  is,  as  a  general  rule,  proportional 
to  the  doseness  of  the  resemblance  of  the  adult  forms; 
whence  it  f  oUows  that  the  more  closely  any  two  animals  are 
allied  in  adult  structure,  the  later  are  their  embryonic 
conditions  distinguishable.  And  this  general  rule  holds  for 
plants  no  less  than  for  animals. 

The  broad  principle,  that  the  form  in  which  the  more 
complex  living  things  commence  their  development  is 
always  the  same,  was  first  expressed  by  Harvey  in  his 
famous  aphorism  "  Onvne  vivwm  ex  ovo"  which  was  intended 
simply  as  a  morphological  generalisation,  and  in  no  wise 
implied  the  rejection  of  spontaneous  generation,  as  it  is 
commonly  supposed  to  do.  Moreover,  Harve/s  study  of 
the  development  of  the  chick  led  him  to  promulgate  that 
theory  of  "  epigenesis,'*  in  which  the  doctrine  that  develop- 
ment 18  a  progress  from  the  general  to  the  special  is 
inq^ieitly  contained. 

Caspar  F.  Wolff  furnished  further,  and  indeed  condu- 


14         THE  ANATOMY  OF  nTYBBTSBBATED  ANIMALS. 

give,  proof  of  the  troth  of  the  theory  of  epigeneais :  but, 
unfortunatelj,  the  anthoritj  of  Haller  and  the  speculatioiiB 
of  Bonnet  led  science  astray,  and  it  was  reserved  for  Yon 
Baer  to  put  the  nature  of  the  process  of  deyelopment  in  its 
true  light,  and  to  formulate  it  in  his  famous  law. 

8.  Deyelopment,  then,  is  a  process  of  differentiation  by 
which  the  primitiyely  similar  parts  of  the  living  body 
become  more  and  more  unlike  one  another. 

This  process  of  differentiation  may  be  effected  in  seyeral 
ways. 

(1.)  The  protoplasm  of  the  germ  may  not  undergo  divi- 
sion and  conversion  into  a  cell  aggregate ;  but  various  parts 
of  its  outer  and  inner  substance  may  be  metamorphosed 
directly  into  those  physically  and  chemically  different 
materials  which  constitute  the  body  of  the  adult.  This 
occurs  in  such  animals  as  the  Infusoria,  and  in  such  plants 
as  the  unicellular  Algm  and  Ftrngi. 

(2.)  The  germ  may  undergo  division,  and  be  converted 
into  an  aggregate  of  dtvmon  masses,  or  hlastomeres,  which 
become  cells  and  give  rise  to  the  tissues  by  undergoing  a 
metamorphosis  of  the  same  kind  as  that  to  which  the  whole 
body  is  subjected  in  the  preceding  case. 

The  body,  formed  in  either  of  these  ways,  may,  as  a  whole, 
undergo  metamorphosis  by  differentiation  of  its  parts ;  and 
this  differentiation  may  take  place  without  reference  to  any 
axis  of  symmetry,  or  it  may  have  reference  to  such  an  axis. 
In  the  latter  case,  the  parts  of  the  body  which  become  dis- 
tinguishable may  correspond  on  the  two  sides  of  the  axis 
(bilateral  symmetry),  or  may  correspond  along  several  lines 
parallel  with  the  axis  (radial  symmetry). 

The  bilateral  or  radial  symmetry  of  the  body  may  be 
further  complicated  by  its  segmentation,  or  separation  by 
divisions  transverse  to  the  axis,  into  parts,  each  of  which 
corresponds  with  its  predecessor  or  successor  in  the  series. 

In  the  segmented  body,  the  segments  may  or  may  not 
give  rise  to  symmetrically  or  asymmetrically  disposed  pro- 
cesses, which  are  appendages,  using  that  word  in  its  most 
general  sense. 


DirFBSMHTIATZON  OF  BTBUOTVBS.  15 

And  the  biggest  degree  of  complication  of  stractnre,  in 
both  aTiiTnalH  and  plants,  it  attained  by  the  body  when  it 
becomes  divided  into  segments  proyided  with  appendages ; 
when  the  segments  not  only  become  veiy  different  from  one 
another,  bnt  some  coalesce  and  lose  their  primitiTe  distinct- 
ness; and  when  the  appendages  and  the  segments  into 
which  thej  are  sabdivided  similarly  become  differentiated 
and  coalesce. 

It  is  in  Tirtne  of  snch  processes  that  the  flowers  of 
plants,  and  the  heads  and  limbs  of  the  Atihropoda  and  of 
the  VerUibraia,  among  animals,  attain  their  extraordinary 
diyerBity  and  complication  of  stracture.  A  flower-bad  is  a 
segmented  body  or  axis,  with  a  certain  number  of  whorls 
of  appendages ;  and  the  perfect  flower  is  the  result  of  the 
gradnal  differentiation  and  confluence  of  these  primitiTcly 
similar  segments  and  their  appendages.  The  head  of  an 
insect  or  of  a  crustacean  is,  in  like  manner,  composed  of  a 
namber  of  segments,  each  with  its  pair  of  appendages, 
which  by  differentiation  and  confluence  are  converted  into 
the  feelers  and  variously  modified  oral  appendages  of  the 
adult. 

In  some  complex  organisms,  the  process  of  differentiation, 
by  which  they  pass  from  the  condition  of  aggregated 
embryo  cells  to  the  adult,  can  be  traced  back  to  the  laws 
of  growth  of  the  two  or  more  cells  into  which  the  embryo 
cell  is  divided,  each  of  these  cells  giving  rise  to  a  particular 
portion  of  the  adult  organism.  Thus  the  fertilised  embryo 
cell  in  the  arcbegonium  of  a  fern  divides  into  four  cells,  one 
of  which  gives  rise  to  the  rhizome  of  the  young  fern,  another 
to  its  first  'rootlet,  while  the  other  two  are  converted  into 
a  placenta-like  mass  which  remains  imbedded  in  the  pro- 
thallus. 

The  stracture  of  the  stem  of  Chora  depends  upon  the 
different  properties  of  the  cells,  which  are  successively 
derived  by  transverse  division  from  the  apical  cell.  An 
hUer-nodal  cell,  which  elongates  greatly,  and  does  not 
divide,  is  succe^ed  by  a  nodal  cell,  which  elongates  but 
Htde,  and   becomes  greatly  subdivided;  this  by  another 


16         THB  ANATOMY  OF  INYEBTBBBATBD  ANIMALS. 

inter-nodal  cell,  and  bo  on  in  r^pilar  alternation.  In  the 
same  way  the  stracture  of  the  stem,  in  all  the  higher  plants, 
depends  upon  the  laws  which  govern  the  manner  of  diyiflioa 
and  of  metamorphosis  of  the  apical  cells,  and  of  their  oon- 
tinnation  in  the  camMwn  layer. 

In  all  animals  which  consist  of  cell-aggregatee,  the  cells 
of  which  the  embryo  is  at  first  composed  arrange  them- 
selves by  the  splitting,  or  by  a  process  of  invagination*  ol 
the  blastoderm  into  two  layers,  the  epibloui  and  the  hffp(h 
hlastf  between  which  a  third  intermediate  layer,  the  meto* 
blast,  appears ;  and  each  layer  gives  rise  to  a  definite  group 
of  organs  in  the  adult.  Thus,  in  the  Veriebraia,  the  epiblast 
gives  rise  to  the  cerebro-spinal  axis,  and  to  the  epidennk 
and  its  derivatives ;  the  hypoblast,  to  the  epithelium  of  the 
alimentary  canal  and  its  derivatives;  and  the  mesobUsi^ 
to  intermediate  structures.  The  tendency  of  recent  in- 
quiry is  to  prove  that  the  several  layers  of  the  germ  evolve 
analogous  organs  in  invertebrate  animals,  and  to  indicate 
the  possibility  of  tracing  the  several  germ  layers  back  to 
the  blastomeres  of  the  yelk,  from  the  subdivision  of  which 
they  proceed. 

It  is  conceivable  that  all  the  forms  of  life  should  have 
presented  about  the  same  differentiation  of  structure,  and 
should  have  differed  from  one  another  by  superficial  charac- 
ters, each  form  passing  by  insensible  gradations  into  those 
most  like  it.  In  this  case  Taxonomy,  or  the  classification 
of  morphological  facts,  would  have  had  to  confine  itaelf  to 
the  formation  of  a  serial  arrangement,  representing  the 
serial  gradation  of  these  forms  in  nature. 

It  is  conceivable,  again,  that  living  beings  should  have 
differed  as  widely  in  structure  as  they  actually  do,  but  that 
the  interval  between  any  two  extreme  forms  should  have 
been  filled  up  by  an  unbroken  series  of  gradations;  in 
which  case,  again,  classification  could  only  effect  the  forma- 
tion of  series — the  strict  definition  of  groups  would  be  as 
impossible  as  in  the  former  case. 

As  a  matter  of  fact»  living  beings  differ  enormously,  not 


\. 


MOBPHOLOOICAL  aBOUPS.  17 

only  in  differentiation  of  stmctnre,  bat  in  the  modes  in 

;  wbicli  that  differentiation  is  brought  abont;  and  the  in- 
tervals between  extreme  forms  are  not  filled  up,  in  the 

I  existing  world,  by  complete  series  of  gradations.  Hence  it 
arises  that  living  beings  are,  to  a  great  extent,  sosceptible 
of  classification  into  groups,  the  members  of  each  group 
resembling  one  another,  and  differing  from  all  the  rest,  by 

.     certain  definite  peculiarities. 

'  U  No  two  liring  beings  are  exactly  alike,  but  it  is  a  matter 
of  observation  that,  among  the  endless  diyei*sitie8  of  living 
things,  some  constantly  resemble  one  another  so  closely 
that  it  is  impossible  to  draw  any  line  of  demarcation 
between  them,  while  they  differ  only  in  such  characters  as 
are  associated  with  sex.  Such  as  thus  <4oeely  resemble  one 
another  constitute  a  morphological  species;  while  different 
morphological  species  are  defined  by  constant  characters 
which  are  not  merely  sexuaL 

The  comparison  of  these  lowest  groups,  or  morphological 
species,  with  one  another,  shows  that  more  or  fewer  of 
them  possess  some  character  or  characters  in  common — 
some  feature  in  which  they  resemble  one  another  and  differ 
from  all  other  species — and  the  group  or  higher  order  thus 
formed  is  a  genus.  The  generic  groups  thus  constituted 
are  susceptible  of  being  arranged  in  a  similar  manner  into 
groups  of  successively  higher  order,  which  are  known  as 
families,  orders,  classes,  and  the  like. 

The  method  pursued  in  the  classification  of  living  forms 
is.  in  fact,  exactly  the  same  as  that  followed  by  the  maker 
of  an  index  in  working  out  the  heads  indexed.  In  an 
alphabetical  arrangement,  the  classification  may  be  truly 
termed  a  morphological  one,  the  object  being  to  put  into 
close  relation  all  those  leading  words  which  resemble  one 
another  in  the  arrangement  of  theii*  letters,  that  is,  in  their 
form,  and  to  keep  apart  those  which  differ  in  structure. 
Headings  which  begin  with  the  same  word,  but  differ  other- 
wise, might  be  compared  to  genera  with  their  species ;  the 
groups  of  words  with  the  same  first  two  syllables  to 
families;  those  with  identical  first  syllables  to  orders  ;  and 


18         THE  ANATOMY  OF  IlfYEBTBBSATED  ANIMALS. 

those  with  the  same  initial  letter  to  classes.  But  there  is 
this  difference  between  the  index  and  the  Taxonomic 
arrangement  of  living  forms,  that  in  the  former  there  is 
nothing  but  an  arbitrary  relation  between  the  various 
classes,  while,  in  the  latter,  the  classes  are  similarly  capable 
of  co-ordination  into  larger  and  larger  groups,  until  all 
are  comprehended  under  the  common  definition  of  living 
beings. 

The  differences  between  "  artificial "  and  "  natural "  clas- 
sifications are  differences  in  degree,  and  not  in  kind.  In 
each  case  the  classification  depends  upon  likeness ;  but  in  an 
artificial  classification  some  prominent  and  easily  observed 
feature  is  taken  as  the  mark  of  resemblance  or  dissemblance ; 
while,  in  a  natural  classification,  the  things  classified  are 
arranged  according  to  the  totality  of  their  morphological 
resemblances,  and  the  features  which  are  taken  as  the  marks 
of  groups  are  those  which  have  been  ascertained  by  ob- 
servation to  be  the  indications  of  many  likenesses  or  un- 
likenesses.  And  thus  a  natural  classification  is  a  great 
deal  more  than  a  mere  index.  It  is  a  statement  of  the 
marks  of  similarity  of  organisation ;  of  the  kinds  of  struc- 
ture which,  as  a  matter  of  experience,  are  found  universally 
associated  together;  and,  as  such,  it  furnishes  the  whole 
foundation  for  those  indications  by  which  conclusions  as  to 
the  nature  of  the  whole  of  an  animal  are  drawn  from  a 
knowledge  of  some  part  of  it. 

When  a  palaeontologist  argues  from  the  characters  of  a 
bone  or  of  a  shell  to  the  nature  of  the  animal  to  which 
that  bone  or  shell  belonged,  he  is  guided  by  the  empirical 
morphological  laws  established  by  wide  observation,  that 
such  a  kind  of  bone  or  shell  is  associated  with  such  and 
such  structural  features  in  the  rest  of  the  body,  and  no 
others.  And  it  is  these  empirical  laws  which  are  embodied 
and  expressed  in  a  natural  classification. 


V 


THX  PHENOMSNA  OF  DISTBTBTTTION.  19 


n.  DiSTBIBUTION. 

Liying  bemgs  occnpj  certain  portions  of  the  surface  of 
the  earth,  inhabiting  either  the  dry  land,  or  the  fresh  or 
salt  waters ;  or  being  competent  to  maintain  their  existence 
in  either.  In  anj  given  locality,  it  is  found  that  these 
different  media  are  inhabited  bj  different  kinds  of  living 
beings;  and  that  the  same  medium,  at  different  heights 
in  the  air  and  at  different  depths  in  the  water,  has  dif- 
ferent living  inhabitants. 

Moreover,  the  living  populations  of  localities  which  differ 
considerablj  in  latitude,  and  hence  in  climate,  alwajs  pre- 
sent considerable  differences.  But  the  converse  proposition 
is  not  true;  that  is  to  saj,  localities  which  differ  in  longi- 
tude, even  if  they  resemble  one  another  in  climate,  often 
have  veiy  dissimilar  Faurue  and  Florce, 

It  has  been  discovered  bj  careful  comparison  of  local 
Faunae  and  FlorsD,  that  certain  areas  of  the  earth's  surface 
are  inhabited  bj  groups  of  animals  and  plants  which  are 
not  found  elsewhere,  and  which  thus  characterize  each  of 
these  areas.  Such  areas  are  termed  Provineea  of  Distrtbu- 
Hon,  There  is  no  parity  between  these  provinces  in  extent, 
nor  in  the  physical  configuration  of  their  boundaries ;  and, 
in  reference  to  existing  conditions,  nothing  can  appear  to 
be  more  arbitrary  and  capricious  than  the  distribution  of 
living  beings. 

The  study  of  distribution  is  not  confined  to  the  present 
order  of  nature;  but,  by  the  help  of  geology,  the  naturalist 
is  enabled  to  obtain  clear,  though  too  fragmentary,  evidence 
of  the  characters  of  the  faun®  and  florae  of  antecedent 
epochs.  The  remains  of  organisms  which  are  contained 
in  the  stratified  rocks  prove  that,  in  any  given  part  of  the 
earth's  surface,  the  living  popidation  of  earlier  epochs  was 
different  from  that  which  now  exists  in  the  locality ;  and 
that,  on  the  whole,  the  difference  becomes  greater  tha 
farther  we  go  back  in  time.  The  organic  remains  which 
are  found  in  the  later  Oainozoic  deposits  of  any  district 

c  2 


20    THB  ANATOMY  OF  INYEBTBBBATED  ANIMALS. 

are  alwajs  closely  allied  to  those  now  found  in  the  province 
of  distribution  in  which  that  locality  is  included ;  while  in 
the  older  Cainozoic  the  resemblance  is  less;  and  in  the 
Mesozoic,  and  the  PalsBozoic  strata,  the  fossils  maj  be  simi- 
lar to  creatures  at  present  liying  in  some  other  province, 
or  may  be  altogether  unlike  any  which  now  exist. 

In  any  given  locality,  the  succession  of  living  forms 
may  appear  to  be  interrupted  by  numerous  breaks — ^the 
associated  species  in  each  fossiliferous  bed  being  quite 
distinct  from  those  above  and  those  below  them.  But  the 
tendency  of  all  palseontological  investigation  is  to  show 
that  these  breaks  are  only  apparent,  and  arise  from  the 
incompleteness  of  the  series  of  remains  which  happens  to 
have  been  preserved  in  any  given  locality.  As  the  area 
over  which  accurate  geological  investigations  have  been 
carried  on  extends,  and  as  the  fossiliferous  rocks  found  in 
one  locality  fill  up  the  gaps  left  in  another,  so  do  the  abrupt 
demarcations  between  the  faunsB  and  florsB  of  successive 
epochs  disappear — a  certain  proportion  of  the  genera  and 
even  of  the  species  of  every  period,  great  or  small,  being 
found  to  be  continued  for  a  longer  or  shorter  time  into  the 
next  succeeding  period.  It  is  evident,  in  fact,  that  the 
changes  in  the  living  population  of  the  globe  which  have 
taken  place  during  its  history,  have  been  effected,  not  by 
the  sudden  replacement  of  one  set  of  living  beings  by 
another,  but  by  a  process  of  slow  and  gradual  introduc- 
tion of  new  species,  accompanied  by  the  extinction  of  the 
older  forms. 

It  is  a  remarkable  circumstance,  that,  in  all  parts  of  the 
globe  in  which  fossiliferous  rocks  have  yet  been  examined, 
the  successive  terms  of  the  series  of  living  forms  which 
have  thus  succeeded  one  another  are  analogous.  The  life 
of  the  Mesozoic  epoch  is  everywhere  characterised  by  the 
abundance  of  some  groups  of  species  of  which  no  trace  is 
to  be  found  in  either  earlier  or  later  formations ;  and  the 
like  is  true  of  the  Palsoozoic  epoch.  Hence  it  follows,  not 
only  that  there  has  been  a  succession  of  species,  but  that 
the  general  nature  of  thai  succession  has  been  the  same  all 


DI8TBIBUTION  IN  TIME.  21 

oyer  the  globe;  and  it  is  on  this  ground  that  fossils  are 
80  important  to  the  geologist  as  marks  of  the  relative  age 
of  rocks. 

The  determination  of  the  morphological  relations  of  the 
species  which  have  thus  succeeded  one  another  is  a  problem 
of  profound  importance  and  difficulty,  the  solution  of  which, 
howerer,  is  already  dearly  indicated.  For,  in  several  cases, 
it  is  possible  to  show  that,  in  the  same  geographical  area,  a 
form  A,  which  existed  during  a  certain  geological  ex)och, 
has  been  replaced  by  another  form  B,  at  a  later  period ; 
and  that  this  form  B  has  been  replaced,  stiU  later,  by  a 
third  form  C.  When  these  forms,  A,  B,  and  C,  are  com- 
pared together  they  are  found  to  be  organized  upon  the 
same  plan,  and  to  be  very  similar  even  in  most  of  the  de- 
tails of  their  structure ;  but  B  differs  from  A  by  a  slight 
modification  of  some  of  its  parts,  which  modification  is 
carried  to  a  still  greater  extent  in  C. 

In  other  words,  A,  B,  and  0  differ  from  one  another  in 
the  same  fashion  as  the  earlier  and  later  stages  of  the 
embryo  of  the  same  animals  differ ;  and,  in  successive  epochs, 
we  have  the  group  presenting  that  progressive  specialisa- 
tion which  characterises  the  development  of  the  individual. 
Clear  evidence  that  this  progressive  specialisation  of 
structure  has  actually  occurred  has  as  yet  been  obtained  in 
only  a  few  cases  {e.g.,  EquidcR,  Crocodilia),  and  these  are 
confined  to  the  highest  and  most  complicated  forms  of 
life;  while  it  is  demonstrable  that,  even  as  reckoned  by 
geological  time,  the  process  must  have  been  exceedingly 
slow. 

Among  the  lower  and  less  complicated  forms,  the  evi- 
dence of  progressive  modification,  furnished  by  compari- 
son of  the  oldest  with  the  latest  forms,  is  slight,  or  absent ; 
and  some  of  these  have  certainly  persisted,  with  very  little 
change,  from  extremely  ancient  times  to  the  present  day. 
It  is  as  important  to  recognise  the  fact  that  certain  forms 
of  life  have  thus  i>ersisted,  as  it  is  to  admit  that  others  have 
undergone  progressive  modification. 

It  luiB  been  said  that  the  successive  terms  in  the  series 


22         THE  ANATOm  OF  INYEBTEBRATED  ANOCALS. 

of  living  forms  are  analogous  in  all  parts  of  the  globe. 
But  the  species  which  constitute  the  corresponding  or 
hcmotcuBie  terms  in  the  series,  in  different  localities,  are  not 
identical.  And,  though  the  imperfection  of  our  knowledge 
at  present  precludes  positive  assertion,  there  is  every  reason 
to  believe  that  geographical  provinces  have  existed  through- 
out the  period  during  which  organic  remains  furnish  us 
with  evidence  of  the  existence  of  life.  The  wide  distribu- 
tion of  certain  Palaeozoic  forms  does  not  militate  against 
this  view ;  for  the  recent  investigations  into  the  nature  of 
the  deep-sea  fauna  have  shown  that  numerous  Orudacea, 
Echinodermata,  and  other  invertebrate  animals,  have  as 
wide  a  distribution  now  as  their  analogues  possessed  in  the 
Silurian  epoch. 

m.  Physiolooy. 

Thus  far,  living  beings  have  been  regarded  merely  as 
definite  forms  of  matter,  and  Biology  has  presented  no 
considerations  of  a  different  order  from  those  which  meet 
the  student  of  Mineralogy.  But  living  things  are  not  only 
natural  bodies,  having  a  definite  form  and  mode  of  struc- 
ture, growth,  and  development.  They  are  machines  in 
action ;  and,  under  this  aspect,  the  phenomena  which  they 
present  have  no  parallel  in  the  mineral  world. 

The  actions  of  living  matter  are  termed  its  funeUons ; 
and  these  functions,  varied  as  they  are,  may  be  reduced  to 
three  categories.  They  are  either — (1),  functions  which 
affect  the  material  composition  of  the  body,  and  determine 
its  mass,  which  is  the  balance  of  the  processes  of  waste  on 
the  one  hand  and  those  of  assimilation  on  the  other.  Or 
(2),  they  are  functions  which  subserve  the  process  of  re- 
production, which  is  essentially  the  detachment  of  a  part 
endowed  with  the  power  of  developing  into  an  independent 
whole.  Or  (3),  they  are  functions  in  virtue  of  which  one 
part  of  the  body  is  able  to  exert  a  direct  influence  on 
another,  and  the  body,  by  its  parts  or  as  a  whole,  ^becomes 
A  ionrce  of  molar  motion.    The  first  may  be  termed  austen' 


riTNCTIONS  AND  OBOAITS.  23 

ioHve,    the    second   generative,  and  the   third    eorreloHve 
functionB. 

Of  these  three  dasses  of  functions  the  first  two  onlj  can 
be  said  to  be  inyariably  present  in  living  beings,  all  of 
which  are  nonrish'ed,  grow,  and  ninltiplj.  But  there  are 
some  forms  of  life,  snch  as  manj  Fwngi,  which  are  not 
known  to  possess  any  powers  of  changing  their  form ;  in 
which  the  protoplasm  exhibits  no  moyements,  and  reacts 
npon  no  stimnlos ;  and  in  which  anj  influence  which  the 
different  parts  of  the  body  exert  upon  one^  another  must 
be  transmitted  indirectly  from  molecule  to  molecule  of  the 
common  mass.  In  most  of  the  lowest  plants,  however, 
and  in  all  animals  yet  known,  the  body  either  constantly 
or  temporarily  changes  its  form,  either  with  or  without  the 
application  of  a  special  stimulus,  and  thereby  modifies  the 
relations  of  its  parts  to  one  another,  and  of  the  whole  to 
surrounding  bodies ;  while,  in  aU  the  higher  animals,  the 
different  parts  of  the  body  are  able  to  affect,  and  be 
affected  by,  one  another,  by  means  of  a  special.tissue,  termed 
nerve.  Molar  motion  is  effected  on  a  large  scale  by  means 
of  another  special  tissue,  muscle;  and  the  organism  is 
brought  into  relation  with  surrounding  bodies  by  means  of 
a  third  kind  of  special  tissue — that  of  the  sensory  organs — 
by  means  of  which  the  forces  exerted  by  surrounding 
bodies  are  transmuted  into  affections  of  nerve. 

In  the  lowest  forms  of  life,  the  functions  which  have 
been  enumerated  are  seen  in  their  simplest  forms,  and 
they  are  exerted  indifferently,  or  nearly  so,  by  all  parts  of 
the  protoplasmic  body ;  and  the  like  is  true  of  the  functions 
of  the  body  of  even  the  highest  organisms,  so  long  as  they 
are  in  the  condition  of  the  nucleated  ceU,  which  constitutes 
the  starting-point  of  their  development.  But  the  first  pro- 
cess in  that  development  is  the  division  of  the  germ  into  a 
number  of  morphological  units  or  blastomeres,  which, 
eventually,  give  rise  to  cells;  and  as  each  of  these  pos- 
sesses the  same  physiological  functions  as  the  germ  itself, 
it  follows  that  each  morphological  iinit  is  also  a  physio- 
logical nnit,  and  the  multicellular  mass  is  strictly  a  com- 


24    THE  ANATOMY  OW   INYEBTEBBATED  ANIMALS. 

pound  organiBm,  made  np  of  a  multitude  of  ph jsiologicallj 
independent  cells.  The  physiological  actiyities  manifested 
bj  the  complex  whole  represent  the  sum,  or  rather  the 
resultant,  of  the  separate  and  independent  physiological 
actiyities  resident  in  e&ch  of  the  simpler  constituents  of 
that  whole. 

The  morphological  changes  which  the  cells  undergo  in 
the  course  of  the  further  development  of  the  organism,  do 
not  affect  their  individuality;  and,  notwithstanding  the 
modification  and  confluence  of  its  constituent  cells,  the 

« 

adult  organism,  however  complex,  is  still  an  aggregate  of 
morphological  units.  Nor  is  it  less  an  aggregate  of  physio- 
logical units,  each  of  which  retains  its  fundamental  inde- 
pendence, though  that  independence  becomes  restricted  in 
various  ways. 

Each  cell,  or  that  element  of  a  tissue  which  proceeds 
from  the  modification  of  a  cell,  must  needs  retain  its 
sustentative  functions  so  long  as  it  grows  or  niaint4unH  a 
condition  of  equilibrium ;  but  the  most  completely  meta- 
morphosed cells  show  no  trace  of  the  generative  function, 
and  many  exhibit  no  correlative  functions.  Contrariwise 
those  cells  of  the  adult  organism  which  are  the  unmeta- 
morphosed  derivatives  of  the  germ,  exhibit  aU  the  primary 
functions,  not  only  nourishing  themselves  and  growing, 
but  multiplying,  and  frequently  showing  more  or  less  ' 
marked  movements. 

Organs  are  parts  of  the  body  which  perform  particular 
functions.  In  strictness,  perhaps,  it  is  not  quite  right  to 
speak  of  organs  of  sustentation  or  generation,  each  of  these 
functions  being  necessarily  performed  by  the  morphological 
unit  which  is  nourished  or  reproduced.  What  are  called 
the  organs  of  these  functions  are  the  apparatuses  by  which 
certain  operations,  subsidiary  to  sustentation  and  genera- 
tion, are  carried  on. 

Thus,  in  the  case  of  the  sustentative  functions,  all  those 
organs  may  be  said  to  contribute  to  these  functions  which 
are  concerned  in  bringing  nutriment  within  the  reach  of 
the  ultimate  ceUs,  or  in  removing  waste  matter  from  them ; 


MTTBCIil  AVD  NBBTI.  25 

while  in  the  case  of  the  generative  function,  all  those  organs 
contribute  to  the  function  which  produce  the  cells  froxD. 
which  germs  are  giren  off;  or  help  in  the  eracuation,  or 
fertilisation,  or  deyelopment  of  these  germs. 

On  the  other  hand,  the  correlative  functions,  so  long  as 
thej  are  exerted  bj  a  simple  undifferentiated  morphological 
unit  or  cell,  are  of  the  simplest  character,  consisting  of 
those  modifications  of  position  which  can  be  effected  bj 
mere  changes  in  the  form  or  arrangement  of  the  parts  of 
the  protoplasm,  or  of  those  prolongations  of  the  proto- 
plasm which  are  called  pseudopodia  or  cilia.  But,  in  the 
higher  animals  and  plants,  the  movements  of  the  organism 
and  of  its  parts  are  brought  about  by  the  change  of  the 
form  of  certain  tissues,  the  property  of  which  is  to  shorten 
in  one  direction  when  exposed  to  certain  stimuli.  Such 
tissues  are  termed  eovUractile;  and,  in  their  most  fully 
developed  condition,  muscular.  The  stimulus  by  which 
this  contraction  is  naturally  brought  about  is  a  molecular 
change,  either  in  the  substance  of  the  contractile  tissue 
itself,  or  in  some  other  part  of  the  body ;  in  which  latter 
case,  the  motion  which  is  set  up  in  that  part  of  the  body 
.uust  be  propagated  to  the  contractile  tissue  through  the 
ii  termediate  substance  of  the  body.  In  plants,  there  seems 
to  be  no  question  that  parts  which  retain  a  hardly  modified 
ceL  ^ar  structure  may  serve  as  channels  for  the  transmis- 
sion of  this  molecular  motion ;  whether  the  same  is  true  of 
animals  is  not  certain.  But,  in  all  the  more  complex 
animals,  a  peculiar  fibrous  tissue — nerve — serves  as  the 
agent  by  which  contractile  tissue  is  affected  by  changes 
occurring  elsewhere,  and  by  which  contractions  thus  ini- 
tiated are  co-ordinated  and  brought  into  harmonious  com- 
bination. While  the  sustentative  functions  in  the  higher 
forms  of  life  are  still,  as  in  the  lower,  fundamentally  de- 
pendent upon  the  powers  inherent  in  all  the  physiological 
units  which  make  up  the  body,  the  correlative  functions 
are,  in  the  former,  deputed  to  two  sets  of  specially  modified 
units,  which  constitute  the  muscular  and  the  nervous  tissues. 

When  the  different  forms  of  life  are  compared  together 


26    THB  ANATOMY  OF  IKYXBTEBRATED  ANXMALS. 

as  physiological  machines,  thej  are  found  to  differ  as 
machines  of  human  constmction  do.  In  the  lower  forms, 
the  mechanism,  though  perfectlj  well  adapted  to  do  the 
work  for  which  it  is  required,  is  rough,  simple,  and  weak ; 
while,  in  the  higher,  it  is  finished,  complicated,  and  powerfuL 
Considered  as  machines,  there  is  the  same  sort  of  difference 
between  a  polype  and  a  horse  as  there  is  between  a  distaff 
and  a  spinning-jenny.  In  the  progress  from  the  lower  to 
the  higher  organism,  there  is  a  gradual  differentiation  of 
organs  and  of  functions.  Each  function  is  separated  into 
many  parts,  which  are  severally  entrusted  to  distinct  organs. 
To  use  the  striking  phrase  of  Milne-Edwards,  in  passing 
from  low  to  high  organisms,  there  is  a  division  of  physio- 
logical labour.  And  exactly  the  same  process  is  observable 
in  the  development  of  any  of  the  higher  organisms;  so 
that,  physiologically  as  well  as  morphologicaUy,  develop- 
ment is  a  progress  from  the  general  to  the  special 

Thus  far,  the  physiological  activities  of  living  matter 
have  been  considered  in  themselves,  and  without  reference 
to  anything  that  may  affect  them  in  the  world  outside  the 
living  body.  But  living  matter  acts  on,  and  is  powerfully 
affected  by,  the  bodies  which  surround  it ;  and  the  study  of 
the  influence  of  the  **  conditions  of  existence  "  thus  deter- 
mined constitutes  a  most  important  part  of  Physiology. 

The  sustentative  functions,  for  example,  can  only  be 
exerted  under  certain  conditions  of  temperature,  pressure, 
and  light,  in  certain  media,  and  with  supplies  of  particular 
kinds  of  nutritive  matter;  the  sufficiency  of  which  supplies, 
again,  is  greatly  influenced  by  the  competition  of  other 
organisms,  which,  striving  to  satisfy  the  same  needs,  give 
rise  to  the  passive  "  struggle  for  existence."  The  exercise 
of  the  correlative  functions  is  influenced  by  similar  condi- 
tions, and  by  the  direct  conflict  with  other  organisms,  which 
constitutes  the  active  struggle  for  existence.  And,  finally, 
the  generative  functions  are  subject  to  extensive  modifi- 
cations, dependent  partly  upon  what  are  commonly  called 
external  conditions,  and  partly  upon  wholly  unknown 
agencies. 


AOAMOOSirBSIS.  27 

In  the  lowest  forms  of  life,  the  only  mode  of  generation 
at  present  known  is  the  division  of  the  body  into  two  or 
more  parts,  each  of  which  then  grows  to  the  size  and 
assumes  the  form  of  its  parent,  and  repeats  the  process  of 
mnltiplication.  This  method  of  mnltiplioation  bj  fission 
is  properly  called  generation,  becanse  the  parts  which  are 
separated  are  seyerally  competent  to  give  rise  to  individoal 
oi^anisms  of  the  same  nature  as  that  from  which  they 


In  many  of  the  lowest  organisms  the  process  is  modified 
■0  far  that,  instead  of  the  parent  dividing  into  two  eqiud 
parts,  only  a  small  portion  of  its  substance  is  detached,  as 
a  bod,  which  developes  into  the  likeness  of  its  parent. 
This  is  generation  by  gemmation.  Generation  by  fission 
and  by  gemmation  are  not  confined  to  the  simplest  forms 
of  life,  however.  On  the  contrary,  both  modes  of  multipli- 
cation are  common  not  only  among  plants,  but  among 
animals  of  considerable  complexity. 

The  multiplication  of  flowering  plants  by  bulbs,  that  of 
annelids  by  fission,  and  that  of  polypes  by  budding,  are 
weU-known  examples  of  these  modes  of  reproduction.  In 
all  these  cases,  the  bud  or  the  segment  consists  of  a  multi- 
tude of  more  less  metamorphosed  cells.  But,  in  other 
instances,  a  single  cell  detached  from  a  mass  of  such  un- 
differentiated cells  contained  in  the  parental  organism  is 
the  foundation  of  the  new  organism,  and  it  is  hard  to  say 
whether  such  a  detached  cell  may  be  more  fitly  called  a  bud 
or  a  segment — whether  the  process  is  more  akin  to  fission 
or  to  gemmation. 

In  all  these  cases  the  development  of  the  new  being  from 
the  detached  germ  takes  place  without  the  influence  of 
other  living  mattsr»  Common  as  the  process  is  in  plants 
and  in  the  lower  animals,  it  becomes  rare  among  the 
higher  animals.  In  these,  the  reproduction  of  the  whole 
organism  from  a  part,  in  the  way  indicated  above,  ceases. 
At  most  we  find  that  the  cells  at  the  end  of  an  amputated 
portion  of  the  organism  are  capable  of  reproducing  the 
lost  part;   in  the  very  highest  animals,  even  this  power 


28    THE  AKATOMY  OF  INYBBTEBBATED  ANIMALS. 

vanishes  in  the  adult;  and,  in  most  parts  of  the  body, 
thongh  the  undifferentiated  cells  are  capable  of  mnltipli* 
cation,  their  progeny  grow,  not  into  whole  organisms 
like  that  of  which  they  form  a  part,  but  into  elements  of 
the  tissues. 

Throughout  almost  the  whole  series  of  living  beings, 
however,  we  find  concurrently  with  the  process  of  agixmiih 
genesis,  or  asexual  generation,  another  method  of  genera- 
tion,  in  which  the  development  of  the  germ  into  an  organism 
resembling  the  parent  depends  on  an  influence  exerted  by 
living  matter  different  from  the  germ.  This  is  gamogenetit 
or  sexual  generation.  Looking  at  the  facts  broadly,  and 
without  reference  to  many  exceptions  in  detail,  it  may  be 
said  that  there  is  an  inverse  relation  between  agamogenedc 
and  gamogenetic  reproduction.  In  the  lowest  organisms 
gamogenesis  has  not  yet  been  observed,  while  in  the  highest 
agamogenesis  is  absent.  In  many  of  the  lower  forms  of 
life  agamogenesis  is  the  common  and  predominant  mode 
of  reproduction,  while  gamogenesis  is  exceptional ;  on  the 
contrary,  in  many  of  the  higher,  while  gamogenesis  is  the 
rule,  agamogenesis  takes  place  exceptionally. 

In  its  simplest  condition,  which  is  termed  *'  conjngaiwn,^ 
sexual  generation  consists  in  the  coalescence  of  two  wTniliiy 
masses  of  protoplasmic  matter,  derived  from  different  parts 
of  the  same  organism,  or  from  two  organisms  of  the  same 
species,  and  the  single  mass  which  results  from  the  fusion 
develops  into  a  new  organism. 

In  the  majority  of  cases,  however,  there  is  a  marked 
morphological,  difference  between  the  two  factors  in  the 
process,  and  then  one  is  called  the  nude,  and  the  other  the 
female  element.  The  female  element  is  relatively  large, 
and  undergoes  but  little  change  of  form.  In  all  the  higher 
plants  and  animals  it  is  a  nucleated  cell,  to  which  a  gpreatei 
or  less  amount  of  nutritive  material,  constituting  a  food- 
yelk,  may  be  added. 

The  male  element,  on  the  other  hand,  is  relatively  smalL 
It  may  be  conveyed  to  the  female  element  by  an  out- 
growth of  the  wall  of  its  cell,  which  is  short  in  many 


OAMOGBITESIS.  29 

[lg(B  and  Fungi,  but  becomes  an  immensely  elongated 
ibnlar  filament,  in  the  case  of  the  pollen  cell  of  flowering 
lants.  But,  more  commonlj,  the  protoplasm  of  the  nude 
dl  becomes  conyerted  into  rods  or  filaments,  which 
gnally  are  in  active  yibratile  moyement,  and  sometimes 
re  propelled  bj  numerous  cilia.  Occasionallj,  however, 
B  in  many  Nematoidea  and  Artkropoda,  they  are  devoid  of 
lobility. 

The  manner  in  which  the  contents  of  the  pollen  tube 
ifect  the  embryo  cell  in  flowering  plants  is  unknown,  as 

0  perforation  through  which  the  contents  of  the  pollen 
abe  may  jmiss,  so  as  actually  to  mix  with  the  substance  of 
be  embryo  cell,  have  been  discovered;  and  there  is  the 
une  difficulty  with  respect  to  the  conjugative  processes 
f  some  of  the  Cryptogamia,  But  in  the  great  nugority 
f  plants,  and  in  all  animals,  there  can  be  no  doubt  that 
be  substance  of  the  male  element  actually  mixes  with  that 
f  the  female,  so  that,  in  all  these  cases,  the  sexual  process 
emains  one  of  conjugation;  and  impregnation  is  the 
hysical  admixture  of  protoplasmic  matter  derived  from 
wo  sources,  which  may  be  either  different  parts  of  the  same 
rganism,  or  different  organisms. 

The  effiect  of  impregnation  appears  in  all  cases  to  be 
bat  the  impregnated  protoplasm  tends  to  divide  into 
ortions  {blagtomeres),  which  may  remain  united  as  a  single 
^-aggregate,  or  some  or  all  of  which  may  become  separate 
rganisms.  A  longer  or  shorter  period  of  rest,  in  many 
ues,  intervenes  between  the  act  of  impregnation  and  the 
ommencement  of  the  process  of  division. 

As  a  general  rule,  the  female  cell  which  directly  receives 
he  influence  of  the  male  is  that  which  undergoes  division 
nd  eventual  development  into  independent  germs;  but 
here  are  some  plants,  such  as  the  FloridecB,  in  which  this 

1  not  the  case.  In  these,  the  protoplasmic  body  of  the 
richogyne,  which  unites  with  the  spermatozooids,  does  not 
mdergo  division  itself,  but  transmits  some  influence  to 
djaoent  cells,  in  virtue  of  which  they  become  subdivided 
nto  independent  germs  or  spores. 


30         THE  ANATOMY  OF  INYBBTEBBATBD  AKIMAIiS. 

There  is  still  much  obscuritj  respecting  the  reprodnctaTe 
processes  of  the  Infusoria ;  but,  in  the  VoHiedlidcR^  it  would 
appear  that  conjugation  merely  determines  a  condition  of 
the  whole  organism,  which  gives  rise  to  the  division  of  the 
endoplast  or  so-caUed  nucleus,  by  which  germs  are  thrown 
off;  and  if  this  be  the  case,  the  process  would  have  some 
analogy  to  what  takes  place  in  the  FloridecB. 

On  the  other  hand,  the  process  of  conjugation  by  which 
two  distinct  DiporpcB  combine  into  that  extraordinary 
double  organism,  the  Diplosoon  paradoxwn,  does  not  directly 
give  rise  to  germs,  but  determines  the  development  of  the 
sexual  organs  in  each  of  the  conjugated  individuals ;  and 
the  same  process  takes  place  in  a  large  number  of  the 
Infusoria,  if  what  are  supposed  to  be  male  sexual  elements 
in  them  are  really  such. 

The  process  of  impregnation  in  the  Floridea  is  remark- 
ably interesting,  from  its  bearing  upon  the  changes  which 
fecundation  is  known  to  produce  upon  parts  of  the  parental 
organism  other  than  the  ovum,  even  in  thohighest  i^wimnla 
and  plants. 

The  nature  of  the  influence  exerted  by  the  male  ^ment 
upon  the  female  is  wholly  unknown.  No  morphological 
distinction  can  be  drawn  between  those  cells  which  are 
capable  of  reproducing  the  whole  organism  without  im* 
pregnation,  and  those  which  need  it,  as  is  obvious  from 
what  happens  in  insects,  where  eggs  which  ordinarily  re- 
quire impregnation,  exceptionally,  as  in  many  moths,  or 
regularly,  as  in  the  case  of  the  drones  among  bees,  develop 
without  impregnation.  Even  in  the  higher  ft-niTrialu^  such 
as  the  fowl,  the  earlier  stages  of  division  of  the  germ  may 
take  place  without  impregnation. 

In  fact,  generation  may  be  regarded  as  a  particular 
case  of  cell  multiplication,  and  impregnation  simply  as  one 
of  the  many  conditions  which  may  determine  or  affect  that 
process.  In  the  lowest  organisms,  the  simple  protoplasmic 
mass  divides,  and  each  part  retains  all  the  physiological  pro- 
perties of  the  whole,  and  consequently  constitutes  a  germ 
whence  the  whole  body  can  be  reproduced,    Ii^  more  ad- 


I 


Tm  TBIOBT  or  nOWDATIOIT,  31a 

need  organimu,  each  ci  the  mnltitade  of  cells  into  which 

eembiTOcell  wconTcrted  at  fint,  probably  retaiiu  all,  or 

■rij  all,  the  phjaiolo^cal  capabQitieH  of  the  whole,  and  is 

pable  of  ■erring  at  a  reprodnctiTe  geim ;  but  at  diTision 

ea  on,  and  many  of  the  cells  which  re«alt  from  divirion 

jnire  special  morphological  and  phjeiological  properties, 

■eema  not  improbable  that  thej,  in  proportion,  loae  their 

)re  general  characteia.  In  proportion,  for  example,  aa  the 

lieacj  of  a  given  cell  to  become  a  mnacle  cell  or  a  car- 

Kge  cell  is  more  nurlced  and  definite,  it  is  readily  con- 

TaUe  that  ita  primitiTe  capacity  to  reproduce  the  whole 

janiam  should  be  reduced,  though  it  might  not  be  alto- 

ther  abolished.    If  this  view  is  well  based,  the  power  of 

pvodncing  the  whole  organism  would  be  limit«d  to  those 

!la  which  had  acquired  no  special  tendencies,  and  conse- 

ently  had  retained  all  the  powers  of  the  primiliye  cell 

which  the  organism  commenced  its  existence.   The  more 

enaively  diSnsed  such  cells  were,  the  more  generally 

■ht  multiplication  by  budding  or  fission  take  place;  the 

e  localised,  the  more  limited  would  be  the  parta  of  the 

nism  in  which  such  a  process  would  take  place.    And 

where  such  cells  occurred,  their  development  or  non- 

opment  might  be  connected  with  conditions  of  nntri- 

It  depends  on  the  nutriment  supplied  to  the  female 

of  abee  whether  it  shall  become  a  neuter  or  a  sexually 

-t  female ;  and  the  sexual  perfection  of  a  large  pro- 

n   of  the   internal  parasites  is   similarly  dependent 

heir  food,  and  perhaps  on  other  conditions,  such  as 

iperature  of  the  medium  in  which  Uiey  live.  Thus  the 

Idisappearanceofagamogenesis  in  tbehigher  animals 

be  related  with   that   increasing   specialisation   of 

t  which  is  their  essential  charact«riatic ;  and  when 

to  occur  altogether,  it  may  be  supposed  that  no  cells 

which  retain  nnmodified  the  powers  of  the  primi- 

i^  cell.     The  organism  is  like  a  society  in  which 

I  ia  so  engrossed  by  bis  special  business  that  he 

a  time  nor  inclination  to  marry. 

be  female  elements  in  the  highest  organisms. 


402  THE  ANATOMY  OF  INTEBTEBBATED  ANIMALS. 

little  as  thej  differ  to  all  appearance  from  undifferentiated 
ceUs,  and  though  thej  are  directlj  derived  from  epithelial 
cells  which  have  undergone  yerj  little  modification  from 
the  condition  of  blastomeres,  are  incapable  of  full  develop- 
ment unless  they  are  subjected  to  the  influence  of  the 
male  element,  which  may,  as  Caspar  Wolff  suggested,  be 
compared  to  a  kind  of  nutriment.  But  it  is  a  living  nutri- 
ment, in  some  respects  comparable  to  that  which  would  be 
supplied  to  an  animal  kept  alive  bj  transfusion,  and  its 
molecules  transfer  to  the  impregnated  embryo  cdl  all  the 
special  characters  of  the  organism  to  which  it  belonged. 

The  tendency  of  the  germ  to  reproduce  the  characters 
of  its  immediate  parents,  combined,  in  the  case  of  sexual 
generation,  with  the  tendency  to  reproduce  the  characters 
of  the  male,  is  the  source  of  the  singular  phenomena  of 
hereditary  transmission.  No  structural  modification  is  so 
slight,  and  no  functional  peculiarity  is  so  insignificant  in 
either  parent  that  it  may  not  make  its  appearance  in  the 
offspring.  But  the  transmission  of  parental  peculiarities 
depends  greatly  upon  the  manner  in  which  they  have  been 
acquired.  Such  as  have  arisen  naturally,  and  have  been 
hereditary  through  many  antecedent  generations,  tend  to 
appear  in  the  progeny  with  great  force;  while  artificial 
modifications,  such  for  example,  as  result  from  mutilation, 
are  rarely  if  ever,  transmitted.  Circumcision  through  in- 
numerable ancestral  generations  does  not  appear  to  have 
reduced  that  rite  to  a  mere  formality,  as  it  should  have 
done,  if  the  abbreviated  prepuce  had  become  hereditary  in 
the  descendants  of  Abraham ;  while  modem  lambs  are  bom 
with  long  tails,  notwithstanding  the  long-continued  prac- 
tice of  cutting  those  of  every  generation  short.  And  it 
remains  to  be  seen  whether  the  supposed  hereditary  trans- 
mission of  the  habit  of  retrieving  among  dogs  is  really  what 
it  seems  at  first  sight  to  be;  on  the  other  side,  Brown- 
Sequard*s  case  of  the  transmission  of  aitificially  induced 
epilepsy  in  guinea-pigs  is  undoubtedly  very  weighty. 

Although  the  germ  always  tends  to  reproduce,  directly 
or  indirectly,  the  organism  from  which  it  is  derived,  the 


THB  AI/TBBNATION  OF  OBNEBATIONS.  801 

lesnlt  of  its  derelopment  differs  somewhat  from  the  parent, 
UsaaUy  the  amount  of  variation  is  insignificant;  but  it 
may  be  considerable,  as  in  the  so-called  "sports;"  and 
sach  Tariations,  whether  useful  or  useless,  may  be  trans- 
mitted with  great  tenacity  to  the  offspring  of  the  subjects 
of  them. 

In  many  plants  and  animals  which  multiply  both  asexu- 
ally  and  sexually,  there  is  no  definite  relation  between  the 
agamogenetic  and  the  gamogenetic  phenomena.  The  or- 
ganism may  multiply  asexually  before,  or  after,  or  con- 
currently with,  the  occurrence  of  sexual  generation. 

But  in  a  great  many  of  the  lower  organisms,  both  animal 
tnd  Tegetable,  the  organism  (A)  which  results  from  the  im- 
pregnated germ  produces  offspring  only  agamogenetically. 
It  thus  gives  rise  to  a  series  of  independent  organisms, 
(B,  B,  B,  .  .  .),  which  are  more  or  less  different  from  A, 
and  which  sooner  or  later  acquire  generative  organs.  From 
their  impregnated  germs  A  is  reproduced.  The  process 
thus  described  is  what  has  been  termed  the  "  alternation 
of  generations  "  under  its  simplest  form, — for  example,  as 
it  is  exhibited  by  the  SalpcB,  In  more  complicated  cases, 
the  independent  organisms  which  correspond  with  B  may 
pre  rise  agamogenetically  to  others  (Bj),  and  these  to  others 
Bj),  and  so  on  (e.g.  Aphis).  But,  however  long  the  series, 
i  final  term  appears  which  developes  sexual  organs,  and 
reproduces  A.  The  "  alternation  of  generations  "  is,  there- 
:are,  in  strictness,  an  alternation  of  asexual  with  sexual 
generation,  in  which  the  products  of  the  one  process  differ 
^m  those  of  the  other. 

The  Hydrozoa  offer  a  complete  series  of  gradations  be- 
tween those  cases  in  which  the  term  B  is  represented  by  a 
Tee,  self -nourishing  organism  (e.g.,  CyancBo),  through  those 
n  which  it  is  free  but  unable  to  feed  itself  (Calycophoridce), 
o  ihoee  in  which  the  sexual  elements  are  developed  in 
xidies  which  resemble  free  zooids,  but  are  never  detached, 
ind  are  mere  generative  organs  of  the  body  on  which  they 
ire  developed  {Cord/ylophora). 

In  the  last  case,  the  "  individual "  is  the  total  product  of 

D 


34         THE  ANATOMY  OV  IVTBBTSBBATBD  AITIMALS. 

the  development  of  the  impregnated  embryo,  all  the  parts 
of  which  remain  in  material  continuity  with  one  another. 
The  multiplication  of  mouths  and  stomachs  in  a  Cordy- 
lophora  no  more  makes  it  an  aggregation  of  different 
individuals  than  the  multiplication  of  segments  and  legs  in 
a  centipede  converts  that  Arthropod  into  a  compound 
animal.  The  Cordylophora  is  a  differentiation  of  a  whole 
into  many  parts,  and  the  use  of  any  terminology  which  im- 
plies that  it  results  from  the  coalescence  of  many  parts  into 
a  whole  is  to  be  deprecated. 

In  Cordylophora  the  generative  organs  are  incapable  of 
maintaining  a  separate  existence;  but  in  nearly  allied 
Hyd/rozoa  the  unquestionable  homologues  of  these  organs 
become  free  zooids,  in  many  cases  capable  of  feeding  and 
growing,  and  developing  the  sexual  elements  only  after 
they  have  undergone  considerable  changes  of  form.  Mor- 
phologically, the  swarm  of  MedMsoi  thus  set  free  fi'om  a 
Hydrozoon  are  as  much  organs  of  the  latter,  as  the  multi- 
tudinous pinnules  of  a  Comahda,  with  their  genital  glands, 
are  organs  of  the  Echinoderm.  Morphologically,  therefore, 
the  equivalent  of  the  individual  Comatula  is  the  Hydrozoic 
stock  plus  all  the  MeduscB  which  proceed  from  it. 

No  doubt  it  sounds  paradoxical  to  speak  of  a  million  of 
Aphides,  for  example,  as  parts  of  one  morphological  indivi- 
dual ;  but  beyond  the  momentary  shock  of  the  paradox  no 
harm  is  done.  On  the  other  hand,  if  the  asexual  Aphides 
are  held  to  be  individuals,  it  follows,  as  a  logical  conse- 
quence, not  only  that  all  the  polyx>es  on  a  Cordylophora 
tree  are  "feeding  individuals,"  and  all  the  genital  sacs 
''generative  individuals,"  while  the  stem  must  be  a 
"  stump  individual,"  but  that  the  eyes  and  legs  of  a  lobster 
are  "ocular"  and  "locomotive  individuals."  And  this 
conception  is  not  only  somewhat  more  paradoxical  than  the 
other,  but  suggests  a  conception  of  the  origin  of  the  com- 
plexity of  animal  structure  which  is  wholly  inconsiBtent 
with  fact. 


•i  ■ 


CAUBXS  OF  THS  PHSNOXBNA  OV  IJFB.  85 


IV.  -Etiology. 

Morphology,  Distribation,  and  Fhjsiologj  inrestigate 
and  determine  the  facts  of  Biology.  Etiology  has  for  its 
object  the  ascertainment  of  the  cansee  of  these  facts,  and 
the  explanation  of  biological  phenomena,  by  showing  that 
they  constitute  particular  cases  of  general  physical  laws. 
It  is  hardly  needful  to  say  that  setiology,  as  thus  conceived, 
is  in  its  infancy,  and  that  the  seething  controversies,  to 
which  the  attempt  to  found  this  branch  of  science  made 
in  the  Origin  of  Species  has  given  rise,  cannot  be  dealt  with 
in  this  place.  At  most,  the  general  nature  of  the  problems 
to  be  solved,  and  the  course  of  inquiry  needful  for  their 
solutioii,  may  be  indicated. 

In  any  investigation  into  the  causes  of  the  phenomena  of 
life,  the  first  question  which  arises  is,  whether  we  have 
any  knowledge,  and  if  so,  what  knowledge,  of  the  origin 
of  living  matter? 

In  the  case  of  all  conspicuous  and  easily-studied  organ- 
isms,  it  has  been  obvious,  since  the  study  of  nature  began, 
that  living  beings  arise  by  generation  from  living  beings 
of  a  like  kind;  but  before  the  latter  part  of  the  17th  cen- 
tury, learned  and  unlearned  alike  shared  the  conviction 
that  this  rule  was  not  of  universal  application,  and  that 
multitudes  of  the  smaller  and  more  obscure  organisms  were 
produced  by  the  fermentation  of  not-living,  and  especially 
of  putrefying  dead  matter,  by  what  was  then  termed  gene- 
ratio  cequivoca  or  eponianea,  and  is  now  called  abiogenesis, 
Redi  showed  that  the  general  belief  was  erroneous  in  a 
multitude  of  instances;  SpaUanzani  added  largely  to  the 
list ;  while  the  investigations  of  the  scientific  helmintholo- 
gists  of  the  present  century  have  eliminated  a  further 
category  of  cases  in  which  it  was  possible  to  doubt  the 
appUcability  of  the  rule  "  omnfie  tntn*m  e  vivo "  to  the  more 
complex  organisms  which  constitute  the  present  fauna  and 
flora  of  the  earth.  Even  the  most  extravagant  supporters 
of  abiogenesis  at  the  present  day  do  not  pretend  that 

D  2 


28         THE  ANATOMY  OF  INYEBTBBRATED  ANIMALS. 

vanishes  in  the  adult;  and,  in  most  parts  of  the  body, 
though  the  undifferentiated  cells  are  capable  of  mnltipli* 
cation,  their  progeny  grow,  not  into  whole  organimiB 
like  that  of  which  they  form  a  part,  but  into  elements  of 
the  tissues. 

Throughout  almost  the  whole  series  of  living  beings, 
however,  we  find  concurrently  with  the  process  of  agamo* 
genesis,  or  asexual  generation,  auother  method  of  genera- 
tion, in  which  the  development  of  the  germ  into  an  organism 
resembling  the  parent  depends  on  an  influence  exerted  by 
Hving  matter  different  from  the  germ.  This  is  gwmogenemM 
or  sexual  generation.  Looking  at  the  facts  broadly,  and 
without  reference  to  many  exceptions  in  detail,  it  may  be 
said  that  there  is  an  inverse  relation  between  agamogenetic 
and  gamogenetic  reproduction.  In  the  lowest  organisms 
gamogenesis  has  not  yet  been  observed,  while  in  the  highest 
agamogenesis  is  absent.  In  many  of  the  lower  forms  of 
life  agamogenesis  is  the  common  and  predominant  moda 
of  reproduction,  while  gamogenesis  is  exceptional ;  on  the 
contrary,  in  many  of  the  higher,  while  gamogenesis  is  the 
rule,  agamogenesis  takes  place  exceptionally. 

In  its  simplest  condition,  which  is  termed  "  eonjugaiion,^ 
sexual  generation  consists  in  the  coalescence  of  two  similar 
masses  of  protoplasmic  matter,  derived  from  different  parts 
of  the  same  organism,  or  from  two  organisms  of  the  same 
species,  and  the  single  mass  which  results  from  the  fusion 
develops  into  a  new  organism. 

In  the  majority  of  cases,  however,  there  is  a  marked 
morphological  difference  between  the  two  factors  in  the 
process,  and  then  one  is  called  the  male,  and  the  other  the 
female  element.  The  female  element  is  relatively  large, 
and  undergoes  but  little  change  of  form.  In  all  the  higher 
plants  and  animals  it  is  a  nucleated  cell,  to  which  a  greater 
or  less  amount  of  nutritive  material,  constituting  a  food' 
yelkf  may  be  added. 

The  male  element,  on  the  other  hand,  is  relatively  small. 
It  may  be  conveyed  to  the  female  element  by  an  out- 
growth of  the  wall  of  its  ceU,  which  is  short  in  many 


OAMOaBNSSIS.  29 

AlgcB  and  Fungi,  but  becomes  an  immenselj  elongated 
tubular  filament,  in  the  case  of  the  pollen  ceU  of  flowering 
plants.  Bnt,  more  commonly,  the  protoplasm  of  the  male 
oeU  becomes  converted  into  rods  or  filaments,  which 
Qsoallj  are  in  active  vibratile  movement,  and  sometimes 
are  propelled  bj  numerous  cilia.  Occasionally,  however, 
as  in  many  Nematoidea  and  Arthropoda,  they  are  devoid  of 
mobility. 

The  manner  in  which  the  contents  of  the  pollen  tube 
affect  the  embryo  cell  in  flowering  plants  is  unknown,  as 
no  perforation  through  which  the  contents  of  the  pollen 
tube  may  pass,  so  as  actually  to  mix  with  the  substance  of 
the  embrjo  cell,  have  been  discovered;  and  there  is  the 
nine  difficulty  with  respect  to  the  conjugative  processes 
of  some  of  the  Cryptogamia,  But  in  the  great  msgority 
of  plants,  and  in  all  animals,  there  can  be  no  doubt  that 
the  substance  of  the  male  element  actually  mixes  with  that 
of  the  female,  bo  that,  in  all  these  cases,  the  sexual  process 
remains  one  of  conjugation;  and  impregnation  is  the 
physical  admixture  of  protoplasmic  matter  derived  from 
two  sources,  which  may  be  either  different  parts  of  the  same 
organism,  or  different  organisms. 

The  effect  of  impregnation  appears  in  all  cases  to  be 
that  the  impregnated  protoplasm  tends  to  divide  into 
portions  {bl4uio7n€re8\  which  may  remain  united  as  a  single 
<^-Aggregatey  or  some  or  all  of  which  may  become  separate 
organisms.  A  longer  or  shorter  period  of  rest,  in  many 
eases,  intervenes  between  the  act  of  impregnation  and  the 
commencement  of  the  process  of  division. 

As  a  general  rule,  the  female  cell  which  directly  receives 
the  influence  of  the  male  is  that  which  undergoes  division 
and  eventual  development  into  independent  germs;  but 
there  are  some  plants,  such  as  the  Floridece,  in  which  this 
is  not  the  case.  In  these,  the  protoplasmic  body  of  the 
trichogyne,  which  unites  with  the  spermatozooids,  does  not 
undergo  division  itself,  but  transmits  some  influence  to 
adjacent  cells,  in  virtue  of  which  they  become  subdivided 
into  independent  germs  or  spores. 


r-i 


38         THB  ANATOICY  OF  INYBBTSBBATBD  ANIMALS. 

that  the  more  careful  the  investigator,  and  the  more  com- 
plete his  mastery  over  the  endless  practical  difficulties 
which  surronnd  experimentation  on  this  subject,  the  more 
certain  are  his  experiments  to  give  a  negative  result ;  while 
positive  results  are  no  less  sure  to  crown  the  efforts  of  the 
clumsy  and  the  careless. 

It  is  argued  that  a  belief  in  abiogenesis  is  a  necessary 
corollary  from  the  doctrine  of  Evolution.  This  may  be  true 
of  the  occurrence  of  abiogenesis  at  some  time ;  but  if  the 
present  day,  or  any  recorded  epoch  of  geological  time,  be  in 
question,  the  exact  contrary  holds  good.  If  all  living  beings 
have  been  evolved  from  pre-existing  forms  of  life,  it  is 
enough  that  a  single  particle  of  living  protoplasm  should 
once  have  appeared  on  the  globe,  as  the  result  of  no  matter 
what  agency.  In  the  eyes  of  a  consistent  evolutionist,  any 
further  independent  formation  of  protoplasm  would  be  sheer 
waste. 

The  production  of  living  matter  since  the  time  of  its  first 
appearance,  only  by  way  of  biogenesis,  implies  that  the 
specific  forms  of  the  lower  kinds  of  life  have  undergone  but 
little  change  in  the  course  of  geological  time,  and  this  is 
said  to  be  inconsistent  with  the  doctrine  of  evolution.  But, 
in  the  first  place,  the  fact  is  not  inconsistent  with  the 
doctrine  of  evolution  properly  understood,  that  doctrine 
being  perfectly  consistent  with  either  the  progression,  the 
retrogression,  or  the  stationary  condition  of  any  particular 
species  for  indefinite  periods  of  time ;  and  secondly,  if  it 
were,  it  would  be  so  much  the  woi^se  for  the  doctrine  of 
evolution,  inasmuch  as  it  is  unquestionably  true,  that 
certain,  even  highly  organised,  forms  of  life  have  persisted 
without  any  sensible  change  for  very  long  periods.  The 
Terebrcdtila  psiUcuxa  of  the  present  day,  for  example,  is  not 
distinguishable  from  that  of  the  Cretaceous  epoch,  while  the 
highly  organised  Teleostean  fish,  BeryXf  of  the  Chalk  differed 
only  in  minute  specific  characters  from  that  which  now 
lives.  Is  it  seriously  suggested  that  the  existing  Tere- 
hratuUB  and  Beryoes  are  not  the  lineal  descendants  of 
their  Cretaceous  ancestors,  but  that  their  modem  represen- 


ORIGIN  OF  8PBCIB8.  39 

tatiyes  have  been  independentlj  dereloped  from  primordial 
germs  in  the  interval  ?  But  if  this  is  too  fantastic  a  sug- 
gestion for  grave  oonsideration,  why  are  we  to  beUeve  that 
the  GlobigerincB  of  the  present  day  are  not  lineally  descended 
from  the  Cretaceous  forms  P  And  if  their  unchanged  gene- 
rations  have  succeeded  one  another  for  all  the  enormous 
time  represented  by  the  deposition  of  the  Chalk  and  that 
of  the  Tertiary  and  Quaternary  deposits,  what  difficulty 
is  there  in  supposing  that  they  may  not  have  persisted 
unchanged  for  a  greatly  longer  period  P 

The  fact  is,  that  at  the  present  moment  there  is  not  a 
shadow  of  trustworthy  direct  evidence  that  abiogenesis  does 
take  place,  or  has  taken  place,  within  the  period  during 
which  the  existence  of  life  on  the  globe  is  recorded.  But  it 
need  hardly  be  pointed  out,  that  the  fact  does  not  in  the 
slightest  degree  interfere  with  any  conclusion  that  may  be 
arrived  at,  deductively,  from  other  considerations  that,  at 
some  time  or  other,  abiogenesis  must  have  taken  place. 

If  the  hypothesis  of  evolution  is  true,  living  matter  must 
have  arisen  from  not-living  matter ;  for  by  the  hypothesis, 
the  condition  of  the  globe  was  at  one  time  such  that  living 
matter  could  not  have  existed  in  it,*  life  being  entirely 
incompatible  with  the  gaseous  state.  But  living  matter 
once  originated,  there  is  no  necessity  for  another  origina- 
tion, since  the  hypothesis  postulates  the  unlimited,  though 
perhaps  not  indefinite,  modifiability  of  such  matter. 

Of  the  causes  which  have  led  to  the  origination  of  living 
matter,  then,  it  may  be  said  that  we  know  absolutely 
nothing.  But  postulating  the  existence  of  living  matter 
endowed  with  that  power  of  hereditary  transmission,  and 
with  that  tendency  to  vary  which  is  found  in  all  such 
matter,  Mr.  Darwin  has  shown  good  reasons  for  believing 
that  the  interaction  between  living  matter  and  surround- 

*  It  nmkefl  no  difference  if  we  reason    for   sapposing    that    all 

adopt  Sir  W.  Thomson's  hypothe-  stellar  and  planetary  components 

sis,  and  sappose  that  the  germs  of  the  universe  are  or  have  been 

uf  liTing  things  have  been  trans-  gaseous,  as  that   the  earth  has 

ported  to  oar  globe  from  some  passed  through  this  stage, 
other,  teeixig  that  there  is  as  much 


40         THB  ANATOHT  OV  IVTEBTBBBATED  ANIMAIidB. 

ing  conditions,  which  results  in  the  snrviyal  of  the  fittest, 
is  sufficient  to  account  for  the  gradual  evolution  of  f^snts 
and  animals  from  their  simplest  to  their  most  complicated 
forms,  and  for  the  known  phenomena  of  Morphology, 
Physiology,  and  Distribution. 

Mr.  Darwin  has  further  endeavoured  to  give  a  physical 
explanation  of  hereditary  transmission  by  his  hjrpothesis 
of  Pangenesis;  while  he  seeks  for  the  principal,  if  not 
the  only  cause  of  variation  in  the  influence  of  changing 
conditions. 

It  is  on  this  point  that  the  chief  divergence  exists 
among  those  who  accept  the  doctrine  of  Evolution  in  its 
general  outlines.  Three  views  may  be  taken  of  the  causes 
of  variation : — 

a.  In  virtue  of  its  molecular  structure,  the  organism 
may  tend  to  vary.  This  variability  may  either  be  indefinite, 
or  may  be  limited  to  certain  directions  by  intrinsic  condi- 
tions. In  the  former  case,  the  result  of  the  struggle  for 
existence  would  be  the  survival  of  the  fittest  among  an 
indefinite  number  of  varieties ;  in  the  latter  case,  it  would 
be  the  survival  of  the  fittest  among  a  certain  set  of  varieties, 
the  nature  and  number  of  which  would  be  predetermined 
by  the  molecular  structure  of  the  organism.  ^ 

b.  The  organism  may  have  no  intrinsic  tendency  to  vary, 
but  variation  may  be  brought  about  by  the  influence  of 
conditions  external  to  it.  And  in  this  case  also,  the  varia- 
bility induced  may  be  either  indefinite  or  defined  by  in- 
trinsic limitation. 

c.  The  two  former  cases  may  be  combined,  and  variation 
may  to  some  extent  depend  upon  intrinsic,  and  to  some 
extent  upon  extrinsic,  conditions. 

At  present  it  can  hardly  be  said  that  such  evidence  as 
would  justify  the  positive  adoption  of  any  one  of  these 
views  exists. 

If  all  living  beings  have  come  into  existence  by  the 
gradual  modification,  through  a  long  series  of  generations, 
of  a  primordial  living  matter,  the  phenomena  of  embryonic 
development  ought  to  be  explicable  as  particidar  cases  of 


PHYLOaSNT.  41 

the  general  law  of  hereditaiy  transmission.  On  this  yiew, 
a  tadpole  is  first  a  fish,  and  then  a  tailed  amphibian,  pro- 
Tided  with  both  gills  and  Itmgs,  before  it  becomes  a  fro^, 
because  the  frog  waa  the  last  term  in  a  series  of  modifica- 
tions whereby  some  ancient  fish  became  an  orodele  amphi- 
bian; and  the  nrodele  amphibian  became  an  anurous 
amphibian.  In  fact,  the  development  of  the  embryo  is  a 
recapitulation  of  the  ancestral  history  of  the  species. 

If  this  be  so,  it  follows  that  the  derelopment  of  any 
organism  should  famish  the  key  to  its  ancestral  history ; 
and  the  attempt  to  decipher  the  full  pedigree  of  organisms 
from  so  much  of  the  family  history  as  is  recorded  in  their 
derelopment  has  given  rise  to  a  special  branch  of  biological 
speculation,  termed  phylogeny. 

In  practice,  however,  the  reconstruction  of  the  pedigree 
of  a  group  from  the  developmental  history  of  its  existing 
members  is  fraught  with  difficulties.  It  is  highly  probable 
that  the  series  of  developmental  stages  of  the  individual 
organism  never  presents  more  than  an  abbreviated  and 
condensed  summary  of  ancestral  conditions;  while  this 
summary  is  often  strangely  modified  by  variation  and 
adaptation  to  conditions;  and  it  must  be  confessed  that, 
in  inost  cases,  we  can  do  little  better  than  guess  what  is 
genuine  recapitulation  of  ancestral  forms,  and  what  is  the 
effect  of  comparatively  late  adaptation. 

The  only  perfectly  safe  foundation  for  the  doctrine  of 
Evolution  lies  in  the  historical,  or  rather  archsBological, 
evidence  that  particular  organisms  have  arisen  by  the 
gradual  modification  of  their  predecessors,  which  is  fur- 
nished by  fossil  remains.  That  evidence  is  daily  increasing 
in  amount  and  in  weight ;  and  it  is  to  be  hoped  that  the 
comparison  of  the  actual  pedigree  of  these  organisms  with 
the  phenomena  of  their  development  may  furnish  some 
criterion  by  which  the  validity  of  phylogenetic  conclusions, 
dednced  from  the  facts  of  embryology  alone,  may  be  satis- 
factorily tested. 


II. 


42         THB  ANATOMT  GF  nrYSBTBBSATBD  AJXJMAIA, 


CHAPTER  I. 

I.— THE   DISTINCTIYE  CHABACTBB8  OF  ANIMALS. 

Tab  more  complicated  forma  of  the  living  things,  the 
general  characters  of  which  have  now  been  discussed,  appear 
to  be  readily  distinguishable  into  widely  separated  groups. 
Animals  and  Plants.  The  latter  have  no  power  of  locomo- 
tion and  only  rarely  exhibit  any  distinct  movement  of  their 
parts  when  these  are  irritated,  mechanically  or  otherwise. 
They  are  devoid  of  any  digestive  cavity ;  and  the  matters 
which  serve  as  their  nutriment  are  absorbed  in  the  gaseous 
and  fluid  state.  Ordinary  animals,  on  the  contrary,  not  only 
possess  conspicuous  locomotive  activity,  but  their  parts 
readily  alter  their  form  or  position  when  irritated.  Their 
nutriment,  consisting  of  other  animals  or  of  plants,  is  taken 
in  the  solid  form  into  a  digestive  cavity. 

But  even  without  descending  to  the  very  lowest  forms 
of  animals  and  plants,  we  meet  with  facts  which  weaken 
the  force  of  these  apparently  broad  distinctions.  Among 
animals,  a  coral  or  an  oyster  is  as  incapable  of  locomotion 
as  an  oak ;  and  a  tape- worm  feeds  by  imbibition  and  not  by 
the  ingestion  of  solid  matter.  On  the  other  hand,  the 
Sensitive  Plant  and  the  Sundew  exhibit  movements  on 
irritation,  and  the  recent  observations  of  Mr.  Darwin  and 
others  leave  little  doubt  that  the  so-called  "insectivorous 
plants  *'  really  digest  and  assimilate  the  nutritive  matters 
contained  in  the  living  animals  which  they  catch  and  de- 
stroy. All  the  higher  animals  are  dependent  for  the  protein 
compounds  which  they  contain  upon  other  animals  or  upon 
plants.  They  are  unable  to  manufacture  protein  out  of 
simpler  substances ;  and  although  positive  proof  is  wanting 
that  this  incapacity  extends  to  all  animals,  it  may  safely  be 


THS  DiarnrcTiYB  cha&actxks  ov  utimals.       43 

lined  to  exist  in  all  those  forms  of  ft.TiiTna.1  life  which 
i  in  solid  nutriment,  or  which  live  parasiticall j  on  other 
nals  or  plants,  in  situations  in  which  thej  are  provided 
1  abundant  supplies  of  protein  in  a  dissolved  state. 
he  great  nugoritj  of  the  higher  plants,  on  the  contrary, 
able  to  manufacture  protein  when  supplied  with  car- 
ic  acid,  ammoniacal  salts,  water,  and  sundry  mineral 
sphates  and  sulphates  :  obtaining  the  carbon  which  they 
lire  by  the  decomposition  of  the  carbonic  acid,  the 
gen  of  which  is  disengaged.  One  essential  factor  in  the 
formance  of  this  remarkable  chemical  process  is  the 
Kzophyll  which  these  plants  contain,  and  another  is  the 
8  light. 

extain  animals  (It^usoria,  Ccelenteraia,  Tu/rbellaria) 
less  chlorophyll,  but  there  is  no  evidence  to  show  what 
i  it  plays  in  tlieir  economy.  Some  of  the  higher  plants 
n  parasitic,  and  a  great  group  of  the  lower  plants,  the 
igi  (which  may  be  parasitic  or  not),  are,  however,  devoid 
chlorophyll,  and  are  consequently  totally  unable  to 
ve  the  carbon  which  they  need  from  carbonic  acid, 
ertheless  they  are  sharply  disting^uished  from  animals, 
much  as  they  are  still,  for  the  most  part,  manufac- 
ra  of  protein.     Thus  such  a  Fungus  as  PenicUlium  is 

to  fabricate  all  the  constituents  of  its  body  out  of 
aonium  tartrate,  sulphate  and  phosphate,  dissolved  in 
*r  (see  su^pra,  p.  6,  note) ;  and  the  yeast-plant  flourishes 
multiplies  with  exceeding  rapidity  in  water  containing 
IT,  ammonitim  tartrate,  potassium  phosphate,  calcium 
iphate,  and  magnesium  sulphate, 
evertheless,  the  experiments  of   Mayer  have    shown 

when  peptones  are  substituted  for  the  ammonium 
rate,  the  nutrition  of  the  yeast-plant  is  favoured 
ead  of  being  impeded.  So  that  it  would  seem  that  the 
(t-plaut  is  able  to  take  in  protein  compounds  and 
milate  them,  as  if  it  were  an  animal ;  and  there  can  be 
reasonable  doubt  that  many  parasitic  Fungi,  such  as 
Botrytis  Bassiana  of  the  silk-worm  caterpillar,  the 
TUBa  of  the  house-fly,  and,  very  probably,  the  Peronospora 


44         THE  UTATOMY  OF  IKYEBTEBRATED  AKHCALS. 

of  the  potato-plant,  directl  j  assiinilate  the  protein  substances 
contained  in  the  bodies  of  the  plants  and  animals  which 
they  infest;  nor  is  it  clear  that  these  Fungi  are  able  to 
maintain  themselyes  upon  less  fully  elaborated  nutriment. 

Cellulose,  amyloid  and  saccharine  compounds  were 
formerly  supposed  to  be  characteristically  Tegetable  pro- 
ducts ;  but  cellulose  is  found  in  the  tests  of  Ascidians ;  and 
amyloid  and  saccharine  matters  are  of  Tery  wide,  if  not 
universal,  occurrence  in  animals. 

And  on  taking  a  comprehensive  survey  of  the  whole 
animal  and  vegetable  worlds,  the  test  of  locomotion  breaks 
down  as  completely  as  does  that  of  nutrition.  For  it  is  the 
rule  rather  than  the  exception  among  the  lowest  plants,  that 
at  one  stage  or  other  of  their  existence  they  should  be 
actively  locomotive,  their  motor  organs  being  usually  eUia, 
altogeUier  similar  in  character  and  function  to  the  motor 
organs  of  the  lowest  animals.  Moreover,  the  protoplasmic 
substance  of  the  body  in  many  of  these  plants  exhibits 
rhythmically  pulsating  spaces  or  e(ynira4;Hle  wicuoUs  of 
the  same  nature  as  those  characteristic  of  so  many  animals. 

No  better  illustration  of  the  impossibility  of  drawing  any 
sharply  defined  distinction  between  animals  and  plants  can 
be  found,  than  that  which  is  supplied  by  the  history  of  what 
are  commonly  termed  '  Monads.' 

The  name  of  '  Monad '  *  has  been  commonly  applied  to 
minute  free  or  fixed,  rounded  or  oval  bodies,  provided  with 
one  or  more  long  cilia  {flagella),  and  usually  provided  with 
a  nucleus  and  a  contractile  vacuole.  Of  sufth  bodies,  all  of 
which  would  properly  come  under  the  old  group  of  Monadidce, 
the  history  of  a  few  has  been  completely  worked  out ;  and 
the  result  is  that,  while  some  {e.g.  ChtamydonKmas,  zoo- 
spores of  Peronogpora  and  Coleochcete)  are  locomotive  condi- 
tions of  indubitable  plants;  others  (Badiolaria,  NodUuca) 
are  embryonic  conditions  of  as  indubitable  animals.  Yet 
others  (zoospores  of  Myxomycetes)  are  embryonic  forms  of 
organisms  which  appear  to  be  as  much  animals  as  plants ; 

*  O.  F.  MUIler,  '  Historia  oontpicuus,  simplicitsimus,  pcl- 
Yexmium/    1773.    "  Vermis  in-      lucidos,  punctifonnis." 


THS  DI8TJJI0TIVJS  CHABACTEB8  OV  AITIMALB.         45 

inasmucli  as  in  one  condition  thej  take  in  solid  nntriment, 
and  in  another  have  the  special  morphological,  if  not 
physiological  peculiaritiee  of  plants;  while,  lastly,  in  the 
case  of  such  monads  as  those  recently  so  carefully  studied 
by  Messrs.  Dallinger  and  Drysdale,  the  morphological 
characters  of  which  are  on  the  whole  animal,  while  their 
mode  of  nutrition  is  xmknown,  it  is  impossible  to  say 
whether  they  should  be  regarded  as  animals  or  as  plants. 

Thus,  traced  down  to  their  lowest  terms,  the  series  of 
plant  forms  gpradually  lose  more  and  more  of  their  dis- 
tinctiye  vegetable  features,  while  the  series  of  wTiimal 
forms  part  with  more  and  more  of  their  distinctive  animal 
characters,  and  the  two  series  converge  to  a  common  term. 
The  most  characteristic  morphological  peculiarity  of  the 
plant  is  the  investment  of  each  of  its  component  cells  by  a 
sac,  the  walls  of  which  contain  cellulose,  or  some  closely 
analogous  compound ;  and  the  most  characteristic  physio- 
logical  peculiarity  of  the  plant  is  its  power  of  manufacturing 
protein  from  chemical  compounds  of  a  less  complex  nature. 

The  most  characteristic  morphological  peculiarity  of  the 
ffTiimstl  is  the  absence  of  any  such  cellulose  investment.* 
The  most  chaxacteristic  physiological  peculiarity  of  the 
^nimal  is  its  Want  of  powcr  to  manufacture  protein  out  of 
simpler  compounds. 

The  great  majority  of  living  things  are  at  once  referable 
to  one  of  the  two  categories  thus  defined ;  but  there  are 
some  in  which  the  presence  of  one  or  other  characteristic 
mark  cannot  be  ascertained,  and  others  which  appear  at 
different  periods  of  their  existence  to  belong  to  different 
categories. 

*  No  analvsis  of  the  tubstanee  with  cellulose  when  heated  with 
composing  the  cyets  in  which  so  the  double  hyposulphite  of  cop- 
many  of  the  Protozoa  inclose  them-  per  and  ammonia,  it  is  possible, 
seWes  temporarily,  haa  yet  been  therefore,  that  the  difference  be- 
made.  But  it  is  not  improbable  tween  the  chitinous  investment  of 
that  it  may  be  analogous  to  diitin ;  an  animal  and  the  cellulose  invest  - 
and  if  so,  it  is  worthy  of  remark  ment  of  a  plant  may  depend  upon 
that  though  ehitin  ic  a  nitroge-  the  proportion  of  nitrogenous 
nous  body,  it  readily  vields  a  matter  which  is  present  in  each 
substance    appareBtly   Identical  case  in  addition  to  the  ehitin. 


46         THB  AVATOMY  OV  nrYBBTBBSATBD  AHIMALS. 


II. — THB  MORPHOLOGICAL  DIFFEBBNTIATIOV  OF 

ANIMALS. 

The  simplest  form  of  animal  life  imaginable  would  be  a 
protoplasmic  body,  devoid  of  motility,  maintaining  itself  bj 
the  ingestion  of  such  proteinaceons,  fattj,  amjloid  and 
mineral  matters  as  might  be  brought  into  contact  with  it 
by  external  agencies ;  and  increasing  by  simple  extension 
of  its  mass.  But  no  animal  of  this  degree  of  simplicity  is 
known  to  exist.  The  very  humblest  a,Tiimalfl  with  which 
we  are  acquainted  exhibit  contractility,  and  not  only  in- 
crease in  size,  but,  as  they  grow,  divide,  and  thus  undergo 
multiplication.  In  the  simplest  known  animals — the  Protozoa 
— ^the  protoplasmic  substance  of  the  body  does  not  become 
differentiated  into  discrete  nucleated  masses  or  cells,  which 
by  their  metamorphosis  give  rise  to  the  different  tissues  of 
which  the  adult  body  is  composed.  And,  in  the  lowest  of 
the  ProtoBoa,  the  body  has  neither  a  constant  form  nor  any 
further  distinction  of  parts  than  a  greater  density  of  the 
peripheral,  as  compared  with  the  central,  part  of  the  proto- 
plasm. The  first  steps  in  complication  are  the  appearance 
of  one  or  more  rhythmically  contractile  vacuoles,  such  as 
are  found  in  some  of  the  lower  plants ;  and  the  segregation 
of  part  of  the  interior  protoplasm  as  a  rounded  mass,  the 
"  endoplast "  or  "  nucleus."  Other  Prototoa  advance  further 
and  acquire  permanent  locomotive  organs.  These  may  be 
developed  only  on  one  part  of  the  surface  of  the  body, 
which  may  be  modified  into  a  special  organ  for  their 
support.  In  some,  a  pedicle  of  attachment  is  formed,  and 
the  body  may  acquire  a  dense  envelope  (Injuaoria),  or 
secrete  an  internal  skeleton  of  calcareous  or  silicious 
matter  (Forammifera,  Badhlaria),  or  fabricate  such  a  skele- 
ton by  gluing  together  extraneous  particles  {Foraminifera), 

A  mouth  and  gullet,  with  an  anal  aperture,  may  be  formed, 
and  the  permeable  soft  central  portion  of  the  protoplasm 
may  be  so  limited  as  to  give  rise  to  a  virtual  alimentary 
tract  between  these  two  apertures.    The  contractile  vacuole 


\ 


MOBPHOLOOIOAL  DIFFBRBHTIATIOIT.  47 

may  be  derreloped  into  a  complicated  sjstem  of  canals 
[Paramaemm),  and  the  endoplast  may  take  on  more  and 
more  definitely  the  characters  of  a  reproductive  organ,  that 
is,  may  be  the  focus  of  origin  of  germs  capable  of  repro- 
ducing the  indiridual  {VoriieeUa).  In  hct,  rudiments  of  all 
the  chief  system  of  organs  of  the  higher  animals,  with  the 
exception,  more  or  less  doubtful,  of  the  nervous,  are  thus 
sketched  out  in  the  Proionoa,  just  as  the  organs  of  the  higher 
plants  are  sketched  out  in  Caulerpa, 

In  the  Meicuoa,  which  constitute  the  rest  of  the  animal 
kingdom,  the  a^iiwiftJ,  in  its  earliest  condition,  is  a  pro- 
toplasmic mass  with  a  nucleus — ^is,  in  short,  a  Protozoon. 
But  it  never  acquires  the  morphological  complexity  of  its 
adult  state  by  the  direct  metamorphosis  of  the  protoplasmic 
matter  of  this  nucleated  body — ^the  ovum — into  the  different 
tissues.  On  the  contrary,  the  first  step  in  the  development 
of  all  the  Mekuoa  is  the  conversion  of  the  single  nucleated 
body  into  an  aggregation  of  such  bodies  of  smaller  size 
— ^the  Morula — ^by  a  process  of  division,  which  usually 
takes  place  with  great  regularity,  the  ovum  dividing  first 
into  two  segments,  which  then  subdivide,  giving  rise  to 
four,  eight,  sixteen,  Ac.,  portions,  which  are  the  so-called 
division  ma9$e$  or  hUuiomerea, 

A  similar  process  takes  place  in  sundry  Protouoa  and 
gives  rise  to  a  protozoic  aggregate,  which  is  strictly 
comparable  to  the  Morula,  But  the  members  of  the 
protozoic  aggregate  become  separate,  or  at  any  rate 
independent  existences.  What  distinguishes  the  metazoic 
aggregate  is  that,  though  its  component  blastomeres  also 
retain  a  certain  degree  of  physiological  independence, 
they  remain  united  into  one  morphological  whole,  and  their 
several  metamorphoses  are  so  ordered  and  related  to  one 
another,  that  they  constitute  members  of  a  mutually 
dependent  commonalty. 

The  MdoMoa  are  the  only  animals  which  fall  under 
common  observation,  and  have  therefore  been  known 
from  ihb  earliest  times.  All  the  higher  lang^uages  possess 
general  naimw  aqpiivalent  to  our  beasts  bird,  reptile,  fish. 


48         THE  AKATOmr  OF  IHrYEBTEBSATBD  AlfTlTATrft. 

insect  and  worm ;  and  this  shows  the  very  early  perception 
of  the  fact,  that  not¥dth8tanding  the  wonderfol  divendtj 
of  i»-TiiTwn.1  forms,  thej  are  modelled  upon  oomparatiyelj 
few  great  types. 

In  the  middle  of  the  last  century  the  founder  of  modem 
Taxonomy,  Linnaeus,  distinguished  animals  into  Mammalia^ 
Aves,  Amphibia,  Pisces,  Insecta  and  Vermes,  that  is  to  say, 
he  converted  common  sense  into  science  by  defining  and 
giving  precision  to  the  rough  distinctions  arrived  at  by 
ordinaiy  observation. 

At  the  end  of  the  century,  Lamarck  made  a  most  impor- 
tant advance  in  general  morphology,  by  pointing  out  that 
mammals,  birds,  reptiles,  and  fishes,  are  formed  upon  one 
type  or  common  plan,  the  essential  character  of  which  is  the 
possession  of  a  spinal  column,  interposed  between  a  cere- 
bro-spinal  and  a  visceral  cavity;  and  that  in  no  other  ajiimals 
is  the  same  plan  of  construction  to  be  discerned.  Hence  he 
drew  a  broad  distinction  between  the  former  and  the  latter, 
as  the  Yebtebbata  and  the  Inyebtebbata.  But  the 
advance  of  knowledge  respecting  the  structure  of  inverte- 
brated  animals,  due  chiefly  to  Swammerdam,  Trembley, 
Reaumur,  Peyssonel,  Goeze,  Boesel,  Ellis,  Fabricius,  O.  F. 
Miiller,  Lyonet,  Pallas,  and  Cuvier,  speedily  proved  that  the 
Invertebrata  are  not  framed  upon  one  fundamental  plan, 
but  upon  several;  and,  in  1795,  Cuvier*  showed  that,  at 
fewest,  three  morphological  types,  as  distinct  from  one 
another  as  they  are  from  that  of  the  vertebrated  animals,  are 
distinguishable  among  the  Invertebrata,  These  he  named 
-pi.  Mollusques ;  II.  Insectes  et  Vers ;  III.  Zoophytes.  In 
^  tne  '  Begne  animal '  (1816),  these  terms  are  Latinised,  Ani- 
"m  malia  MoUusca,  Artietdata,  and  Badiaia.  Thus,  says  Cuvier : 
"It  will  be  found  that  there  exist  four  principal  forms, 
four  general  plans,  if  it  may  thus  be  expressed,  on  which  all 
animals  appear  to  have  been  modelled;  and  the  ulterior 
divisions  of  which,  under  whatever  title  naturalists  may 
have  designated  them,  are  merely  slight  modifications, 
founded  on  the  development  or  addition  of  certain  parts. 
*  Tableau  ^lementaire  de  llilttoire  det  animaux.    An  vi. 


COMMON  PLANS.  49 

These  four  common  plans  are  those  of  the  Vertebrata,  the 
MoUusea,  the  Ariictdaia,  and  the  Radiata." 

For  extent,  variety,  and  exactness  of  knowledge,  Cuvier 
was,  beyond  all  comparison,  the  greatest  anatomist  who  has 
ever  lived ;  but  the  absence  of  two  conditions  rendered  it 
impossible  that  his  survey  of  the  animal  kingdom  should 
be  exhaustive,  grand  and  comprehensive  as  it  was. 

Up  to  the  time  of  Cuvier's  death  in  1832,  microscopic  inves-" 
tigation  was  in  its  infancy,  and  hence  the  great  majority  of 
the  lowest  forma  were  either  imknown  or  little  understood ; 
and  it  was  only  in  the  third  decade  of  the  present  century 
that  Rathke,  Dollinger  and  Yon  Baer  commenced  that  won- 
derful series  of  exact  researches  into  embryology,  which 
Yon  Baer  org^anised  into  a  special  branch  of  morphology, 
developing  all  its  most  important  consequences  and  raising 
it  to  its  proper  position,  as  the  criterion  of  morphological 
theories. 

Upon  embryological  grounds  Yon  Baer  arrived  at  the 
same  conclusion  as  Cuvier,  that  there  are  four  common 
plans  of  animal  structure. 

In  the  course  of  the  last  half -century  the  activity  of 
anatomists  and  embryologists  has  been  prodigious,  and  it 
may  be  reasonably  doubted  whether  any  form  of  animal 
life  remains  to  be  discovered  which  will  not  be  found  to 
accord  with  one  or  other  of  the  common  plans  now 
known.  But  at  the  same  time  this  increase  of  knowledge 
has  abolished  the  broad  lines  of  demarcation  which  formerly 
appeared  to  separate  one  common  plan  from  another. 

Even  the  hiatus  between  the  Vertehrata  and  the  IrvceV' 
td^aia,  is  partly,  if  not  wholly,  bridged  over ;  and  though 
among  the  Invertebrata,  there  is  no  difficulty  in  distinguish- 
ing the  more  completely  differentiated  representatives  of 
such  types  or  common  plans  as  those  of  the  Arthropoday  the 
AjMtelida,  the  MoUuaca,  the  Tunicaia,  the  Echinodermaiay  the 
CcBUfnieralay  and  the  Porifera,  yet  every  year  brings  forth 
fresh  evidence  to  the  effect,  that  just  as  the  plan  of  the 
plant  is  not  absolutely  distinct  from  that  of  the  animal,  so 
that  of  the  Yertebra^  has  its  points  of  commimity  with 


50         THE  ANATOMY  OF  INYEBTEBBATED  ANIMALS. 

that  of  certain  of  the  Invertebrates;  that  the  Arthropod, 
the  Mollusk,  and  the  Echinoderm  plans  are  united  by  that 
of  the  lower  worms,  and  that  the  plan  of  the  latter  is 
separated  by  no  very  great  differences,  from  that  of  the 
Coelenterate  and  that  of  the  Sponge. 

Whatever  speculative  views  may  be  held  or  rejected  as  to 
the  origin  of  the  diversities  of  animal  form,  the  facts  of 
anatomy  and  development  compel  the  morphologist  to 
regard  the  whole  of  the  Metcaoa  as  modifications  of  one 
actual  or  ideal  primitive  type,  which  is  a  sac  with  a  double 
cellular  wall,  enclosing  a  central  cavity  and  open  at  one  end. 
This  is  what  Haeckel  terms  a  Oagtrcea,  The  inner  wall  of 
the  sac  is  the  hypoblast  {endoderm  of  the  adult),  the  outer 
the  epiblast  [ectoderm).  Between  the  two,  in  all  but  the 
very  lowest  Metazoa,  a  third  layer,  the  mesoblast  {mesoderm 
of  the  adult),  makes  its  appearance. 

In  the  Porifera,  the  terminal  aperture  of  the  gastrsea 
becomes  the  egestive  opening  of  the  adult  animal,  and  the 
ingestive  apertures  are  numerous  secondary  pore-like 
apertures  formed  by  the  separation  of  adjacent  cells  of  the 
ectoderm  and  endoderm.  The  body  may  become  variously 
branched,  a  fibrous  or  spicular  endoskeleton  is  usually  deve- 
loped in  the  ectoderm,  and  no  perivisceral  cavity  is  developed. 
There  are  no  appendages  for  locomotion  or  prehension ;  no 
nervous  system  nor  sensory  organs  are  known  to  exist ;  nor 
are  there  any  circulatory,  respiratory,  renal,  or  generative 
organs. 

In  the  Coelenterataf  the  terminal  aperture  of  the  gastraea 
becomes  the  mouth,  and  if  pores  perforate  the  body  walls, 
they  do  not  subserve  the  ingestion  of  food.  There  is  no 
separate  perivisceral  cavity,  but,  in  many,  an  enteroccele  or 
system  of  cavities,  continuous  with,  but  more  or  less  separate 
from  the  digestive  cavity,  extends  through  the  body. 
Prehensile  appendages,  tentaeula,  are  developed  in  great 
variety.  A  chitinous  exoskeleton  appears  in  some,  a 
calcareous  or  chitinous  endoskeleton  in  others.  There  are 
no  circulatory,  respiratory,  or  renal  organs  (though  it  is 
possible  that  certain  cells  in  the  PorpiUB,  e,g,  may  have  an 


AKNULOSB  DI7FBBBNTIATION.  51 

nropoietic  f xmction) ;  but  special  genital  organs  make  their 
appearance,  as  do  a  definitelj-arranged  nervous  system  and 
organs  of  sense. 

The  lowest  TurheUaria  are  on  nearly  the  same  grade 
of  organisation  as  the  lower  CcdentercUa,  but  the  thick 
mesoderm  is  traversed  by  canals  which  constitute  a  water- 
vascular  tydem.  In  the  adult  state  these  canals  open, 
on  the  one  side,  into  the  interstices  of  the  mesodermal 
tissues,  and,  on  the  other,  communicate  with  the  exterior. 
Their  analogy  to  the  contractile  vacuoles  of  the  Infusoria 
on  the  one  hand,  and  to  the  segmental  organs  of  the 
Annelids  on  the  other,  lead  me  to  think  that  they  are  formed 
by  a  splitting  of  the  mesoblast,  and  that  they  thus  represent 
that  form  of  perivisceral  cavity  which  I  have  termed  a 
fdiiaaecde.  A  nervous  system  consisting  of  a  single  or 
doable  ganglion  with  two  principal  longitudinal  nerve  cords, 
is  found  in  many ;  and  there  may  be  eyes  and  auditory  sacs. 

Upon  this  foundation  a  gradual  complication  of  form  is 
based,  brou^t  about  by — 

1.  The  elongation  of  the  bilaterally  symmetrical  body 
and  the  formation  of  a  chitinous  exoskeleton. 

2.  The  development  of  a  secondary  aperture  near  the 
anterior  end  of  the  body,  which  becomes  the  permanent 
mouth. 

3.  The  division  of  the  mesoblast  into  successive  segments 
(gomites), 

4.  The  development  of  two  nervous  ganglia  in  each  somite. 

5.  The  outgrowth  of  a  pair  of  appendages  from  each 
somite,  and  their  segmentation. 

6.  The  gradual  specialisation  of  the  somites  into  cephalic, 
thoracic  and  abdominal  groups;  and  that  of  their  appen- 
dages into  sense  organs,  jaws,  locomotive  limbs,  and  respi- 
ratory organs. 

7.  The  conversion  of  the  schizocoele  into  a  spacious 
perivisceral  cavity  oontaining  blood ;  the  reduction  of  the 
water- vascular  system  and  the  appearance  of  pseudo-hsemal 
vessels ;  and  the  replacement  of  these,  in  the  higher  forms, 
by  a  heart,  arteries,  and  veins,  which  contain  blood. 

£  2 


52    THE  ANATOMY  OF  INYBBTEBBATED  ANIMALS. 

8.  The  converaion  of  the  simple  inner  sac  of  the  gastrsea 
into  a  highly  complex  alimentary  canal,  with  special  glan- 
dular appendages,  representing  the  liver  and  the  kidneys. 

9.  A  similar  differentiation  of  the  genital  apparatus. 

10.  A  gradual  complication  of  the  eye,  which,  in  its  most 
perfect  form,  presents  a  series  of  crystal-clear  conical  rods, 
disposed  perpendicularly  to  fhe  transparent  corneal  region 
of  the  chitinous  ezoskeleton,  and  connected  by  their  inner 
ends  with  the  optic  nerves  of  the  prse-oesophageal  ganglia. 

By  such  modifications  as  these  the  plan  of  the  simple 
Turbellarian  gradually  passes  into  that  of  the  highest 
Arthropod. 

Starting  from  the  same  point,  if  the  mesoblast  does  not 
become  distinctly  segmented;  if  few,  probably  not  more 
than  three,  pairs  of  ganglia  are  formed;  if  there  are  no 
segmented  appendages,  but  the  chief  locomotive  organ  is  a 
muscular  foot  developed  in  the  neural  aspect  of  the  body ; 
if,  in  the  place  of  the  chitinous  exoskeleton,  a  shell  is 
secreted  by  a  specially  modified  part  of  the  hsBmal  wall 
termed  the  mantle ;  if  the  schizocoele  is  converted  into  a  blood 
cavity,  which  communicates  with  the  exterior  by  an  organ 
of  Bojanus,  which  appears  to  represent  the  water-vascular 
system  and  the  segmental  organs ;  and  if,  along  with  these 
changes,  the  alimentary,  circulatory,  respiratory,  genital, 
and  sensory  organs  take  on  special  characters,  we  arrive  at 
the  complete  Molluscan  plan. 

From  the  Turbellarian  to  the  Tunicate,  or  Ascidian,  the 
passage  is  indicated,  if  not  effected,  by  Balanoglasstu,  which, 
in  its  larval  state,  is  comparable  to  an  Appendievlaria  with- 
out its  caudal  appendage.  On  the  other  hand,  the  large 
pharynx  of  the  Tunicaia  and  the  circle  of  tentacula  around 
the  oral  aperture,  with  the  single  ganglion,  approximate 
them  to  the  Polyzoa,  In  the  perforation  of  the  pharynx  by 
lateral  apertures,  which  communicate  with  the  exterior, 
either  directly  or  by  the  intermediation  of  an  atrial  cavity, 
the  Tunio(dareBeiah\eordjBaJanoglo88U8  and  the  VerMnrata. 
The  axial  skeleton  of  the  caudal  appendage  has  no  parallel 
except  in  the  yertebrate  notochord.    In  the  structure  of 


THB   PLAN  OF  THE  ECHINODEBMS.  53 

it  and  the  regular  reversal  of  the  direction  of  its 
tions,  the  Tunieata  stand  alone.  The  general 
»e  of  a  test  solidified  by  cellulose  is  a  marked 
rity,  but  in  estimating  its  apparent  singularity  the 
ce  of  cellulose  as  a  constituent  of  chitin  must  be 
leered.  Finally,  the  tadpole-like  larvsB  of  many  Asci- 
are  comparable  only  to  the  CerearioB  of  Trematodcs, 
one  hand,  and  to  vertebrate  larval  forms  on  the 


another  apparently  very  distinct  type  is  met  with  in 
ensive  group  of  the  Echinodermata, 
1  the  other  Metazoa,  except  the  Porifera  and  Ccelen' 
the  plan  of  the  body  is,  obviously,  bilaterally  sym- 
il,  the  halves  of  the  body  on  each  side  of  a  median 
L  plane  being  similar.  Any  disturbance  of  this  sym- 
such  as  is  found  in  some  Arthropoda  and  in  many 
Ml,  arises  from  the  predominant  development  of  one 
But,  in  a  Sea-urchin  or  Star-fish,  five  or  more  similar 
parts  are  disposed  around  a  longitudinal  axis,  which 
i  mouth  at  one  end  and  the  anus  at  the  other ;  there 
lial  symmetry,  as  in  a  sea  anemone  or  a  Ctenopho- 
N^evertheless,  close  observation  shows  that,  as  is  also 
le  in  the  Actinia  or  Ctenophoran,  this  radial  sym- 
is  never  perfect,  and  that  the  body  is  really  bila- 
symmetrical  in  relation  to  a  median  plane  which 
les  the  centre  of  length  of  one  of  the  radiating 
eres. 

ther  marked  peculiarity  of  the  Echinoderm  type, 
general,  if  not  universal,  presence  of  a  system  of 
jocral  vessels "'  consisting  of  a  circular  canal  around 
>uth,  whence  canals  usually  arise  and  follow  the 
line  of  each  of  the  ambulacral  metameres.  And  in 
deal  Echinoderm,  these  canals  give  off  prolongations 
enter  certain  diverticula  of  the  body  wall,  the  pediceh 
cers. 

Schinoderms  have  a  calcareous  endoskeleton. 
le  chapter  allottei  to  these  animids,  it  will  be  shown 


54         THE  AKATOMY  OF  nTYBBTSBBATBD  ANIMALS. 

that  they  are  modificatioiis  of  the  Tnrbellaria.n  type,  brought 
about  by  a  singular  series  of  changes  undergone  by  the 
endoderm  and  mesoderm  of  the  larva  or  Echinopoedium. 


III. — THE  PHYSIOLOGICAL  DIFFERENTIATION  OF  ANIMALS, 
AND  THE  MOBPHOLOaiCAL  DIFFERENTIATION  OF  THEIB 
OBOANS. 

Regarded  as  machines  for  doing  certain  kinds  of  work, 
animals  differ  from  one  another  in  the  extent  to  which  this 
work  is  subdivided.  Each  subordinate  group  of  actions  or 
functions  is  allotted  to  a  particular  portion  of  the  body,  which 
thus  becomes  the  organ  of  those  functions ;  and  the  extent 
to  which  this  division  of  physiological  labour  is  carried  differs 
in  degree  within  the  limits  of  each  common  plan,  and  is 
the  chief  cause  of  the  diversity  in  the  working  out  of  the 
common  plan  of  a  group  exhibited  by  its  members. 
Moreover,  there  are  certain  types  which  never  attain  the 
same  degree  of  physiological  differentiation  as  others  do. 

Thus,  some  of  the  Protozoa  attain  a  grade  of  physiologi- 
cal complexity  as  high  as  that  which  is  reached  by  Uie  lower 
Metazoa.  And  notwithstanding  the  multiplicity  of  its 
parts,  no  Echinoderm  is  so  highly  differentiated  a  physio- 
logical machine  as  is  a  snail. 

A  mill  with  ten  pairs  of  millstones  need  not  be  a  more 
complicated  machine  than  a  mill  with  one  pair;  but  if 
a  mill  have  two  pairs  of  millstones,  one  for  coarse  and  one 
for  fine  grinding,  eo  axranged  that  the  substance  ground 
passes  from  one  to  the  other,  then  it  is  a  more  complicated 
machine — a  machine  of  higher  order — ^than  that  with  ten 
pairs  of  similar  grindstones.  In  other  words,  it  is  not  mere 
multiplication  of  organs  which  constitutes  physiological 
differentiation;  but  the  multiplication  of  organs  for  dif- 
ferent functions  in  the  first  place,  and  the  degree  in  which 
they  are  co-ordinated,  so  as  to  work  to  a  common  end,  in 
the  second  place.  Thus,  a  lobster  is  a  higher  animal, 
from  a  physiological  point  of  view,  than  a  Cyclops,  not 


THE  TEOUMBNTABY  SYSTEM.  55 

because  it  has  more  distingoishable  organs,  bnt  because 
these  organs  are  so  modified  as  to  perform  a  much  greater 
variety  of  functions,  while  they  are  all  co-ordinated  towards 
the  maintenance  of  the  animal,  by  its  well-developed 
nervous  system  and  sense  organs.  But  it  is  impossible  to 
say  that  e.g,  the  Arthropoda,  as  a  whole,  are  physiologically 
higher  than  the  MoUusca,  inasmuch  as  the  simplest  embodi- 
ments of  the  common  plan  of  the  Arthropoda  are  less 
differentiated  physiologically  than  the  great  majority  of 
Mollusks. 

I  may  now  rapidly  indicate  the  mode  in  which  physio- 
logical differentiation  is  effected  in  the  different  groups  of 
organs  of  the  body  among  the  Metazoa. 

Iniegumentary  Organs, — In  the  lowest  Metazoa,  the  inte- 
gument and  the  ectoderm  are  identical,  but  so  soon  as  a 
mesoderm  is  developed,  the  layer  of  the  mesoderm  which 
is  in  contact  with  the  ectoderm  becomes  virtually  part  of 
the  integument,  and  in  all  the  higher  animals  is  distin- 
g^uished  as  the  dermis  {enderon),  while  the  ectodermal  cells 
constitute  the  epidermis  {ecderon).  The  connective  tissue 
and  muscles  of  the  integument  are  exclusively  developed  in 
the  enderon ;  while,  from  the  epidermis,  all  cuticular  and 
cellular  ezoskeletal  parts,  and  all  the  integumentary  glands 
are  developed.  The  latter  are  always  involutions  of  the 
epidermis.  The  hard  protective  skeletons  in  all  invertebrate 
Metaaoa,  except  the  Porifera,  the  Actiiiozoa,  the  Echinoder- 
maioj  and  the  Tunicata,  are  cuticular  structures,  which 
may  be  variously  impregnated  with  calcareous  salts  formed 
on  the  outer  surface  of  the  epidermic  cells. 

In  the  Porifera^  the  calcareous  or  silicious  deposit  takes 
place  within  the  ectoderm  itself,  and,  probably,  the  same 
process  occurs,  to  a  greater  or  less  extent,  in  the  Actinozoa. 
In  those  Tunicaia  which  possess  a  test,  it  appears  to  be  a 
structure  sui  generis,  consisting  of  a  gelatinous  basis  excreted 
by  the  ectoderm,  in  which  cells  detached  from  the  ectoderm 
divide,  multiply,  and  give  rise  to  a  deposit  of  cellulose. 
The  test  may  take  on  the  structure  of  cartilage  or  even  of 


56         THE  ANATOMY  OF  INYEBTEBKATED  ANIMALS. 

oonnective  tissue.  In  the  Vertebrata  alone  do  we  find  hard 
exoskeletal  parts  formed  by  the  comification  and  cohesion 
of  epidermic  cells. 

In  the  Actinozoa  and  the  Echinodermata,  the  hard  skeleton 
is,  in  the  main,  though  perhaps  not  wholly,  the  result  of 
calcification  of  elements  of  the  mesoderm.  In  some  Mol- 
lusks,  portions  of  the  mesoderm  are  converted  into  true 
cartilage,  while  the  enderon  of  the  integument  often 
becomes  the  seat  of  calcareous  deposit.  The  endoskeleton 
and  the  dermal  ezoskeleton  of  the  Vertebrata  are  cellular 
(cartilage,  notochord)  or  fibrouH  (connective  tissue)  modifi- 
cation of  the  mesoderm,  which  may  become  calcified  (bone, 
dentine).  Recent  investigations  tend  to  show  that  the 
enamel  of  the  teeth  is  derived  from  the  ectoderm. 

The  Alimentary  Apparatus. — Prom  the  simple  sac  of  the 
Hydra  or  aproctous  Twrbellarian,  we  pass  to  the  tubular 
alimentary  tract  of  the  proctuchous  Turbellaria,  In  the 
Botifera  and  Polyzoa^  there  is  a  marked  distinction  into 
buccal  cavity,  pharynx,  oesophagus,  stomach  and  intestines ; 
while  distinct  salivary,  hepatic,  and  renal  glands,  are  found 
in  the  majority  of  the  higher  invertebrates,  and,  not  un- 
frequently,  ghmds  secreting  an  odorous  or  coloured  fluid, 
appear  in  the  region  of  the  termination  of  the  alimentary 
canal. 

The  oral  and  gastric  regions  are  armed  with  cuticular 
teeth  in  many  Ini>ert€brata ;  but  teeth  formed  by  the  calcifi- 
cation of  papillary  elevations  of  the  enderon  of  the  lining  of 
the  mouth,  are  confined  to  the  Vertebrata ;  unless,  as  seems 
probable,  the  teeth  of  the  Echinidea  have  a  similar  origin. 

The  lining  membrane  of  the  oral  cavity  is  capable  of 
being  everted,  as  a  proboscis,  in  many  Invertebrata.  The 
margins  of  the  mouth  may  be  raised  into  folds,  armed  with 
c'uticular  plates.  In  the  Vertebrata,  the  jaws  are  such 
folds,  supported  by  endoskeletal  cartilages,  belonging  to 
the  system  of  the  visceral  arches,  or  by  bones  developed 
in  and  around  them;  but,  in  the  Arthropoda,  what  are 
usually  termed  jaws  are  modified  limbs. 


THE   BLOOD  8T8TBM.  57 

2%«  Blood  cmd  CircuUdory  Apparatus, — In  the  Codenierata, 
the  aomatio  cayitj,  or  enteroccele,  is  in  free  communication 
with  the  digestive  cavity,  and  not  nnf  requentl j  communicates 
with  the  exterior  hj  other  apertures.  The  fluid  which  it 
contains  represents  hlood ;  it  is  moved  by  the  contractions 
of  the  body,  and,  generally,  by  cilia  developed  on  the  endo- 
dermal  lining  of  the  enteroccele.  In  the  Twrhellaria,  Trema" 
toda  and  Cestoidea,  the  lacimee  of  the  mesoderm  and  the 
interstitial  fluid  of  its  tissues  are  the  only  representatives  of 
a  blood- vascular  system.  It  is  probable  that  these  communi- 
cate directly  with  the  terminal  ramifications  of  the  water- vas- 
cular system.  In  the  Botifera,  a  spacious  perivisceral  cavity 
separates  the  mesoderm  into  two  layers,  the  gplanehiwplevTe, 
which  forois  the  enderon  of  the  alimentary  canal,  and  the 
somaioplefure,  which  constitutes  the  enderon  of  the  integu- 
ment. The  terminations  of  the  water  vessels  open  into  this 
cavity.  In  Annelids,  there  is  a  similar  perivisceral  cavity 
communicating  in  the  same  way  with  the  segmental  organs ; 
but,  in  most,  there  is,  in  addition,  a  system  of  canals  with 
contractile  walls,  which,  in  some,  communicate  freely  with 
the  perivisceral  cavity;  but,  in  the  majority,  are  shut  off  from 
it.  These  canals  are  filled  by  a  clear,  usually  non-corpuscu- 
lated  fluid,  which  may  be  red  or  green,  and  constitute  the 
pseitd-hcemal  system.  The  fluid  which  occupies  the  peri- 
visceral cavity  contains  nucleated  corpuscles,  and  has  the 
characters  of  ordinary  blood.  It  seems  probable  that  the  fluid 
of  the  pseud-hfiemal  vessels,  as  it  contains  a  substance  resem- 
bling haemoglobin,  represents  a  sort  of  respiratory  blood. 

In  the  Arthropodat  no  segmental  organs  or  pseud-hsemal 
vessels  are  known.  In  the  lowest  forms,  the  perivisceral 
cavity  and  the  interstices  of  the  tissues  represent  the  whole 
blood  system,  and  colourless  blood  cells  float  in  their  fluid 
contents.  In  the  higher  forms,  a  valvular  heart,  with 
arteries  and  capillaries,  appears,  but  the  venous  system  re- 
mains more  or  less  lacunar.  In  the  MoUusca,  the  same 
gradual  differentiation  of  the  blood- vascular  system  is  ob- 
servable. In  very  many,  if  not  all,  the  blood  cavities 
communicate  directly  with  the  exterior  by  the  '  organs  of 


^t.1 


58    THB  ANATOMY  OF  IKYBHTEBBATBD  ANIMALS. 

Bojanns' — ^whicH  resemble  very  simple  segmental  organs, 
and  appear  to  be  always  associated  with  the  renal  apparatus. 
In  the  Vertebrataf  AmphiooBus  has  a  system  of  blood  vessels 
with  contractile  walls,  and  no  distinct  heart.  In  aU  the  other 
Yertebrates  there  is  a  heart  with  at  fewest  three  chambers 
{Hnua  venosuSf  cUriwm,  ventricle)^  arteries,  capillaries,  and  veins, 
and  a  system  of  lymphatic  vessels  connected  with  the  veins. 
The  lymphatic  fluid  consists  of  a  colourless  plasma,  with 
equally  colourless  nucleated  corpuscles ;  the  blood  plasma 
contains,  in  addition,  red  corpuscles,  which  are  nucleated  in 
Ichthyopsida  and  Sauropsida,  but  have  no  nucleus  in  the 
Mcmtmalia,  The  lymphatic  vessels  always  communicate 
with  the  interstitial  lacunsB  of  the  tissues,  and,  in  the  lower 
Vertebrates  are  themselves,  to  a  great  extent,  irregular 
sinuses.  The  venous  system  presents  many  large  sinuses  in 
the  lower  vertebrates;  while,  in  the  higher  forms,  these 
sinuses  are  for  the  most  part  replaced  by  definite  vessels  with 
muscular  walls.  But  the  "  serous  cavities  "  remain  as  vast 
lymphatic  lactmsB.  Yalves  make  their  apx>earance  in  the 
lymphatics  and  in  the  veins,  and  the  heart  becomes  sub- 
divided in  such  a  manner  as  to  bring  about  a  more  and 
more  complete  separation  of  the  systemic  circulatory  appa- 
ratus from  that  which  supplies  the  respiratory  organs. 

The  BespircUory  System. — In  the  lower  Metiizoa  respira- 
tion is  effected  by  the  general  surface  of  the  body.  In  the 
Annelids,  processes  of  the  integument,  which  are  sometimes 
branched  and  usually  are  abundantly  ciliated  and  supplied 
with  pseud-hffimal  vessels,  give  rise  to  hranchi4B,  Bi'anchiffi, 
abundantly  supplied  with  blood-vessels,  but  never  ciliated, 
attain  a  great  development  in  the  Crustacea,  The  access 
of  fresh  water  to  them  is  secured  by  their  attachment  to 
some  of  the  limbs ;  and,  in  the  higher  Crustaceans,  one  of 
the  appendages,  the  second  maxilla,  serves  as  an  accessory 
organ  of  respiration.  Although  especially  adapted  for 
aquatic  respiration,  they  are  converted  into  air-breathing 
organs  in  the  land  crabs,  being  protected  and  kept  moist  in 
a  large  chamber  formed  by  the  carapace.  ^ 


THE    BESPIRATOliY   SYSTEM.  59 

In  some  molliiBks  {e,g.  Fieropoda),  the  delicate  lining 
nemhrane  of  the  pallial  cavity  seires  as  the  respiratory 
aigan ;  but,  in  most,  branched  or  laminated  processes  of  the 
body  give  rise  to  distinct  branchiffi.  The  mantle  becomes 
in  aocesaory  organ  of  respiration,  being  so  modified  as  to 
direct,  or  to  canse,  the  flow  of  currents  of  water  over  the 
bnmcbicB  contained  in  its  cavity.  In  many  adult  urodele 
Aw^^kibia  {Perennibranehiata),  and  in  the  embryonic  con- 
dition of  all  Amphibia  and  of  many  fishes,  branchifls  of  a 
Bmilar  character,  abundantly  supplied  with  blood  vessels, 
are  attached  to  more  or  fewer  of  the  visceral  arches. 

In  all  these  cases  the  branchisB  are  external,  and  are 
developed  from  the  integument.  In  Crustaceans  and  Mol- 
Insks  the  blood  with  which  they  are  supplied  is  return- 
ing to  the  heart ;  while,  in  the  Vertebrata  mentioned,  it  is 
flowing  from  the  heart;  and  it  will  be  observed  that  the 
gradual  perfectioning  of  the  respiratory  machinery  consists, 
first,  in  the  outgrowth  of  parts  of  the  integument  specially 
adapted  to  subserve  the  interchange  between  the  gases 
contained  in  the  blood  and  those  in  the  surrounding 
medium;  secondly,  in  the  increase  of  the  surface  of  the 
branchise,  so  as  to  enable  them  to  do  their  work  more 
rapidly ;  thirdly,  in  the  development  of  accessory  organs,  by 
which  the  flow  of  water  over  the  branchias  is  rendered 
definite  and  constant,  and  may  be  increased  or  diminished 
in  accordance  with  the  needs  of  the  (Bconomy. 

It  is  probable  that  the  water- vascular  system  and  the 
segmental  organs  of  Tnrbellarians  and  Annelids ;  the  cloacal 
tubes  of  the  Gephyrea  and  of  some  Holothuridea ;  the  ambii- 
lacral  vesicles  of  the  Eohinoderms,  and  the  large  pharyngeal 
cavity  of  the  Polyzoa ;  to  a  greater  or  less  extent,  subserve 
respiration,  and  constitute  internal  respiratory  organs. 

In  Myriapoda  and  Insecta,  the  tracJieoe — tubes  which  open 
on  the  surface  of  the  body  and  contain  air,  and  are  curiously 
Kiftiilar  in  their  distribution  to  the  water  vessels  of  the 
worms— constitute  a  very  complete  internal  aerial  re8pii*a- 
tory  apparatus. 

In  Arachnida,  trachee  may  exist  alone,  or  be  accompanied 


60         THE   ANATOMY  OF   INYEBTEBBATED  ANIMALS. 

bj  folded  pulmonary  sacs,  or  the  latter  may  exist  alone,  as 
in  the  Scorpion.  In  this  case,  these  lungs  are  supplied  bj 
blood  which  is  returning  from  the  heart. 

In  these  animals,  the  flow  of  air  into  and  out  of  the  air 
cavities  is  governed  by  the  contractions  of  muscles  of  the 
body,  disposed  so  as  to  alter  its  vertical  and  longitudinal 
dimensions.  In  the  higher  forms,  the  entrance  and  exit  of 
air  is  regulated  by  valves,  placed  at  the  external  openings 
(stigmata)  of  the  trachess,  and  provided  with  muscles,  by 
which  they  can  be  shut. 

In  the  Enteropneuata  and  the  Tunicata  a  new  form  of 
internal  aquatic  respiratory  apparatus  appears.  The  large 
pharynx  is  perforated  by  lateral  apertures,  which  place  its 
cavity  in  communication  with  the  exterior ;  and  water,  taken 
in  by  the  mouth,  is  driven  through  these  branchial  clefts  and 
aerates  the  blood,  which  circulates  in  their  interspaces. 

The  respiratory  apparatus  of  Amphioxus,  of  aU  adult 
fishes,  and  of  the  tadpoles  of  the  higher  anurous  Amphibia^ 
in  a  certain  stage  of  their  existence,  is  of  an  essentially 
similar  character.  The  accessory  respiratory  apparatus  for 
the  maintenance  and  the  regulation  of  the  currents  of 
water  over  the  gills  is  furnished  by  the  visceral  arches  and 
their  muscles;  and  the  respii*atory  blood  flows  from  the 
heart. 

In  MoUusks  which  live  on  land  (PtUmogaderopoda), 
the  lining  wall  of  the  mantle  cavity  becomes  folded  and 
highly  vascular,  and  subserves  the  aeration  of  the  venous 
blood,  which  flows  through  it  on  its  way  to  the  heart. 
The  lung  is  here  a  modification  of  the  integument,  and 
might  be  termed  an  external  lung.  The  lungs  of  the  air- 
breathing  Vertebrata,  on  the  contrary,  are  diverticula  of 
the  alimentary  canal,  posterior  to  the  hindermost  of  the 
visceral  arches.  They  receive  their  blood  from  the  hinder- 
most  aortic  arch.  It  therefore  flows  from  the  heart.  The 
gradual  improvement  of  these  lungs  as  respiratory  machines 
is  effected,  first,  by  the  increase  of  the  surface  over  which 
the  venous  blood  brought  to  the  lungs  is  distributed; 
secondly,  by  changes  in  the  waUs  of  the  cavity  in  which 


THE  UBOPOIBTIC  SYSTEM.  61 

the  limgs  are  contained,  bj  which  that  cavitj  gradually 
becomes  shut  off  from  the  peritoneal  chamber,  and  divided 
from  it  by  a  mnscular  partition.  Concurrently  with  these 
modifications,  a  series  of  alterations  takes  place  in  the 
accesaory  apparatus  of  respiration,  wheref>y  the  machinery 
of  inspiration,  which,  in  the  lower  Vertebrata,  is  a  buccal 
force-pump,  which  drives  air  into  the  lungs,  in  the  same 
way  aa  water  is  driven  through  the  branchiss,  is  replaced 
by  a  thoracic  suction-pump,  which  draws  air  into  the  lungs 
by  dilatation  of  the  walls  of  the  closed  cavity  in  which  they 
are  contained.  Along  with  these  changes,  modifications  of 
the  heart  take  place,  in  virtue  of  which  one  half  of  its  total 
mechanical  power  becomes  more  and  more  exclusively 
appropriated  to  the  task  of  driving  the  blood  through  the 
lungs.  The  term  '  double  circulation '  applied  to  the  course 
of  the  blood  in  the  highest  VertebrcUa  is,  however,  a  mis- 
nomer. In  the  highest,  as  in  the  lowest,  of  these  animals, 
the  blood  completes  but  one  circle,  and  the  respiratory 
organ  is  in  the  course  of  the  outward  current. 

Many  animals  are  truly  amphibious,  combining  aquatic 
and  aerial  respiratory  organs. 

Thus,  among  MoUusks,  AmptdLaria  and  Onchidum  combine 
branchisD  with  pulmonary  organs ;  many  Teleostean  fishes 
have  the  lining  membrane  of  the  enlarged  branchial  chamber 
vascular  and  competent  to  subserve  aerial  respiration. 
And  in  the  Ganoids  and  Teleostei,  the  presence  of  an  air 
bladder,  which  is  both  functionally  and  morphologically  of 
the  same  nature  as  a  lung,  is  very  common.  But,  in  the 
majority  of  the  Teleoatei,  the  air  bladder  is  turned  aside 
from  its  pulmonary  function  to  subserve  mechanical  pur- 
poses, in  affecting  the  specific  gravity  of  the  body.  On  the 
other  hand,  in  the  Ganoids  and  Dipnoh  the  whole  series  of 
modifications  by  which  the  air  bladder  passes  into  the  lung 
are  patent.  In  such  lower  Amphibia  as  Proteus  and  Metw- 
branchns,  branchial  respiration  is  predominant,  and  the  lungs 
are  subsidiary ;  but  in  the  higher,  the  lungs  acquire  greater 
importance,  while  the  branchi®  diminish,  and  eventually 
dinppear. 


62         THE  ANATOMY  OF  nTYEBTEBRATED  ANIMALS. 

The  UropaieUe  System. — ^Uropoietic  organs,  distinct  from 
tHe  alimentajy  canal,  are  probably  represented  bj  the 
water-vascular  system  and  segmental  organs  of  the  worms. 
The  'organs  of  Bojanus'  of  Mollusks  are  sacs  or  tubes 
opening,  on  the  one  side,  on  the  exterior  of  the  bodj,  and,  on 
the  other,  into  some  part  of  the  blood-vascular  system.  So 
far,  as  Gregenbaur  has  shown,  they  resemble  the  segmental 
organs  of  Annelids.  In  the  majority  of  the  MoUusca,  some 
part  of  the  wall  of  the  organ  of  Bojanus  is  in  close 
relation  with  the  venous  system  near  the  heart,  and  the 
nitrogenous  waste  of  the  body  is  here  eliminated  from  the 
venous  blood.  In  the  Vertebraia,  the  renal  apparatus  is 
constructed  on  the  same  principle.  If  for  simplicity's  sake 
we  reduce  a  mammalian  kidney  to  an  ureter  with  a  single 
uriniferous  tubule,  it  corresponds  with  an  organ  of  Bojanus, 
so  far  as  it  contains  a  cavity  communicating  with  the 
exterior  at  one  end,  and  having  a  vascular  plexus — ^the 
MaJpighian  body — in  intimate  contact  with  the  opposite  end. 
In  the  adult  mammal  there  is  no  direct  communication 
between  the  urinary  duct  and  the  blood-vascular  system. 
But,  inasmuch  as  recent  researches  have  proved  that  the 
ureter  is  formed  by  subdivision  of  the  Wolfl5an  duct,  and  that 
the  WolflBan  duct  is  primitively  a  diverticulum  of  the  perito- 
neal cavity,  and  remains  for  a  longer  or  shorter  time  (per- 
manently, in  some  of  the  lower  Yertebrata,  as  Myxine)  in 
communication  therewith;  and  since  it  has  further  been 
shown  that  the  peritoneal  cavity  communicates  directly 
with  the  lymphatics,  and  therefore  indirectly  with  the  veins  ; 
it  follows  that  the  vertebrate  kidney  is  an  extreme  modifica- 
tion of  an  organ,  the  primitive  type  of  which  is  to  be  found 
in  the  organ  of  Bojanus  of  the  Mollusk,  and  in  the  seg- 
mental organ  of  the  Annelid ;  and,  to  go  still  lower,  in  the 
water- vascular  system  of  the  Turbellarian.  And  this,  in  its 
lowest  form,  is  so  similar  to  the  more  complex  conditions  of 
the  contractile  vacuole  of  a  Protozoon,  that  it  is  hardly 
straining  analogy  too  far  to  regard  the  latter  as  the  primary 
form  of  uropoietic  as  well  as  of  internal  respiratory  ap- 
paratus. 


THE  NBBYOnS  SYSTEM.  63 

The  Nervous  System, — In  its  essential  nature,  a  neire 
ii  a  definite  tract  of  living  substance,  through  which  the 
molecular  changes  which  occur  in  anj  one  part  of  the 
arganism  are  conveyed  to  and  affect  some  other  part. 
Thofl,  if,  in  the  simple  protoplasmic  bodj  of  a  Profcozoon, 
a  sdmulos  applied  to  one  part  of  the  body,  were  more 
readily  transmitted  to  some  other  part,  along  a  particular 
tract  of  the  protoplasm,  that  tract  would  be  a  virtual  nerve, 
althoagh  it  might  have  no  optical  or  chemical  characters 
which  should  enable  us  to  distinguish  it  from  the  rest 
of  the  protoplasm. 

It  is  important  to  have  this  definition  of  nerve  clearly 
before  us  in  considering  the  question  whether  the  lowest 
Miimiila  possess  nerves  or  not.  Assuredly  nothing  of  the 
kind  is  discernible,  by  such  means  of  investigation  as  we 
it  present  possess,  in  Ptvtozoa  or  Porifera ;  but  any  one  who 
has  attentively  watched  the  ways  of  a  Colpoda,  or  still 
more  of  a  Vorticella,  will  probably  hesitate  to  deny  that 
they  possess  some  apparatus,  by  which  external  agencies 
give  rise  to  localised  and  co-ordinated  movements.  And 
when  we  reflect  that  the  essential  elements  of  the  highest 
nervous  system — the  fibrils  into  which  the  axis  fibres  break 
up — are  filaments  of  the  extremest  tenuity,  devoid  of  any 
definite  structural  or  other  characters,  and  that  the  nervous 
system  of  animals  only  becomes  conspicuous  by  the  gather- 
ing together  of  these  filaments  into  nerve  fibres  and  nerves, 
it  will  be  obvious  that  there  are  as  sti*ong  morphological, 
as  there  are  physiological,  grounds  for  suspecting  that  a 
nervous  system  may  exist  very  low  down  in  the  animal 
scale,  and  possibly  even  in  plants. 

The  researches  of  Kleinenberg,  which  may  be  readily 
verified,  have  shown  that,  in  the  common  Hydra,  the  inner 
ends  of  the  cells  of  the  ectoderm  are  prolonged  into  deli- 
cate processes,  which  are  eventually  continued  into  very 
fine  longitudinal  filaments,  forming  a  layer  between  the 
ectoderm  and  the  endoderm. 

Kleinenberg  terms  these  neuro-muscular  elements,  and 
thinlrg  that  they  represent  both  nerve  and  muscle  in  their 


64         THE  ANATOMY  OF   INYEBTEBHATBD  ANIMALS. 

nndifferentiated  state.  But  it  appears  to  me  tHat  while 
the  assumed  contractility  of  these  fibres  might  account  for 
the  shortening  of  the  body  of  the  Polype,  they  can  have 
nothing  to  do  with  its  lengthening.  As  the  latter  move- 
ments are  at  least  as  vigorous  as  the  former,  we  are  there- 
fore obliged  to  assume  sufficient  contractility  in  the  general 
constituents  of  the  body  to  account  for  them.  And  if  so, 
what  ground  is  there  for  supposing  that  this  contractility 
can  be  exerted  by  only  one  tissue  when  the  body  shortens  ? 
To  my  mind,  it  is  more  probable  that  "  Kleinenberg's 
fibres"  are  solely  intemuncial  in  function,  and  therefore 
the  primary  form  of  nerve.  The  prolongations  of  the  ecto- 
dermal cells  have  indeed  a  strangely  close  resemblance  to 
those  of  the  cells  of  the  olfactory  and  other  sense  organs 
in  the  Vertebrata;  and  it  seems  probable  that  they  are 
the  channels  by  which  impulses  affecting  any  of  the  ceUs 
of  the  ectoderm  are  conveyed  to  other  «cells  and  excite  their 
contraction. 

The  researches  of  Eimer*  upon  the  nervous  system  of 
the  Cienophora  are  in  perfect  accordance  with  this  view. 
The  mesoderm  is  traversed  in  all  directions  by  very  fine 
fibrils,  varying  in  diameter  from  j^j^j^  to  ttoiht  ^^  <^  inch. 
These  fibrils  present  numerous  minute  varicosities,  and,  at 
intervals,  larger  swellings  which  contain  nuclei,  each 
with  a  large  and  strongly  refracting  nucleolus.  These 
fibrils  take  a  straight  course,  branch  dichotomously,  and 
end  in  still  finer  filaments,  which  also  divide,  but  become 
no  smaller.  They  terminate  partly  in  ganglionic  cells,  partly 
in  muscular  fibres,  partly  in  the  cells  of  the  ectoderm  and 
endoderm.  Many  of  the  nerve  fibrils  take  a  longitudinal 
course  beneath  the  centre  of  each  series  of  paddles,  and  these 
are  accompanied  by  ganglionic  cells,  which  become  particu- 
larly abundant  towards  the  aboral  end  of  each  series.  The 
eight  bands  meet  in  a  central  tract  at  the  aboral  pole  of  the 
body ;  but  Eimer  doubts  the  nervous  nature  of  the  cellular 
mass  which  lies  beneath  the  lithocyst  and  supports  the  eye- 
spots. 

*  '  Zoologiflche  Studien  anf  Capri.'    Leipzig,  1873. 


8BH80BT  OBOAKS.  65 

The  neirous  sjstem  of  the  Ctenophoran  is,  therefore, 
jost  such  as  would  arise  in  Hydra,  if  the  deyelopment  of  a 
thick  mesoderm  gave  rise  to  the  separation  and  elongation 
of  Kleinenberg's  fibres ;  and  if  special  bands  of  snch  fibres, 
developed  in  relation  with  the  chief  organs  of  locomotion, 
united  in  a  central  tract  directly  connected  with  the  higher 
sensory  organs.  We  haye  here,  in  short,  virtual,  though 
incompletely  differentiated,  brain  and  nerves. 

All  recent  investigation  tends  more  and  more  completely 
to  establish  the  following  conclusions:  firstly,  that  the 
central  ganglia  of  the  nervous  system  in  all  animals  are 
derived  from  the  ectoderm ;  secondly,  that  all  the  nerves  of 
the  sensory  organs  terminate  in  cells  of  the  ectoderm; 
thirdly,  that  all  motor  nerves  end  in  the  substance  of  the 
mnscnlar  fibres  to  which  they  are  distributed.  So  that,  in 
the  highest  animals,  the  nervous  system  is  essentially 
oimila.T'  to  that  of  the  lowest ;  the  difference  consisting,  in 
part,  in  the  proportional  size  of  the  nerve  centres,  and,  in 
part,  in  the  gathering  together  of  the  intemuncial  filaments 
into  bundles,  having  a  definite  arrangement,  which  are  the 
nerveBf  in  the  ordinary  anatomical  sense  of  the  term. 

And  as  respects  the  ectodermal  ceUs  which  constitute  the 
fondamental  part  of  the  organs  of  the  special  senses,  it  is 
becoming  clear  that  the  more  perfect  the  sensory  apparatus, 
the  more  completely  do  these  sensigenous  cells  take  on  the 
form  of  delicate  rods  or  filaments.  Whether  we  consider 
the  organs  of  the  lateral  line  in  Fishes  and  Amphibia ;  the 
gustatory  bulbs ;  the  olfactory  cells ;  the  auditory  cells ;  or 
the  elements  of  the  retina,  this  rulu  holds  good, 

Every  one  of  the  organs  of  the  higher  senses  makes  its 
appearance  in  the  animal  series  as  a  part  of  the  ectoderm, 
the  oeHs  of  which  have  undergone  a  slight  modification.  In 
the  case  of  the  eye,  accessory  structures,  consisting  of 
variaoflly-coloured  masses  of  pigment,  which  surround  the 
risiial  cells,  and  of  a  transparent  refracting  cuticular  or 
f^Xhnl^r  stnicture  which  lies  superficially  to  them — a  rudi- 
■wntary  choroid  and  cornea — are  next  added.  The  highest 
form  of  oomponnd  Arthropod  eye  differs  from  this  only  in 


^         THE  ANATOMY  OF  nrTBBTBBBATBD  ANUCALS. 

the  differentiation  of  the  lajer  of  sensigenoas  ceUs  into  the 
crystalline  cones  and  their  appendages,  and  it  has  not  been 
clearly  made  ont  that  the  simple  eyes  of  most  other  Inver- 
UbraJka  have  undergone  any  farther  change. 

Bnt  in  NaviiluB  the  nerre  cells  and  choroid  line  the  walls 
of  a  deep  cnp  open  externally ;  which,  thongh  its  develop- 
ment has  not  been  traced,  may  be  safely  assumed  to  result 
from  the  involution  of  the  retinal  ectoderm.  It  may  be 
compared  to  an  arthropod  compound  eye  become  concave 
instead  of  convex. 

In  the  higher  Cephabpadat  the  margins  of  the  ocular 
pouch  unite  and  give  rise  to  a  true  cornea,  which,  how- 
ever, frequently  remains  perforated ;  and  a  crystalline  lens 
is  developed.  In  the  higher  Vertebraia  the  retina  is  still 
a  modified  portion  of  the  ectoderm^  For  inasmuch  as  the 
anterior  cerebral  vesicle  is  formed  by  involution  of  the 
epiblast,  and  the  optic  vesicle  is  a  diverticulum  of  the 
anterior  cerebral  vesicle — it  neoessafily  follows  that  the 
outer  wall  of  the  optic  vesicle  4s  I'eally  i>art  of  the  ecto- 
dtfm,  its  inner  face  being,  morphologically,  a  portion  of  the 
surface  of  the  body^  The  rods  and  cones  of  the  verte- 
brate eye,  therefore,  exactly  correspond  with  the  crystalline 
cones,  &c.,  of  the  Arthropod  eye ;  and  the  reversal  of  the 
ends  which  are  turned  towairds  the  light  in  the  Vertebraia, 
is  a  necessary  result  of  the  extraordinary  change  of  position 
which  the  retinal  surface  undergoes  in  them% 

In  the  part  of  the  ectoderm  which  takes  on  the  auditory 
function,  two  kinds  of  accessory  organs,  solid  particles 
suspended  in  a  fluid  and  fine  hair-like  filaments,  are  deve- 
loped in  close  relation  with  the  neirve  endings.  In  the 
Crudacea  both  are  combined^  and  an  involution  of  the 
sensory  region  takes  place,  which  usually  remains  open 
throughout  life,  and  represents  the  niost  rudimentary  form 
of  auditory  labyrinth.  The  Orustaoean  ear  is  the  parallel  of 
the  Nautilua  eye^  In  the  VerMfraicL,  the  membranous  laby- 
rinth is  similarly  an  involution  of  the  integument,  which 
remains  open  throughout  life  in  many  Fishes,  but  becomes 
■hut  off  and  surrounded  by  thick  mesoblaatie  stractures  in 


KSPRODUcnrs  obgavb.  67 

all  the  higlier  VerUbrata,  The  Uffnpaimtm  aad  the  ossicula 
audUus  are  additional  aoceesorj  stmctares,  formed  at  the 
expense  of  the  hjomandibnlar  cleft  and  its  boundary  walls. 

Hie  Bqirod/iidwe  System, — The  relation  of  the  reprodne- 
tire  elements  to  the  primitive  layers  of  the  germ,  is  as  jet 
uncertain.  E.  van  Beneden  has  brought  forward  verj 
strong  evidence  to  the  effect  that  in  Hydractinia,  the 
spermatozoa  are  modified  cells  of  the  ectoderm,  and  the 
ova  of  those  of  the  endoderm;  but  whether  it  can  be 
safely  condnded  that  this  rale  holds  good  for  animals 
generally,  is  a  question  that  can  only  be  settled  by  much 
and  difficult  investigation.  The  fact  that,  in  the  Vertebrata, 
the  ova  and  spermatozoa  are  products  of  the  epithelial 
lining  of  the  peritoneal  cavity,  and  therefore  proceed  from 
the  mesoblast,  appears  at  first  sight  directly  to  negative  any 
such  generalisation.  But  it  must  be  remembered  that  the 
origin  of  the  mesoblast  itself  is  yet  uncertain,  and  that  it  is 
quite  possible  that  one  portion  of  that  layer  may  originate 
in  the  ectoderm  and  another  in  the  endoderm. 

Theare  is  some  reason  to  suspect  that  hermaphrodism 
was  the  primitive  condition  of  the  sexual  apparatus,  and 
that  unisexuality  is  the  result  of  the  abortion  of  the  organs 
of  the  other  sex,  in  males  and  females  respectively. 

Yery  low  down  in  the  animal  series,  among  the  TwrbeUaria, 
the  accessory  organs  of  generation  acquire  a  great  com- 
plexity* In  the  lower  Turbellaria  the  excretory  duct  is  a 
ave  short  wide  passage.  But,  in  the  higher  Turbellaria  and 
Timmatoda,  the  female  apparatus  presents  a  germarium,  in 
which  the  ova  are  developed ;  viteUarian  glands,  which  give 
rise  to  a  supplemental  or  food  yelk ;  an  oviduct ;  a  uterus 
ad  TAgina;  and  a  spermatheca,  in  which  the  semen  is 
tered  up.  The  male  apparatus  presents  a  testis,  a  vas 
and  a  penis.  The  function  of  the  viteUarian 
may  be  taken  on  by  cells  of  the  ovary,  or  oviduct; 
yelk  substance  may  be  formed  within  the  pri- 
■ikiire  omxn  itself,  in  the  ^ri^ropoda  and  in  most  MoUueea ; 
hit  the  vefj^roduotive  organs  in  all  these  animals  are  redn- 
to  the  Turbellarian  type. 

t2 


68    THE  ANATOMY  OF  IKYEBTSBBATBD  ANIMALS. 

In  the  Annelids  {OligochoBta  and  Polychaia),  the  oyaria  and 
tastes  often  have  no  special  dnots,  and  their  products  make 
their  waj  out  of  the  body  bj  canals  which  appear  to  be 
modified  segmental  organs. 

In  the  Cephalopoda^  again,  the  ovaria  and  testes  part  with 
their  contents  hj  dehiscence  into  chambers  connected  with 
the  water  cavities,  which  are  prolongations  of  the  organs  of 
Bqjanns.  And  they  are  conveyed  away  from  these  chambers 
by  ducts,  the  oviducts  or  vasa  def erentia,  which  commence 
by  open  mouths  in  them. 

In  the  Vertebrata,  the  reprpductive  organs  either  dehisce 
and  pour  their  contents  into  the  peritoneal  cavity,  whence 
they  are  conveyed  outwards  by  abdominal  por^  (Marsipo- 
branehii,  many  Teleottei),  or  they  are  continued  into  ducts 
which  open  behind  the  anus  separately  from  the  renal 
opening  in  the  females,  but  in  common  with  it  in  the  males 
(most  Teleosteans) ;  or  their  ducts  are  derived  from  portions 
of  the  prin^iitive  renal  apparatus  which,  as  we  have  seen,  is 
a  structure  of  the  same  order  as  the  organs  of  Bojanus  and 
the  segmental  organs.  The  testes  is  usually  convprtcd  into 
a  mass  of  tubuli,  which  eventually  open  directly  into  the 
ducts  (epididymis,  vc^s  deferens)  derived  from  the  renal 
org^ans.  The  ovary,  on  the  other  hand,  becomes  an  aggre- 
gation of  sacs — the  Graafian  f  oUideq — and  th^  oviducts  open 
into  the  peritoneal  cavity, 

Development, — The  embryo  either  passes  through  all 
stages  from  the  morula  to  a  condition  differing  from  the 
adult  only  in  size,  proportions,  and  sexual  characters,  or  it 
leaves  the  egg  in  a  condition  more  or  less  remote  from  the 
adult  state,  and  sometimes  exceedingly  different  from  it. 
In  the  latter  case,  the  animal  is  said  to  undergo  a  meiamor- 
phosis.  Each  of  these  modes  of  development  occurs  in  mem- 
bers of  the  same  group,  and  often  in  closely  allied  forms :  as, 
for  example,  the  former  in  the  crayfish  (Astaeus),  and  the 
latter  in  the  lobster  {Homarus). 

When  metamorphosis  occurs,  the  larva  may  live  under 
oonditiona  totally  different  from  those  under  which  the 
ftdnlt  paaaee  its  eodatence,  and  its  stractnre  maybe  variously 


DSYSLOPMSNT. 


69 


wM>i^^fiw«1  in  relation  to  these  conditions.  Thus  the  larva  of 
an  *«^w»«1  which  is  fixed  in  the  adult  state  maj  be  provided 
with  largely  developed  locomotive  organs ;  while  that  of  an 
adult  which  f eedis  bj  suction  maj  be  provided  with  power- 
ful afiparataB  for  the  seiznre  and  manducation  of  vegetable 
and  animal  prey. 

Tha  larva  of  a  free  adult  maj  be  parasitic,  ot  ih&t  of  a 
parasitic  adtilt  free  and  activelj  locomotive.  Moii-eover,  the 
whole  course  of  development  may  take  place  outside  the 
body  of  the  parent,  or  more  or  less  extensivel j  within  it ; 
whence  the  distinction  of  oviparous,  owwiviparous,  and 
wf^^arous*  animals. 

Finally,  when  development  takes  place  within  the  body 
of  the  parent,  the  fcetus  may  receive  nourishment  from  the 
latter  by  means  of  an  apparatus  termed  a  placenta,  by  which 
an  exchange  between  the  parental  and  f oBtal  blood  is 
readily  effected.  Examples  of  placente  are  found  not  only 
in  the  higher  mammals,  but  in  some  Plagiostome  fishes 
and  among  the  Tunieata. 

In  many  Insects  and  in  the  higher  Vertebrates,  the  embryo 
acquires  a  special  protective  envelope,  the  amnion,  which 
is  thrown  off  at  birth ;  while,  in  many  Y ertebrates,  another 
foetal  appendage,  the  allantoie,  subserves  the  respiration 
and  nutrition  of  the  fodtus. 

The  strange  phenomena  included  under  the  head  of  the 
Alternation  of  GknerationSj  and  which  result  from  the 
division,  by  budding  or  otherwise,  of  the  embryo  which 
leaves  the  egg,  into  a  succession  of  independent  zooids, 
only  the  last  of  which  acquires  sexual  organs,  have  already 
been  generally  discussedi 


*  As  eggi  capable  of  develop- 
ment are  alive,  ttiis  terminology  is 
ety Biologically  bad;  and  otwriri- 
panmt  is  particularly  objection, 
able,  as  ail  animals  bring  forth 
live  eggB  or  that  which  proceeds 
from  them.  But  as  understood 
to  apply  to  animals  which  lay 


eggs ;  to  those  in  which  the  eggs 
are  hatched  within  the  interior 
of  the  body,  without  any  special 
foetal  nutritive  apparatus;  and 
to  those  in  which  the  young  are 
provided  with  such  an  apparatus, 
they  have  a  certain  convenience. 


70         THB  AN ATOMT  OF  IHYSBTBBBATBD  ANIMALS. 


IV.— THB  DISTBIBUTIOK  OP  ANIMALS. 

The  distribution  of  aTiinmlH  has  to  be  considered  under 
two  points  of  view ;  first,  in  respect  of  the  present  condition 
of  natare;  and  secondly,  in  respect  of  past  conditions. 
The  hret  is  commonly  termed  Cfeographieal,  the  second 
Qtologieal,  or  PakBowMogieal,  DistrOmtion,  A  little  con- 
sideration, howerer,  will  show  that  this  classification  of  the 
facts  of  distribution  is  sssentially  faulty,  inasmuch  as  many 
of  the  phenomena  included  under  the  second  head  are  of  the 
same  order  as  those  comprehended  under  the  first.  Zoologi- 
cal Distribution  comprehends  all  the  facts  which  relate 
to  the  occurrence  of  animals  upon  the  earth's  surface, 
throughout  the  time  during  which  animal  life  has  existed 
on  the  globe.    Therefore  it  embraces*- 

First,  Zoologieai  Chronology,  or  the  duration  and  order 
of  succession  of  living  forms  in  time ;  and — 

Secondly,  Zoological  Geography,  or  the  distribution  of  life 
on  the  earth's  surface  at  any  given  epoch. 

What  is  commonly  termed  Gleographical  Distribution, 
is  simply  that  distribution  which  obtains  at  the  present 
epoch;  but  it  is  obvious,  that  at  any  given  moment  in 
their  past  history,  animals  must  have  had  some  sort  of 
geographical  distribution;  and  considerable  acquaintance 
with  the  nature  of  that  distribution  has  now  been  obtained 
for  all  the  epochs,  the  nature  of  the  livmg  population  of 
which  has  been  revealed  by  fossil  remains.  I  do  not  propose 
to  deal  at  length  with  either  branch  of  .distribution  in  this 
place,  but  a  few  broad  truths  which  have  been  established 
may  be  mentioned, 

Oeogrc^hical  Digtrtbtdion  ai  the  present  epoch, — ^The  Fauna 
of  the  deep  sea  (below  500  fathoms)  has  been  shown  by 
the  investigations  of  Wy  ville  Thomson  and  his  associates 
of  the  '  Ohallenger,'  to  present  a  striking  general  uniformity 
in  all  parts  of  the  world  hitherto  explored,  in  correspondence 
with  the  general  uniformity  of  conditions  at  such  depths. 


MABIini  DISTBIBUTIOK.  71 

Witli  reepeot  to  the  surface  of  the  eea,  the  ohservationB 
of  the  same  naturalists  tend  to  establish  a  like  uniformity 
of  the  great  tjpes  of  Foraminiferal  life  throughout  the 
tropical  and  temperate  zones — ^with  a  diminution  in  the 
fthandance  of  that  life  towards  the  arctic  and  antarctic 
regioma,  where  it  appears  to  be  replaced  by  Radiolaria  and 
Diatomaceoos  plants. 

With  regard  to  higher  organisms,  the  oceanic  Hydrosoa 
and  the  Cienophara  are  undoubtedly  yery  widely  spread. 
it  is  probable  that  they  attain  their  maximum  develop- 
flwnt  in  warm  seas,  though  the  known  facts  are  insuf&cient 
for  the  definite  conclusion.  SagiUa  and  Appendiculaaria, 
with  many  genei>a  of  Copepoda,  Crtuiacea,  and  Pteropoda, 
are  of  world-wide  distribution ;  and  it  is  at  present  doubtful 
whether  any  well-marked  pfoyinces  of  the  ocean  can  be 
defined  by  the  occuirence  of  purely  pelagic  animals.  On 
the  other  hand,  shallow-water  marine  animals  fall  into 
aaaemblages  characteristic  of  definite  areas  or  provinces  of 
diMtribuiion — that  is  to  say,  though  many  species  have 
a  world-wide  distribution,  others  occur  only  in  particular 
localities,  and  certain  geographical  areas  are  marked  by  the 
existence  in  them  of  a  number  of  such  peculiar  species. 
The  basins  of  the  Pacific,  the  Indiau  Ocean,  the  Atlantic, 
the  Mediterranean,  and  the  Arctic  seas,  are  thus  especially 
characterised;  and  even  limited  areas  of  these  great 
geographical  diyisions,  such  as  the  Celtic,  the  Lusitanian, 
and  the  Australian,  have  their  peculiar  features. 

But  though  the  shallow- water  marine  Faun®  thus  follow 
the  broad  features  of  physical  geography,  and  though,  with- 
in each  great  province  of  distribution  thus  marked  out,  tem- 
perature and  other  physical  conditions  have  an  obvious 
influence  in  determining  the  range  of  species;  yet,  on 
comparing  any  two  great  areas  together,  differences  in  cli- 
matal  conditions  are  at  once  seen  to  be  inadequate  to 
account  for  the  differences  between  the  Faunae  of  the  two 
areas.  Climate  in  no  viray  enables  us  to  understand  why 
the  Trigonia,  the  pearly  NawtUus,  the  Cetiracion^  the 
eared  seals,  and  the  penguins  are  found  in  the  Pacific, 


72 


THE  ANATOMY  OF  nfYBHTSBKATSD  ANIMAI/S. 


and  not  in  the  Atlantic  area ;  *  nor  why  the  Cetacea  of 
the  arctic  and  antarctic  regions  should  he  as  different 
as  they  are.  When  we  torn  to  the  distrihntion  of  land 
aninlals,  the  boundaries  of  the  provinces  of  distribu- 
tion correspond  neithei*  with  physical  features  nor  with 
climatic  conditions;  MatnnialB,  birds,  reptiles,  and  am- 
phibians are  so  distributed  at  the  present  day  as  to  mark 
out  f oui^  great  areas  or  provinces  of  distribution  of  very 
unequal  extent,  in  each  of  which  a  number  of  chlu-acteristic 
types,  not  found  elsewhere,  occur.  These  are,  1.  The 
Aretogoeal,  including  North  America,  Europe,  Africa^  and 
Asia  as  far  as  Wallace's  line,  or  the  boundary  between  the 
Indian  and  the  Papuan  divisions  of  the  Indian  Archipeki.go. 
2.  The  AuitrOcolwnhian,  comprising  all  the  American  con- 
tinent south  of  Mexico.  3.  The  Aushxtlian,  from  Wallace's 
line  to  Tasinania.  4.  The  Novotelanian,  including  the 
islands  of  N^w  Zealand.f 

There  is  n6w  no  doubt  that  provinces  of  distribution, 
closely  corresponding  with  these,  existed  at  the  time  of  the 
Quatemaiy  and  later  Tertiary  rocks.  In  Eurox>e,  North 
America,  and  Asia,  the  Arctogsal  province  was  as  distinctly 
characterised  in  the  Miocene,  and  probably  in  the  Eocene 
epoch,  as  it  is  at  present  What  may  have  been  the  case  in 
Austrocolumbia,  Australasia,  iuid  Novozelania  we  have  no 
means  of  being  certain,  in  the  absence  of  sufficient  knowledge 
of  the  Miocene  and  Eocene  deposits  of  those  regions. 

Our  present  knowledge  of  the  geographical  distribution 
which  obtained  in  the  older  periods,  does  not  enable  us  to 
speak  with  any  confidence  as  to  the  limits  of  the  provinces 
of  distribution  in  the  past.  But  this  much  is  certain,  that 
as  far  back  as  the  epoch  of  the  Trias — at  the  dawn  of  the 


*  Penguins  are  found  at  the 
Cape  of  Good  Hope  and  at  the 
Falkland  Islands,  bnt  not  in  the 
northern  parts  of  the  We»t  Coast 
of  Africa,  nor  of  the  East  Coast 
of  South  America.  In  the  Pacific 
they  stretch  nortli  to  the  Papuan 
and  Peruvian  ooasts. 

t  On  the  clasrification  and  dit- 


tribntion  of  the  Aledommorpha 
and  Heteromorp/uB :  Proceedings 
of  the  Zoological  Society,  186S. 
Plater  on  the  'Geographical 
Distribution  of  Birds.'  Ibid, 
vol.  ii.  Pucheran,  *Revne  et 
Magasin  de  Zoologie,'  18*^5. 
Blumy,*  The  Geographical  Dis- 
tribution of  Maminals.' 


BXTINCT  TBANSmOKAL  FOB1C8.  73 

Seooadttrj  period — ^the  Beptilia  and  Amphibia  of  Europe, 
laduk  sad  South  Africa,  and  probablj  North  America, 
pwentod  the  same  kind  of  resemblance  as  the  mammals 
ind  birdB  of  the  corresponding  Arctogseal  Fauna  do  now. 
But  then  there  is  no  information  respecting  the  Reptiles 
and  Amphibians  of  the  corresponding  epoch  in  Austro- 
eohimbia  and  Australia,  so  that  it  is  impossible  to  say 
whether,  in  Triassic  times,  the  Arctogseal  province  was 
Umited  aa  it  is  now. 

Outside  the  limits  of  the  Arotogseal  province,  the 
materials  for  forming  a  judgment  of  the  distribution  of 
aniroalu  are  altogether  insufficient  to  enable  us  to  draw  any 
conclnBion  as  to  the  existence,  and  still  less  as  to  the  boun- 
daries} of  definite  provinces  of  distribution  in  Paleozoic 
timesi  No  remains  of  land  animals  have  yet  been  dis- 
coveredi  The  fresh-Water  fauna  consists  of  Amphibians 
and  Fishes,  and  we  know  nothing,  or  next  to  nothing  of 
these  in  any  part  of  the  world  except  the  Arctogseal  pro- 
vince. 

A  good  deal  is  known  of  the  older  Silurian  fauna  outside 
the  boundaries  of  the  present  Arctogseal  province,  and 
within  those  of  both  the  Austrocolumbian  and  Australasian 
provinces.  With  a  generally  similar  fades  the  faunsB  of 
these  regions  present  clear  differences.  And,  considering 
that  the  groups  of  animals  which  are  represented  are  chiefly 
deep  sea  and  pelagic  forms,  it  is  not  wonderful  that  this 
similarity  of  facies  should  exist;  The  investigations  of 
the  '  Challenger '  expedition  show  that  such  forms  present 
a  like  similarity  of  facies,  at  the  present  day. 

One  of  the  most  important  facts  which  have  been  esta- 
blished under  the  head  of  Zoological  Chronology,  is,  that 
in  all  parts  of  the  world,  the  faima  of  the  later  part  of 
the  Tertiary  period,  in  any  province  of  distribution,  was 
made  up  of  forms  either  identical  with,  or  very  similar  to 
those  now  living  in  that  area. 

For  example,  the  elephants,  tigers,  bears,  bisons,  and 
hippopotamuses  of  the  later  tertiary  deposits  of  England 
are  all  closely  allied  to  members  of  the  existing  ArctogSBal 


74         THB  AHATOMT  OF  IKTIItTSBSATED  AKIMALS. 

fauna ;  the  great  armadilloe,  anteaters,  and  platjrrhine  apes 
of  the  cavea  of  South  America  are  a^  cloeelj  related  to  the 
existing  AnstroooloiBbian  fauna;  and  the  fossil  kang^arooe, 
wombats  and  phalangers  of  the  Australian  tertiaries  to 
those  which  now  live  in  the  Australasian  province. 

No  remains  of  elephants  occur  in  Australia,  nor  kan- 
garoos in  Austrocolumbia ;  nor  anteaters  and  armadilloB 
in  Europe  in  tertiary  deposits. 

But  as  we  go  back  in  time  from  the  Tertiary  to  the 
Secondary,  this  law  no  longer  holds  good.  Most  of  the 
few  terrestrial  mammals  of  secondary  age  which  have  been 
discovered  belong  to  Australasian  and  not  to  Arctogseal 
types,  and  the  marine  fauna  resembles  that  of  the  existing 
Pacific  more  than  it  does  that  of  the  Atlantic  area,  but 
differs  from  both  in  the  presence  of  numerous  wholly  extinct 
groups.  It  looks  as  if ,  in  the  latter  part  of  the  Cretaceous 
epoch,  a  great  change  in  the  limits  of  the  then  existing 
distributional  area  had  taken  place,  and  the  types  now 
characteristic  of  the  Arctogseal  province  had  invaded  re- 
gions from  which  they  had  before  been  shut  out.  And  the 
assumption  of  a  process  of  a  similar  character  appears  to 
me  to  be  the  only  rational  explanation  of  the  rapid  advent 
of  types  absent  in  the  palaeozoic  deposits  known  to  us,  in  the 
earlier  Secondary  rocks. 

Yet  other  results  of  first-rate  importance  have  come  out 
of  the  study  of  the  chronological  relations  of  fossil  remains. 
Cuvier's  investigations  proved  that  the  hiatuses  between 
existing  groups  of  ungulate  mammals  tend  to  be  filled  up 
by  extinct  forms.  Later  investigations  have  not  only  con- 
firmed this  conclusion,  but  have  shown  that,  in  several  cases, 
an  existing  much  modified  form  can  be  shown  to  have  been 
preceded  in  time,  in  the  same  distributional  area,  by  exactly 
such  forms  as  it  is  necessary  should  have  existed,  if  the 
much  modified  existing  animal  had  proceeded  by  way  of 
evolution  from  a  simpler  form. 

For  certain  groups  of  animals,  then,  there  is  as  much 
and  SB  good  evidence  of  their  having  been  evolved  by  suc- 
cessive modification  of  a  primitive  form  as  the  nature  of 


TBB  OLDB8T  SHOWN  FAUKA. 


75 


the  ease  permitB  ub  to  expect.  But  the  groupe  in  which 
Uwfe  is  eridenoe  of  such  modifications  daring  geologically 
raooided  tuooie,  all  belong  to  the  most  differentiated  members 
of  their  clamien  Lower  forms,  co-extensive  in  duration,  ex- 
hibit no  sign  of  haying  undergone  any  notable  modification. 
While  the  former  are  mutable,  the  latter  are  penident  types 
m  relation  to  geological  time. 

Leaving  the  debateable  question  of  the  nature  of  Eoaoon 
made,  the  oldest  f  ossilif  erous  rocks  are  the  Cambrian.  The 
Msntj  fauna  therein  preserved  consists  of  forms  which  are 
aeitlMr  Protoaoa  nor  Pori/era,  nor  even  appertain  to  the 
knrestgrovips  of  their  respective  classes.  There  is  no  reason 
to  bdiere  that  it  gives  a  just  notion  of  the  contemporaneous 
fnna*  nor  is  there  any  vaHd  reason  for  the  supposition 
that  it  r^ffesents  the  forms  of  animal  life  which  were  the 
list  to  make  their  appearance  on  our  planet 


76         THE  ANATOHT  OF  INYBBTBBllATBD  AKIMALS. 


CHAITER  II. 

THB     t»BOTO^OA. 

In  its  fd^bleet  manifestations,  the  contraotilitj  of  animaJB 
results  in  niere  changes  of  the  form  of  the  body,  as  in  the 
adult  QregarifUB ;  but,  from  the  sluggish  shortenings  and 
lengthenings  of  the  different  diameters  of  the  body  which 
these  creatures  exhibit^  all  gradations  are  traceable,  through 
those  o-Tiimnln  which  push  out  and  retraci^  broad  lobular 
processes,  to  those  in  which  the  contractile  prolongatiouB 
take  the  form  of  long  and  slender  filaments.  YiThether 
thick  or  filamentous,  such  contractile  processes  are  called 
*'  pseudopodia,"  when  their  movements  are  slow,  irreg^ar. 
and  indefinite ;  '*  cilia  "  or  "  flagellar"  when  they  are  rapid 
and  occur  rhythmically  in  a  defiinite  direction ;  but  the  two 
kinds  of  organs  are  essentially  of  the  same  nature.  It  will 
be  convenient  to  distinguish  those  Protozoa  which  possess 
pseudopodia,  as  myxopods,  and  those  which  ai^  provideil 
with  cilia  or  flagella,  as  nuistigopods. 

The  Protozoa  are  divisible  into  a  lower  and  a  higher 
group.  In  the  former — the  Monbba — ^no  defiinite  structure 
is  discernible  in  the  protoplasm  of  the  body ;  in  the  latter 
— ^the  Endoplastica — a  certain  portion  of  this  substance 
(the  so-called  nucleus)  is  distinguishable  from  the  rest ;  * 
and,  Yety  commonly,  one  or  more  "  contractile  vacuoles  " 
ai*e  present.  The  name  of  oontraetile  va€W)le8  is  given  to 
spaces  in  the  protoplasm,  which  slowly  become  filled  with  a 
clear  watery  fluid,  and,  when  they  have  attained  a  certain 

*  I  adopt  this  distinction  as  a      whether  it  will  stand  the  test  of 
matter  of  tmnporarjr  convenience,      further  inv  estigatiou. 
thoogh  I  entertain  great  doubt 


1 

I 


THB  PROTOZOA.  77 

oxe,  are  suddenly  obliterated  by  the  coming  together,  on 
all  sides,  of  the  protoplasm  in  which  they  lie.  This  systolic 
and  diastolic  movement  nsnally  occurs  at  a  fixed  point  in  the 
protoplasm,  at  regolar  intervals,  or  rhythmically.  But  the 
TBcnole  has  no  proper  wall,  nor,  in  most  cases,  is  any  trace 
of  it  discernible  at  the  end  of  the  systole.  Occasionally, 
the  vacuole  certainly  communicates  with  the  exterior,  and 
there  is  some  reason  to  think  that  such  a  communication 
may  always  exist.  The  function  of  these  organs  is  entirely 
onknown,  though  it  is  an  obvious  conjecture  that  it  may 
be  respiratovy  or  excretoiy. 

The  **  nucleus  "  is  a  structure  which  is  often  wonderfully 
similar  to  the  nucleus  of  a  histological  cell,  but,  as  its 
identitj  with  this  is  not  fully  made  out,  it  may  better  be 
tennad  "endoplast."  It  is,  usually,  a  rounded  or  oval 
bod^  embedded  in  the  protoplasm,  and  but  slightly  dif- 
ferent therefrom  in  either  its  optical  or  chemical  characters* 
Generally  it  becomes  more  deeply  stained  by  such  colouring 
matters  as  hBematoxylin  or  carmine,  and  resists  the  action 
of  acetic  acid  better  than  the  surrounding  protoplasm. 

In  a  few  Protozoa  there  are  many  endoplasts  in  the  sub- 
gtajice  of  the  body,  and  the  protoplasm  shows  some  tendency 
to  become  partially  differentiated  into  cells.  But  where, 
■8  in  the  higher  Infusoria,  the  body  presents  a  definite 
organisation,  with  permanently  differentiated  constituents, 
which  may  be  properly  termed  tissues,  these  tissues  do  not 
result  from  the  metamorphosis  of  cells,  but  originate  from 
the  protoplasm  directly  by  changes  of  its  physical  and 
<^iemical  characters. 

Conjugation*  followed  by  the  development  of  germs, 
which  are  set  free  and  assume  the  form  of  the  parent,  has 
been  observed  in  several  groups  of  the  Protozoa,  but  it  is 
not  yet  quite  certain  how  far  sexual  distinctions  are  esta- 
blished among  these  animals. 


78  THE    ANAT(1MY    OF    INVERTKBRATED    ANIMALS. 


I. — THB  ICONEBA. 

In  these  lowest  forms  of  aniinalB  the  entire  liying  body 
consists  of  a  particle  of  gelatinous  protoplasm,  in  which  no 
nucleus,  contractile  vacuole,  or  other  definite  structure  is 
visible ;  and  which,  at  most,  presents  a  separation  into  an 
outer,  more  clear,  and  denser  layer— the  eeto9are;  and  an 
inner,  more  granular  and  fluid  matter  —  the  endo9arc. 
The  outer  layer  is  the  seat  of  active  changes  of  form, 
whereby  it  is  produced  into  pseudopodia»  which  attain  a 
certain  length  and  are  then  retracted,  or  are  effaced  by  the 
development  of  others  from  adjacent  parts  of  the  body. 
These  pseudopodia  are  sometimes  broad  short  lobes,  at 
others,  elongated  filaments.  When  lobate,  the  pseudopodia 
remain  distinct  from  one  another,  their  margins  are  clear 
and  transparent,  and  the  granules  which  they  may  contain 
plainly  flow  into  their  interior  from  the  more  fluid  central 
part  of  the  body.  But,  when  they  are  filiform,  they  are  very 
apt  to  run  into  one  another,  and  give  rise  to  networks,  the 
constituent  filaments  of  which,  however,  readily  separate 
and  regain  their  previous  form ;  and,  whether  they  do  this 
or  not,  the  surfaces  of  these  pseudopodia  are  often  beset  by 
minute  granules,  which  are  in  incessant  motion — ^like  those 
which  are  observable  on  the  reticulations  of  the  jxrotoplasm 
of  the  cells  in  a  TradescanHa  hair. 

The  myxopod  thus  described  moves  about  by  means  of 
its  contractile  pseudopodia,  and  takes  the  solid  matters 
which  serve  as  its  food  into  all  parts  of  its  body  by  their 
aid;  while  the  undigested  exuvia  of  the  food  are  r^ected 
from  all  parts  of  the  body  in  the  same  indiscriminate  way. 
It  is  an  organism  which  is  devoid  of  any  visible  organs 
except  pseudopodia;  and,  so  far  as  is  known  at  present^  it 
multiplies  by  simple  division. 

The  Protamcoba  (with  lobate  pseudopodia)  and  Protogenes 
(with  filamentous  pseudopodia)  of  Haeckel  are  Monera  of 
this  estremely  simple  character.  In  Mymodiatywn  (Haeckel) 
the  pieodopodia  of  a  number  of  such  Monera  run  together, 


THB  MONBSA.  79 

and  give  rise  to  a  complex  network,  or  common  plas- 
modium. 

It  IB  open  to  doubt,  however,  whether  either  Froiamoeba, 
Ptotogenet,  or  Mymodieiywm  is  anything  but  one  stage  of  a 
cjcle  of  forms,  which  are  more  completely,  though  perhaps 
not  jet  wholly,  represented  by  some  other  very  int^esting 
MomerOt  also  described  by  HaeckeL 

ThiUy  the  genus  VamvpyreUa  is  a  myxopod  with  filamen- 
tous pseudopodia,  a  species  of  which  infests  one  of  the 
stalked  Diatomacesa,  Chmphonema,  feeding  upon  the  soft 
parts  of  the  frustules  of  its  host,  by  inserting  some  of  its 
pseudopodia  through  the  raphe  of  the  frustide,  which  it 
enrelopee,  and  absorbing  the  contained  protoplasm*  Having 
thus  provided  itself  with  abundant  noiuishment,  by  creep- 
ing fromfrustule  to  frustule  of  ih<^fihmphonemaf  it  thrusts 
aside  the  last  evacuated  frustule  from  its  peduncle,  and, 
taking  its  place,  draws  in  its  pseudopodia,  becomes  sphe- 
rical, and  surrounds  itself  with  a  structureless  cyst,  enclosed 
in  which  it  remains,  perched  upon  the  peduncle  of  the 
Qnfmphcmema,  Soon,  its  protoplasm  undergoes  division  into 
four  equal  masses,  and  each  of  these  becoming  converted 
into  a  young  VanupyreUOf  escapes  from  the  cyst,  and  re- 
oommences  the  predatory  life  of  its  parent.  In  this  case, 
Uie  myxopod  becomes  encysted,  and  then  undergoes  fission 
into  bodies,  each  of  which  passes  directly  into  the  form  of 
the  parent. 

In  another  genus  (JfffHXiiinim)  an  additional  complication 
is  introduced ;  the  myxopod  becomes  encysted,  and  then 
divides  into  many  portions ;  each  of  these  elongates,  and 
mrrounds  itself  with  a  delicate,  fusiform,  silicious  case. 
Thus  enclosed,  the  germs  are  set  free  by  the  bursting  of  the 
cyst;  and,  after  a  while,  the  contents  of  the  silicious  cases 
emerge,  and  pass  at  once  into  the  myxopod  state. 

In  other  genera,  not  only  does  the  myxopod  become 
encysted,  before  it  undergoes  fissive  multiplication,  but  the 
forms  thus  produced  differ  from  the  myxopod  in  being 
fr^ee-swimming  org^anisms,  propelled  by  a  long  vibratile 
fnifcTpjmt  or  flagellum,  like  those  flagellate  If^vMoria  which 


TBI  ABATOHT  Or  HTVXBTEBKATKD  A 


I. THB    MONERA. 

In  Uieae  lowest  forms  of  ftnimala  the  entu 
conaista  of  a  particle  of  gelatinous  protoplaai 
nncl^is,  contractile  vacnole,  or  other  definil 
-risible;  and  which,  at  moat,  presents  a  sepft 
outer,  more  clear,  and  denser  lajer— the  Ml 
inner,  more  granular  and  fluid  matt«r  — 
The  outer  lajer  is  the  seat  of  active  cImi 
wherebj  it  is  produced  into  pseudopodia,  w 
certain  leoigdi  and  are  then  retracted,  or  an 
derelopment  of  otliers  from  a^acent  parte 
These  psendopodia  »re  sometimes  broad  d 
others,  elongated  filaments.  When  lobate,  tti 
remain  .WhuuA  Fn>iu  .^n^-  imolh^-r.  iWir  lunq 
and  transpureut,  anil  tlio  ^ujiule^  which  thl{ 
plainly  flow  into  their  int^arior  from  the  t 
part  of  the  body.  But,  when  they  are  filifof! 
apt  to  nm  into  one  another,  and  give  rise  it 
conatituent  filamente  i.>f  which,  kowever,  t 


rHE  ARA^TOmr  OT  UmSTEBBATCD  AiriMAI.8. 

Tig.  1. 


„  _       .    ,  ,  ,       Bckel),— o,  the  ilill  condition  ior- 

Toandad  b*  k  itmcturelsn  syit ;  l>,  encntcd  ferm,  tb«  pRiIoplum 
of  which  U  diTidiDg;  c,  ths  otR  biintinf[  ud  giving  exit  to  tin 
bodin  Into  whioli  the  prolopltim  bntkt  ap.  There  m  at  fint 
*  moittdl,*  d,  neh  being  pravlded  with  >  flsgcllilbna  dUuin,  b;  mean* 


THI  FOBAMINIF£BA«  81 

of  which  it  propels  itself  (d).  After  a  time  each  monad  retracts  its 
cilium  and  resumes  an  Amoeba-like  form ;  (e)  many  of  these  coalesce 
and  form  a  single  Plasmodium,  which  grows  and  feeds  under  the 
form  /.  The  specimen  figured  contains  a  Ffridinium  (above),  three 
IHetyocysUe  (below),  and  two  IsthmuB  (Diatomaceous  plants)  in  the 
centre.    (Haeckel,  *  Studien  iiber  Moneien,'  1870.) 

are  termed  "  monads."  After  swimming  about  for  a  while, 
these  mastigopods  draw  in  their  flagella,  and  become  creep- 
ing myxopods.  This  cycle  of  forms  is  exhibited  bj  the 
genus  Protomonaa  of  Haeckel.  Lastly,  in  Proiomyxa  (Fig.  1) 
(Haeckel),  there  is  an  alternation  of  a  mastigopod  {d)  with  a 
myxopod  form  (e),  as  in  Protomonas.  But  each  myxopod 
does  not  usually  become  encydted  alone.  On  the  contrary, 
a  certain  number  of  the  myxopods  unite  together,  and 
become  fused  into  an  active  Plasmodium  (/),  which  exhibits 
no  trace  of  their  primitive  separation.  The  plasmodium 
becoming  qxdescent  and  spheroidal,  surrounds  itself  with  a 
structureless  cyst  (a),  divides  into  numerous  portions  (5), 
which  are  converted  into  flagellate  mastigopods,  and  these 
finally  return  to  the  myxopod  condition  (c,  d,  e).  The  cycle 
of  life  is  here  singularly  sinulai'  to  that  presented  by  the 
Myxomycetes,  which  have  hitherto  been  usually  regarded  as 
plants. 

There  is  no  means  of  knowing  whether  the  cycle  of  forms 
presented  by  Protomonas  and  Protomyxa  is  complete,  or 
whether  some  term  of  the  series  is  still  wanting ;  and  con- 
sidering how  low  down  among  plants  the  sexual  process 
occurs,  it  seems  quite  possible  that  some  corresponding 
sexual  process  yet  waits  to  be  discovered  among  the  Monera. 
It  is  possible  that  the  fusion  of  separate  Myxodictya  and 
Protamyza  into  a  plasmodium  may  be  a  process  of  sexual 
conjugation.  On  the  other  hand,  it  may  well  be  that  these 
extremely  simple  organisms  have  not  yet  reached  the  stage 
of  sexual  differentiation. 

The  FoBAMiNiPEBA. — ^Doubtless  many  Monera  remain  to 

be  discovered,  but  they  will  probably  be  minute  and  inconspi- 

caooB  organisms  like  the  majority  of  those  already  described. 

The  Fcraminifera,  on  the  other  hand,  are  Monera  of  the 

Protof^enea  type,  which,  nevertheless,  play  and  have  played 

o 


Ha        TBI  AlTXTOn  or  mnsTIBBATBD  anhialb. 

on  important  part  in  the  liistory  of  th«  ^lobe,  by  reason  of 
their  power  of  fabricating  Bkeletons  or  ahelle,  whicb  maj 
be  compoeed  of  homj  (chitinoaa  Pj  matter,  or  of  carbonate 
of  lime,  secreted  from  the  water  in  which  they  live,  or  may 
be  fabricated  by  sticking  together  extraneotia  matters,  sncb 
aa  porticlea  of  aand. 

The  first  step  from  such  an  organism  as  Prologeaet  to  the 
Foramin^era  is  seen  iath6LUi>erkiihnia  of  Claparede,  where 
the  peeudopodia  are  given  off  from  only  a  small  part  of  the 
Borface  of  the  body,  the  rest  remaining  naked  and  flexible. 

In  Oromia  there  is  a  similar  retrtnction  of  the  area  from 

T]g  a. 


which  psendopodia  proceed,  bat  the  rest  of  the  body  is  in- 
vested by  a  case  of  a  membranous  eubstance.  Let  this 
case  become  hardened  by  the  attachment  of  foreign  bodies 
— as  particles  of  sand,  or  fragments  of  shelly  matter,  as  in 
the  so-called  arenaoeons  Foratnitt\fera, — or  let  a  deposit 
of  calcareons  salts  take  place  in  it,  and  the  Gromia  would 
be  converted  into  a  Foraminifer. 

The  infinitely  diversified  characters  of  the  skeleton  of  the 
fbraminiftra  depend — firstly,  upon  the  structure  of  the 
skeletal  enbatonce  itself ;  and,  secondly,  upon  the  form  of 
the  protoplasmic  body,  which  last,  again,  is  largely  depen- 


TBI  voKixnrirsaA.  S3 

dent  upon  the  numner  in  whick  *ncc«saiTe  bods  of  proto< 
plasm  are  developed  from  the  parent  mau,  which,  to  begin 
wiUi,  a  alwaje  rample  in  form  and  oommoiilf  globular. 

The  enbstance  of  the  calcareoas  skeleton  itaelf,  whatever 
be  its  form,  is  dtlier  perforated  or  imperforate.  In  the  7m- 
perforata  (OnHntdcE,  LUuitida,  IfUiolida)  the  psendopodia 
are  protruded  from  on!;  one  end  of  the  body,  the  rest  of 
which  is  cnt  off  from  the  ecterior  by  the  skeleton.  In 
Ute  Pmforata,  the  rabstance  of  the  Bhell  is  traversed  bj 
more  or  less  delicate  canals,  filled  with  the  protoplasm, 


Fig.  3 


'#-^ 


fig-  S.— DUgimna  of  Fi>ramiiiifera.~~A,  monothftUinlaii ;  B,  C,  poly- 
thkUmJu;  D,  horiiontal;  E  ukd  F,  vvrllcal  woliaiii  of  hel]a>id 
fbtrn.  la  E,  the  otiMnben  of  e«oh  torn  of  Che  iplnl  oTerlap  their 
pndxetmon  md  conceal  them,  W  in  the  gentu  NnmmHlita. 

which  thus  reaches  the  sorface  and  gives  off  psendopodia 
all  over  the  bodj.  Hence,  while  the  hard  parts  of  the 
Imparforata  form  a  sort  of  exo-skeleton,  those  of  the 
Perforata  have  rather  the  nature  of  an  endo-skeleton. 

The  simplest  skeletons  are  spherical  or  flaaV-sbaped,  and 
single-chambered.  Bnt  complication  ariees  bj  the  addition 
of  new  chambers,  which  maj  form  a  linear  series,  or  becoiled 
npou  one  another  in  various  ways,  or  be  irregnlarly  aggre- 
gat«d.  Horeover,  the  new  chambers  maj  overlap  those 
a  2 


84         THE  ANATOKT  OF  IKTBSTBBBATED  ANIMALS. 

already  formed  in  different  degrees,  and  the  interspaces 
between  the  walls  of  the  chambers  maj  be  Tariouslj  filled 
up  by  secondary  deposition,  until  such  large  and  apparently 
complicated  bodies  as  the  Nummulites  are  built  up. 

The  Foraminifera  are  almost  all  marine  animals,  living  in 
the  sea,  from  the  surface  to  great  depths,  sometimes  free» 
and  sometimes  attached  to  other  bodies. 

The  investigations  of  Major  Owen,  confirmed  and  extended 
by  the  recent  work  of  H.M.S.  *  Challenger,*  have  proved 
that  such  forms  as  Ghbigerina,  PvlvinulcMria,  and  Orbulina 
constantly  occur  at  the  surface  of  all  temperate  and  tropical 
seas,  and,  together  with  the  Radiolaria  and  the  Diatomaceous 
plants  which  accompany  them,  form  an  important  ingre- 
dient in  he  food  of  pelagic  animals,  such  as  the  Sdlpce. 

It  is  no  less  certain  that  at  all  depths  down  to  2400 
fathoms  or  thereabouts,  Ghbigermce  in  all  stages  of  growth 
and  containing  more  or  less  protoplasmic  matter  are  found 
at  the  bottom,  mixed  with  the  cases  of  the  surface  Diatoms 
and  the  skeletons  of  Badiolaria,  The  proportion  of  Olohi- 
geriruB,  OrbvlincB,  and  PtUvintdarice  in  the  deep-sea  mud 
increases  with  the  depth,  until,  at  depths  beyond  1000 
fathoms,  the  sea- bottom  is  composed  of  a  fine  chalky  ooze 
made  up  of  little  more  than  the  remains  of  these  Foramini- 
fera and  their  associated  Diatoms  and  Baddolaria, 

It  may  be  regarded  as  certain,  therefore,  that  some  of 
the  chalky  ooze  arises  from  the  precipitation  to  the  bottom 
of  the  skeletons  of  dead  GhligerincB,  PtUvinularicB  and 
OrhulincBy  and  it  may  be  that  the  whole  has  this  origin.  On 
the  other  hand,  it  may  be  that  a  greater  or  smaller  pro- 
portion of  these  Foraminifera  really  live  at  the  bottom, 
as  their  congeners  are  known  to  do  at  less  depths. 

It  has  been  said  that  the  condition  of  the  surface  waters 
and  sea-bottom  which  has  just  been  described,  obtains  in 
all  temperate  and  hot  seas ;  or,  speaking  roughly,  for  55^  on 
either  side  of  the  equator.  Towards  the  northern  and 
southern  limits  of  this  zone  the  Foraminifera  diminish,  while 
BadioUma  remain  and  IHaUmuLeem  increase  in  proportion, 
80  that,  in  the  circnmpolar  areas  north  and  aouUi  of  60°  in 


PROTOZOA  AS  BOCK-BniLl>£B8.  85 

each  liemispliere,  the  siirf  ace  organisms  are  chiefly  such  as 
have  silicious  skeletons.  In  accordance  with  this  condition 
of  the  Borface  life,  the  ooze  coyering  the  sea-bottom  in  these 
r^ons  is  no  longer  calcareous  but  silicious,  being  composed 
of  the  cases  of  Diatoms  and  the  skeletons  of  Badiolaria 
often  largely  mixed  with  ice,  drifted  mud,  stones,  gravel, 
and  boidders. 

If  we  suppose  the  globe  to  be  uniformly  covered  with  an 
ocean  1000  fathoms  deep,  the  solid  land  forming  its  bottom 
would  be  out  of  reach  of  rain,  waves,  and  other  agents  of 
degradation  and  no  sedimentary  deposits  woidd  be  formed. 
But  if  Foraminifera  and  Diatoms,  following  the  same  laws 
of  distribution  as  at  present  obtain,  wert)  introduced  into 
this  ocean,  the  fine  rain  of  their  silicious  and  calcareous  hard 
parts  woidd  commence ;  and  a  circumpolar  cap  of  silicious 
deposit  would  begin  to  make  its  appearance  in  the  north 
and  in  the  south ;  while  the  intermediate  zone  would  be 
covered  with  Ghhigerina  ooze,  containing  a  comparatively 
small  proportion  of  silicious  matter.  The  thickness  of  the 
calcareo-silicious  and  silicious  beds  thus  formed  would 
be  limited  only  by  time  and  the  depth  of  the  ocean.  These 
strata,  once  accumulated,  would  be  liable  to  all  those 
influences  of  percolating  moisture  and  subterranean  heat, 
which  are  known  to  suffice  to  convei-t  silicious  matters  into 
opal,  or  quartzite,  and  calcareous  matters  into  the  various 
forms  of  limestone  and  marble.  And  such  metamorphic 
agencies  might  more  or  less  completely  obliterate  the  traces 
of  their  primitive  structure. 

But  yet  other  changes  might  be  effected.  At  the  present 
day,  in  the  Gulf  of  Mexico,  off  the  Agulhas  bank,  and  else- 
where, at  no  great  depths  (100  to  300  fathoms)  the  Fora- 
minif eral  mud  is  undergoing  a  metamorphosis  of  another 
character.  The  chambers  of  the  Foraminifera  become 
filled  by  a  green  silicate  of  iron  and  alumina,  which 
penetrates  into  even  their  finest  tubuli,  and  takes  ex- 
quisite and  almost  indestructible  casts  of  their  interior. 
The  calcareous  matter  is  then  dissolved  away,  and  the 
casts  are  left,  constituting  a  ^q  dark  sand,  which,  when 


86         THE  ANATOMY  OF  nTYBBTEBBATED  ANIMALS. 

crashed,  leayes  a  greenisli  mark,  and  is  known  as  *  Green- 
sand.' 

Moreover,  the  researches  of  the  '  Challenger '  have  shown, 
that  in  great  areas  of  the  Atlantic  and  Pacific  oceans 
over  which  the  sea  has  a  depth  exceeding  2400  fathoms — 
areas  in  some  cases  of  many  thousand  square  miles  in 
superficies — ^the  bottom  is  covered  not  by  Glohigerina  ooze, 
but  by  a  fine  red  clay,  which  is  also  a  silicate  of  iron  and 
alumina.  In  this  clay  no  remains  of  Gtohigerina  or  other 
calcareous  organisms  are  found;  but  where  these  great 
depths  graduidly  pass  into  shallower  water,  they  make  their 
appearance  in  a  fragmentary  condition  —  graduaUy  be- 
coming more  and  more  perfect  as  the  depth  diminishes  to 
2400  fathoms  or  thereabouts. 

Nevertheless  the  OlobigerinoB  and  other  Foraminifera 
abound  at  the  surface  over  these  areas  as  they  do  elsewhere, 
and  their  remains  must  be  rained  down  upon  it.  Why  they 
disappear,  and  what  relation  the  red  clay  mud  has  to  them, 
is  a  problem  not  yet  satisfactorily  solved.  It  has  been 
suggested  that  they  are  dissolved  and  that  the  red  clay 
is  merely  the  insoluble  residue,  left  after  the  calcareous 
portion  of  their  skeletons  has  disappeared.  In  this  case 
the  red  clay,  like  the  Ohbigerina  ooze,  the  silicious  mud,  and 
the  greensand,  will  be  an  indirect  product  of  living  action. 

Metamorphic  processes  operating  upon  clay,  however, 
may  convert  it  into  slate ;  and  thus,  all  the  fundamental 
minerals  of  which  rock  masses  are  composed  may  have 
formed  part  of  living  organisms,  though  no  trace  of  their 
origin  may  be  discernible  in  them  in  their  final  state. 

FalsBontology  lends  much  support  to  the  view  that  what 
is  here  suggested  as  a  theoretically  possible  origin  of 
much  of  the  superficial  crust  of  the  globe,  may  have  been 
its  actual  origin. 

The  nummulitic  limestones  of  the  Eocene  epoch  cover  an 
enormous  area  of  central  and  southern  Europe,  North 
Africa,  West  Asia  and  India.  And  their  chief  mass  is 
made  up  of  the  more  or  less  metamorphosed  remains  of 
Foramiwifera. 


PROTOZOA  JL8  BOCK-BUILDEBB.  87 

The  beds  of  chalk  which  underlie  the  nummnlitic  lime- 
stones, and  occnpj  a  still  greater  area,  are  essentially 
identical  with  the  Olohigerina  ooze,  the  species  of  Glohi' 
gerina  found  in  it  being  indistinguishable  from  those  now 
living.  The  remains  of  Foraminifera  have  been  detected 
in  the  limestones  r>f  all  epochs  as  far  as  the  Silurian, 
and  Ehrenberg  discovered  that  an  old  Silurian  greensand, 
near  St.  Petersburg,  is  composed  of  casts  of  Foraminifera 
just  such  as  are  now  being  formed  in  the  Gulf  of  Mexico. 
And  if  the  Eozoon  canademe  be,  as  it  appears  to  be,  nothing 
but  an  encrusting  form  of  Foraminifer,  the  existence 
of  these  organisms  is  carried  back  to  an  epoch  far 
beyond  that  at  which  any  other  evidence  of  life  has 
yet  been  found.  So  that  it  is  possible  that,  as  Wyville 
Thomson  has  suggested,  the  enormously  thick  "azoic" 
slaty  and  other  rocks,  which  constitute  the  Laurentian  and 
Cambrian  formations,  may  be  to  a  great  extent  the  meta- 
morphosed products  of  Foraminif  eral  Hf  e. 

Hence  the  words  of  Linnseus  may  be  literally  true— 

**  Petrefacta  non  a  calce,  sed  calx  a  petrefactis.  Sic  lapides  ab 
animalibus,  nee  vice  versa.  Sic  rupes  saxei  non  primsevi,  sed  temporis 
filias." 

And  there  may  be  no  part  of  the  common  rocks,  which 
enter  into  the  earth's  crust,  which  has  not  passed  through  a 
living  organism  at  one  time  or  another. 


n. — THE  ENDOPLASTICA. 

1.  The  Radiolabia. — Most  species  of  the  genus  Actino- 
phry8  or  "  sun-animalcule,"  which  is  common  in  ponds,  are 
simply  free  swimming  myxopods  with  stiffish  pseudopodia, 
which  radiate  from  all  sides  of  the  globular  body.  The  sab- 
stance  of  the  latter  presents  one  or  more  "  contractile  spaces  " 
or  "  vacuoles,"  which,  rhythmically,  become  distended  vrith 
water,  and  are  then  obliterated  by  the  contraction  of  the 
surrounding  protoplasm.  But  in  the  Actinophrys  (or  more 
properly  AeHnaaphcBrivmi)  Eiehhomii  (Fig.  4),  the  central 
part  of  the  protoplasm  is  distinguished  from  the  rest  by 


THB  XHATOlfT  OF 


ooDtaiuing  a  number  of  endoplasta.    It  thos  leads  to  the 
BadiotiOria  [FolyaMitia  of  Ehienbei^),  the  eimplest  forms  of 


Fig.  4.—ActiMoipliariirm  EiMonui  (»HtT  Bertwig  knd  Lener,  '  lleber 

Bhliopaden,' SehnlK's  Aiohi*,  1676). 
I.— The  endre  anlinkl ;  r,  c,  eoutnctlle  vacnala. 
TI._Put  of  the  petiphcrf  maoh  nugnlfled  -,  a,  a,  a,  paeudopodu  wilh 

■UffuUI  nibituice;  ■,  nuclei  or  endoplMti. 
in. — A  va7  young  Adno^iliiirmai,  wiUi  onljr  tiro  micld  Uid  tiro 

pModopMls,  much  nxgnlfied. 

wludi  ooiuUt  Msentiallj  of  a  myxopod,  prorided  with 
filamentoufl,  radiating,  and  often  anastomoHiiig,  peendo- 


TBI  kU>IOLUtUL. 


podia,  ntecflntreof  the  body  iaooonpiedbj  a  capsule  filled 

wiih  protoplaemj  this  Bometdmen  containa  onlj  an  oil- 

fig  i. 


—  A,  a  nun  oftha  n: 
tiro  of  tbe  oral  ecntral  ma  wlUi  tha  onlonrad  vetlo 


Flc.6. 


1 


-^ 


"»:"«'^ 


-^Si^'i^""^ 


1) 


Flf .  6.~(!pAiEn»owK 


(mfter  Hteckel),  magnified. 


globule,  at  others  cella  or  nnclei,  and  ci^BtaUine  bodies.    In 
the  layer  of  protoplaam  from  which  the  paeudopodia  proceed, 


90    THE  AKATOMT  OF  ZNYBSTEBBATED  ANIMALS. 

cellffif orm  bodies  of  a  briglit  jellow  colonr,  whicli  liave  been 
found  to  contain  starcli,  are  usaally  developed,*  and  this 
layer  also  gives  rise  to  a  skeleton  of  a  homy,  or,  more  osuallj, 
silicions  cbaracter,  which  may  have  the  form  of  detached 
spicula,  or  of  coarticulated  rods,  or  of  networks,  or  of  plates 
of  silicions  matter,  often  of  the  most  exquisite  delicacy  and 
beauty.  Most  of  the  Eadiolaria  are  simple,  solitary,  and 
microscopical  in  size ;  but  some,  such  as  CoUoaphcBra  and 
8ph€Bro%oum  (Figs.  5  and  6),  are  formed  of  aggregates  of 
such  simple  forms,  and  float,  as  visible  gelatinous  masses,  at 
the  surface  of  the  sea,  which  is  the  habitation  of  the  great 
majority  of  the  Badiolaria, 

The  manner  of  multiplication  and  the  development  of 
the  Rcfdiolaria  have  not  yet  been  thoroughly  worked  out. 
Gienkowsky,  however,  has  observed,  in  CoUosphasra,  that 
the  protoplasm  contained  in  the  central  capsule  breaks  up 
into  numerous  rounded  masses.  The  several  capsules  which 
are  associated  together  in  the  compound  Badiolarian  then 
become  isolated,  by  the  dissolution  of  the  protoplasm  which 
invested  and  connected  them,  and  finally  burst,  giving 
exit  to  the  rounded  bodies;  which,  while  yet  within  the 
capsules,  were  observed  to  be  in  active  motion.  The  germs 
(for  such  they  appear  to  be)  thus  set  free  are  0'008  mm. 
long,  ovate,  and  carry  two  flagellif  orm  cilia  at  their  nar- 
row ends;  so  that  they  are  'monads.'  Each  has  in  its 
interior  a  crystalline  rod  and  a  few  minute  oil-globules. 
The  further  development  of  these  mastigopods  has  not 
yet  been  traced;  but  if ,  as  is  probable,  they  pass  into 
young  Eadiolaria  (which,  according  to  Haeckel,  possess  no 
capsule,  but  resemble  ActinospIuBria),  the  Badiolaria,  as 
members  of  the  Endoplcuiica,  would  typify  ProtoTnonas 
among  the  Monera,  Neither  conjugation  nor  fission  has 
been  observed  among  the  ordinary  Eadiolaria,  but  both 
these  processes  take  place  in  AcHnosphoBriwen, ;  and,  consider- 
ing the  resemblance  of  the  young  Badiolaria  to  ActinO' 

*  Even  after  the  death  of  the  multiply,  and  the  possibility  that 
Badiolaiian,  these  jellow  oellf  are  they  may  be  parasites  most  be 
said  by  Gifliikowiky  to  thrive  and      borne  in  mind. 


THB  PBOTOPLA0TA.  9l 

iphcerium,  it  seems  probable  that  coigugation  and  fission 
will  yet  be  discoyered  among  them. 

AetinosphcBrium  has  been  observed  to  undergo  multiplica- 
tion, hj  division  of  its  central  substance  into  a  certain 
number  of  spheroids,  and  every  spheroid  becomes  enclosed 
in  a  silicious  case.  After  a  period  of  rest,  a  young  Actmo- 
wphiBrivmih  emerges  from  each  of  these  cysts. 

The  marine  Badiolaria  all  inhabit  the  superficial  stratum 
of  the  sea,  and  must  fabricate  their  skeletons  at  the  expense 
of  the  infinitesimally  small  proportion  of  silex  which  is 
dissolved  in  sea-water ;  but  when  they  die,  these  skeletons 
sink  to  the  bottom,  and  there  accumulate,  together  with  the 
Fcraminifera^  in  warm  and  temperate  regions;  and  with 
the  cases  of  the  diatomaceous  plants,  which  abound  at  the 
surface,  along  with  the  B^Mdiolaria,  all  over  the  globe  (see 
p.  85).  The  late  investigations  of  Archer  and  others  have 
demonstrated  the  existence  of  a  considerable  number  of 
fresh- water  Badiolaria, 

Extensive  masses  of  tertiary  rock,  such  as  that  which  is 
found  at  Gran,  and  that  which  occurs  at  Bissex  Hill,  in 
Barbadoes,  are  very  largely  made  up  of  exquisitely  preserved 
skeletons  of  Badiolaria.  But,  though  there  can  be  little 
doubt  that  Badiolaria  abounded  in  the  cretaceous  sea,  none 
are  found  in  the  chalk,  their  silicious  skeletons  having 
probably  been  dissolved  and  redeposited  as  flint. 

2.  The  Peotoplasta. — The  proper  Avuj^hb  have  broad 
and  ovate  pseudopodia,  and  resemble  Frotamaba  (p.  78)  very 
closely ;  but  they  present  an  advance  upon  its  structure  by 
exhibiting  a  distinct  endoplast  (nucleus)  and  a  contractile 
vacuole.  In  ArceUa,  there  are  many  such  nuclei.  They 
thus  stand  in  somewhat  the  same  relation  to  FrotamoBba  as 
Actvnaphrya  does  to  Frotogenes. 

Moreover,  there  are  AmcebcB  in  which  the  power  of  throw- 
ing out  pseudopodia  is  confined  to  one  region  of  the  body ; 
and  others,  as  Arcella,  in  which  a  shell  is  formed  over  the 
rest  of  the  body.  In  other  Amcebce,  as  A.  radiosa,  the  pseu- 
dopodia are  few,  narrow,  and  but  little  mobile.  But 
the  AmodbcB  present  no  such  diversity  of  skeletal  develop- 


92    THE  ANATOMY  OF  ZNYBBTBBBATBD  ANIMALS. 

ment  as  the  Foraminifera  do.  They  multiply  by  division, 
and  in  some  cases — e.g.,  A.  sphcaroeoecua  of  Haeckel — become 
encysted  before  they  divide. 

AtruBlHB  (the  "  proteos  animalcules  '*  of  the  older  writers) 
are  not  uncommon,  and  sometimes  are  very  abundant,  in 
fresh  waters ;  they  also  occur  in  damp  earth  and  in  the  sea, 
but  there  is  much  doubt  whether  many  of  them  are  to  be 
regarded  as  independent  organisms,  or  whether  they  are  not 
rather  stages  in  the  development  of  other  animals  or  even  of 
plants,  such  as  Myxomycetee.  Leaving  out  the  contractile 
vacuole,  the  resemblance  of  an  Amoeba  in  its  structure, 
manner  of  moving,  and  even  of  feeding,  to  a  colourless 
corpuscle  of  the  blood  of  one  of  the  higher  animals  is  par- 
ticularly noteworthy.* 

3.  The  Gbegabinidje  are  very  closely  allied  to  the 
AmcdHB,  but,  in  the  cycle  of  forms  through  which  they 
pass,  they  curiously  resemble  Myxastrum,  In  form,  they 
are  spheroidal  or  elongated  oval  bodies,  sometimes  divided 
by  constrictions  into  segments.  Occasionally,  one  end  of 
the  body  is  produced  into  a  sort  of  rostrum,  which  may 
be  armed  with  recurved  homy  spines. 

In  the  ordinary  GregarincB,  the  body  presents  a  denser 
cortical  layer  (ectosarc)  and  a  more  fluid  inner  substance 
(endosarc),  in  which  last  the  endoplast  (nucleus)  is  imbedded. 
The  presence  of  contractility  is  manifested  merely  by  slow 
changes  of  form,  and  nutrition  appears  to  be  effected  by 
the  imbibition  of  the  fluid  nutriment,  prepared  by  the 
organs  of  the  wTiiTn5i.1a  in  which  the  QregarinoB  are  parasitic. 
There  is  no  contractile  vacuole. 

The  GregariruB  have  a  peculiar  mode  of  multiplication, 
sometimes  preceded  by  a  process  which  resembles  conjuga- 
tion. A  single  Gregarina  (or  two  which  have  become 
applied  together)  surrounds  itself  with  a  structureless  cyst. 
The  nucleus  disappears,  and  the  protoplasm  breaks  up  (in  a 
manner  very  similar  to  that  in  which  the  protoplasm  of 
a  sporangium  of  Mucor  divides  into  spores)  into  small 

*  Gontraetile  vaenoles  have  been  observed  in  the  colourlete  blood 
MTpnsclet  of  Awnpkiinu  under  certain  oonditiont. 


TBI  aBKaAAurisx.  93 

bodiea,  each  of  which  acqnirefl  a  Bpindle-ehaped  case,  and 
ia  known  as  a  pasudo-nameella.  On  the  bnrsting  of  the 
cjnt  theoe  bodies  are  net  free,  and,  when  placed  in  favour* 
able  circnmatancea,  the  contained  protoplasm  eacapea  aa 
a  amaU  active  body  like  a  Prolam<eba.  M.  E.  van  B^ieden 
has  recently  diacorered  a  vei;  large  Greganva  [Q.  gigantea), 
which  inhabits  the  intestiiie  of  the  lobster,  ojid  hia  careful 


Fig.  7. 


paoida-iuTieellK  ;  G,  H,  fr(«  uniebiform 


iiiTestigatioti  of  its  Htmctnre  and  derelopment  has  yielded 
very  interesting  reaolts. 

Qregarina  giganUa  attains  a  leng;th  of  two-thirds  of  an 
inch.  It  is  long  and  slender,  and  tapers  at  one  extremity, 
while  the  other  ia  obtnse,  roonded,  and  separated  by  a  slight 
constarictum  fnnn  the  rest  of  the  body,  which  is  i^lindroidaL 


94         THE  ANATOlfT  OF  IKYEBTEBBATED  AKIHALS. 

The  outer  inyeBtment  of  the  body  is  a  thin  stractureless 
onticle ;  beneath  this  lies  a  thick  cortical  lajer  (ectosarc),  dis- 
tinguished bj  its  clearness  and  firmness  from  the  semifluid 
central  substance  (endosaro),  which  contains  many  strongly 
refracting  granules.  In  the  centre  of  the  body,  the  ellipsoid 
"  nucleus,"  with  its  "  nucleolus/'  fills  up  the  whole  cavity  of 
the  cortical  layer,  and  thus  divides  the  medullary  substance 
into  two  portions.  The  body  of  this  Qregarina  may  present 
longitudinal  striations,  arising  from  elevations  of  the  inner 
surface  of  the  cortical  layer,  which  fit  into  depressions  of 
the  medullary  substance;  but  these  are  inconstant.  On 
the  other  hand,  there  are  transverse  striations  which  are 
constant,  and  which  arise  from  a  layer  of  what  are  ap- 
parently muscular  fibrillee,  developed  in  a  peripheral  part 
of  the  cortical  layer,  immediately  below  the  cuticle.  The 
fibrills  themselves  are  formed  of  elongated  corpuscles 
joined  end  to  end.  A  transverse  partition  separates  the 
cephalic  enlargement  from  the  body,  and  the  layer  of 
muscular  fibres  only  extends  into  the  posterior  part  of  the 
enlargement. 

The  embryos  of  Gregarina  gigantea,  when  they  leave 
their  pseudo-navicellse,  are  minute  masses  of  protoplasm 
similar  to  Protamoebce,  and  like  them  devoid  of  nucleus 
and  contractile  vacuole.  They  soon  cease  to  show  any 
change  of  form,  and  acquire  a  globular  shape,  the  peri- 
pheral region  of  the  body  at  the  same  time  becoming  clear. 
Kext,  two  long  processes  bud  out  from  this  body;  one 
is  actively  mobile,  the  other  stilL  The  former,  detaching 
itself,  assumes  the  appearance  and  exhibits  the  motions 
of  a  minute  thread- worm,  whence  M.  van  Beneden  terms 
it  a  pseudo'filafia.  The  enlargement  at  one  end  becomes 
apparent,  the  pseudo-filaria  passes  into  a  quiescent  state, 
and  the  "  nucleolus "  makes  its  appearance  in  its  interior. 
Around  this  a  clear  layer  is  differentiated,  giving  rise  to 
the  **  nucleus,"  and  the  pseudo-filaria  passes  into  the  con- 
dition of  the  adult  Qregarina  gigantea. 

4.  The  Oatallacta  of  Haeokel,  represented  by  the  genus 
Magottphcera^  are,  in  one  Btage,  myxopods  with  long  pseudo- 


TBI  HfTUBOBU.  95 

>du,  whicli,  broad  and  lobe-like  at  the  haae,  break  up  into 

le  filaments  at  their  ends,  and  tnaj  therefore  be  said 

be  intenuediatfl  between  tho«e  of  Protogenea  and  those 

Prolammba.    Tike  myiopod  is  provided  with  a  dUtinct 

idoplaet  and  a  well-marked  contractile    apace.    When 

ilj  fed,  it  eecretea  a  cjet  and  diridea  into  a  number  of 

aasea,  each  of  which  it  converted  into  a  conical  bodj, 

ith  its  baoe  tnrned  ontwarda  and  ita  apex  inwards.     These 

inical  bodiea  are  imbedded  in  a  gelaiinoas  matter,  and 

iHs  cohere  into  a  ball,  from  the  centre  of  which  tbej 

diat«.    Each  derelopea  cilia  around  ita  baae,  and  contain  a 

1  endoplast  and  a  contractile  vacnole.    After  the  complex 

obe  thus  formed  has  bnrst  ita  envelope,  it  awima  about 

r  a  while,  like  a  Folttw.    The  several  ciliated  animalcnlei 

ed  bj  taking  in  solid  particlea  thronj^h  the  disk.    Tbej 

m  aeparote.  and,  finallj,  retracting  their  cilia,  become 

lopoda   ench   aa  thoae   with  which  the   aeriea   Htart«d. 

goaphcera  ia  thus  very  nearly  an  endoplaatic  repetition 

the   moneran  Frotomonaa — the   maatigopod  being  pro- 

d  with  many  small  cilia,  instead  of  with  a  couple  of 

1  fla^ella.    On  the  other  hand,  the  Calallacta  are  closely 

1  to  the  next   group,   and,   I  am  diapoaed  to   think, 

t  well  be  included  in  it. 

rhe  IirrusoBU. — Excluding  from  the  miscellaneous 

blage  of  heterogeneous  forms,  which  have  passed 

this  name,  the  Deamidia,  Dialomaeeas,  VolvociTteiB,  and 

nda,  which  are  true  plants,  on  the  one  hand ;  and 

uparatirely  highly  organised  Rotifera,  on  the  other; 

tmain  three  assemblages  of  minute  organisms,  which 

conveniently  comprehended  under  the  general  title 

iori&.    These  are — (o)  the  ao-called  "  Monads,"  or 

t  jbxgdUita ;   {b)  the  AotneUE,  or  lafaaoria  tetttaca- 

jd  (c)  the  Infmaria  ciliata. 

e  Plaoxllata. — Theae  are  characterised  by  pos- 
nly  one  or  two  long  whip-like  cilia,  sometimes 
-e  than  one  are  present]  situated  at  the  same  end 
r,  eometimea  far  apart.  The  body  very  generally 
endoplaat  and  a  contractile  vacuole.    There  is 


96         THE  ANATOMY  OF  IHnTEBTEBBATED  AKIMALS. 

no  permanently  open  oral  aperture,  but  there  is  an  oral 
region,  into  which  the  food  is  forced,  and,  passing  into  the 
endosarc,  remains  for  some  time  surrounded  by  a  globule 
of  contemporaneously  ingested  water — a  so-called  "food 
racuole."  Professor  H.  James  Clark,  who  has  recently 
carefully  studied  the  FlageUatay  points  out  that,  in  Bicosceea 
and  Codonoeea,  a  fixed  monadif  orm  body  is  enclosed  within  a 
structureless  and  transparent  calyx.  In  Codosiga  a  similar 
transparent  substance  rises  up  round  the  base  of  the  flagel- 
lum,  like  a  collar.  In  Salpingceca  the  coUar  around  the 
base  of  the  flagellum  is  combined  with  a  calycine  inrest- 
ment  for  the  whole  animal  In  Anthophyaa,  there  are  two 
motor  organs — ^the  one  a  stout  and  comparatively  stiff 
flagellum,  which  moves  by  occasional  jerks,  and  the  other  a 
very  delicate  cilium,  which  is  in  constant  vibratoiy  motion. 

The  discrepancy  between  the  two  kinds  of  locomotive 
organs  attains  its  maximum  in  Anisonema,  which  presents 
interesting  points  of  resemblance  to  Noctiluca, 

Multiplication  by  longitudinal  fission  was  observed  in 
Codosiga  and  Ardhophysa,  and  probably  occurs  in  the  other 
genera.  In  Codosiga  the  flagellum  is  retracted  before  fission 
takes  place,  but  the  body  does  not  become  encysted;  in 
Anthophysa  the  body  assumes  a  spheroidal  form,  and  is 
surrounded  by  a  structureless  cyst,  before  division  occurs. 

Conjugation  has  not  been  directly  observed  among  most 
of  the  Infusoria  flageUata,  nor  do  any  of  them  exhibit  a 
structure  analogous  to  the  endoplastule  of  the  CUiata. 

Messrs.  Dallinger  and  Drysdale  have  recently  worked  out 
the  life  history  of  several  flagellate  "  Monads,"  which  occur 
in  putref3ring  infusions  of  fish.  They  show  that  these 
FlageUata  not  only  present  various  modes  of  agamic  multi- 
plication by  fission,  preceded  or  not  by  encystment,  but 
that  they  conjugate,  and  that  the  compound  body  which 
results  (the  equivalent  of  the  zygospore  in  plants)  becomes 
encysted.  Sooner  or  later,  the  contents  of  the  cyst  become 
divided  either  into  comparatively  larg^  or  excessively 
minnte  bodies,  which  enlarge  and  gradually  take  on  the 
form  of  the  parent. 


THE  FLAOELLATA.  97 

The  careful  inyestigatioiiB  of  these  authors  lead  them  to 
oiclnde  that,  while  the  adult  forms  are  destroyed  at  from 
L**-8(P  C,  the  excessively  minute  sporules  which  have  been 
mentioned,  and  which  may  have  a  diameter  of  less  than 
\^^^(i  of  an  inch,  may  be  heated  to  148^  G.  without  the 
astruction  of  their  vitality. 

In  Euglena  viridis  (which,  however,  may  be  a  plant) 
tein  *  has  observed  a  division  of  the  "  nucleus  "  to  take 
lace,  whereby  it  becomes  converted  into  separate  masses, 
>me  of  which  acquire  an  ovate  or  fusiform  shape,  sur- 
^unding  themselves  with  a  dense  coat,  while  others  become 
un-waUed  sacs,  full  of  minute  granules,  each  of  which  is 
rovided  with  a  single  cilium.  The  ultimate  fate  of  these 
)die8  has  not  been  traced. 

A  careful  study  of  the  singular  genus  Noctiluca,  led  me. 
1 1855,  to  assign  it  a  place  among  the  Infusoria^  and  recent 
vestigations  have  conclusively  proved  that  it  is  one  of  the 
ageUata. 

The  spheroidal  body  of  Noctihtca  miliaris  (Fig.  8)  is  about 

^eightieth  of  an  inch  in  diameter,  and,  like  a  peaob,  pre- 

ts  a  meridional  groove,  at  one  end  of  which  the  mouth  is 

ated.     A  long  and  slender,  transversely  striated  ten- 

2  overhangs  the  mouth,  on  one  side  of  which  a  hard- 

^ed  ridge  projects.    Close  to  one  end  of  this  is  a  vibratHe 

m.     A  funnel-shaped  depression  leads  into  a  central 

of  protoplasm,  connected  by  fine  radiating  bands  with 

er  of  the  same  substance  which   lines  the  cuticular 

>pe  of  the  body.     There  is  no  contractile  vacuole,  but 

il  endoplast  lies  in  tlie  central  protoplasm.     Bodies 

are  ingested  are  lodge<l  in  vacuoles  of  the  latter  until 

■e  digested. 

rding  to  the  observations    of    Cienkowsky.t   if   a 

w  be  injured,  the  body  bursts  and  coUapses,  but  tbo 

ismic  and  other  contents,  together  with  the  tentacle, 

irregular  mass,  the  periphery  of  which  eventually 

nismas    der  Infusions-       (Schiilze's   *Archiv  fur    Mikro 
M.  skop.  Anutomie,'  1872.) 

tr  Koctiluca  miliaria.** 


98         THE  AHATOHY  Of  IITTBItTEBIUTSD  A1IJ11A1£. 

becomes  vacuolated,  enloi^ea.  and  secretes  a  new  inveat- 
ment.  But  even  a  small  portion  of  the  pixitoplasm  of  a 
mutilated  NoetUvca  is  able  to  become  a,  perfect  animal. 
Under  some  conditions,  the  tentacle  of  a  Noctiluea  maj  be 
retracted  into  the  bod;,  and,  at  all  times  of  the  jear. 
spheroidal  NodUuca,  devoid  of  flageUum,  tooth,  or  meridio- 
nal groove,  hut  otherwise  normal,  are  t«  be  found.  These 
last  are  probabl;  to  be  regarded  as  encjBt«d  form«.  Multi- 
plication ma;  take  place  in  at  least  two  wajs.    Fission  majr 


Fig.  8. —  ffncfiltica  «i7iari(.— «,  Guirin  vacuule;  jr,  radiating  Elunents; 
'  ""■[  aterture.  (f) 

occur  in  the  spbcroidsl  forma,  aa  well  as  in  those  poBsessed 
of  a  tentacle ;  it  is  inaugurated  bj  the  enlargement,  con- 
striction, and  division  of  the  endoplajst.  This  process  takes 
plac«  more  especially  in  the  latter  part  of  the  year. 

Another  mode  of  aaemal  multiplication,  which  has  a  sin- 
gular resemblance  to  the  process  of  partial  jelk  division, 
occun  onlf  in  the  spheroidal  NbctUveee.  The  endoplaat 
Aisftppesra^  and  th^  proto^asmt  sconmnlating  on  the  inner 


THX  FLAOELLATA. 

i  of  one  region  of  the  cnticle,  divides  first  into  t 
Q  four,  eight,  sixteen,  thirty-two,  or  more  masses :  t 
!sion  of  the  protoplasm  being  accompanied  by  the  ele\ 
I  of  the  cuticle  into  protaberances,  which,  at  first,  con 
nd  in  number  and  dimensions  with  these  division  masse 
len  the  division  masses  have  become  very  numerous 
b  protrudes  upon  the  surface,  and  is  converted  into  i 
i  monadiform  germ,  provided  with  an  endoplast,  a  beak, 
i  a  long  tentacle,  which  is  hardly  to  be  distinguished  from 
agellif  orm  cilium. 

lie  process  of  conjugation  has  been  directly  observed. 
0  NoctiliteoB,  applying  themselves  by  their  oral  surfaces, 
lere  closely  together,  and  a  bridge  of  protoplasm  con- 
ting  the  endoplasts  of  the  two  becomes  apparent.    The 
taenia  are  thrown  off,  the  two  bodies  gradually  coalesce, 
'   the  endoplasts  fuse  into  one.      The  whole  process 
ipies  five  or  six  hours.    Spheroidal  or  encysted  Noctllucce 
conjugate  in  a  similar  manner.     In  this  case,  the  re- 
3  nearest  the  endoplasts  are  those  which  become  applied 
her.     Whether  this  process  is  of  a  sexual  nature,  or 
3  not  clearly  made  out.     Cienkowsky  admits  that  it 
lasten  the  process  of  multiplication  by  monadiform 
described  above. 

Uuca  is  extremely  abundant  in  the  superficial  waters 

ocean,  and  is  one  of  the  most  usual  causes  of  the 

>rescence  of  the  sea.     The  light  is  given  out  by  the 

•al  layer  of  protoplasm  which  lines  the  cuticle. 

Tridinece  (see  Fig.  1./}  form  another  aberrant  group  of 

Uata,  which  lead  to  the  Ciliata.  The  body  is  enclosed 

case  (sometimea  produced  into  rays),  which,  at  one 

ents  a  groove-like  interruption,  laying  bare  the  con- 

>toplasm,  in  which  lies  an  endoplast,  and  in  some 

itractile  vacuole.     One  or  more  flagelliform  cilia, 

Y  a  wreath  of  short  cilia,  are  protruded  from  the 

,  and  serve  as  locomotive  organs.     The  mouth  is 

1,  whence,  in  some  cases,  an  (esophageal  canal  is 

ad  terminates  abruptly  in  the  semi-fluid  central 

!  the  body,  the  food-particles  being  lodged  in 

H  2 


100       THB  AB&TOKT  OT  IHVEKTEBKATBD  ANIMALS. 

TBcnolea  fontied  at  its  extremity,  ae  in  the  CUiaia.  'So 
other  mode  of  multiplication  than  that  by  fission  has  yet 
been  observed  in  the  Peridme(s ;  but  this  fission  is  some- 
times preceded  by  the  encloBure  of  the  nninipi  in  an 
elongat«d  crescent-shaped  cyst. 

(6.)  The  TENTACULiFKa*.— The  Acindm  (Pig.  9,  D,  E, 
F.  G)  have  no  oral  aperture  of  theordinary  kind,  but  filiform 
procesBea  ot  teutacula,  which  are  usually  aleuder,  eimple, 
and  more  or  less  ri^nd,  radiate  from  the  surface  of  the  body 

Fig.  9. 


rig.  9. 


generttUy,  or  from  one  or  more  regions  of  that  surface.  At 
first  sight,  these  tentacula  resemble  the  radiating  pseudo- 
podia  of  AcHnophryg,  but,  on  closer  inspection,  they  are  seen 
to  have  a  different  cbaiwtter.  Each,  in  fa«t,  is  a  delicate 
tube,  presenting  a  stractnreleBS  ertemal  wall,  with  a  semi- 
flnid  granular  axis,  and  nsoally  ends  in  a  slight  enlargement 
or  knob.  It  may  be  alowly  pushed  ont  or  retracted,  ordi- 
TSTBoly  bent    Bat*  instfad  of  playing  the  part  of  mer« 


THB   INFUSOBIA. 


101 


snslle  organs,  these  tentacles  act,    in    addition,    as 

srs ;   the  Aeineta  applying  one  or  more  of  these  organs 

e  body  of  its  prey* — ^usually  some  other  species  of 

loriam, — when  the  substance  of  the  latter  travels  along 

iterior  of  the  sucker  into  the  body  of  the  Aeineta.    Solid 

is  not  ingested  through  these  tentacles,  so  that  the 

d(B  cannot  be  fed  with  indigo  or  carmine.    In  the 

lor  of  the  body  there  is  an  endoplastf  with  one  or 

contractile  vacuolea,  and  it  may  be  either  fixed  by  a 

or  free. 

e  AcineUB  multiply  by  several  methods.  One  of  these 
nple  longitudinal  fission,  which  appears  to  be  rare 
Lg  them.  Another  method  consists  in  the  development 
liated  embryos  in  the  interior  of  the  body.  These 
yos  result  from  the  separation  of  a  portion  of  the 
plast,  and  its  conversion  into  a  globular  or  oval  germ, 
b,  in  some  species,  is  wholly  covered  with  vibratile 


tein  (*  Der  Organismus  der 
onsthiere/  i.  76)  thus  de- 
a  the  method  by  which  an 
ta  seizes  its  prey :  *Mf  an 
irium  swims  within  reach 
e  Aeineta,  the  nearest  ten- 
are  swiftly  thrown  towards 
d,  at  the  same  time,  often 
le  much  elongated,  bent, 
^ularly  twisted  about.  The 
like  ends  of  these  tentacles, 
I  come  into  immediate  con- 
rith  the  surface  of  the  en- 
»d  prey,  spread  out  into 
and  adhere  fixedly  to  it. 
I  many  of  the  tentacles  have 
kttacbed  Uiemselves,  the  ira- 
led  animal  is  no  longer  able 
ape,  its  movements  become 
r,  and  at  length  cease, 
tentacles  which  have  fixed 
«lves  most  firmly  shorten 
bieken,  and  draw  the  prey 
r  to  the  body  .  . .  Suddenly, 
m  aa  the  sucking  disk  has 
through  the  cuticula  of  the 
a  very  rapid  stream,  in- 
id  by  the  fatty  particles 
i  it  carries,  seis  along  the 


axis  of  the  tentacle,  and,  at  its 
base,  pours  into  the  neighbouring 
part  of  the  body  of  the  Aeineta. 
.  . .  The  cause  of  the  movement 
is  unknown.  It  is  not  accom-* 
panied  by  any  discernible  move- 
ment of  the  walls  of  the  tentacle." 

t  No  endoplastule,  such  as  ex- 
ists in  other  Infusoria,  has  been 
observed  as  yet  in  the  Aeineta:. 
Under  some  circumstances,  the 
Aeineta  draw  in  their  radiating 
processes,  and  surround  them- 
selves with  a  structureless  cyst ; 
but  this  process  does  not  appear 
to  have  any  relation  to  either 
mode  of  multiplication. 

In  Aeineta  myataciyia  and  Podo- 
phrya  fixa,  a  peculiar  mode  of 
multiplication  by  division  occurs. 
At  the  free  end  of  the  body  a 
portion  becomes  constricted  off, 
together  with  part  of  the  endo- 
plast,  from  the  remaining  stalked 
part.  The  tentacula  are  drawn 
in,  and  the  segment  becoming 
elongated,  developes  cilia  over 
its  whole  surface  and  swims  away. 


V 


102       THE   AK ATOMY  OF  INYESTEBBATED  ANIMALS. 

cilia,  while,  in  others,  the  cilia  are  confined  to  a  zone  around 
the  middle  of  the  embrjo.  The  germ  makes  its  escape  hj 
bursting  through  the  body  wall  of  its  parent.  After  a 
short  existence  (sometimes  limited  to  a  few  minutes)  in  the 
condition  of  a  free  swimming  animalcule,  provided  with  an 
endoplast  and  a  contractile  vacuole,  but  devoid  of  a  mouth, 
the  characteristic  knobbed  radiating  processes  make  their 
appearance,  the  cilia  vanish,  and  the  animal  passes  into  the 
Acineta  state. 

The  AcinetcB  have  frequently  been  observed  to  conjugate, 
the  separate  individuals  becoming  completely  fused  into 
one,  and  their  endoplasts  coalescing  into  the  single  endo- 
plast of  the  resultant  Acineta ;  but  it  is  not  certainly  made 
out,  whether  this  process  has,  or  has  not,  anything  to  do 
with  the  process  of  the  development  of  ciliated  embryos  just 
described. 

(c.)  The  CiLiATA.  —  The  characteristic  feature  of  the 
CUiata  is,  that  the  outer  surface  of  the  body  is  provided  with 
numerous  vibratile  cilia,  which  are  the  organs  of  prehension 
and  locomotion.  According  to  the  distribution  of  the  cilia. 
Stein  has  divided  them  into  the  Holotricha,  in  which  the 
cilia  are  scattered  over  the  whole  body,  and  are  of  one  kind; 
the  Heterotricha,  in  which  the  widely  diffused  cilia  are  of 
different  kinds,  some  larger  and  some  smaller;  the  Hypo- 
triehat  in  which  the  cilia  are  confined  to  the  under  or  oral 
side  of  the  body ;  and  the  Peritricha,  in  which  they  form  a 
zone  round  the  body.  The  great  majority  of  these  animals 
are  asymmetrical. 

In  the  simplest  and  smallest  CUiaJta,  the  body  resembles 
that  of  one  of  the  Fla^ellata  in  being  differentiated  merely 
into  an  ectosarc  and  endosarc,  with  an  endoplaat  and  a 
contractile  vacuole.  In  most,  if  not  all  cases,  however, 
there  is  not  only  an  oral  region,  through  which  the  in- 
gestion of  food  takes  places,  but  an  oesophageal  depression 
leads  from  this  into  the  endosarc ;  and  it  may  be  doubted 
whether,  even  in  the  simplest  CUiaia,  there  is  not  an  anal 
area  through  which  the  undigested  parts  of  the  food  are 
thrown  out. 


THS  IKFU80BIA.  103 

The  genus  Colpoda,  which  is  very  common  in  infusions  of 
haj,  is  a  good  example  of  this  low  form  of  ciliated  Infu- 
sorium. It  has  somewhat  the  form  of  a  bean  flattened  on 
one  side,  and  moves  actively  about  by  means  of  numerous 
cilia,  the  longest  of  which  are  situated  at  the  anterior  end 
of  the  body.  At  the  posterior  end  is  the  contractile  vacuole, 
while  a  large  endoplast  lies  in  the  middle,  as  Stein  origin- 
ally discovered.  Colpoda  frequently  become  quiescent, 
retract  their  cilia,  and  surround  themselves  with  a  structure- 
less cyst.  Each  encysted  Colpoda  then  divides  into  two, 
four,  or  more  portions,  which  assume  the  adult  form  and 
escape  from  the  cysts  to  resume  an  active  existence. 

Allman  has  described  the  encystment  of  a  Yorticellidan, 
followed  by  division  of  the  nucleus  into  many  germs,  with- 
out any  antecedent  process  of  conjugation ;  and  Everts  has 
observed  that  the  progeny  of  an  encysted  Vorticella  take  on 
the  form  of  Trichodina  grandineUa,  The  TrichodincB  mul- 
tiply by  transverse  divisions,  and  then  grow  into  Voi-ti- 
eellce,* 

Encystment,  whether  followed  or  not  by  division,  is  very 
common  among  all  the  CilioUay  and  a  species  of  Amphileptus 
has  been  seen  to  swallow — or  rather  envelope — a  stalked 
1>ell-animalcule  (Vorticella) y  and  then  become  encysted  upon 
the  stalk  of  its  prey,  just  as  Vampyrella  becomes  perched 
upon  the  stalk  of  the  devoured  Gomphoneftna. 

In  the  higher  Ciliata,  the  protoplasm  of  the  body  becomes 
directly  differentiated  into  various  structures,  in  the  same 
way  as  has  already  been  seen  to  be  the  case  in  Gregarina 
giganiea,  but  to  a  much  greater  degree. 

Thus,  in  the  Per'itricha,  of  which  the  bell-animalcules,  or 
VorticeUm  (Fig.  9,  A,  B,  c),  are  the  commonest  examples,  the 
oral  region  presents  a  depression,  the  vestibule  (Fig.  9,  a), 
from  which  a  permanent  (Esophageal  canal  leads  into  the  soft 
and  semi-fluid  endosarc,  where  it  terminates  abruptly ;  and 
immediately  beneath  the  mouth,  in  the  vestibule,  there  is  an 
anal  region  which  gives  exit  to  the  refuse  of  digestion,  but 
[resents  an  opening  only  when  fsecal  matters  are  passing 

*  AUman,  'Piesidential  AJUress  to  the  Linncan  Society,*  1S7J. 


104       THE  ANA.TOJIZ  C 


INTIBTKBIU.TKI>  AKIMALS. 


out.  Eic«pt  where  the  ciliated  circlet,  or  rather  epiral,  is 
situated,  the  outer  wall  of  the  bodj  gives  rise  to  a  relativelj 
dense  eulieula,  and  not  nnfreqaently  aecretes  a  transparent 
cap  or  case,  foreshadowing  the  theca  of  hjdrozoal  poljpes. 
Moreover,  in  the  permanently  iixed  Vorticetia,  the  atalk  of 
attachment  may  preaent  a  central  muscnlar  fibre  (Pig.  9,/l, 
by  the  sudden  contraction  of  wbich  the  body  is  retracted. 
the  Btaikbcingat  the  Bame  time  thrown  into  aspiral.  In  the 
Pig.  10- 


Fl)r.  10. „ „,.. 

from  the  dorent  (ide ;  a 
c,  canrraclile  apace;  d  d" 


S(eln) 

rer  of  th. 


<:    Chloi 


ewrd  rmm  the  venlnl  Bide:  a.  depreMiod  leading  I 
A.  moutb;  c.  gulleL;  d,  ODdoptut ;  li',  PDiiopLostiite :  r,  central  pnit< 
plaam.    In  both  thesa  flgurea  the 
circulstlon. 
C,  /■arodiimMa  diTidinjt  traniversely 


endop 


contractile  apace* ;  b  b, 


holotrichous  Paramteeiitm  (Fig,  10)  beneath  the  thin  super- 
ficial transparent  cuticle  f i-om  which  the  cilia  proceed,  there 
is  ft  very  distinct  cortical  layer,  fibritlated  in  a  direction  per- 
pendiinilartothe8nrface,and,  in  some  species  of  this  or  other 
genera,  as  Stromindium  and  Polyhrieot  (Butschli),  beset  with 
minnte  rod-like  bodies  similarly  disposed,  which,  nnder  some 
circumstances,  shoot  out  into  long  filaments,  and  have  been 


THE  IKFTTSOBIA.  105 

termed  triehoeysts.  In  P.  hurmria,  minute  green  granules 
of  chlorophyll  axe  dispersed  through  this  layer,  and  Oohn 
demonstrated,  in  1851,  that  these  yield  the  same  reactions 
as  the  chlorophyll  grains  of  the  Algse.  In  Balaniidium, 
NycMhervs,  Spirostomum,  and  many  others,  the  cortical 
layer  is  divided  hy  linear  markings  into  bands,  which  there 
is  reason  to  believe  are  rudimentary  muscular  fibres. 

In  many  Ciliata,  the  endosarc  appears  to  be  almost  fluid. 
The  food,  which  is  driven  into  the  mouth  and  down  the 
(BsophaguB  by  the  constant  action  of  the  ciUa,  accumulates 
at  the  bottom  of  the  cesophagus ;  and  then,  with  the  water 
which  surrounds  it,  is  passed,  at  intervab,  with  a  sort  of 
jerk,  into  the  endosarc,  where  it  lies,  close  to  the  end  of  the 
oesophagus,  as  a  food  vacuole,  for  a  short  time.  But  it  soon 
begins  to  move,  and,  along  with  other  such  vacuoles  formed 
before  and  after  it,  circulates  in  a  definite  course  up  one 
side  of  the  body  and  down  the  other,  between  the  cortical 
layer  and  the  endoplast.  This  movement  is  particulai'ly 
free  and  unrestricted  in  Balaniidium ;  in  Faramcedurriy  the 
tract  through  which  the  food  vacuoles  move  is  more  de- 
finitely limited,*  while,  in  Nyctotherusy  it  appears  to  be 
confined  to  a  part  of  the  body  between  the  end  of  the 
gullet  and  the  anal  region,  which,  in  this  Infusorium,  is 
seated  at  one  end  of  the  body.  In  fact,  the  finely  granular 
endosarc  of  Nyctotherus  so  limits  the  passage  of  the  food 
Tacuoles,  that  the  tract  along  which  they  pass  might  pro- 
perly be  described  as  a  rudimentary  inteatiual  cansJ. 

The  oral  cavity  is  usually  ciliated :  sometimes,  as  in  Chi- 
lodon,  it  has  a  chitiuous  armature,  which  becomes  some- 
what complicated  in  ErvUia  (Dysteria  f)  and  the  Didinium 
described  by  Balbiani. 

TarqucUella  (Lankester)  has  a  plicated  membrane  around 
the  mouth  in  the  place  of  cilia. 

The  contractile  vacuoles  attain  their  greatest  complexity 

*  In      Paraauxcium     bursaria,  inch  in  a  second. 

Cohn  observed  that  the  circula-  t    Uuxley,    *^On     D^steria." 

tion  was  completed  in   1^  to  2  (^Quarterly    Journal  of   Micro- 

minates,  which  gives  a  rate  of  scop.  Science/  1857.)    ^ 
totatioo  of  9^  to  liijsth  of  an 


106       THS  ANATOMY  OF  INYEBTEBBATED  ANIMALS. 

in  the  Paramceda,  in  which  there  are  two— one  towards 
each  end  of  the  body.  Thej  are  lodged  in  the  cortical 
layer,  and,  in  diastole,  a  portion  of  their  outer  peripheiT' 
is  bounded  only  by  the  cuticle,  through  which  it  is  very 
probable  that  they  communicate  with  the  erterior.  When 
the  systole  takes  place,  a  number  of  fine  canals,  which 
radiate  from  each  vacuole,  are  seen  to  become  distended 
with  clear  watery  fluid.  These  canals  are  constant  in 
their  position,  and  some  of  them  may  be  traced  nearly 
as  far  as  the  mouth ;  so  that  the  canals  and  vacuoles  form  a 
permanent  water- vascular  system.  The  endoplast  is  finely 
granular,  like  the  substance  of  the  endosarc.  It  is  frequently 
said  to  be  enveloped  in  a  distinct  membrane,  but  I  am  dis- 
posed to  think  that  this  is  always  a  product  of  reagents. 
Attached  to  one  part  of  it  there  is  very  generally  (but  not 
in  the  Voriicelke)  a  small  oval  or  rounded  body,  the  so-called 
"  nucleolus  "  or  endoplcisMe.  The  endoplast  is  commonly 
said  to  be  imbedded  in  the  cortical  layer,  but  this  is  cer- 
tainly not  the  case  in  Colpoda,  Paramcecium,  Bcdantidivm, 
or  Nyctotherus. 

The  outermost,  or  cuticular,  layer  of  a  large  portion  of  the 
body  becomes  hardened  and  forms  a  sort  of  shell,  in  many  of 
the  free  Infusoria,  In  the  free  marine  Didyocystida  and 
Codonellida  of  Haeckel,  the  body  has  a  bell-shaped  envelope, 
which  in  the  Dictyocydida  (see  Fig.  1,)  is  strengthened  by  a 
silicious  skeleton  like  that  of  a  Badiolarian.  In  both 
genera  the  circular  lip  which  surrounds  the  oral  end  is 
provided  with  numerous  long  flagelliform  cilia.* 

Most  of  the  Ciliata,  while  in  full  activity,  multiply  by 
division;  this  is  generally  effected  by  the  formation  of 
a  more  or  less  transverse  constriction,  whereby  the  body 
becomes  divided  into  two  parts,  which  separate,  each  de- 
veloping those  structures  which  are  needed  for  its  comple- 
tion. The  endoplast,  however,  always  elongates  and  divides, 
one  portion  going  along  with  each  product  of  fission. 
Neither  budding  nor  longitudinal  fission  occurs  among  the 
free  Infusoria,  the  appearances  which  have  been  regarded 
*  Haeckel,  *  Zur  Morphologie  dcr  InfuBoricc,'  1873. 


THE  INFT780BIA.  107 

as  evi'lence  of  these  processes  being  due  to  the  opposite 
operation  of  conjugation.  M.  Balbiani,*  its  discoverer, 
thus  describes  this  process  of  conjugation  in  ParamoBcium 
burgaria : — 

"  The  Paramcsda  assemble  in  great  numbers  either  to- 
wards the  bottom  or  on  the  sides  of  the  vessel  in  which  they 
are  contained.  They  then  conjugate  in  pairs,  their  an- 
terior ends  being  closely  united ;  and  they  may  remain  in 
this  state  for  five  or  six  days  or  more.  During  this  period, 
the  nucleus  and  nucleolus  become  transformed  into  sexual 
organs. 

"  The  nucleolus  is  changed  into  an  oval  capsule,  marked 
superficiaUy  by  longitudinal  strise.  Sooner  or  later,  it  usually 
becomes  divided  into  two  or  four  portions,  which  grow  in- 
dependently, and  form  many  separate  capsules.  About  the 
time  of  separation,  each  of  these  is  found  to  be  a  capsule 
containing  a  bundle  of  curved  rods  (baguettes),  enlarged  in 
the  middle,  and  thinner  at  the  ends. 

"  The  nucleus  also  becomes  enlarged,  and  gives  rise — in  a 
manner  not  clearly  explained — to  small  spherical  bodies 
analogous  to  ovules. 

"  It  is  usually  about  the  fifth  or  sixth  day  after  conjugation 
that  the  first  germs  appear,  as  little  rounded  bodies,  formed 
of  a  membrane  which  is  rendered  visible  by  acetic  acid,  and 
of  greyish  pale  homogeneous  or  almost  imperceptibly  granu- 
lar contents,  in  which,  as  yet,  neither  nucleus  nor  contrac- 
tile vacuole  is  distinguishable.  It  is  only  later  that  these 
org^ans  appear.  The  observations  of  Stein  and  of  F.  Cohn 
have  shown  how  these  embryos  leave  the  body  of  the  mother 
under  the  form  of  Acinetce,  provided  with  knobbed  tentacles 
and  true  suckers,  by  means  of  which  they  remain  for  some 
time  adherent  to  her,  and  nourish  themselves  from  her 
substance.  But  their  investigations  have  not  disclosed  the 
ultimate  fate  of  the  young. 

"  I  have  been  able  to  follow  them  for  a  long  period  after 
their  detachment  from  the  maternal  organism ;  and  I  have 

•  Rilhianl,  "Note  relative  li  rExistenre  d'une  Gendration  Sexiielle 
chez  leg  iiifuaoiros."    (*  Juurnul  do  la  Pii^'siu  ogle,'  toine  i.,  1833.; 


lOS       THE   ANATOMY  OF  IKTBBTEBRATED  AKIMALS. 

been  able  to  assure  myself  that,  after  baying  lost  tbeir  ten- 
tacles, becoming  clothed  with  vibratile  cilia,  and  acquiring 
a  mouth,  which  makes  its  appearance  as  a  longitudinal 
groove,  they  return  definitely  to  the  parental  form,  develop- 
ing in  their  interior  the  green  granules  which  are  charac- 
teristic of  this  Paramoeciwm,  without  undergoing  any  more 
extensive  metamorphosis." 

In  Figs.  19-22  of  Plate  lY.,  which  accompanies  his  x>aper, 
Balbiani  figures  all  the  stages  by  which  the  acinetiform 
embryo  becomes  a  ParamcBcium. 

So  far  as  the  fact  of  conjugation,  the  changes  in  the 
"  nucleolus,"  and  the  development  of  filaments  in  it,  with 
the  subsequent  detachment,  by  division,  of  masses  fi*om  the 
"  nucleus  "  are  concerned,  these  statements  have  not  been 
modified  by  M.  Balbiani,  while  they  are  fully  confirmed  by 
the  observations  made  by  himself,  ClaparMe  and  Lachman, 
Stein,  Kolliker,  and  others,  in  Paramoecium  buraarioy  P. 
aurelia,  and  other  ciliated  Infusoria, 

In  the  closely  allied  ParamoBcium  aurelia,  the  occurrence 
of  the  various  stages  of  conjugation,  conversion  of  the 
"  nucleolus  "  into  bundles  of  spermatozoa,  and  subsequent 
division  of  the  **  nucleus  "  is  also  established  by  the  coinci- 
dent testimony  of  Balbiani  and  Stein.  Balbiani  affirms 
that,  in  this  species,  the  clear  globular  bodies  which  result 
from  the  division  of  the  "  nucleus "  pass  out  of  the  body 
without  undergoing  any  further  modification,  and  he 
considers  them  to  be  ovules.  Stein  also  admits  that  he 
has  never  seen  acinetiform  embryos  in  this  species. 

But,  as  it  would  seem,  on  the  strength  of  these  nega- 
tive observations  in  Paraw/cecium  awrelia,  Balbiani,  in  his 
later  publications,  asserts  that  the  "  acinetiform  embryos  " 
observed  not  only  in  PararruBcium,  but  in  Siylonychia, 
Stentor,  and  many  other  ciliated  Infuaoriay  are  not  embryos 
at  all,  but  parasitic  Acinetce;  and  he  makes  this  assertion, 
without  explicitly  withdrawing  the  statement  given  above 
of  his  own  obsen'ation  of  the  passage  of  the  acinetiform 
embryo  of  ParamcBciwm,  buraaria  into  the  parental  form. 
Engelmann  and  Stein,  on  the  other  band,  hold  by  Balbiani's 


THE  INFT7SOSIA.  109 

original  doctrine,  and  give  strong  reasons  for  so  doing. 
Among  the  most  forcible  analogical  arguments  are  those 
afforded  by  the  process  of  sexual  reproduction  observed  by 
Stein  in  the  peritrichous  Infusoria, 

In  the  Peritricha  (VorticeUidoe,  OphrydidoB,  Trichodidce) 
conjugation  takes  place  by  the  complete  and  permanent 
fusion  of  two  individuals,  which  are  sometimes  of  equal 
dimensions ;  though,  in  other  cases,  one  is  much  smaller  than 
the  other,  and,  while  it  is  in  course  of  absorption,  looks  like 
a  bud,  and  was  formerly  taken  fur  such  (Fig.  9,  A,  g,  h).  The 
small  individuals  usually  take  their  origin  from  a  group  of 
small  stalked  VorticelloR,  which  are  produced  by  the  repeated 
longitudinal  division  of  a  VorticeUa  of  the  ordinary  size. 
The  result  of  the  conjugative  act  is  that  the  **  nuclei  *'  of 
the  two  individuals,  either  before  or  after  their  coalescence, 
break  up  into  a  number  of  segments.  The  segments  may 
remain  separate  or  coalesce  into  a  single  mass,  called  by 
Stein,  placenta.  In  the  former  case,  some  of  the  segments 
become  germ  masses,  while  the  others  reunite  to  form  a  new 
"  nucleus ; "  in  the  latter,  the  placenta  throws  out  a  number 
of  germ  masses,  and  then  assumes  the  form  of  an  ordinary 
"  nucleus."  The  germ  masses  give  off  portions  of  their 
substance,  including  part  of  their  **  nucleus,"  and  these 
become  converted  into  ciliated  embryos,  which  escape  by  a 
special  opening.  Knobbed  tentacles,  like  those  of  the 
AdneUB,  have  not  been,  observed  in  the  embryos  of  the 
Teritricha,  nor  has  their  development  been  traced  out. 

If  the  bodies  regarded  as  acinetiform  embryos  of  the 
CUiata  are  really  such,  they  may  be  taken  to  represent  the 
myxopod  stage  of  the  Catallacta,  and  the  relations  of  the 
Aeineice  to  the  CUiata  would  appear  to  be  that  they  are 
modifications  of  a  common  type,  differing  from  the  Catal- 
laeia  in  having  tentacula  instead  of  ordinary  pseudopodia. 
In  the  Acindos,  the  tentaculate  stage  is  the  more  permanent, 
the  ciliated  stage  transitory;  while,  in  the  CUiata,  the 
ciliated  stage  is  the  more  permanent,  and  the  tentaculate 
stige  transitory. 


110       THE  ANATOMY  OF  INYEBTEBRATED  AKIHA1.S. 


CHAPTER  in. 

THE   POBIPBKA  AND  THE   COELENTE&ATA. 

1.  The  PoEiFESAor  Sponoida. — It  has  been  seen  that,  in 
the  Protozoa,  the  germ  undergoes  no  process  of  division 
analogous  to  the  "  yelk  division  "  of  the  higher  animals,  and 
to  the  corresponding  process  by  which  the  embryo  cell  of 
every  plant  but  the  very  lowest  becomes  converted  into  a 
cellular  embryo.  Consequently,  there  is  no  blastoderm ;  the 
body  of  the  adult  Protozoon  is  not  resolvable  into  mor- 
phological units,  or  cells,  more  or  less  modified;  and  the 
alimentary  cavity,  when  it  exists,  has  no  special  lining. 
Moreover,  the  occurrence  of  sexual  reproduction  in  most 
of  the  Protozoa  is  doubtful,  and  there  is,  at  present,  no 
evidence  of  the  existence  of  male  elements,  in  the  form  of 
filamentous  spermatozoa,  in  any  group  but  the  Infusoria ; 
and  even  here  the  real  nature  of  these  bodies  is  still  a 
matter  of  doubt. 

In  all  the  Jtfe^ozoa,  the  germ  has  the  form  of  a  nucleated 
cell.  The  first  step  in  the  process  of  development  is  the 
production  of  a  blastoderm  by  the  subdivision  of  that  cell, 
and  the  cells  of  the  blastoderm  give  rise  to  the  histological 
elements  of  the  adult  body,  With  the  exception  of  certain 
parasites,  and  the  extremely  modified  males  of  a  few  species, 
all  these  animals  possess  a  permanent  alimentary  cavity, 
lined  by  a  special  layer  of  cells.  Sexual  reproduction 
always  occurs;  and,  very  generally,  though  by  no  means 
invariably,  the  male  element  has  the  form  of  filiform 
spermatozoa. 

The  lowest  term  in  the  series  of  the  Metaaoa  is  un- 
doubtedly represented  by  the  Pori/cra  or  Sponges,  which, 


THE  POBIFEBA.  Ill 

after  oscillating  between  the  vegetable  and  tbe  animal  king- 
doms, have,  in  recent  times,  been  recognised  as  animals 
by  all  who  have  sufficiently  studied  their  structure  and  the 
manner  in  which  their  functions  are  performed. 

But  the  place  in  the  Animal  Kingdom  which  is  to  be 
assigned  to  the  sponges  has  been,  and  still  is,  a  matter  of 
debate.  It  is  certain  that  an  ordinary  sponge  is  made  up 
of  an  aggregation  of  corpuscles,  some  of  which  have  all  the 
characters  of  Amoebce,  while  others  are  no  less  similar 
to  Monads ;  and  therefore,  taking  adult  structure  only  into 
account,  the  comparison  of  a  sponge  to  a  sort  of  compound 
Proiozaon  is  perfectly  admissible,  and  in  the  absence  of 
other  evidence,  would  justify  the  location  of  the  sponged 
among  the  Frotozoa, 

Bat,  within  the  last  few  years,  the  development  of  the 
sponges  has  been  carefully  investigated;  and,  as  in  so 
many  other  cases,  a  knowledge  of  that  process  necessitates  a 
reconsideration  of  the  views  suggested  by  adult  structure. 

The  impregnated  ovum  undergoes  regular  division;  a 
blastoderm  is  formed,  consisting  of  two  layers  of  cells — 
an  epiblast  and  a  hypoblast, — and  the  young  animal  has 
the  form  of  a  deep  cup,  the  wall  of  which  is  composed  of 
two  layers,  an  ectoderm  and  an  endoderm,  which  proceed 
respectively  from  the  epiblast  and  hypoblast.  The  embryo 
sponge  is,  in  fact,  similar  to  the  corresponding  stage  of 
a  hydrozoon,  and  is  totally  unlike  any  known  condition 
of  a  protozoon. 

Beyond  this  early  stage,  however,  the  sponge  embryo 
takes  a  line  of  its  own,  and  its  subsequent  condition  differs 
altogether  from  anything  known  among  the  Coshewteraia ; 
all  of  which,  on  the  other  hand,  present  close  and  intimate 
resemblances  in  their  further  development,  as  in  their  adult 
structure. 

It  is  not  long  since  the  only  sponge  of  the  structure 
and  development  of  which  we  were  accurately  informed 
was  the  SpongUla  fluviatilis,  or  fresh-water  sponge,  the 
sabject  of  the  elaborate  researches  of  Lieberkiihn  and 
Garter.    But,  recently,  a  flood  of  light  has  been  thrown 


113       THE  AKATOHT  OF  IKTESTSBSATED  iXIUALB. 
Fie.  ". 


Fig.  U.—Aietltaprimordialii  (kftar  Hwckel). 

I.,  A  m»turB  ^KTfta.pwt  of  one  itde  of  Uie  body  of  «hiflit«  removed; 
o,  lh«  exiulukt  apaiturt ;  p,  lolMltst  pore*  Id  Um  wtll  of  tit*-,  bod; ; 


THI  POBIFEBA. 


113 


Iflnn ;  e^  eotod«nii ;  y,  ova.    The  trindiate  splcula  are  seen 

Bd  in  the  ectoderm. 

rtion  of  the  endoderm,  with  two  pores  (/>) ;  t,  endodermal 

bote  round  the  margins  of  the  pores  have  their  cilia  directed 

I ;  e.  ectodermal  syncytium ;  y,  ova ;  «,  sperm  cells. 

maaiform  endodermal  cell. 

ndodermal  cell,  with  retracted  dllom,  and  having  the  charac- 

m  Amaba, 

iliated  embryo  of  Ateetta  mirabilis, 

same  embryo  in  optical  longitudinal  section ;  e,  epiblast ; 

ilaat ;  v,  blastoccele. 

)  morphology  and  phjsiologj  of  the  marine  sponges, 
irly  of  those  sponges  with  calcareons  skeletons, 
ire  termed  CalcupongioB,  by  Lieberklihn,  Oscar 
,  and  especially  HaeckeL  It  has  become  clear 
mgiUa  is  a  somewhat  aberrant  form,  and  that 
Ismental  type  of  Poriferal  organisation  is  to  be 
imong  the  CdUigponguB,  In  the  least  complicated 
ikareoos  sponges,  the  body  has  the  form  of  a  cnp, 
^tached  by  its  closed  extremity.  The  open  extremity 
vuluntf  and  leads  directly  into  the  spacious  ventri' 
cavity  of  the  cup.  The  comparatively  thin  wall  of 
LB  composed  of  two  layers,  readily  distinguishable 
structure — ^the  outer  is  the  ectoderm,  the  inner 
derm.  The  ectoderm  is  a  transparent,  slightly 
,  gelatinous  mass  in  which  nuclei  are  scattered, 
^h,  in  the  unaltered  state,  shows  no  trace  of  the 
)  distinctness  of  the-  cells  which  contain  these 
nd  is  therefore  termed  by  Haeckel  a  syncytiwm, 
stic  and  contractile,  and  sometimes  exhibits  an 
L  to  fibrillation. 

idoderm,  on  the  contrary,  is  composed  of  a  layer 
istinct  cells,  each  of  which  contains  a  nucleus  and 
lore  contractile  vacuoles,  and  is  produced  at  its 
^mity  into  a  long  solitary  cilium  or  flagellum. 
the  base  of  this,  the  transparent  outer  portion  of 
plasm  of  the  cell  is  produced  into  an  upstanding 
e  a  collar,  so  that  each  cell  has  a  wonderful 
ace  to  some  forms  of  flagellate  Infusoria,  Micro- 
ertures — the  pores — scattered  over  the  outer  sur- 
e  cup,  lead  into  short  passages  which  perforate  the 


114       THB  ANATOMY  OF  INYBBTSBRATED  ANIMALS. 

ectoderm  and  endoderm,  and  thus  place  the  yentricnlas 
in  communication  with  the  exterior.  The  working  of  the 
flagella  of  the  endodermic  cells  causes  the  water  contained 
in  the  gastric  cavity  to  flow  out  of  the  osculum ;  to  make 
good  this  outflow,  minute  streams  set  in  hy  the  pores, 
which  have  consequently  been  called  inhalewl,  while  the 
osculum  has  been  termed  the  eashalent  aperture.  It  is  said, 
however,  that  the  direction  of  these  currents  is  not  invari- 
able ;  and  it  is  certain  that  the  pores  are  not  constant,  but 
that  they  may  be  temporarily  or  permanently  closed,  and 
new  ones  formed  in  other  positions. 

The  skeleton  of  the  calcareous  sponges  always  consists 
of  a  multitude  of  separate  spicula,  composed  of  an  animal 
substance,  more  or  less  strongly  impregnated  with  carbonate 
of  lime,  which  is  deposited  in  concentric  layers  around  a 
central  axis,  formed  by  the  animal  basis.  This  skeleton  is 
developed  exclusively  in  the  ectoderm,  and  is  not  supported 
by  any  framework  of  fibrous  animal  matter. 

The  calcareous  sponges  are  frequently,  if  not  always, 
hermaphrodite.  The  reproductive  elements  are  ova  and 
spermatozoa.  There  is  some  reason  for  assuming  that  the 
latter  originate  in  metamorphosed  cells  of  the  endoderm, 
as  they  are  found  scattered  between  ordinary  cells  of 
the  latter.  The  ova,  on  the  other  hand,  occur  sometimes 
between  the  cells  of  the  endoderm,  sometimes  imbedded  in 
the  syncytium  itsell  But  the  question  of  i^e  origin  of 
the  sexual  elements  in  these  and  other  animals,  needs  much 
further  investigation.  The  spermatozoa  are  very  delicate 
and  have  minute  rod-like  heads,  with  long  flagella.  The 
ova  present  the  normal  germinal  vesicle  and  spot,  but 
exhibit  active  amoeboid  movements. 

Impregnation  is  effected,  and  the  first  stages  of  develop- 
ment take  place,  while  the  ova  are  still  imbedded  in  the 
body  of  the  sponge. 

Metschnikoff*  has  recently  described  the  development 

*  «  Zur  Entwickelangs  -  ge  Zoologie,'  Bd.  xxiv.)  F.  E.  Schulxe, 
•ohiohte  der  Kulksohwl&mine.**  so  far  as  I  follow  Uaeckert  ac- 
('SSeltMhr.  fOr  WiMensohaftUohe      ootmt  of  hia  recent  obaervatioiif 


THB  POBIFEBA. 


115 


«>f  Sffcon  eUiaiiMn,  Tbe  ovum,  after  impregnation,  be- 
comes a  morula,  with  a  central  cleavage  cavity  or  blasto- 
code.  But  the  blastomeres  of  the  two  halves  of  the  morula 
take  on  different  characters — those  of  the  one  half  elon- 
gating and  acquiring  flagellif  orm  cUia,  while  those  of  the 
opposite  half  remain  globular  and  develope  no  cilia.  The 
latter  now  coalesce  into  a  syncytium,  and  develope  spicula, 
while  the  layer  of  ciliated  cells  becomes  invaginated  within 
the  syncytium.  More  usually,  however,  it  appears  that  a 
gastrula  is  formed  by  invagination  of  the  morula,  the 
ectoderm  of  which  has  the  structure  of  the  endoderm  of  the 
adult,  while  the  cells  of  the  endoderm,  or  lining  membrane 
of  the  gastric  cavity,  are  devoid  of  cilia.  The  embryo  quits 
the  parent,  prox>elled  by  the  flagelliform  cilia  which  cover 
the  outer  surface  of  the  ectoderm.  After  a  time,  it  fixes 
itself  by  the  closed  end ;  the  flagella  of  the  cells  of  the  ecto- 
derm are  retracted,  the  cells  themselves  become  flattened 
and  coalesce  so  completely  that  their  boundaries  cease  to 
be  distinguishable,  and  the  ectoderm  passes  into  the  con- 
dition of  a  syncytium.  At  the  same  time,  the  cells  of  the 
endoderm  multiply,  elongate,  and  take  on  the  form  which 
characterises  them  in  the  adult.  In  this  state  the  young 
sponge  is  termed  an  Ascula.  The  transition  to  the  iinal 
condition  is  effected  by  tiie  development  of  the  spicula  in 
the  syncytium  and  the  separation  of  some  of  the  con- 
stituent cells  of  the  syncytium  to  form  the  inhalent  pores. 

In  the  simplest  Caldgpongioe,  forming  the  f amOy  to  which 
Haeckel  applies  the  name  of  Ascones,  the  wall  of  the  ventri- 
culus  is  thin,  and  the  pores  open  directly  into  the  ventri- 
cular cavity;  but  in  another  family,  the  Leu^cones^  the 
syncytium  becomes  greatly  thickened,  and  the  pores  are 
consequently  prolonged  into  canals  (which  may  be  ramifled 


(*I>ie  Gsstmla  nnd  die  Eifur- 
ehangder  'Dilere/  p.  158),  agrees 
with  Metsehnikoff  as  to  the  first 
slagci  of  dcveiopmeoty  bat  differs 
in  reganl  to  tubseqiient  stages. 
Haeekd  withdiaws  bis  earlier  ao- 


count  of  the  formation  of  the  gas* 
trula  by  delamination,  or  splitting 
of  the  walls  of  an  oval  shut  pla- 
nula-MC  into  two  layers,  and  the 
subsequent  opening  of  the  planula 
at  one  end. 

T  2 


116       THE  AKATOHT  OF  IKYEBTEBBATBD  ANIKiXS. 

and  anastomose),  connecting  the  yentriciilus  with  the  ex- 
terior. The  endodermic  cells,  which  in  these,  as  in  the 
Atcones,  at  first  form  a  continuous  lajer,  are  eventuallj 
restricted  to  the  canals,  or  even  to  local  dilatations  of  these 
canals — the  so-called  "  ciliated  chambers." 

The  same  relative  disproportion  of  the  ectoderm,  with  the 
consequent  development  of  passages  which  traverse  the  mass 
of  the  spoBge,  and  are  provided  at  intervals  with  ciliated 
chambers,  is  found  in  the  silicious  sponges,  in  which  the 
spicula,  if  they  possess  anj,  are  formed  hj  a  deposit  of 
silez ;  and  in  which,  as  a  rule,  the  sponge  corpuscles  are 
supported  hj  a  more  or  less  complete  skeleton  of  a  tough 
animal  substance,  termed  keratoae, 

HaliMTca,  however,  is  devoid  both  of  skeleton  and  spicula, 
and  the  minute  structure  of  the  curious  boring  sponges — 
the  Clionce — has  yet  to  be  elucidated. 

Haliphysema  and  Chttirophysema,  of  Haeckel,  appear  to 
be  sponges  which  get  no  further  than  the  Gkutrula  con- 
dition, and  thus  form  a  connecting  link  between  the 
Sponges  and  the  Hydrotaa, 

The  fresh-water  sponge  (SpongiUa)  has  been  studied  with 
extreme  care  by  Lieberkuhn,  and  the  following  account, 
based  upon  the  investigations  of  that  author,  is  given  for 
the  use  of  the  student  to  whom  SpongiUa  fluvialu  is  likely 
to  be  the  most  readily  accessible  of  the  sponges. 

The  fresh-water  sponge  grows  on  the  banks  of  docks, 
canals,  rivers,  and  on  floating  timber,  in  the  form  of  thick 
encrusting  masses,  which  usually  have  a  green  colour,  and 
require  a  constant  supply  of  fresh  water  for  their  healthy 
maintenance.  The  surface  presents  irregular  conical  emi- 
nences perforated  at  their  summit  like  smsdl  volcanic  craters, 
and  from  these  exhalent  funnels,  which  answer  to  the  oaeula 
of  the  CalcifpoTigias,  currents  of  the  water  are  continually 
flowing.  Careful  examination  of  the  surface  of  the  SpongiUa 
between  the  exhalent  craters,  shows  that  it  is  formed  by  a 
delicate  membranous  expansion,  separating  which  from  the 
deeper  substance  of  the  SpongiUa  are  a  number  of  irregular 
cavities.    In  some  cases,  these  run  into  one  great  water- 


THK  POBIFEBA.  117 

cliamber.  The  superficial  chambers,  or  chamber,  communi- 
cate with  the  exterior  bj  pores,  which  perforate  the  mem- 
branous expansion,  are  similar  to  those  in  the  outer  surface 
of  the  yentricular  wall  of  a  simple  calcareous  sponge,  and 
Bubserre  the  same  inhalent  function.  On  their  inner  face, 
or  floor,  the  superficial  chambers  exhibit  the  apertures  of 
innumerable  canals,  which  trayerse  the  deep  substance  of 
the  SpongiUa  in  all  directions,  and,  sooner  or  later,  unite 
into  passages  which  lead  directly  into  the  cavities  of  the 
exhalent  craters.  Dilatations  of  the  canals  occur  at  in- 
terrals,  and  are  lined  bj  the  characteristic  monadiform 
endodermic  cells,  which  are  restricted  to  the  walls  of  these 
ciliated  chambers.  It  is  hj  the  working  of  the  cilia  of  these 
cells  that  currents  of  water  are  made  continuallj  to  enter 
bj  the  inhalent  pores  and  to  pass  out  hj  the  exhalent 
craters.  The  whole  fabric  is  supported  and  strengthened 
bj  a  skeleton,  which  consists,  in  the  first  place,  of  bands 
and  filaments  of  keratose,  and,  secondly,  of  silicious  spi- 
cnla,  the  majority  of  which  resemble  needles  pointed  at 
each  end,  and  contain  a  fine  central  canal  filled  with  an 
unsilicified  substance.  The  individuality  of  these  animals 
is  so  little  marked  that  two  SpongillcBj  when  brought  into 
contact,  before  long  fuse  into  one ;  while  they  may  divide 
spontaneously,  or  be  separated  artificially  into  different 
portions,  each  of  which  will  maintain  an  independent 
existence. 

A  process  analogous  to  the  formation  of  cysts,  which 
is  ao  common  among  the  Protozoa,  takes  place  in  the 
deeper  substance  of  the  body,  especially  in  the  autumn. 
A  number  of  adjacent  sponge  corpuscles,  losing  their 
granular  appearance,  become  filled  with  clear  strongly 
refracting  granules,  the  nucleus  ceasing  to  be  visible.  The 
sponge  corpuscles  which  surround  these  become  closely 
appUed  together,  and  secrete  coats  of  keratose,  which  fuse 
with  those  of  the  adjacent  corpuscles.  In  the  intei*ior  of 
each  a  singular  silicious  spiculum  is  formed,  consisting  of 
two  toothed  disks,  like  cogged  wheels,  united  by  an  axis. 
At  this  **  aimphidMCua  "  enlarges,  the  protoplasm  of  the  cor- 


118   THE  ANATOMY  OF  INYEBTSB&ATED  ANIMALS. 

puscle  disappears,  and  at  length  nothing  is  left  but  the 
envelope  of  keratose,  with  the  imbedded  amphidisks,  dis- 
posed perpendicolarlj  to  its  surface.  At  one  point  of  the 
spheroidal  envelope,  a  email  opening  is  left,  and  the  so- 
called  "seed"  of  the  SpongiUa  is  complete.  It  remains 
throughout  the  winter  unchanged ;  but,  with  the  return  of 
warmth,  the  sponge  corpuscles  enclosed  within  the  coat 
of  the  "  seed,"  or  more  properly  cyst,  slowly  escape  through 
the  pore,  become  perforated  by  inhaJent  and  exhalent 
apertures  and  canals,  and  develope  the  characteristic  spicula 
of  a  young  SpongUla, 

This  process  of  encystment,  which  may  be  regarded  as 
a  kind  of  budding,  akin  to  propagation  by  bulbs  among 
plants,  has  not  been  observed  among  maiine  sponges. 

Sexual  propagation  takes  place  in  the  same  way  as  in 
the  CalciepongioBf  and  the  embryo  passes  through  morula 
and  planula  stages.  But  the  ciliated  cells  which  form  the 
outer  wall  of  the  latter,  and  constitute  its  locomotive 
apparatus,  seem  to  vanish  when  the  embryo  fixes  itself,  and 
the  body  of  the  young  Fibrospongia  appears  to  be  developed 
out  of  the  inner  cells,  which,  in  the  meanwhile,  have  become 
spiculigerous.  However,  the  details  of  the  mode  of  develop- 
ment  of  the  FihrospongioB  require  further  elucidation. 

In  both  the  marine  and  the  fresh- water  sponges  the 
ingestion  of  solid  matters — such  as  carmine  and  indigo — 
by  the  monadiform  endodermic  cells  has  been  seen  by 
several  observers.  According  to  Haeckel,  the  solid  par- 
ticles, which  usually  are  taken  in  between  the  flagellum  and 
the  collar,  may  also  be  ingested  at  other  parts  of  the  surface 
of  the  endodermic  cell.  In  the  course  of  such  experiments, 
also,  granules  of  the  pigment  may  be  found  in  the  ectoderm, 
but  whether  they  ent^r  it  directly,  or  secondarily  from  the 
endoderm  is  unknown.  Sponges  absorb  oxygen,  and  give 
off  carbonic  acid  with  great  rapidity ;  and  the  manner  in 
which  they  render  the  water  in  which  they  live  impure, 
and  injurious  to  other  organisms,  suggests  the  elimination 
of  nitrogenous  waste  matter. 

The  syncytium  may  contract  as  a  whole,  and  is  liable 


THS  POBIFBBA.  119 

itractions,  as  when  the  oecula  or  the  pores  shut 
nie  contours  of  the  cells  of  which  it  is  composed 
le  in  the  fresh  state,  and  hence  it  appears  as 
larcode"  or  transparent  gelatinous  contractile 
in  which  nuclei  and  granules  ai*e  imbedded  here 
But  Lieberkiihn  has  shown  that,  when  the 
rhich  SpongiOa  lives  is  heated  to  the  point  at 
mc  coagulation  of  the  protoplasm  of  the  cells 
ir  boundaries  at  once  become  defined,  and  the 
onlj  detach  themselyes  from  one  another.  The 
is  therefore  formed  bj  the  close  union,  and  not 
lal  fusion,  of  the  cells  of  the  bodj. 
317  interesting  fact  that  thread-cells,  similar  to 
1  are  so  abtmdant  in  the  CcdentertUat  are  said  to 
»me  singes.  Eimer*  finds  these  structures  in 
the  BenierifUB,  The  thread-cells  are  scattered 
>th  endoderm  and  ectoderm,  and  abound  on  the 
e  of  the  former,  where  it  limits  the  canals  of 
I,  but  do  not  occur  on  the  outer  surface  of  the 
The  same  observer  states  that  he  found  partly 
smains  of  small  crustaceans  in  the  ventriculajr 
id   passages    of  both  silicious  and  calcareous 

ifera  present  three  principal  modifications — 
wngioR,  the  CatcUpongioe,  and  the  FihrospongixB, 
otpongicB  being  altogether  devoid  of  skeleton ; 
wngicB  possessing  calcareous  spicula,  but  no 
atose  skeleton;  and  the  Fibrogpongi<B  having 
skeleton;    and  (usually)   spicula  of  a  silicious 

0  these  it  is  probable  that  the  Clwnidce  must  be 

1  fourth  type,  devoid  of  a  fibrous  skeleton,  but 
silicious  spicula  of  a  very  peculiar  Idnd,  by  the 
ich  they  are  able  to  burrow  pai-asitically  in  the 
ollusks.  FinaUy,  Haliphysema  and  Qasirophysema 
te  even  simpler  than  the  Myxoapongice. 

don  of  the  Myxospongiw  contains  only  the  gela- 

lellen  and  Saamen  bci  See-Schwammen."  (*  Archiv  f&r 
Mbe  Anatomie/  viii.,  1872.) 


120       THB  ANATOMY  OF  IKYSBTBBBATBD  AIOMALS. 

tinoiiB  Halisarea,  The  Calcisp<mffUB,  in  addition  to  the  two 
families  of  Ascones  and  Leucones,  already  referred  to, 
include  a  third — ^the  Sycones,  which  are  essentiallj  com- 
posite Asconea,  The  FibrospongioB  present  a  great  diversity 
of  form  and  structure.  They  may  have  the  form  of  flattened 
or  globular  masses,  arborescent  tree-like  growths,  flagellate 
expansions,  or  wide  or  deep  cups.  The  sponge  of  commerce 
derives  its  value  from  the  fact  that  its  richly  developed 
fibrous  skeleton  is  devoid  of  spicula.  On  the  other  hand, 
in  such  sponges  as  Hyalonema  and  Eupledella,  the  silicious 
spicula  attain  a  marvellous  development  and  complexity  of 
arrangement.  In  the  latter  genus,  they  form  a  fibrous  net- 
work with  reg^ar  polygonal  meshes.  These  appear  to  be 
the  representatives  of  the  VerUricvlUes,  which  were  so 
common  in  the  seas  of  the  Cretaceous  epoch. 

8eepaffel2l. 

Fig.  12.— A,  Hypothetical  section  of  a  Spongilla:  a,  superficial  layer; 
bj  inhalent  i^rtores ;  c,  ciliated  chambers ;  <2,  an  exhalent  aperture ; 
e,  deeper  substance  of  the  sponge.  The  arrows  indicate  the  direction 
of  the  currents.  B,  a  small  Sponffilla  with  a  dngle  exhalent  aper- 
ture, seen  from  above  (after  Lieberkfihn):  a,  inhalent  apertures; 
c,  ciliated  chambers ;  d,  exhalent  aperture.  C,  a  ciliated  chamber. 
D,  a  free-swimming  ciliated  embryo. 

Sponges  abound  in  the  waters  of  all  seas,  but  SpongiUa 
is  the  sole  fresh-water  form.  CUonidce  existed  in  the 
Silurian  epoch,  but  the  most  plentiful  remains  of  sponges 
have  been  yielded  by  the  chalk. 

The  OcELBNTBBATA. — This  group  of  the  Metazoa  con- 
tains those  animals  which  are  commonly  known  as  Polypes, 
Jelly-fishes,  or  MeduscBy  Sea  anemones,  and  Corals.    They . 
exhibit  two  well-marked  series  of   modifications,  termed 
the  Hydrozoa  and  the  Actinozoa, 

The  Htdbozoa. — The  fundamental  element  in  the 
structure  of  this  group  is  the  Hydrawtk,  or  PolypUe.  This 
is  essentially  a  sac  having  at  one  end  an  ingestive  or  oral 
opening,  which  leads  into  a  digestive  cavity.  The  wall  of 
the  sac  is  composed  of  two  cellular  membranes,  the  outer 


TBB  FOSIFEBA. 


THE  AKATOmr  0 


'  mVBBTXBBATKD  AITDULS. 


of  wliich  istennedtke  Mfod«rm,  and  the  umer  the  entoderm, 

the  former  h&Ting  the  morphological  valne  of  the  epidermis 

Ftg.  13. 


Fig.  13.— DiagniM  lIlmtntiTe  of  tbe  mnlokl  relatioiu  of  Uw  Hgdn- 

I.  Hydra.      5.  Sertuluiui.      3.  Caljeophoridu.     4.  PhfiDphoriilui. 

5.  Lucenuriao. 
o.  Eetoderm.    b.  Endodenn.    e.  The  dlgntiTe  and  tomattfl  eavity. 
P.  TentaclM.      N.  Neotooalyx.      T.   CcFnotare.    B.  HydniphjlllaiD. 

C.  BTdrothMia.      B.  Qjdiantlu     G.  Gonopbore.     A.  Air  Vcriole 

ooatalncdin  W.  PneniDMoplioTe.    e.  Dlgnttve  and  winalio  oavlty. 
1.,  n,.  III.,  IV~  rnmmt  tbs  aacceaslTe  BUca  of  deTclopment  of  a 

Madndfon-  


THE  HTDBOZOA. 


123 


of  the  higher  animals,  and  the  latter  that  of  the  epitheliam 
of  the  adimentary  canaL*    Between  these  two  lajers,  a 


♦  ••  The  bodj  of  ererj  Hydro- 
loon  is  ewentially  a  8«c  composed 
of  two  membranes,  an  external  and 
an  internal,  which  have  been  con- 
venientlj  denominated  by  the 
tamM  ectoderm  ai»demdoderm.  The 
caTitT  of  the  sac,  which  will  be 
called  the  aomatie  earify,  contains 
a  fluid,  charsed  with  nutiitive 
matter  in  scuution,  and  some- 
times, if  not  always,  with  sus- 
pended solid  particles,  which  per- 
form the  functions  of  the  blood 
in  animak  of  higher  organisation, 
and  may  be  termed  the  tomatie 
Jimid.  .  .  .  Notwithstanding  the 
extreme  variety  of  form  exhibited 
by  the  Hydrocoa,  and  the  multi- 
plicity and  complexity  of  the 
orxaos  which  some  of  them 
possess,  they  never  lose  the  traces 
of  this  primitive  simplicity  of  or- 
ganisation; and  it  is  but  rarely 
that  it  is  even  disguised  to  anpr 
considerable  extent.  .  .  .  This 
important  and  obvious  struc- 
tural peculiarity  could  hardlv  es- 
cape notice,  and  1  find  it  to  have 
been  observed  by  Trembley. 
Baker  and  Laurent,  Corda  and 
Ecker  in  Hydra;  by  Rathke,  in 
Coryne  ;  by  Frey  and  Leuckart,  in 
Lmeentariai  and  it  is  given  as  a 
character  of  the  hydroid  polypes 
in  general  {Hytlrasy  Corymida,  and 
SerttU4rrkUt\in  the  second  edition 
of  Cnrier's  *  Le9ons.'  I  points  it 
out  as  the  general  law  of  structure 
fif  the  hydroid  polypes,  I}ipf^€Ue 
and  PhywophoridUtj  in  a  paper  ^ 
sent  to  the  Linnean  Society,  from 
Australia,  in  1847,  but  not  read 
before  that  body  till  January, 
1849 ;  and  1  extended  the  general- 
isation to  the  whole  of  the  Hy- 
drozoay  in   a  'Memoir   on   the 


Anatomy  and  Affinities  of  the 
Medusctj*  read  before  the  Hoyal 
Society  in  June  1849. 

**  Professor  AUman,  in  his  valu- 
able memoir  *On  Gordylophora ' 
(PhiL  Trans.  1855),  has  adopted 
and  confirmed  this  morphological 
law,  introducing  the  convenient 
terms  *  ectoderm'  and  'endo- 
derm,'  to  denote  the  inner  and 
outer  membranes,  and  Gegenbaur 
(*Beitrage  sur  naheren  Kennt- 
niss  der  Schwimmpolypen,'  1854, 
p.  42)  has  partially  noticed  its 
exemplification  in  ApoUnua  and 
Hhizo§^iyai  but  it  seems  singu- 
larly enough  to  have  failed  to 
attract  the  attention  of  other 
excellent  German  observers,  to 
whose  late  important  investiga- 
tions I  shall  so  often  have  occa- 
sion to  advert.  l*he  peculiarity 
in  the  structure  of  the  body  walls 
of  the  Hydrozoa  to  which  i  have 
just  referred,  possesses  a  singular 
interest  in  its  bearing  upon  the 
truth  (for,  with  due  limitation,  it 
is  a  great  truth)  that  there  is  a 
certain  similarity  between  the 
adult  states  of  the  lower  animals, 
and  the  embryonic  conditions  of 
those  of  higher  organisation. 

^  For  it  is  well  known  that,  in  a 
very  early  state,  the  germ,  even  of 
the  highest  animals,  is  a  more  or 
less  complete  sac,  whose  thin  wall 
is  divisible  into  two  membranes, 
an  inner  and  an  outer ;  the  latter 
turned  towards  the  external 
world;  the  former,  in  relation 
with  the  nutritive  liquid,  the 
velk.  The  inner  layer,  as  Remak 
has  more  particularly  shown,  un- 
dergoes but  little  histological 
change,  and  throughout  life  re- 
mains more  particularly  devoted 


I'ObiervatSoDsnpan  the  ADAtomyof  pborldc.'  An  abstract  of  this  cesaj 
the  Diphyte,  and  tne  Cnitj  of  Orfpui-  was  published  in  the  *  froceeding*  of 
taatkn  oC  the   Diphyda   and  Pbyao-       the  Linnean  Society '  for  1849. 


124   THB  ANATOMY  OF  INYBBTABBATED  ANIMALS. 

third  layer — ^the  mesoderm, — ^which  represents  the  structures 
which  lie  between  the  epidermis  and  the  epithelium  in 
more  complex  animals,  may  be  developed,  and  sometimes 
attains  a  great  thickness,  but  it  is  a  secondary  and,  in  the 
lower  Hydrozoa,  inconspicuous  production. 

All  the  Hydrozoa  are  provided  with  tentcicula.  These  are 
elongated  and  sometimes  filiform  organs  of  prehension, 
which  are  generally  diverticula  of  both  ectoderm  and  endo- 
derm,  but  may  be  outgrowths  of  only  one  of  them. 

Thread-cells,  ornemMtocystSf  are  very  generally  distributed 
through  the  tissues  of  the  Ccetenterata,  In  its  most 
perfect  form,  a  nematocyst  is  an  elastic,  thick-walled  sac, 
coiled  up  in  the  interior  of  which  is  a  long  filament,  often 
serrated  or  provided  with  spines.    The  filament  is  hollow. 


to  the  functions  of  alimentation, 
while  the  outer  gives  rise,  by 
manifold  differendations  of  its 
tissue,  to  those  complex  structures 
which  we  know  as  integument, 
bones,  muscles,  nerves,  and  sen- 
sorv  apparatus,  and  which  espe- 
cially subserve  the  functions  of 
relation.  At  the  same  time,  the 
various  organs  are  produced  by 
a  process  of  budding  from  one 
or  other,  or  both,  of  these  primary 
layers  of  the  germ. 

*'  Just  so  in  the  Hydrozoon :  the 
ectoderm  gives  rise  to  the  hard 
tegumentary  tissues,  to  the  more 
important  masses  of  muscular 
fibres,  and  to  those  organs  which 
we  have  every  reason  to  believe 
are  sensory,  while  the  endoderm 
undergoes  but  very  little  modifi- 
cation. And  every  organ  of  a 
Hydrozoon  is  produced  by  bud- 
ding from  one,  or  other,  or  both 
of  these  primitive  membranes; 
the  ordinary  case  being  that  the 
new  part  commences  its  ezistence 
as  a  papillary  process  of  both 
membranes,  including,  of  course, 
a  divertiottlam  of  toe  tomatic 

>vi^. 


**  Thus  there  is  a  very  real  and 
genuine  analogy  between  the 
adult  Hydrozoon  and  the  embryo- 
nic vertebrate  animal ;  but  I  need 
hardly  say  it  by  no  means  justi- 
fies the  assumption  that  the 
Hydrozoa  are  in  any  sense  'ar- 
rested developments'  of  higher 
organisms.  All  that  can  justly 
be  affirmed  is,  that  the  Hydrozoon 
travels  for  a  certain  distance 
along  the  same  sreat  highway  of 
development  as  the  higher  animal, 
before  it  turns  off  to  follow  the 
road  which  leads  to  its  special 
destination.'* 

In  this  passage  of  my  work  on 
the  *  Oceanic  Hvdrozoa,'  (1859,) 
1  eznanded  the  idea  enunciated  in 
the  Memoir  on  the  Medusse  here 
referred  to,  that,  **  the  outer  and 
inner  membranes  appear  to  bear 
the  same  physiological  relation 
to  one  another  as  do  the  serous 
and  mucous  layers  of  the  germ.'* 
The  diagram  (Fig.  13),  exhibit- 
ing the  relations  of  the  different 
groups  of  the  Hydrozoa,  was  pub- 
lished in  the  *  Medical  Times  and 
Gazette'  in  June,  1856. 


THB   HTDBOZOA. 


125 


and  is  continuous  with  the  wall  of  tlie  sac  at  its  thicker  or 
basal  end,  while  its  other,  pointed,  end  is  free.  Yery  slight 
pressure  causes  the  thread  to  be  swiftly  protruded,  appar- 
ently by  a  process  of  evagination,  and  the  nematocyst  now 
i^peara  as  an  empty  sac,  to  one  end  of  which  a  long  fila- 

Fig.  14. 


Fig.  14. — Sacenlas  of  a  tentacle  with  nematocysts  of  Athoryhia,  A. 
peduncle  or  stalk,  and  B,  involucrum  of  the  sacculus  C ;  D.  fila- 
menta ;  d^  ectoderm ;  e,  endoderm  ;  /,  nematocysts ;  1,  small  nema- 
tocysts of  the  filaments  and  involucrum ;  2,  8,  larger  nematocysts  of 
the  sac ;  4,  largest  nematocysts. 


ment,  often  provided  with  two  or  three  spines  near  its  base, 
is  attached.  Many  of  the  CkBlerUercUa,  and  notably  the 
Fkyacdia,  give  rise  to  violent  urtication  when  their  tentacles 
come  in  contact  with  the  human  skin,  whence  it  may  be 
concluded  that  the  nematocjrsts  produce  a  like  injurious 
effect  upon  the  bodies  of  those  animals  which  are  seized 
and  swallowed  by  the  Polypes  and  Jelly-fishes. 

As  regards  the  existence  of  a  nervous  system  in  the 
HfdrotocLf  Y&rj  diverse  opinions  have  been  entertained,  and 
it  may  be  doubted  if  the  problem  has  even  yet  received 
its  final  solution.    I  have  already  discussed  Sileinenberg^s 


!:!♦>    THK  ANATOMY  OF  IN VERTERKATED  ANIMATS. 

suggestion,  that  the  branched  prolongations  of  the  iniior 
ends  of  the  cells  of  the  ectoderm  in  Hydra,  which  end  in 
the  longitudinal  fibres  which  lie  between  the  ectoderm  and 
the  endoderm  maj  be  nerres  in  their  earliest  stage  of 
differentiation.  Haeckel  describes  a  nervous  system  in 
Olo88oeodon  and  Carmarina,  It  consists  of  a  circular  band 
which  lies  on  the  inner  side  of  the  circular  canal  of  the 
bell-shaped  swimming  organ  of  these  Medusce,  and  presents 
a  ganglionic  enlargement  at  the  base  of  each  of  the  litho- 
cysts.  Of  these  eight  ganglia,  the  four  which  correspond 
to  the  openings  of  the  four  radial  canals  into  the  circular 
canal,  are  the  larger.  Each  of  these  gives  off  four  branches, 
one  of  which  follows  the  course  of  the  radial  canal  to  the 
central  poljpite  or  manubrium;  two  others  go  to  the 
adjacent  tentacles,  and  the  last  to  the  Hthocyst.* 

There  can  be  little  doubt  that  the  lithocysUy  or  sacs  con- 
taining mineral  particles,  which  are  so  frequently  found  in 
the  Medusse,  are  of  the  nature  of  auditory  organs;  while 
the  masses  of  pigment,  with  imbedded  refracting  bodies, 
which  often  occur  associated  with  the  lithocysts,  are  doubt- 
less rudimentary  eyes. 

The  sexual  reproductive  elements  are  ova  and  spermatozoa 
— the  ova  being  very  often  devoid  of  a  vitelline  membrane. 
The  fully  formed  generative  elements  lie  between  the  ecto- 
derm and  the  endodeim  of  that  part  of  the  body  wall  in 
which  they  make  their  appearance.  In  HydracHnia,  as 
has  already  been  pointed  out,  the  ova  appear  to  be  modified 
cells  of  the  endoderm,  and  the  spermatozoa  modified  cells 
of  the  ectoderm ;  but  it  remains  to  be  seen  how  far  this 
rule  is  of  general  application. 

Usually,  the  region  of  the  body  in  which  the  generative 
organs  are  produced  undergoes  a  special  modification 
before  the  reproductive  elements  make  their  appearance 
in  it,  giving  rise  to  a  peculiar  organ,  the  gonophore.    In  its 

*  Hfteekel,      *  Beitrige      sur  important   observations  of    Mr. 

HatunccMhichte   der   Uydrome-  Romanes    on     the     Locomotor 

duaea*     The  anatomical  disposi-  system  of  Medusse.  (Proceedings 

don  of  this  nervous  apparatus  of  the  Boyai  Society,  December 

•oeordt  very  well  with  the  recent  1875.) 


THE  HTDBOZOA.  127 

simplest  condition  the  gonopbore  is  a  mere  sac-like  diyer- 
ticnlam,  or  outward  process  of  the  body  wall.  Bat,  from 
this  state,  the  gonophore  presents  eyerj  degree  of  complica- 
tion, nntil  it  acquires  the  form  of  a  beU-shaped  body,  called 
from  its  resemblance  to  a  Medusa  or  jelly-fish,  a  medusoid* 

In  its  most  complete  form,  the  medusoid  consists  of  a 
disk  having  the  form  of  a  shallow  or  deep  cup  (nectocalyx), 
from  the  centre  of  the  concayity  of  which  projects  a  sac 
termed  the  manubrium.  The  cavity  of  the  sac  is  continaed 
into  that  of  sundry  symmetrically  disposed  canals,  most 
commonly  four  in  number,  which  radiate  from  the  centre 
of  the  disk  to  its  circumference,  where  they  open  into  a 
circular  marginal  canal.  A  membranous  fold,  the  velum, 
which  contains  muscular  fibres  arranged  concentrically  to 
its  free  margin,  is  attached  to  the  inner  circumference  of 
the  mouth  of  the  bell,  and  projects,  like  a  shelf,  into  its 
interior.  Lithocysts  are  usually  developed  on  the  margins 
of  the  bell,  which  may  also  give  rise  to  tentacles.  The 
manubrium,  opening  at  its  free  end,  may  become  function- 
ally, as  well  as  structurally,  a  hydrantb,  and  may  serve 
to  feed  the  medusoid  when  it  is  detached  from  the  hydro- 
foino,  or  body  of  the  hydrozoon.  However  complex  its 
structure  may  be,  the  medusoid  commences  as  a  simple 
bud-like  outgrowth,  which  thickens  at  its  free  end;  the 
central  part  of  this  thickening  becomes  the  manubriimi, 
while  its  periphery,  splitting  away  from  the  manubrium,  is 
converted  into  the  disk  (Fig.  13).  A  single  prolongation  of 
the  somatic  cavity  is  continued  into  the  manubrium,  while 
several,  usually  four,  symmetrically  arranged  diverticula 
extend  into  the  nectocalyx  and  become  its  radiating  canals. 
The  distal  ends  of  these  subsequently  throw  out  lateral 
branches,  which  unite  and  give  rise  to  the  circular  canal. 

The  lithocysts  are  usually,  but  not  always,  free  and 

*  From  the  Imperfection  of  our  stricted  to  what  are  known  to  be 

knowledf  e  respecting  the  origin  f^nophores  developed  by  gemma- 

of    many    of    the    medusiform  tion,^*medu8a"  may  be  employed, 

IfydmzoOjit  in  difflealt  to  employ  in  a  general  sense,  as  the  equiva- 

anj  lefminology  with  strict  con-  lent  of  the  somewhat  inconvenient 

^stenoy.    If  ^medusoid"  is  re-  vernacular  term  **Jelly-flsh." 


128       THE  ANATOMY  OF  IKYBBTSBRATBD  ANIMALS. 

prominent,  and  the  one  or  many  solid  mineral  bodies  which 
thej  contain  are  enclosed  in  special  envelopes.  Their 
structure  appears  to  be  more  complicated  in  the  GeryonidcB 
than  in  other  MednssB.    (Haeckel,  2.  c.) 

In  some  of  these  medasoid  gonophores,  the  reproductive 
elements  are  developed  while  the  gonophore  is  still  attached 
to  the  hydrosoma,  and  then  thejr  always  make  their  appear- 
ance in  the  wall  of  the  manubrium.  But,  in  other  cases, 
the  medusoid  becomes  detached  before  the  development  of 
the  reproductive  elements,  and,  feeding  itself,  increases 
largely  in  size  before  the  ova  or  spermatozoa  appear. 
Sooner  or  latter,  however,  the  reproductive  organs  are 
developed,  either  in  the  walls  of  the  manubrial  hydranth, 
or  in  those  of  the  canals  of  the  nectocalyz  of  the  medusoid. 

In  an  early  stage  of  its  existence,  every  hydrozoon  is 
represented  by  a  single  hydranth,  but,  in  the  great  majority 
of  the  Hydrozoa,  new  hydranths  are  developed  from  that 
first  formed,  by  a  process  of  gemmation  or  of  fission.  In 
the  former  case  the  bud  is  almost  always  an  outgrowth 
or  diverticulum  of  the  ectoderm  and  endoderm,  into  which 
a  prolongation  of  the  cavity  of  the  body  extends.  Some- 
times the  hydranth  formed  by  gemmation  becomes  de- 
tached from  the  body;  but,  in  many  cases,  the  buds 
developed  from  the  primary  hydranth  remain  connected 
together  by  a  common  stem  or  ecenoaarc,  and  thus  give  rise 
to  a  compound  body,  or  hydrosoma. 

In  many  Hyd/rowa,  the  ectoderm  gives  rise  to  a  hard 
cuticular  coating,  and  in  some  of  these  {CampanuUmdoB, 
SerMaridcB,  Fig.  13,  2),  this  cuticular  investment,  on  the 
hydranth,  takes  the  shape  of  a  case  or  *'  cell " — the  hydroiheca 
— ^into  which  the  hydranth  may  be  more  or  less  completely 
retracted.  In  other  Hyd/rowoa,  protective  coverings  are 
afforded  to  the  hydranths  by  the  development  of  processes 
of  the  body  wall,  which  become  thick,  variously-shaped, 
glassy  lamdlse.  These  appendages  are  termed  hydrophyllia 
(Kg.  18,  3). 

Again,  certain  groups  (the  Ccdycophcrida  and  most 
Thpophorida)  are   provided  with  bell-shaped  organs  of 


THI  HTSBOPHOKl.  129 

ipnlaioii,  prodnoed  hy  the  metamoTphoms  of  laterul  budi 
th»  lufimmma,  Thcae  tMrfoetuyoet  have  Uie  atructure 
k  madiuoid,  doroid  of  a  maiinbriaiiL  In  others  (Phyto- 
trida),  one  extramit;  of  tbe  iyitoKimA  ii  dilated,  con- 
na  air  onclosed  wiUiin  a  sac  formed  hj  an  iiiTolatioii  of 
I  ttctodenn,  ttnd  oonetitateB  a  float  or  jmnMuilophora ; 
i]«  in  yet  othen  (Diteophora),  the  aboral  end  of  the 
dranth  ia  dilated  into  a  disk  or  MmbreUo,  which  ia  ens- 
>tibl«  of  rhjthmical  oontractile  morementa,  \>j  which 
)  bodj  ia  propelled  throng  the  water.  Thus,  notwith- 
nding  ita  different  mode  of  development,  it  haa  a  cloae 
3  to  a  medmoid.  According  to  the  eziBt«mce 
e  of  tliete  Ttkrious  append^^s,  and  the  manner 
which  tliey  are  diapoeed,  the  SijAmoa  are  distingoish* 
Le  into  three  gronpa — 1,  Uie  Sydrophora;  2,  the  Di*eo- 
wa;  3,  the  Stphonopftoro. 

The  Htdbophora  are,  in  all  caeea  but  that  of  Bydra, 

1  ramified  h7droBome8,  on  which  manj  hjdranths  and 

iphorea  Eire  developed.    The  oomatic  cavitj  contained 

he   hjdroHoma  alwajs  retaina  a  free  commnnicatioii 

the  gastric  cavitiea  of  the  hjdranths.    In  other  words, 

m  mittooxle.    The  tentocola  are  either  scattered  over 

rdranths  (Coryne),  or  are  arranged  in  one  circle  rooiid 

oath  [BertuiaTia) ;  or  in  two  circlee,  one  close  to  the 

,  and  one  near  the  aboral  end  (Ttibvlarui).     Yery 

Uj — e.g.,  in   all    Berialarida,  Campawdarida,   and 

Hdce — there  is  a  hard,  chitinooa,  cuticular  skeleton. 

«  <rf  Allman,)  which  freqnently  gives  rise  to  hydro- 

ito  which  the  hydrautha  can  be  retracted  (Fig.  13,  z). 

^nophorcfl    present    everj    varietj,  from   simple 

diverticula  of  the  hjdroBomSi  to  free  Bwimniiug 

Is.    The  inner  margin  of  the  bell  in  these  meda- 

ilwBjB  produced  into  a  velum,  and  otolithic  sacs 

ipota  are  very  generally  disposed  at  regular  in- 

snnd  the  circumference  of  the  bell.     The  great 

of  what  were  formerly  t«rmed  the  naked-eyed 

Jfm/KOphtkalMaia)  are  merely  the  free-swimming 


180       THE  AKATOITY  0»  I]tVaSTBBBl.TKD  AITDULS. 

goDophowaof  theBjdrojjfcora.  Thus  the  medueoida  known 
M  BartiadtB  ore  the  free  ^nopliores  of  the  Corynida ;  ihe 
Aou^intMitUra  and  Lwice  of  the  Ewdtfiulrula) ;  many 
Ooeanitke  proceed  from  Z^i&HlarM&B  j  ThaumanUdiB  and 
.^^rwmdte  from  OainfMinMlarute. 
tn  Bome  Sy<lrqp&ora  (e.9.,  CoV'I'a)  t^  morgiiu  ol  the 

Fig.  15. 


I  (atUr    Gegenlwur).— A,   Hjdnnth;  e,    lU 
!t»;  D,  month;  te,  tentuin;  jI*,  digeatiTe  uTln, 

le  MUiutio  cavity  i,  contained  in  tbs  pednncla  and 

in  tbe  creeping  atem,  8.  B,  gonangium  containing  two  mednjifonD 
■ooldi  or  gODC^ibom  u  ;  the  •omatie  cavity  If  itia  connecIioD  witfa 
ttaal  of  the  creeping  atem.     C,  Bud. 

hjrdrotheca  are  prolonged  into  triaagular  processes,  which 
eerre  aa  an  openmlutn. 

Gertam  PbutttUarida  are  provided  with  promineikMa  of 
the  hjdrosoma  sorroiinded  b;  a  chitinona  iiiTestmant, 
which  ia  open  at  the  extremitj.  The  encloaed  aoft  ectoderm 
□Boallj  ooDtaine  manj  thread-ceUa,  and  has  the  power  of 
throwing  out  oontTKctile  pseadopodial  prooeaacM.      These 


THK  trmBOFHOSA. 


131 


hare  been  termed  nmtatophoret  by  Hr.  Biuk.*  la  Ophiadtt 
Hincks)  tbej  are  tentaculiform. 

It  freqnentlj  happens  that  the  ^nophoree  are  developed 
npon  epecial  stalka,  each  of  which  haa  eeaeutiall;  the 
■Cnieturc  of  a  moathleaa  hjdranth.  This  ia  termed  a 
blaitottfU.  In  some  fakatoatjrlea  (Fig.  16),  dnring  the  de- 
Tektpmcnt  of  the  bnda  of  the  gonophores,  the  eotodorm 


Fig. !«. 


aftitm  into  two  lajers — am  inner,  which 
inreats  the  central  axis  formed  b;  the 
endoderm  with  the  contained  prolon- 
gation of  the  somatic  cavit;;  and  an 
outer,  chiefly,  if  not  wholly,  chitinons 
layer.  Into  tiie  interspace  between  theee 
two,  the  budding  gonophores  prcrjeot, 
and  may  emerge  from  the  enmmit  of 
the  goiumgnua,  thm  formed,  either  to 
derelope  the  reprodnctive  elements,  and 
Bhed  them  while  atill  attached,  or  to  be 
set  at  liberty  as  free  mednsoide  (Figf.  16). 

Allmiiii  f  has  shown  that,  in  Du:oryne  fj„ 
am/eria,  the  gonophore  contained  in  a 
gonsn^nm,  somewhat  like  that  of  Lao- 
medea,  is  set  free  aa  a  ciliated  bitenta- 
cnlate  body,  on  the  central  axis  of 
which  the  ora  and  spermatozoa  are  de- 
yeloped. 

In    the   genua  Aglaophenia   [Plnmu- 
larida-),  gronpe  of  gonangia  are  enclosed 
in  a  common  receptacle  [corbula,  Allman),  formed  by  the 
development  and  anion  of  lateral  processes  (comparable  in 
some  respects  to  the  hydrophyllia  of  the  Calyetyphorida) 


•  They  are  dexaibed  onder  the 
auni  of  "cUiata  orguis,"  4ad 
euniiared  with  the  tentacle*  of 
Diplmda  Id  m;  Hamoir  on  the 
"AfinitiB  of  tha  Medow."  (Phil. 
Tnitt.  iat9.) 

t  '  HoMwimph  of  tb*  Gynrno- 
biwtte,  or  Tubnlarlui  Hjdniiil*,' 


MaiuBiform 
loold  of  Campami- 
laria  (afta-  Gegen- 
bur).       A,   necto- 


briuni,aTiclMiag  the 
dignliveeaTlly;  o, 
moulb;   i",   ladial 


much  InfarQullon  reapectiog  cho 


132       THS  ABATOMT  OT  UimTKBKATED  A1TIMAI.B. 

bom  th&t  region  of  the  hifdroeoiua,  vhicli  bears  ike  gono- 
phores. 

Some  medneoide,  such  ae  Sariia  prolifera  and  WUUia,  Ute 
liTdroid  stages  of  which  ore  not  at  present  certami;  known, 
bnt  which  are  probably  coiTniform,  produce  mednsoids 
similar  to  themselfes  bj  budding.  The  buds  may  bo  de- 
veloped either  from  the  mannbrium,  or  from  the  marginal 
canal  of  the  neotocalTx,  or  from  the  baaes  of  the  tentaonla, 
or  even  from  their  whole  length. 

Fif.  IT. 


Fig.  17.—  Wabia,  ap.— A,  the  nedDM,  with  budding  stoloni.  B,  ons 
of  the  budi  dmlopad  on  ■  itolon;  k,  nditl  ouul  of  the  noclo- 
mXjx  ;  «,  manubrium.  C.  s  atoloa;  jr,  it*  free  end  bcMtwith  Demi^ 
tocTsla ;  b,e,d,  budding  raedufoLdi ;  /,  meduaold  Dearly  read;  to 
be  detached;  t.  Its  manobrium  ;  d,  lu  nectocalfi ;  A,  a  radial  esoal. 

In  Angnst,  1849,  while  in  the  North  Pacific,  off  tlie 
Luoisiade  Archipelago,  I  took  a  species  of  WHlna  (Fig.  17), 
in  which  stolons  were  developed  at  the  bifurcation  of  each  of 
the  four  principal  radiating  canals  of  the  nectooaljx.  Each 
stolon  was  terminated  bj  a  knobbed  extremity  containing 
many  uematooysts  (0,  g),  and  gave  rise,  on  one  side,  ta  a 
series  of  bnds,  of  which  those  nearest  the  free  end  of  the 


THB  DI8COPHO&A.  1S3 

stolon  bad  acquired  the  form  of  complete  medosoida.  They 
had  four  Tmbranched  radiating  canals  and  four  tentacles ; 
but  it  is  probable  that  they  wonld  aasmne  the  form  of  the 
parent  stock  after  detachment. 

In  striking  contrast  with  the  complexity  of  these  repro- 
doctiYe  processes,  the  gonophore  is  represented,  in  Hydra, 
by  a  mere  enlargement  of  the  body  wall,  sitoated  close  to 
the  bases  of  the  tentacnla,  in  the  case  of  the  testes,  and 
nearer  the  attached  end  of  the  body  in  that  of  the  ovary. 
The  OYaiy  developes  a  single  ovum,  which,  as  Kleinenberg 
has  shown,  nnderg^oes  division  and  invests  itself  with  a 
chitinons  coat  while  still  attached  to  the  body  of  the  parent. 
This  chitinons  investment  is  more  or  less  spinose,  and  is 
often  confonnded  with  an  egg-shelL  It  obviously  answers 
to  iheperUarc  of  a  Tnbnlarian,  and  its  presence  in  the  em- 
bryo of  the  Hydra,  in  which  no  perisaro  is  developed  by  the 
adnlt,  saggests  that  Hydra  may  not  represent  the  simplest 
primaiy  condition  of  a  Hydrophoran,  but  may  be  a  reduced 
modification  of  a  Tubnlarian. 

2.  The  DiscOPHO&A. — These  "Medusffi"  resemble  the 
more  perfect  free  medusoid  gonophores  of  the  Hydrophora, 
in  so  far  as  they  consist  of  a  hydranth  or  polypite  attached 
to  the  centre  of  a  gelatinous  contractile  swimming  disk. 
But  they  differ  from  the  medusoids  of  the  Hydrophora, 
inasmuch  as  they  are  developed  either  directly  from  the  im- 
pregnated ovum ;  or  by  gemmation  from  a  Medusa  which 
arises  in  this  way ;  or  by  the  transverse  fission  of  the  hydri- 
form  product  of  the  development  of  the  impregnated  ovum. 

In  some  of  these  (e.^.,  Carmarvna,  Polyxenia,  JEginopsis, 
Traehynema),  the  disk  is  similar  to  the  nectocaJyx  of  one  of 
the  medusoids  of  the  Hydrophora ;  and,  like  it,  is  provided 
with  a  velum.  But  in  the  rest  (Lueemaria  and  the  Steganoph- 
thalmata)  the  disk  is  either  devoid  of  a  velum,  or  possesses 
only  a  rudiment  of  that  structure,  and  is  termed  an  urn- 
brdla.  The  edges  of  the  umbrella  are  divided  into  lobes 
by  marginal  notches  in  which  the  lithocysts  are  lodged. 
Moreover  in  these,  the  mineral  particles  of  the  lithocysts 


134       THE  ABATOXJ  OF  nrTaBTIBKA.TKD  AITDIALS. 

Rre  nomerons,  and  not  encloaed  in  Hepontte  sacs.  The 
Uthocjsts  are  often  covered  by  liood-like  prooeaaea  of  the 
nmbrella,  whence  they  haye  be^i  teimed  "  oovered-ejed  "  or 
Steganopkthahaata. 

Lucaraaria  ia  fixed  by  the  aboral  aide  of  its  nmbrella 
(Fig.  13,  s),  hj  means  of  &  longer  or  Bhorter  pedoncle.  The 
nmbrella  is  divided  into  eight  lobee,  at  the  extremities  of 
each  of  which  there  is  a  gronp  of  short  tentacles.    The 

Ftg.  18. 


II.  Dndcr  view  of  s  MgBiMit  of  ths  dJik,  to  it 
tbfl  ndlBling  c»n»lg ;  tha  kperture  of  ft  gooltal  cbamber  and  ths 

EUlled  genltBl  membruie  ihowipg  tbroiuh  ill  ventral  wall ;  and  ft 
tlia«7rt  with  Iti  protective  hood  (a). 

hjdranth  stands  np  in  tite  centre  of  the  nmbrella,  and  its 
oavitj  commnnioateB  with  a  central  chamber,  whence  fonr 
wide  chambers  pass  into  the  lobes.  These  chambers  are 
separated  by  septa,  the  free  central  edges  of  which  are 
beset  with  slender  tentacles.  The  reprodnctive  organs  are 
doable  radiating  series  of  thickening*  of  the  oral  wall  of 
each  chamber.* 


THB  DI800PH0KA. 


135 


An  the  other  Diseophorti,  which  are  what  are  commonly 
known  as  "  JeUy-fish,"  are  free,  and  some  attain  a  very  large 
aie.  In  the  adnlt  (Fig.  18)  the  umbrella  is  thick  and  divided 
bj  small  marginal  notches  into  as  many  (nsnaUy  eight) 
lobes.  At  the  bottom  of  each  notch,  often  protected  by 
special  lobnles,  is  an  oyal  lithocyst,  supported  by  a  cylin- 
drical pednnde,  the  cavity  of  which  is  in  direct  commnni- 
cation  with  one  of  the  radiating  canals  of  the  umbrella 
(Fig.  28,  lY.).  This  canal  communicates  with  the  exterior 
on  the  aboral  side  of  the  base  of  the  peduncle.*  The  thick 
mesoderm  of  which  the  great  mass  of  the  umbrella  con- 
sists is  composed  of  a  gelatinous  oonnectiye  tissue,  in  the 
meshes  of  which  is  a  watery  fluid,  containing  numerous 
nucleated  cells  which  exhibit  amcsboid  movements.  On 
the  oral  &ce  there  is  a  broad  cone  of  striped  muscle,  made 
up  of  fusiform  fibres  placed  side  by  side.  In  Aurelia 
auriia,  the  angles  of  the  four-sided  hydranth  are  produced 
into  long  foliaceous  lips,  the  margins  of  which  are  beset 
with  minute  solid  tentacula  (Fig.  18).  The  gastric  cavity 
contained  in  the  hydranth  terminates,  beneath  the  centre  of 
the  umbrella,  in  a  somatic  cavity  which  passes  into  four 
radially-disposed  wide  offshoots,  or  gewUal  sinuses,  the  oral 
walls  of  which  constitute  the  roof  of  the  genital  chambers 
(Fig.  18,  IL).  From  their  margins  the  narrow  branching 
radial  canab  are  given  off.  The  peripheral  ends  of  these 
unite  when  they  reach  the  margin. 

Each  genital  chamber  is  a  recess,  surroimded  by  a  thick 
wall  of  the  oral  face  of  the  umbrella,  in  the  centre  of 


tenaehangen  fiber  niedere  See- 
tUere'  (1862),  in  his  monograph 
on  the  genus,  fully  confirms  this 
view,  and  Prof.  H.  J.  Clark 
arrived  independently  at  the  same 
eonelnsion :  **  Lueemaria  the  Cce- 
notype  of  the  Acalephot"  (Pro- 
ceedings of  the  Boston  Society 
of  Satxinl  History,  1862).  The 
Lmeemaria  (^Carduella,  Allman') 
afothifonmia  of  Sars  differs  much 
from   the   ordinAry   LueermaritBj 


especially  in  the  position  of  the 
genital  organs  as  longitudinal 
thickenings  in  the  walls  of  the 
gastric  cavity.  See  Allman,  "  On 
me  Structure  of  Cardueila  cyathi- 
formu**  (Trans.  Microscop.  So- 
ciety, viii) 

*  The  circular  canal  of  the 
nectoodyx  communicates  ^th 
the  exterior  by  apertures  on  the 
summits  of  papillose  elevations  in 
some  medosoids. 


136       TRX  AITATOKT  0 


nmSTIBE^TSD  .UtUIALB. 


which  011I7  a  amall  aperture  ia  left  (Fig.  18,  L  a).  The  roof 
of  this  cavity  is  the  floor  of  the  genital  sinos;  it  is  mnch 
pUit«d  and  folded,  and  the  genitiJ  elements  are  developed 
in  it.  Its  inner  or  endoderm&l  wall  ie  beaeb  with  email  ten- 
tacular filamenta  (Fig.  28,  m.).  TheoTaortheepermatozoa 


rwU*;  c,  tb 

tli«ni ;  0,  tha  ]^lUn  which  nup«nd  the  braohiferoDi  disk  vbicb 
fortoi  the  floor  of  the  lab-niiibreUar  wvlt; ;  I,  ihort  olavila  teu- 
tMlei  IwtwBen  the  af«I  pone. 

poaa  out  of  the  apertnrea  of  the  genital  ohaml>er8,  and  the 
ova  are  received  into  small  pouches  or  folds  of  the  lips, 
and  there  undergo  the  preliminaiy  stages  of  their  develop- 
ment. 

In  the  jB&wsfomiiin  (as  was  ori^nallj  snggestAd  b;  Ton 


TBI  BHIZOBTOXmX. 


Bmt  and  haa  been  proved  b;  L.  Aguaiz  and  A.  Brandt,*) 
tlw  nutrgina  of  the  lips  of  the  hydraoth  nnite,  leaving  only 
■  mnltitade  of  nnall  apertarefl  for  the  ingeation  of  food  on 
the  long  anna,  which  represent  prolongatione  of  the  lipa  of 
the  hydranth  (Piga.  19,  20,  21).  The  polyatomatons  con- 
ditwnt  Ihna  brought  about,  by  the  aDbdiviaion  of  a  primi- 
tirely  aiinple  oral  cavity,  ia  obvionaly  quite  difTerent  In  its 
natore  from  tbat  which  occurs  in  the  Por^fnv, 


—  C^thta  Bcrllata  (f ).— A,  p«rt  of  Uis  umbrella,  viewed  from 

below,  to  ihow  the  plaited  KeolMl  membrmna  if)  and  the  diridgd 
aUaohmmt  of  one  of  the  jdTlan  :  d,  plaoe  of  one  of  the  lilhoejatj. 

SODS  of  the  onl  porei  (m)  aurroundad  by  tentaculii  (■•) ;  p,  oae 
the  olaTftte  teatsclea  intenpened  between  the  onl  pines.  C,  one 
of  the  pedaoculkted  lithocyite  (t)  In  Iti  notch  (d)  ttta  trom  beloir, 
with  tiieovtit  plate  from  which  moscular  fibre*  (&3  take  their  origia; 
*,  tba  racllKtJDg  ean&l  with  !(■  cnwl  Utenl  bruohes,  g. 

In  most  of  the  S}iiio$t<nnid<E,  not  only  do  the  edges  of  the 
lips  unite,  but  the  opposite  walls  of  the  hydranth  beneath 
the  nmbrella  are,  as  it  were,  poshed  in,  ao  aa  to  form  four 
chambers,  the  walla  of  which  unite,  become  perforated,  and 
thus  give  riae  to  a  anb-nmbrellar  cavity  with  a  root  formed 
•  <Hte.del'Acsd.de9t.P«tenbon^,'ivi.,  IS70. 


138       THB  ANATOMY  OF  HTYBBTIBBATED  AKDCALS. 

by  the  umbrella  and  a  floor,  the  hrachiferous  disk,  suspended 

Fig.  21. 


A      i 


Fig.  2\,—C«phea  oceUata  (0-— A,  lithocytt  enlarged  with  its  hood  (k) 
and  the  alx>nl  pore  of  the  canal  (c)  ;  <£,  the  notch  of  the  margin  of 
the  umhrella.  B,  the  brachiferous  dii k  ^th  the  origins  of  the  anns ; 
/,  endoderm ;  o,  ectoderm.  C,  tentaculate  lip  of  an  oral  pore  en- 
larged; «,  oral  cayity;  n,  nematocysts. 

by  four  pillars.    In  the  roof  the  plaited  genital  membranes 
are  developed.    The  floor  (Fig.  21,  b)  gives  off  the  subdivided 

Fig.  22. 


Fig.  22. — A,  Dipkyei  appendiculaia, — a,  hydranths  and  hydrophvUia 
on  the  hydroBoma ;  o,  proximal  nectocalyx ;  c,  aperture  of  distal 
neotoodvx ;  dy  somatocyst ;  e,  prolongation  of  the  distal  nectocalyx. 
by  which  it  is  attached  to  the  hydrosoma ;  /,  point  of  attachment  ot 
the  hydrosoma  in  the  cavity,  or  hvdrcecium,  of  the  proximal  necto- 
adjTz.  B,  the  distal  nectocalyx  with  the  canal  (through  which  the 
br&le  a  is  passed),  which  is  traversed  by  the  hydrosoma  in  A.  C, 
estremity  of  the  distal  nectocalyx,  with  its  muscular  velum. 


arms,  the  free  margina  of  which  bear  the  oral  pores,  and 


TBB  BHUOBTOIEIDX.  13& 

wlueb  mn  t»Tcned  bj  canals  which  unite,  paw  throagh  the 
{nUani,  Bod  open  into  tlie  central  oavitjr  of  the  umbrella.* 


Fig.  23.— A,  B,  Diphyioold  (Sphenoida),  Istenl  uid  front  Tiewi.  C, 
DIph^Kxiid  of  jUyla  iCMOotda),  a,  t,  EonopboTe  or  nproducMve 
orgmn ;  b,  h^dnnlh  ;  c,  phylloojit  or  cavity  of  hydrophjllliim,  with 
iU  proeeu  (J).    D,  free  gonopbore,  its  manabrliua  (a)  eonlaiuing 


whichU 
■H  obulnad  in  the  Soath  Pacific 
BOv  the  LoulilMle  Arohlpaluo, 
oa  the  1 1th  of  July,  1849.  ifie 
iboni  florfaoe  of  ue  ombrellB 
WH  of  ■  brownlih-gre]'  colaor, 
Tarlcgated  witli  OT*i  wbltc  >pot) : 
til*  oral  Boiface,  light  brown  with 
•ieht  bloiib-grcen  Uhm  radia- 
tiiig  tomid*  tha  Uthoeyiti:   tba 


bnehla  gre;  with  browD  dot*. 
Tlig  brachU  divide  into  two  at 
their  origia,  and  theo  aubdivlde 
into  an  i^nityofamallbnacheB. 
The  general  oolour  of  the  amallcr 
branches  is  light  brown,  tho 
■mall  IntersperMd  elavate  tea- 
tulea  belag  wblto.  The  long 
lanCacle*  whioh  terminal*  each 
braohlum,  aie  bine  and  oylin- 
diieal  at  their  origin,  hut  become 


140      TBK  ABATOKT  07  nTCBTKBRATZD  ANIIUXS. 

3.  The  SiPHOKOPHOBA. — In  Uub  group  the  hTdroBoma  is 
alwajB  free  and  flexible,  the  ectoderm  dereloping  no  hard 
ohltinoaH  eioBkeletoo,  save  in  the  cose  of  the  pneomato- 
phoree  of  some  apeciee.  In  moat,  the  hTdronthB  are  of  eqoal 
size;  bnt  in  TekUa  and  Porjnta,  the  hjdranth  aitnated  in 
the  centre  of  the  diacoidal  bod^  is  Tury  mnch  larger  than 
the  ittfb,  which  ocoapjr  a  oiromnferential  zone  around  it ; 

Fig.  S4. 


Fig-M.—AOiorybiaivaeta.  A.  Utenlvjew;  B,  from  >batc;  C,  D, 
detaobcd  hTdniphjUla ;  a,  poljrpita ;  b,  tentulo ;  c,  necnli  of  the 
taatoolM ;  4,  hjrdntphyllik ;  /,  pnmmmtophore. 

Bad  the  principal  function  of  which  ia  to  derelope  the 
gonophores  from  their  pedicles.  In  these  two  genera  the 
tflntacnla  are  separ&te  from  the  hydranths,  and  form  the 
OBtermoBt  circle  of  appendages. 

The  hjdranthB  of  the  Siphonophora  (Fig.  25,  A)  never 
poMew  a  oirclet  of  tentacnla  roond  the  month,  which. 


Mgonal  ftvUm  on,  wh«re  Ibay  anBata  of  Prdd  umI  Leraeoi  ? 
uvilwdad  with  brown  uiilnaai.  The  ladiTidaal  figured  wm  a 
Ii  It  l*'""™^  wUh  tha  C^Am      yomiKnait. 


THS  8IPHONOPHOBA. 


Ul 


whok  expanded,  is  trompet-sliaped.  The  endoderm  of  the 
hjdnuith  is  ciliated,  and  viUiu-like  prominences  project 
into  its  cavity.  The  interior  of  these  frequently  contains 
vaeaolar  spaces  (Fig,  24,  B,  0).  A  yalynlar  'pyloms' 
separates  the  gastric  from  the  somatic  cavity  in  the 
Cai§caphorida.  Long  tentacles,  frequently  provided  with 
unilateral  series  of  branches,  are  developed,  either  one 
from  the  base  of  each  hydranth,  or,  independently  of 
the  hydranths,  from  the  ccenosarc 
In  the  CaJyeophoridcB  and  many  PhysophoridcBj  complex 

Fig.  25. 


fig.  25. — AthoiTfbia  rxmaeta, — A,  ft  hydranth  with  villi  (a).  B,  one  of 
the  villi  in  ita  elongated  state,  enlarged.  C,  a  small  retracted  villas, 
still  more  magnified,  with  its  yacuolar  spaces  and  ciliated  surfkce. 

organs,  containing  a  sort  of  battery  of  thread  cells,  terminate 
each  lateral  branch  of  a  tentacle  (Figs.  24  and  26).  Each 
consists  of  an  elongated  %acwlu9,  terminated  by  two  fila- 
mentous appendages,  and  capable  of  being  spirally  coiled 
up.  In  this  state  it  is  invested  by  an  intH>2i4crum,  which  sur- 
rounds its  base.  The  somatic  cavity  is  continued  through 
the  branch,  which  constitutes  the  peduncle  of  this  organ,  into 
the  saoculus  and  its  terminal  filaments.  In  the  latter,  it  is 
narrow,  and  their  thick  walls  contain  numerous   small 


142   THE  ANATOMY  OF  INTSBTSB&ATSD  ANIMALS. 

spherical  nematocTsts.  In  the  saocnlus,  the  cavity  is  wider. 
One  wall  is  yerj  thick,  and  multitudes  of  elongated  nema- 
tocjsts,  the  lateral  series  of  which  are  sometimes  larger 
than  the  rest,  are  disposed  parallel  with  one  another,  and 
perpendicular  to  the  surface  of  the  sac.    Like  the  other 

Fig.  26. 


Fig.  26. — Athorybia  rotoofo.— The  ends  of  the  tentacular  branohee  in 
variouB  stages  of  development.  A,  lateral  branch,  commencing  as 
a  bad  from  the  tentacle.  In  B,  terminal  papillae,  the  rudiments 
of  the  filaments,  are  developed  at  the  extremity  of  the  branch ;  and, 
in  C,  the  saccnlus  is  beginning  to  be  marked  off,  and  thread  cells 
have  appeared  in  its  walls ;  in  D,  the  diyision  into  inyolucrum  and 
sacculus  is  apparent :  in  £,  the  involucrum  has  invested  the  sacculus, 
the  extremi^  of  which  is  straighti  while  the  lateral  processes  have 
curled  round  it 

organs,  each  of  these  tentacular  appendages  commences  as 
a  simple  diverticulum  of  the  ectoderm  and  endoderm,  and 
passes  through  the  stages  represented  in  Fig.  26. 

In  Phyacdia  the  tentacola  may  be  several  feet  kng.  They 
have  no  lateral  brandies,  bat  the  large  nematocysts  are 


THB  8IPHOKOPHORA.  143 

sitiuifted  in  transverse  renif orm  thickenings  of  the  wall  of 
the  tentacle,  which  occur  at  regular  intervals. 

HydrophjUia  aregeneralljpresent,  and,  like  the  tentacula, 
are  developed  either  from  the  pedicle  of  a  hjdranth,  in 
which  case  they  enclose  the  hydranth  with  its  tentacle  and 
a  group  of  gonophores  {CalycophoricUB),  or,  independently 
of  the  hydranths,  from  the  coBnosarc  (many  Physophoridce), 

The  hydrophyllia  are  transparent,  and  often  present  very 
beautifully  defined  forms,  so  that  they  resemble  pieces  of 
cut  ^ass.  They  are  composed  chiefly  of  the  ectoderm 
(and  mesoderm)  but  contain  a  prolongation  of  the  endoderm, 
with  a  corresponding  diverticulum  of  the  somatic  cavity. 
They  are,  in  fact,  developed  as  csBcal  processes  of  the  en- 
doderm and  ectoderm ;  but  the  latter,  with  the  mesodermal 
layer,  rapidly  predominates. 

^e  gonophores  of  the  Si^honophora  present  every  va- 
riety, from  a  simple  form,  in  which  the  medusoid  remains  in 
a  state  of  incomplete  development,  to  free  medusoids  of  the 
Gymnophthalmatous  iype.  As  an  example  of  the  former 
condition  the  gonophores  of  Athoryhia  may  be  cited  (Fig. 
27) ;  of  the  latter,  the  gonophores  of  Physalia,  Porpita,  and 
VeleUa, 

In  Atharybia,  groups  of  gonophores,  together  with  pyri- 
form  sacs,  which  resemble  incompletely  developed  hy- 
dranths {hydroeysis)  (Fig.  27,  A,  a),  are  borne  upon  a  com- 
mon stem,  and  constitute  a  gonohlastidium  (Fig.  27,  A).  The 
groups  of  male  and  female  gonophores  (Fig.  27,  A,  6,  c)  are 
borne  upon  separate  branches  of  the  gonoblastidium 
(androphores  and  ffynophores).  Each  female  gonophore 
contains  only  a  single  ovum,  which  projects  into  the  cavity 
of  the  imperfectly  differentiated  manubrium,  and  narrowing 
its  cavity  at  different  points  gives  rise  to  the  irregular 
canals  (Fig.  27,  D,  d).  In  the  male  gonophore,  the  necto- 
calyx  is  more  distinct  from  the  manubrium,  and  its  ex- 
tr^nity  has  a  rounded  aperture  (Fig.  27,  E). 

In  the  CaiyeophoridcB,  as  in  the  elongated  Physophoridce, 
the  development  of  new  hydranths  and  their  appendages, 
which  is  ooBBtaatly  oocuiring,  takes  place  at  that  end  of  the 


144       THl  ASATOKT  OF  IimBnBRl.TXD  J 

IiTdTCMoma,  which  oorrasponds  to  the  fixed  extremity  of  one 

Fig.  37. 


Fig.  ST. — AMhaybia  maaa. — A,  gonablutidiDiii  beulnB  thrae  hjdro- 
cnit,  a !  nnopborv,  b,  tod  two  aiidniiiborM,  c.  S,  fen»l«  nno- 
pborei  on  Uudr  common  item  or  Ejnopboni,  uowing  the  included 
oTum,  1,  wid  the  Tmdi«l  c«nftU,  i,  cTDf  ™)*1*  gonophona  enlaigml : 
u,  germuul  vcalole :  b,  tJUUiu  ;  c,  ndkl  cankli  of  tho  Impnfect 
neetoctiyx ;  d,  uatli  of  tbo  nunabrial  cstI^.    B,  malt  gon^bore. 

of  the  Hydrophara;   and,  if  we  conaidear  this  to  be  the 


THB  8IFH0K0PH0BA.  145 

proKunal  end«  new  buds  are  developed  on  the  proximal  side 
of  those  already  formed.  Moreover,  these  buds  are  formed 
on  one  side  only  of  the  hydrosoma.  Hence  the  appendages 
are  strictly  nnilateral,  though  they  may  change  their  position 
so  as  eventually  to  appear  bilateral  or  even  whorled.  In 
the  CdhfcopharidtB,  the  saccular  proximal  end  of  the  ccenosarc 
(Fig,  22,  A,  <i)  is  enclosed  within  the  anterior  nectocalyx, 
at  the  posterior  end  of  which  is  a  chamber,  the  hydroecium 
(Fig.  22,  A,  c).  The  second,  or  posterior,  nectocalyx  is  attached 
in  snch  a  way  that  its  anterior  end  is  enclosed  within  the 
hydrcBcium  of  the  anterior  nectocalyx,  while  its  contractile 
chamber  lies  on  the  opposite  side  of  the  axis  to  that  on 
which  the  anterior  nectocalyx  is  placed  (Fig.  22,  A).  Bets 
of  appendages  (Fig.  22,  A,  a ;  Fig.  23),  each  consisting  of  a 
hydrophy Ilium,  a  hydranth  with  its  tentacle,  and  gonophores, 
which  last  bud  out  from  the  pedicle  of  the  hydranth — are 
developed  at  regular  intervals  on  the  ccenosarc,  and  the 
long  chain  trails  behind  as  the  animal  swims  with  a 
darting  motion,  caused  by  the  simultaneous  rhythmical 
contraction  of  its  nectocalyces,  through  the  wat^r  (Fig.  22). 

From  what  has  been  said,  it  follows  that  the  distal  set  of 
appendages  is  the  oldest,  and,  as  they  attain  their  full  de- 
velopment, each  set  becomes  detached,  as  a  free  swimming 
complex  Diphyzooid  (Fig.  23).  In  this  condition  they  grow 
and  alter  their  form  aud  size  so  much,  that  they  were 
formerly  regarded  as  distinct  genera  of  what  were  termed 
monogastric  Diphydcs.  The  gonophores,  with  which  thcBe 
are  provided,  in  their  turn  become  detached,  increase  in 
size,  become  modified  in  form,  and  are  set  free  as  a  third 
series  of  independent  zooids  (Fig.  23,  D).  But  their  manu- 
brium does  not  develop  a  mouth  and  become  a  functional 
hydranth;  on  the  contrary,  the  generative  elements  are 
developed  in  its  wall,  and  are  set  free  by  its  dehiscence. 

In  the  PhysapharidcBf  the  proximal  end  of  the  hydrosoma 
is  provided  with  a  pneumatophore.  This  is  a  dilatation, 
into  which  the  ectoderm  is  invagiuated,  so  as  to  form  a  recep- 
tacle, which  becomes  filled  with  air  and  sometimes  has  a 
terminal  opening,  through  which  the  air  can  be  expelled 


146       THB  ANATOICT  OF  HTYBBTBBBATBD  ANIMAS. 

(Fig.  13,  4).  It  is  sometimes  small,  relatiyelj  to  the  hydro- 
soma  (AgcUma,  Phyaaphora),  sometimes  so  Lurge  (Atharybia, 
(Fig.  24),  Physalia,  PorpUOf  Vdelia),  that  the  whole  hydro- 
soma  becomes  the  investment  of  the  pyrif  orm  or  discoidal 
air-sac ;  while  the  latter  is  sometimes  converted  into  a  sort 
of  hard  inner  shell,  its  cavity  being  subdivided  by  septa 
into  nnmerons  chambers  {PorpUa,  Velella). 

Nectocalyces  may  be  present  or  absent  in  the  Physo* 
pTioridcB.  When  present,  their  number  varies,  but  they  are 
confined  to  the  region  of  the  hydrosoma  which  lies  nearest 
to  the  pneumatophore. 

In  the  gre&t  minority  of  the  Hydrotoa,  the  ovum  under- 
goes cleavage  and  conversion  into  a  morula,  and  sub- 
sequently into  a  planula,  possessing  a  central  cavity  en- 
closed in  a  double  cellular  wall,  the  inner  layer  of  which 
constitutes  the  hypoblast,  and  the  outer  the  epiblast. 

In  most  Hydrophora  the  ciliated,  locomotive,  planula  be- 
comes elongated  and  fixed  by  its  aboral  pole.  At  the  oppo- 
site end,  the  mouth  appears  and  the  embryo  passes  into  the 
g^trula  stage.  Tentacles  next  bud  out  round  the  mouth, 
and  to  this  larval  condition,  common  to  all  the  Hydrophora, 
Allman  has  given  the  name  of  Aciinula, 

Generally,  the  embryo  fixes  itself  by  its  aboral  extremity 
at  the  end  of  the  planula  stage;  but,  in  certain  Tubularidije, 
while  the  embryo  is  still  free,  a  circlet  of  tentacles  is 
developed  close  to  the  aboral  end ;  and  this  form  of  larva 
differs  but  very  slightly  from  that  which  is  observed  in 
the  IHgcophora. 

In  the  genus  Pelagia,  for  example,  the  tentacles  are 
developed  from  the  circumference  of  the  embryo,  midway 
between  the  oral  and  aboral  poles;  but  it  neither  fixes 
itself  nor  elongates  into  the  ordinary  actinula-f  orm.  On 
the  contrary,  it  remains  a  free-swimming  organism,  and, 
by  degprees,  that  moiety  of  the  body  which  lies  on  the 
aboral  side  of  the  tentacular  circlet  widens  and  is  converted 
into  the  umbrella,  the  other  moiety  becoming  the  hydranth, 
or  "  stomach,''  of  the  Medusa. 


THB  DBTBLOPMBNT  OF  THE  HYDBOZOA.     147 

In  Lncemaria,  it  is  probable  that  the  lai*va  fixes  iteelf  be- 
fore or  during  the  development  of  the  umbrella,  and  passes 
directly  into  the  adult  condition.  But,  in  most  Discophora, 
the  embryo  becomes  a  fixed  actinula  (the  so-called  Hydra 
tuba  or  SetfphisUyma,  Fig.  28, 1.)  multiplies  agamogenetically 
by  budding,  and  gives  rise  to  permanent  colonies  of  Hydri- 
form  polypes.  At  certain  seasons  of  the  year,  some  of  these 
enlmrge  and  undergo  a  further  agamogenetic  multiplication 
by  fiflsion  (Fig.  28,  II.).  In  fact,  each  divides  transversely 
into  a  number  of  eight-lobed  discoidal  medusoids  ('*  Ephyr<E  " 
or  ** Medusas  hifidtE**  Fig.  28,  II.  and  III.),  and  thus  passes 
into  what  has  been  termed  the  Strohila  stage.  The  Ephyrce 
becoming  detached  from  one  another  and  from  the  stalk  of 
the  SMbila,  are  set  free,  and,  undergoing  a  great  increase 
in  nie,  take  on  the  form  of  the  adult  Discophore,  and 
aoqtiire  reproductive  organs.  The  base  of  the  Strobila  may 
develope  tentacles,  (Fig.  28,  II.)  and  resume  the  Scyphistoma 
condition. 

MetBchnikoff  *  has  recently  traced  out  the  development 
of  Oeryonia  {Carmarind),  Polyzeniay  Mginopsia,  and  other 
Diflcophora,  which  differ  from  the  foregoing  in  possessing 
a  relum;  and  in  these,  as  in  the  TrachynevML  eiliatum, 
observed  by  Gegenbaur,t  the  process  appears  to  be  of 
essentially  the  same  nature  as  in  Pelagia,  The  Scyphistoma 
of  Aurelia,  Cyanoea  and  their  allies  is  probably  to  be  re- 
garded, like  the  larva  of  Pelagia^  as  a  Discophore  vnth  a  rudi- 
mentary disk ;  in  which  case,  the  production  of  the  Ephyra- 
forms  of  young  Discophora  will  not  be  comparable  to  the 
development  of  medusoid  gonophores  among  the  Hydro- 
phcTCL^  but  will  merely  be  a  process  of  multiplication,  by 
transverse  fission,  of  a  true,  though  undeveloped,  Discophore. 

In  the  8iphonophora,X  the  result  of  yelk  division  is  the 
formation  of  a  ciliated  body  consisting  of  a  small-celled 
ectoderm  investing  a  solid  mass  of  large  blastomeres,  which 

*  ^  Stodien  fiber  die  Entwicke-  wechsel,'  1854. 

hmg  der  Medusen  tmd  Siphono-  X  ^^  especially  the  late  ob- 

phoren."    (*  Zeitschrift  fOr  Wisa.  servations  of  Metscbnikoff,  ioc. 

Zoolj*  wriv.)  eit. 

f  *  Zor  Ldire  der  Generations- 

L  2 


148       TBK  AKATOKT  or  IirTBBTBBBATED  ANIUALS. 

Fig.  as. 


Flif.  !B._FiKB.  I.  and  II.— Cyama  cBplllala  (^tler  Vki  Beneden.*) 
1.  Tun)   Hgdm  Mv  {ScgphiMoma   atan),  exhibiting  their  on!in>T]r 

charooten.  uid  between  tben  tiro  (a,  &,)  whioh  we  undergoing  fiafion 

(SfmUja  itage).  

*  '  Becharolwi  nr  U  Fuiu  litlonla  dc  Bdfliiua.    Palj>pe^'    1666. 


THB  DBVXLOPMENT  OF  THE  HYDBOZOA.  149 

n.  The  two  Strobihty  a  and  6,  three  days  later.  In  a,  tentacles  are 
dereloped,  beneath  the  lowest  of  the  Ephfra^  from  the  stalk  of  the 
StrobUOf  which  will  persist  as  a  Hydra  tuba. 

III.  Half  the  disk  of  an  Epk^a  of  AurtHa  aurita,  seen  from  the  oral 
fiUM.  The  small  tentacles  which  lie  between  the  mouth  and  the 
baad  of  circular  muscular  fibres  are  inside  the  somatic  cavity, 
wlMBoe  sixteen  short  and  wide  radial  canals  extend  to  the  periphery, 
where  they  are  united  by  transverse  branches.  Eieht  of  the  radial 
eaoala  enter  the  corresponding  l«»bes,  and  finally  divide  into  three 
branehes ;  one  which  enters  the  peduncle  of  the  lithocyst,  and  two 
latarml  e«ca.    Badiating  bands  of  muscular  fibres  accompany  these 


IT.  flkloTlewof  oneof  the  lithocysts  with  its  peduncle.    The  arrow 
the  direction  in  which  the  cilia  of  the  exterior  work. 


eFentnaliy  pass  into  the  cells  of  the  endoderm.  This  body 
does  not  take  the  form  of  an  actinula.  On  the  contrary, 
it  i^pears  to  be  the  rale  that  buds  from  which  a  hydro- 
pbjUinm,  a  nectocalyx,  a  tentacle,  or  pneomatophore,  or 
even  all  of  them,  will  be  developed,  take  their  origin  ante- 
cedently to  the  formation  of  the  first  polypite  and  of  the 
gastric  cavity. 

As  Metschnikoff  well  remarks,  the  mode  of  development 
of  the  Siphanophora  is  wholly  inconsistent  with  the  doctrine 
that  the  various  appendages  of  the  hydrosoma  in  these 
animals  represent  individuals.  The  Hydrozoa  are  not  pro- 
perly compound  organisms,  if  this  phrase  implies  a  coales- 
cence of  separate  individualities ;  but  they  are  organisms, 
the  organs  of  which  tend  more  or  less  completely  to  become 
independent  existences,  or  zooids.  A  medusoid,  thoiigh  it 
feeds  and  maintains  itself,  is,  in  a  morphological  sense, 
simply  the  detached  independent  generative  organ  of  the 
hydrosoma  on  which  it  was  developed ;  and  what  is  termed 
the  "  alternation  of  generations,"  in  these  and  like  cases,  is 
the  result  of  the  dissociation  of  those  parts  of  the  organism 
on  which  the  generative  function  devolves,  from  the  rest.* 

In  certain  Discopliora  belonging  to  the  group  of  Traehy- 
nemata,  a  method  of  midtiplication  by  gemmation  has  been 

*  I  have  seen    no    reason  to  ture  published  in  the  '  Annals  and 

depart    from    the    opinions    on  Mai^azineof  Natural  Uisiory' lor 

the  subkct  of  *'  Animal  indivi-  June  1852. 
dualiqr''  enonclated  in  my  lee- 


150       THB  ANATOMY  OF  INYEBTEBBATED  ANIMALS. 

observed,  which  is  nnknown  among  the  other  Hydrozoa, 
It  may  be  termed  entogastric  gemmation,  the  bud  growing 
out  from  the  wall  of  the  gastric  cayity,  into  which  it  even- 
tually passes  on  its  way  outwards;  while,  in  all  other 
cases,  gemmation  takes  place  by  the  formation  of  a  diver- 
ticulum of  the  whole  wall  of  the  gastro-vascular  cavity, 
which  projects  on  to  the  free  surface  of  the  body,  and  is 
detached  thence  (if  it  become  detached),  at  once,  into  the 
circumjacent  water.  The  details  of  this  process  of  entogastric 
gemmation  have  been  traced  by  Haeckel*  in  Carmarina 
hiutcUa,  one  of  the  OeryonidcB,  As  in  other  members  of 
that  family,  a  conical  process  of  the  mesoderm,  covered  by 
the  endoderm,  projects  from  the  roof  of  the  gastric  cavity 
and  hangs  freely  down  into  its  interior.  Upon  the  surface 
of  this,  minute  elevations  of  ^^th  of  an  inch  in  diameter 
make  their  appearance.  The  cells  of  which  these  outgrowths 
are  composed  next  become  differentiated  into  two  layers — 
an  external  clear  and  transparent  layer,  which  is  in  contact 
with  the  cone,  and  invests  the  sides  of  the  elevation ;  and 
an  inner  darker  mass.  The  external  layer  is  the  ectoderm 
of  the  young  medusoid,  the  inner  its  endoderm.  A  cavity, 
which  is  the  commencement  of  the  gastric  cavity,  appears 
in  the  endodermal  mass,  and  opens  outwards  on  the  free 
side  of  the  bud.  The  latter,  now  f^th  of  an  inch  in  dia- 
meter, has  assumed  the  form  of  a  plano-convex  disk,  fixed 
by  its  flat  side  to  the  cone,  and  having  the  oral  aperture  in 
the  centre  of  its  convex  free  side.  The  disk  next  increasing 
in  height,  the  body  acquires  the  form  of  a  flask  with  a 
wide  neck.  The  belly  of  the  flask  is  the  commencement  of 
the  umbrella  of  the  budding  medusoid;  the  neck  is  its  gas- 
tric division.  The  belly  of  the  flask,  in  fact,  continues  to 
widen  out  until  it  has  the  form  of  a  flat  cup,  from  the  centre 
of  which  the  relatively  small  g^astric  neck  projects,  and  the 
bud  is  converted  into  an  unmistakable  medusoid,  attached 
to  the  cone  by  the  centre  of  the  aboral  face  of  its  umbrella. 
In  the  meanwhile,  the  gelatinous  transparent  mesoderm  has 
appeared,  and,  in  the  umbrella,  has  acquired  a  gi'eat  rela- 
*  '  Beitrage  zur  Naturgeschichte  der  Hydromodusen,'  1865. 


V088IL  HTDBOZOA.  151 

tire  thickness.  Into  this,  eight  prolongations  of  the  gastric 
cavity  extend,  and  give  rise  to  the  radial  canals,  which 
become  nnited  into  a  circnlar  canal  at  the  circumference 
of  the  disk.  The  velum,  tentacula,  and  lithocjsts  are 
dereloped,  and  the  bud  becomes  detached  as  a  free  swim- 
ming medusoid.  But  this  medusoid  is  very  different  from 
the  Carmarina  from  which  it  has  budded.  For  example,  it 
haa  eight  radial  canals,  while  the  Carmarina  has  only  six ; 
it  has  solid  tentacles,  while  the  adult  Carmarina  has  tubular 
tentacles ;  it  has  no  g^astric  cone,  and  has  differently  dis- 
posed lithocysts.  Haeckel,  in  fact,  identifies  it  with  Cunina 
rhododadyla,  a  form  which  had  hitherto  been  considered 
to  be  not  only  specifically  and  generically  different  from 
Carmarina,  but  to  be  a  member  of  a  distinct  family — ^that 
of  the  JBginidiB. 

What  makes  this  process  of  asexual  multiplication  more 
remarkable  is,  that  it  takes  place  in  Carmarince  which  have 
already  attained  sexual  maturity,  and  in  males  as  well  as  in 
females. 

There  is  reason  to  believe  that  a  similar  process  of  ento- 
gastric  proliferation  occurs  in  several  other  species  of 
.^IginidoBf — .^gineta  prolifera  (Gregenbaur),  EuryaUmia  ruin- 
gino9um  (Kolliker),  and  Cunina  Kollikeri  (F.  Mtdler) ;  but, 
in  all  these  cases,  the  medusoids  which  residt  from  the 
gemmative  process  closely  resemble  the  stock  from  which 
they  are  produced. 

As  might  be  expected,  the  Hydrozoa  are  extremely  rare 
in  the  fossil  state,  and  probably  the  last  animal  the  dis- 
covery of  fossil  remains  of  which  could  be  anticipated,  is 
a  jelly-fish.  Nevertheless,  some  impressions  of  Medusae,  in 
the  Solenhofen  slates,  are  sufficiently  well  preserved  to 
allow  of  their  determination  as  members  of  the  group  of 
RhiMOtiomid<B.*  The  apparent  absence  of  the  remains  of 
Hydrophora  in  the  mesozoic  and  newer  palteozoic  rocks,  is 
very  remarkable.    Some  singular  organisms,  termed  Orap- 

*  *Haeckel,  **  Ueber  swei  neae  fossile  Medusen  nus  der  Fusille  der 
Bhiivjttomidon."    OJi^^l>ucii  liir  Mineralogie/ 1866.) 


152       THE  JLKATOICT  OF  IKYSBTBBBATED  ANIMALS. 

MUeSf  which  abound  in  the  Silurian  rocks,  may  possibly 
be  Hydrozoat  though  they  present  points  of  resemblance 
with  the  Polyuoa,  They  are  simple  or  branched  stems, 
sometimes  slender,  sometimes  expanded  or  foliaceous;  occa- 
sionally the  branches  are  connected  at  their  origin  by  a 
membranous  expansion.  The  stems  are  tubular,  and  beset 
on  one  or  both  sides  with  minute  cup-shaped  prolongations, 
like  the  thecffi  of  a  Sertularian.  A  solid  thickening  of  the 
skeleton  may  ha^e  the  appearance  of  an  independent  axis. 
Allman  has  suggested  that  the  theciform  projections  of 
the  Graptolite  stem  may  correspond  with  the  nematophores 
of  Sertularians,  and  that  the  branches  may  have  been 
terminated  by  hydranths.  Appendages  which  appear  to 
be  analogous  to  the  gonophores  of  the  Hydrophara,  have 
been  described  in  some  Graptolites.* 

With  a  very  few  exceptions  {Hydra,  Cordylophora,)  the 
Hydrotoa  are  marine  animals ;  and  a  considerable  number, 
like  the  CahfcophoridcB  and  PhyBopharidce,  are  entirely 
pelagic  in  their  habits. 

The  AcTiNOZOA. — ^The  essential  distinctions  between  the 
Aetinozoa  and  the  Hydrozoa  are  two.  In  the  first  place, 
Uie  oral  aperture  of  an  Aotinozoon  leads  into  a  sac,  which, 
without  prejudice  to  the  question  of  its  exact  function, 
may  be  termed  "  gastric,"  and  which  is  not,  like  the  hy- 
dranth  of  the  Hydrozoon,  free  and  projecting,  but  is  sunk 
within  the  body.  From  the  walls  of  the  latter,  it  is  separated 
by  a  cavity,  the  sides  of  which  are  divided  by  partitions, 
the  mesewteriea,  which  radiate  from  the  wall  of  the  gastric 
sac  to  that  of  the  body,  and  divide  the  somatic  cavity  into 
a  corresponding  number  of  intermesenieric  chambera.  As 
the  gastric  sac  is  open  at  its  inner  end,  however,  its  cavity 
is  in  free  communication  with  that  of  the  central  space 
which  communicates  with  the  intermesenteric  chambers; 
and  the  central  space,  together  with  the  chambers,  which 

*  Hall:    *GraptoIites    of  the      of    the    BriUsh    GraptoUaUe,' 
Quebec  Series  of  North  America,'       1872. 
1865.     Nicholson:   *Moziogiaph 


THB  ACTINOZOA.  158 

ten  collectively  termed  the  "  body  carity  "  or  "  peri" 
il  cavity,'*  are,  in  reality,  one  with  the  dig^estive  cavity, 
•  in  the  Hydrotoa,  constitute  an  erUeroecBle,  Thus  an 
noon  might  be  compared  to  a  Lncemaria,  or  still  better 
Jatrduella,  in  which  the  outer  face  of  the  hydranth 
«d  with  the  inner  face  of  the  umbrella ;  under  these 
utancee  the  canals  of  the  umbrella  in  the  Hydro- 
roold  answer  to  the  intermesenteric  chambers  in  the 
>ioon. 

nidly,  in  the  AeHnoaoci,  the  reproductive  elements  are 
ped  in  the  walls  of  the  chambers  or  canals  of  the 
cosle,  just  as  they  so  commonly  are  in  the  walls  of  the 
-vascular  canals  of  the  Hydroioaf  but  the  generative 
I  thus  constituted  do  not  project  outwardly,  nor  dis- 
)  their  contents  directly  outwards.  On  the  contrary, 
•A  and  spermatozoa  are  shed  into  the  enterocoele,  and 
lally  make  their  way  out  by  the  mouth.  In  this  re- 
again,  the  Actiuozoon  is  comparable  to  a  Lucemaria 
ed  by  the  union  of  the  hydranth  with  the  ventral  face 
umbrella ;  under  which  circumstances  the  reproduc- 
ements,  which,  in  all  Hydrozoa,  are  developed,  either 
waUs  of  the  hydranth  or  in  those  of  the  oral  face 
I  umbrella,  would  be  precluded  from  making  their 
f  any  other  route  than  through  the  gastro-vascular 
and  the  mouth. 

he  fundamental  composition  of  the  body  of  an  ecto- 
uid  endoderm,  with  a  more  or  less  largely  developed 
erm,  and  in  the  abundance  of  thread-cells,  the  Acti- 
%gree  with  the  Hydrozoa, 

lost  of  the  Actinoioa,  the  single  polype,  into  which  the 
0  is  converted,  gives  rise  by  budding  to  many  zooids 
form  a  coherent  whole,  termed  by  Lacaze-Duthiers, 
\hodeme. 

CosALLiGENA. — The  Actinozoa  comprehend  two 
I — ^the  Corcdligena  and  the  Ctenophora, — ^which  are 
different  in  appearance,  though  fundamentally  similai* 
cture.  In  the  former,  the  mouth  is  always  surrounded 

or  more  circlets  of  tentacles,  which  may  be  slender 


164      THB  ^NATOirr  of  DrVIBTBBRATED  AITIHALB. 

and  conical,  or  ihort,  broad  and  fimbriated.  The  month  is 
lunall;  eloDKated  in  one  direction,  and,  at  the  eztremitiee  of 
the  long  diameter,  preaente  folds  which  are  continued  into 
the  gastric  cavity.  The  arrangement  of  the  parU  of  the 
bodj  is  therefore  not  so  oompletdy  radiate  aa  it  appears  to 
be.  The  enteroctele  is  divided  into  six,  eight,  or  more,  wide 
intermesenteric  chambers,  which  oommonicate  with  the 
cavities  of  the  tentacles,  and  Bometimes,  directly  with  the 
exterior,  by  apertures  in  the  parietea  of  the  body.  The 
mesenteries  which  separate  these  wide  chambers  are  thin 
Fig.  89. 


Fig.  29.— ParpendJcalir  iMtlon  of  ^cftua  hobatira  (■ftrr  Vnj  and 
jleuclart} — a,  aoulh;  (,  nitilo  cavity;  e.  common  aiity,  into 
which  the  gailric  uvity  and  tba  inlermeaenWric  chambtn  opeti ;  d, 
Intennesenteiio  ohamben ;  i,   tblekaDCd   fnt  margin,  oontaining 
threid-celli  of,^  a  mcaentery ;  g,  reproduoCiva  organ  ;  A,  tentacle, 
and  membranons.      Two   of  them,  at  opposite  ends  of  a 
transrerse  diameter  of  the  Actinozoon,  are  often  different 
from   the  rest.     Each   mesentcTy  ends,  at   ite   aboral   ex- 
tremity, in  a  free  edge,  often  provided  with  a  thickened  and 
folded  margin;  and  these  free  edges  look  towards  thecentre 
of  an  axial  cavity,*  inte  which  the  gastric  sao  and  all  the 
intermesenteric  chambers  open. 
In  the  Coralligena,  the  outer  wall  of  the  body  is  not  pro- 

*  Partiillv  digested  iubttia<!ei  that  It  may  functionally  represent 
are  often  Aiuud  In  thii  axial  theilamachDrthecomir>enc«Df?nt 
■liM*,  and  It  U  Dot  improbable       of  tlw  iniallne  in  lilgher  anlmali. 


THB  CO&ALUOBNA.  155 

▼ided  with  bands  of  large  paddle-like  cilia.  Most  of  them 
aie  fixed  temporarily  or  permanently,  and  many  g^ye  rise 
by  gemmation  to  turf -like,  or  arborescent,  zoanthodemes. 
l^e  great  majority  possess  a  hard  skeleton,  composed  prin- 
cipally of  carbonate  of  lime,  which  may  be  deposited  in  per- 
manently disconnected  spicnla  in  the  walls  of  the  body ;  or 
the  spicnla  may  mn  into  one  another,  and  form  solid  net- 
works, or  dense  plates,  of  calcareous  matter.  When  the 
latter  is  the  case,  the  calcareous  deposit  may  invade  the 
base  and  lateral  walls  of  the  body  of  the  Actinozoon,  thus 
giving  rise  to  a  simple  cup,  or  theca.  The  skeleton  thus 
formed,  freed  of  its  soft  parts,  is  a  "  cup-coral,"  and  receives 
the  name  of  a  eoraUUe, 

In  a  zoanthodeme,  the  various  polypes  {anthoMOoids), 
formed  by  gemmation  may  be  distinct,  or  their  several 
enterocceles  may  communicate;  in  which  last  case,  the 
common  connecting  mass  of  the  body,  or  cceno»arc,  may  be 
traversed  by  a  regular  system  of  canals.  And,  when  such 
compound  AcHnoaoa  devcdope  skeletons,  the  coraUites  may 
be  distinct,  and  connected  only  by  a  substance  formed 
by  the  calcification  of  the  ccenosarc,  which  is  termed 
eoenenehyma ;  or  the  thecsB  may  be  imperfectly  developed, 
and  the  septa  of  adjacent  corallites  run  into  one  another. 
There  are  cases,  again,  in  which  the  calcareous  deposit  in 
the  several  polypes  of  a  compound  Actinozoon,  and  in  the 
superficial  parts  of  the  codnenchyma,  remains  loose  and  spicu- 
lar,  while  the  axial  portion  of  the  coenosarc  is  converted  into 
a  dense  chitinous  or  calcified  mass — ^the  so-called  aclerdbuse. 

The  mesoderm  contains  abundantly  developed  muscular 
fibres.  The  question  whether  the  Coralligena  possess  a 
nervous  system  and  organs  of  sense,  hai^dly  admits  of  a 
definite  answer  at  present.  It  is  only  in  the  Actinidce 
that  the  existence  of  such  organs  has  been  asserted ;  and 
the  nervous  circlet  of  Actinia,  described  by  Spix,  has  been 
seen  by  no  later  investigator,  and  may  be  safely  assumed 
to  be  non-existent.    Professor  P.  M.  Duncan,  F.R.S.,*  how- 

*  *  On  the  Nervous  System  of  Actinia.'  (Proceedings  of  the  Royal 
Sodety,  October  9,  I87;5.) 


156       THE  AKATOICT  OF  IirYSBTBBRATED  ANIMALS. 

ever,  has  recently  described  a  nervous  apparatus,  consist- 
ing of  fusiform  ganglionic  cells,  united  bj  nerve  fibres, 
which  resemble  the  sympathetic  nerve  fibrils  of  the  Verte- 
brata,  and  form  a  plexus,  which  appears  to  extend  through- 
out the  pedal  disk,  and  very  probably  into  other  parts  of 
the  body.  In  some  of  the  AcHnidcB  {e.g..  Actinia  mesemhry- 
anthemum),  brightly  coloured  bead-like  bodies  are  situated 
in  the  oral  disk  outside  the  tentacles.  The  structure  of 
these  "  chromatophores,"  or  "  bourses  calicinales,"  has  been 
carefully  investigated  by  Schneider  and  Botteken,  and  by 
Professor  Duncan.  They  are  diverticula  of  the  body  wall, 
the  surface  of  which  is  composed  of  close-set  "bacilli," 
beneath  which  lies  a  layer  of  strongly-refracting  spherules, 
followed  by  another  layer  of  no  less  strongly-refracting 
cones.  Subjacent  to  these.  Professor  Duncan  finds  ganglion 
cells  and  nerve  plexuses.  It  would  seem,  therefore,  that 
these  bodies  are  rudimentary  eyes. 

The  sexes  are  united  or  distinct,  and  the  ovum  is  ordi- 
narily, if  not  always,  provided  with  a  vitelline  membrane. 
The  impregnated  ovum  gives  rise  to  a  ciliated  morula,  which 
may  either  be  discharged  or  undergo  further  development 
within  the  somatic  cavity  of  the  parent.  The  morula  be* 
comes  a  gastrula,  but  whether  by  true  invagination  or  by 
delamination,  as  in  most  of  the  HydroMa,  is  not  quite  clear. 
The  gastrula  usually  fixes  itself  by  its  closed  end,  while 
tentacles  are  developed  from  its  oral  end.  It  can  hardly  be 
doubted  that  the  intermesenteric  chambers  are  diverticula 
of  the  primitive  enterocoele;  but  the  exact  mode  of  their 
origin  needs  further  elucidation. 

Lacaze-Duthiers  *  has  recently  thrown  a  new  light  upon 
the  development  of  the  CoraUigena,  and  particularly  of  the 
AcHnicB  {Actinia,  SagarHa,  Bunodes),  These  animals  are 
generally  hermaphrodite,  testes  and  ovaria  being  usually 
found  in  the  same  animal,  and  even  in  the  same  mesenteries ; 
but  it  may  happen  that  the  organs  of  one  or  the  other  sex 
are,  at  any  given  time,  exclusively  developed.    The  ova 

*  **  Developpement  dee  Coralliaires."  (*  Archives  de  Zoologie  ex- 
perimenule,*  1872.) 


THE   DEVELOPMBNT  OF  THE  COSALLIOBNA. 


157 


undergo  the  early  stages  of  their  development  within  the 
body  of  the  parent.  The  process  of  jelk  division  was  not 
observed,  and  in  the  earliest  condition  described  the  embryo 
was  an  oval  plannla-like  body,  composed  of  an  inner 
coloured  substance  and  an  outer  colourless  layer.  The 
outer  layer  (epiblast = ectoderm)  soon  becomes  ciliated.  An 
oval  depression  appears  at  one  end,  and  becomes  the  mouth  * 
and  gastric  sac,  while,  at  the  opposite  extremity,  the  cilia 
elongate  into  a  tuft.  The  ectoderm  extends  into  and 
lines  the  gastric  sac,  while  the  interior  of  the  coloured 
hypoblast  becomes  excavated  by  a  cavity,  the  enterocoele, 
which  communicates  with  the  gastric  sac.  In  this  con- 
dition the  embryo  swims  about  with  its  oral  pole  directed 
backwards. 

The  oral  aperture  changes  its  form  and  becomes  elongated 
in  one  direction,  which  may  be  termed  the  oral  axis.  The 
mesenteries  are  paired  processes  of  the  transparent  outer 
layer  (probably  of  that  part  which  constitutes  the  meso- 
derm) which  mark  off  corresponding  segments  of  the 
enterocoele.  The  first  which  make  their  appearance  are 
directed  nearly  at  right  angles  to  the  oral  axis  near,  but  not 
exactly  in,  the  centre  of  its  length.  Hence  they  divide  the 
enterocoele  into  two  primitive  chambers,  a  smaller  (A)  at 
one  end  of  the  oral  axis,  and  a  larger  (A')  at  the  other. 
This  condition  may  be  represented  by  A  -f-  A' ;  the  dots 
indicating  the  position  of  the  primitive  mesenteries,  and 
the  hyphen  that  of  the  oral  axis.  It  is  interesting  to 
remark  that,  in  this  state,  the  embryo  is  a  bilaterally 
symmetrical  cylindrical  body,  vnth  a  central  canal,  the 
^  future  gastric  sac ;  and,  communicating  therewith,  a  bilobed 
enterocoele,  which  separates  the  central  canal  from  the 
body  wall.    In  fact,  in  principle,  it  resembles  the  early 


*  Kowalewsky  describes  the 
finrmation  of  a  gastrula  hy  inva- 
giaatioii  in  a  species  of  Actinia 
•ad  in  CTeanthut,  the  aperture 
cf  invagination  becoming  the 
Sonth  (liofmann  and  Schwalbe, 
^Jahretbericht/  Bd.  U.  p.  '26 j). 


In  other  species  of  Actinia  and  in 
AlcyoHium,  the  planula  seems  to 
delarainate.  Ordinary  yelk  divi- 
sion occurs  in  some  AmhozoOy 
while  iu  others  {Afcyonium)  the 
process  rather  resembles  that 
which  occurs  in  most  Arthropods. 


158       THB  ANATOMY  OF  HTYBBTSBBATBD  ANIMALS. 

condition  of  the  embryo  of  a  Ctenophore,  a  Brachiopod, 
or  a  Sagitta, 

Another  pair  of  mesenteric  processes  now  makes  its 
appearance  in  the  larger  chamber  A',  and  cuts  off  two 
lateral  chambers,  BB,  which  lie  between  these  secondary 
mesenteries  and  the  primary  ones.    In  this  state  the  eu- 

teroccele  or  somatic  cavity  is  four-chambered  I  ^^  "t-  ^  A'  Y 

Next  a  third  pair  of  mesenteries  appear  in  the  smaller 
chamber  (A),  and  divide  it  into  three  portions,  one  at 
the  end  of  the  oral  axis  (A),  and  two  lateral  (CO).    In  this 

stage  there  are  therefore  six  chambers  (  A  rj-r-g  A'  1 ;  but 

almost  immediately  the  number  is  increased  to  eight, 
by  the  development  of  a  fourth  pair  of  mesenteries  in 
the  chambers  B,  B,  which  thus  g^ve  rise  to  the  chambers 
D,  D,  between  the  primitive  mesenteries  and  themselves. 
The  embryo  remains   in   the   eight- chambered  condition 

A  Qt-i-^  B  ^  7  ^^^  some  time,  until  all  the  chambera 

and  their  dividing  mesenteries  become  equal.  Then  a  fifth 
and  a  sixth  pair  of  mesenteries  are  formed  in  the  chambers 
0,  0,  and  D,  D ;  two  pairs  of  new  chambers,  E  and  F,  are 
produced,  and  thus  the  Aetinia  acquires  twelve  chambers 

(-^  n  E"^  D  B  '^ /*  ^^®  ^^  which  result  from  the  sub- 
division of  the  smaller  primary  chamber,  and  seven  from 
that  of  the  larger  primary  chamber.  The  various  chambers 
now  acquire  equal  dimensions,  and  the  tentacles  begin  to  bud 
out  from  each.  The  appearance  of  the  tentacles,  however, 
is  not  simultaneous.  That  which  proceeds  from  the 
chamber  A'  is  earliest  to  appear,  and  for  some  time  is 
largest,  and,  at  first,  eight  of  the  tentacles  are  larger  than 
the  other  four. 

The  coiled  marginal  ends  of  the  mesenteries  appear  at 
first  upon  the  edges  of  the  two  primary  mesenteries ;  then 
upon  the  edge  of  the  fourth  pair,  and  afterwards  upon  those 
of  Uie  other  pairs. 


THE  OCTOCOIIAUJL.  159 

For  the  farther  changes  of  the  young  Actinia,  I  mnst  refer 
to  the  work  cited.  Sufficient  has  been  said  to  show  that 
the  development  of  the  ActinuB  follows  a  law  of  bilateral 
symmetry,  and  to  bring  out  the  important  fact  that,  in 
the  course  of  its  development,  the  finally  hezamerous 
Anthozoon  passes  through  a  tetramerous  and  an  octomerous 
stage. 

Phenomena  analogous  to  the  "alternation  of  genera- 
tions," which  is  so  common  among  the  Hydrozoay  are 
unknown  among  the  great  majority  of  the  Actinozoa,  But 
Semper  *  has  recently  described  a  process  of  agamogenesis 
in  two  species  of  Fungias,  which  he  ranks  under  this  head. 
The  FungicB  bud  out  from  a  branched  stem,  and  then  be- 
come detached  and  free,  as  is  the  habit  of  the  genus.  To 
make  the  parallel  with  the  production  of  a  medusoid  from 
a  hydroid  polype  complete,  however,  the  stem  should  be 
notirished  by  a  sexless  anthozooid  of  a  different  character 
from  the  forms  of  FungicB  which  are  produced  by  gemma- 
tion.   And  this  does  not  appear  to  be  the  case. 

In  one  division  of  the  Coralligerui — ^the  Octocoralla — eight 
enterocoele  chambers  are  developed,  and  as  many  tentacles. 
Moreover,  these  tentacles  are  relatively  broad,  flattened, 
and  serrated  at  the  edges,  or  even  pinnatifid.  The  Acti- 
nozoon  developed  from  the  e^g  may  remain  simple  (Haimea, 
Milne-Edwards),  but  usually  gives  rise  to  a  zoanthodeme. 

The  CQBnosarc  of  the  zoanthodeme  in  the  Octocoralla  is 
a  substance  of  fleshy  consistence,  which  is  formed  chiefly  of 
a  peculiar  kind  of  connective  tissue,  containing  many  mus- 
cular fibres  developed  in  the  thickened  mesoderm.  The 
axial  cavity  of  each  anthozooid  is  in  communication  with  a 
system  of  large  canals.  In  Alcyonium,  a  single  large  canal 
descends  from  each  anthozooid  into  the  interior  of  the 
zoanthodeme,  and  the  eight  mesenteries  are  continued  as 
so  many  ridges  throughout  its  entire  length,t  so  that  these 
tubes  have  been  compared  to  the  thecal  canals  of  the  Mille- 

*  *  Ueber  Generations-Wechsel       tributlon  k  rAnatomie  des  Alcy- 
beiSteiukorailen.'    Leipzig,  1872.       onaires."     (*  Journal  d'Anatomie 
t  Poodiet  and  Myevre»  '*  Con-      et  de  la  Fbysiologie/  1870.) 


Pig.  30.— Oanlliim  nbnm  (■»«-  LuMBv-Diithien  •}. 

I.  The  and  of  ■  bnach  vlth  A,  B,  C,  Uitm  aDllixinoidi  In  dlOen 
degrcet  rif  pxpaiiilon ;  i,  thp  moutti ;  a,  that  ptrl  i<f  ihe  ciraini 
wUoh  rises  Into  a  cup  arouitd  tlia  liata  of  aacb  ai  " 


<  miMIn  Natoralla  dn  CoitU,'  IBtt. 


THB  ACTINOZOA.  161 

II.  Portion  of  a  branch,  the  coenosmro  of  which  hu  been  divided 
longitudinally  and  partially  removed ;  B,  B\  B",  anthosooids  in  sec- 
tion ;  B^  anthosooia  with  expanded  tentacles ;  A,  mouth ;  m,  gastric 
sac ;  t,  Its  inferior  edge ;  j,  mesenteries. 

B*,  anthosooid  retracted,  with  the  tentacles  (d)  drawn  back  into  the 
intermesenteric  chambers ;  c,  orifices  of  the  cavities  of  the  in  vagi- 
Dated  tentacles ;  e,  drcum-oral  cavity ;  6,  the  part  of  the  body  which 
forms  the  projecting  tube  when  the  anthosooid  is  expanded ;  a,  fes- 
tooned edges  of  the  cup. 

B",  anthosooid,  showing  the  transverse  sections  of  the  mesenteries. 

A,  A,  Coenosarc,  with  its  deep  longitudinal  eanats  (/),  and  superficial, 
imgolar,  reticulated  canals  (A).  P,  The  hard  axis  of  the  coral,  with 
loogitiidinal  grooves  (ff)  answering  to  the  longitudinal  v<;9sels. 

ni.,  Iv.     free  ciliated  embryos. 

pores.  In  the  red  coral  of  commerce  (Gordlliwn  rubrumf 
Fig.  90),  tbe  large  canals  mn  parallel  with  the  axial  skele- 
ton. A  delicate  network,  which  traverses  the  rest  of  the 
substance  of  the  ccenosarc,  appears  to  be  sometimes  BoHd 
and  sometimes  to  form  a  system  of  fine  canals  opening^  into 
the  larger  ones.  The  anthozooids  possess  nnmerons  muscles 
by  which  their  movements  are  effected.  The  fibres  are 
delicate,  pale,  and  not  striated.  Nerves  have  not  been 
certainly  made  out. 

It  is  in  these  OetocoraUa  that  the  form  of  skeleton  which 
is  termed  a  aclerohasef  which  is  formed  by  comification  or 
calcification  of  the  axial  connective  tissue  of  the  zoantho- 
deme,  occurs.  It  is  an  unattached  simple  rod  in  Pennaiula 
and  VeretiUum,  but  fixed,  tree-like,  branched,  and  even  re- 
ticulated, in  the  Chrgonice  and  the  red  coral  of  commerce 
{CoraJUum),  In  the  Alcyonia,  or  "Dead  men's  fingers,'* 
of  our  own  shores,  there  is  no  sclerobase,  nor  is  there 
any  in  Tubipcra,  the  organ  coral.  But,  whereas  in  all 
the  other  OetocoraUa  the  bodies  of  the  polypes  and  the 
coenosarc  are  beset  with  loose  spioula  of  carbonate  of 
lime,  Tuhipora  is  provided  with  solid  tubiform  thecce,  in 
which,  however,  there  are  no  septa. 

Dimorphism  has  been  observed  by  Kolliker  to  occur 
extensively  among  the  Pennatulidce.  Each  zoanthodeme 
presents  at  least  two  different  sets  of  zooids,  some  being 
fully  developed,  and  provided  with  sexual  organs,  while  the 
others  have  neither  tentacles  nor  generative  organs,  and 


162   THE  ANATOMY  OF  IKTBBTEBSATED  ANIMALS. 

exhibit  some  other  peculiarities.*  These  abortive  zooids 
are  either  scattered  irregularly  among  the  others  {e,g, 
Sarcophyton,  Veretillum),  or  may  occupy  a  definite  position 
{e.g.  Vtrgtdaria). 

In  the  other  chief  division  of  the  CaraUigena — ^the  Hexa- 
ecraUa — ^the  fundamental  number  of  enterocode  chambers 
and  of  tentacles  is  six,t  and  the  tentacles  are,  as  a  rule, 
rounded  and  conical,  or  filiform. 

The  Actinozoon  developed  from  the  egg  in  some  of  the 
Heooaeoralla  remains  simple,  and  attains  a  considerable  size. 
Of  these — the  Actinidm — many  are  to  some  extent  loco- 
motive, and  some  (Minyaa)  float  freely  by  the  help  of  their 
contractile  pedal  region.  The  most  remarkable  form  of  this 
group  is  the  genus  CereanthtUy  which  has  two  circlets,  each 
oomposed  of  numerous  tentacles,  one  immediately  around 
the  oral  aperture,  the  other  at  the  margin  of  the  disk. 
The  foot  is  elongated,  subcorneal,  and  generally  presents 
a  pore  at  its  apex.  Of  the  diametral  folds  of  the  oral 
aperture,  one  pair  is  much  longer  than  the  other,  and  is 
produced  as  far  as  the  pedal  pore.  The  lalra  is  curiously 
like  a  young  hydrozoon  with  four  tentacles,  and,  at  one 
time,  possesses  four  mesenteries. 

The  Zoan^idoR  differ  from  the  AcHnidib  in  little  more 
than  their  multiplication  by  buds,  which  remain  adherent, 
either  by  a  common  connecting  expansion  or  by  stolons; 
and  in  Uie  possession  of  a  rudimentary,  spictllat,  skeleton. 
In  thd  AntipaihidoR  there  is  a  sclerobasio  dceleton.  The 
proper  stone-corals  are  essentially  ActinioBy  which  Ibieoome 
converted  into  zoanthodemes  by  gemmation  or  fission,  and 
develope  a  continuous  skeleton. 

The  skeletal  parts  ^  of  all  the  AciinoMoa,  consist  either  of 
a  substance  of  a  homy  character ;  or  of  an  organic  basis 
impregnated  with  earthy  salts  (chiefly  of  Ume  and  mag- 
nesia), but  which  can  be  isolated  by  the  action  of  dilute 

*  *  Abhandlungen  der  Senken-  they  are  either  six  or  some  mul- 

bergiaohen  N  atunonohenden  Ge-  tiple  of  dz. 

telltolMlt,'  fid.  vU.  viii.  1  See  KdlUker,  *Ieoiiet  Histo- 

t  That  It  to  M7,  in  the  adult,  logioii,'  16^ 


THB  ACTIHOZOA.  163 

acids ;  or  finall j,  of  caJoareous  salts  in  an  almost  crystalline 
state,  forming  rods  or  corpuscles,  which,  when  treated  with 
acids,  leaye  onlj  an  inappreciable  and  stractnreless  film  of 
organic  matter.  The  hard  parte  of  all  the  Aporo8a,  Pefforaia, 
and  7}abHlaia  of  Milne-Edwards  are  in  the  last-mentioned 
condition;  while,  in  the  OetocoraUa,  except  TkfnporOf  and 
in  the  Ani^paihidcB,  and  Zoanihidcs,  among  the  HetoaeoraUa, 
the  skeleton  is  either  homy ;  or  ocmsists,  at  any  rate,  to 
begin  with,  of  definitely  formed  spicBla,  which  contain  an 
organic  basis,  and  frequently  present  a  laminated  stmcture. 
In  the  organ  coral  {Tubipora),  the  skeleton  has  the  character 
of  that  of  the  ordinary  stone-corals,  except  that  it  is  per- 
forated by  numerous  minute  canals. 

The  skeleton  api>ear8,  in  all  cases,  to  be  deposited  within 
the  mesoderm,  and  in  the  intercellular  substance  of  that 
layer  of  the  body.  Eyen  the  definitely  shaped  spicula  of 
the  Oetoeorcdla  seem  not  to  result  from  the  metamor- 
phosis of  cells.  In  the  simple  aporose  corals  the  calcifica- 
tion of  the  base  and  side  walls  of  the  body,  gives  rise  to 
the  cup  or  theca ;  from  the  base  the  calcification  extends 
upwards  in  lamellsB,  which  correspond  with  the  interspaces 
between  the  mesenteries,  and  gires  rise  to  as  many  vertical 
tepta,^  the  spaces  between  which  are  termed  loeulii  while, 
in  the  centre,  either  by  union  of  the  septa  or  indepen* 
dently,  a  column,  the  eolumeUa,  grows  up.  Small  separate 
pillars  between  the  columella  and  the  septa  are  termed 
pahUL  From  the  sides  of  adjacent  septa  scattered  processes 
of  calcified  substance,  or  aignapHculmy  may  grow  out  toward 
one  another,  as  in  the  Fungidm ;  or  the  intermption  of  the 
cavitiee  of  the  loculi  may  be  more  complete  in  consequence 
of  the  formation  of  shelves  stretching  from  septum  to 
septom,  but  lying  at  diiferent  heights  in  adjacent  loculi. 
These  are  inienepUd  dissepimenU,  Finally,  in  the  TabukUa, 
horizontal  i^tes,  which  stretch  completely  across  the  cavity 
of  the  theca,  are  formed  one  above  the  other  and  constitute 
idMar  di$$epimeni9. 

*  Lsssse-Diitfaien'  invettieations  on  Astrtsa  ecilycularU  prove  th&t 
te  septa  b^gin  to  b«  funned  belbre  the  theoa. 


164   THB  ANATOMY  OF  IKYSBTEBRATED  AKHCALS. 

In  the  Aporosa  the  theca  and  septa  are  almoet  inyariablj 
imperforate ;  but,  in  the  Perforata,  they  present  apertures, 
and,  in  some  Madrepores,  the  whole  skdeton  is  reduced  to  a 
mere  network  of  dense  calcareous  substance.  When  the 
HexacoraUa  multiply  bj  gemmation  or  fission,  and  thus 
give  rise  to  compound  massive  or  arborescent  aggregations, 
each  newlj-f ormed  coral  polype  developes  a  skeleton  of  ita 
own,  which  is  either  confluent  with  that  of  the  others,  or  is 
united  with  them  by  calcification  of  the  connecting  sub- 
stance of  the  common  body.  This  intermediate  skeletal 
layer  is  then  termed  eoeneMiihyiMi, 

The  septa  in  the  adult  Hexacoralla  are  often  yery  numerous 
and  of  different  lengths,  some  approaching  the  c^itre  more 
closely  than  others  do.  Those  of  the  same  lengths  are 
members  of  one '  cycle; '  and  the  cycles  are  numbered  accord- 
ing to  the  lengths  of  the  septa,  the  longest  being  counted 
as  the  first.  In  the  young,  six  equal  septa  constitute 
the  first  cycle.  As  the  coral  grows,  another  cycle  of  six 
septa  arises  by  the  development  of  a  new  septum  between 
each  pair  of  the  first  cycle ;  and  then  a  third  cycle  of  twelve 
septa  divides  the  previously  existing  twelve  interseptal 
chambers  into  twenty-four.  If  we  mark  the  septa  of  the 
first  cycle  A,  those  of  the  second  B,  and  those  of  the  third 
0,  then  the  space  between  any  two  septa  (AA)  of  the  first 
cycle  will  be  thus  represented  when  the  third  cycle  is 
formed— A  G  B  C  A. 

When  additional  septa  are  developed,  the  fourth  and 
following  cycles  do  not  consist  of  more  than  twelve  septa 
each ;  hence  the  septa  of  each  new  cycle  appear  in  twelve 
of  the  previously  existing  interseptal  spaces,  and  not  in  all 
of  them  ;  and  the  order  of  their  appearance  follows  a  definite 
law,  which  has  been  worked  out  by  Milne-Edwards  and 
Haime.  Thus,  the  septa  of  the  fourth  cycle  of  twelve  (d) 
bisect  the  interseptal  space  A  C;  and  those  of  the  fifth 
cycle  (e)  the  interseptal  space  B  G ;  the  septa  of  the  sixth 
cycle  (f),  A  d  and  d  A ;  those  of  the  seventh  cycle  (g),  e  B 
and  B  e ;  those  of  the  eighth  cycle  (h),  d  G  and  G  d ;  and 
those  of  the  ninth  cycle  (i),  G  e  and  e  C. 


THB  '^TABUULTA.  165 

Henoe,  after  the  f onnation  of  nine  c jclee,  the  septa  added 
between  every  pair  of  primary  septa  (A,  A)  will  be  thus 
arranged — ^A  fdhOiegBgeiOhdf  A.* 

The  stone-corals  ordinarily  known  as  MiUeporet  are 
characterised  by  being  traversed  by  numerous  tubular 
cayities,  which  open  at  the  surface,  and  the  deeper  parts  of 
which  are  divided  by  numerous  close-set  transverse  par- 
titions, or  tabtUar  diM^fnmenU,  while  vertical  septa  are 
rudimentary  or  altogether  absents  These  were  regarded 
as  Anihosoa,  and  classed  together  in  the  division  of  Tahidaia, 
until  the  elder  Agassiz  f  published  his  observations  on  the 
living  MiUepora  aleicomiM,  which  led  him  to  the  conclusion 
that  the  Tabulata  are  Hydrozoa  allied  to  HydracUnia,  and 
that  the  extinct  Btigoaa  were  probably  of  the  same  nature. 

The  evidence  adduced  by  Agassiz,  however,  was  insuffi- 
cient to  prove  his  conclusions;  and  the  subsequent  dis- 
covery by  Yerrill  that  another  tabulate  coral,  PociUopora,  is 
a  true  Hexacorallan,  while  Moseley  ^  has  proved  that  Selio- 
pora  ccarviea  is  an  Octocorallan,  gave  further  justification 
to  those  who  hesitated  to  accept  Agassiz'  views. 

The  recent  very  thorough  and  careful  investigation  of  a 
species  of  Millepora  occurring  at  Tahiti,§  by  Mr.  Moseley, 
although  it  still  leaves  us  in  ignorance  of  one  important 
point,  namely,  the  characters  of  the  reproductive  organs, 
yet  permits  no  doubt  that  Millepora  is  a  true  Hydrozoon 
allied  to  Hydr<MeHniaf  as  Agassiz  maintained.  The  surface 
of  the  living  MiUepora  presents  short,  broad  hydranths, 
the  mouth  of  which  is  surrounded  by  four  short  tentacles. 
Around  each  of  these  alimentary  zooids  is  disposed  a  zone 
of  from  five  to  twenty  or  more,  much  longer,  mouthless 
zooids,  over  the  bodies  of  which  numerous  short  tentacles 
are  scattered.     Each  of  these  zooids  expands  at  its  base 

*  That  the  order  of  oecarrence  United  States/  vols.  ill.  and  iv., 

of  the  septa  of  various  lengths,  at  1 860-62. 

the  different  stages  of  growth  of  %  Moseley,  **  The  Stnictare  and 

a  oorallite,  is  that  indicated,  seems  Relations   of    the    Alcyonarian, 

to  be  clear,  whatever  may  be  the  Heliopora  earulea^*  &c.      (Proc. 

exact  mode  of  development  of  the  Royal  Society,  Nov.  1875.) 

seirta  in  each  cycle.  §  Proceedings   of    the   Royal 

t  *Matacal     History    of    the  Society,  1876. 


166       THE  ANATOMY  OF  nfYSBTEBRATED  ANIMALS. 

into  a  dilatation,  whence  tabular  processes  proceed,  whicli 
ramify  and  anastomose,  giving  rise  to  a  thin  expanded 
hydrosoma.  The  calcareous  matter  (composed  as  usual  of 
carbonate,  with  a  small  proportion  of  phosphate,  of  lime) 
forms  a  dense  oontinuous  crust  upon  tiie  ectoderm  of  the 
ramifications  of  the  h  jdrosoma,  that  part  of  it  which  under- 
lies the  dilatations  of  the  zooids  constituting  the  septa. 
As  the  first  formed  hjdrosomal  expansion  is  completed, 
another  is  formed  on  its  outer  surface,  and  it  dies.  The 
^  thecal "  canals  of  the  coral  arise  from  the  correspondence 
in  position  of  the  dilatations  of  the  zooids  of  successiye 
hydrosomal  lay^:^  and  the  tabula  are  their  supporting 
plates. 

Thus  the  group  of  the  Tabulaki  ceases  to  exist,  and  its 
members  must  be  gprouped  either  with  the  HexacoraUa,  the 
Odocoralla,  or  the  ffydrozwi. 

The  Bugoaa  constitute  a  group  of  extinct  and  mainl j 
Palffiozoic  stone->corals,  the  thecsa  of  which  are  provided 
with  tabular  diss^iments,  and  generally  have  the  septa  less 
developed  than  those  of  the  ordinary  stone-corals.  The 
arrangement  of  the  parts  of  the  adult  Bugoaa  in  fours,  and 
the  bilateral  symmetry  which  they  sometimes  exhibit,  are 
interesting  peculiarities  when  taken  in  connection  with  the 
tetramerous  and  asymmetrical  states  of  the  embryonic 
HewacoriiUa.  On  the  other  hand,  some  of  the  Btigoaa  possess 
opercula,  which  are  comparable  to  the  skeletal  appendages 
of  the  Alcyonarian  Primnoa  observed  by  Lindstrom,  and 
the  tetramerous  arrangement  of  their  parts  suggests  affinity 
with  the  OdocaraUa.  It  seems  not  improbable  that  these 
ancient  corals  represent  an  intercalary  type  between  the 
HexacoraUa  and  the  OetocoraUa. 

All  the  Actinoaoa  are  marine  animals.  The  AcHnicB, 
among  the  HexacoraUa,  and  various  forms  of  Oetoeonilla, 
have  an  exceedingly  wide  distribution,  while  the  latter  are 
found  at  very  great  depths. 

The  stone-corals,  again,  have  a  wide  range,  both  as  re- 
spects depth  and  temperature,  but  they  are  most  abundant 


THE  BSBF-BinLDDrO  CO&AL8.  167 

in  hot  seas,  and  many  are  confined  to  sncli  regions.  Some 
of  these  stone-corals  are  solitary  in  habit,  while  others  are 
social,  growing  together  in  great  fields,  and  forming  what 
are  called  "  coral  reefs."  The  latter  are  restricted  within 
that  comparatively  narrow  zone  of  the  earth's  surface 
which  lies  between  the  isotherms  of  60°,  or,  in  other  words, 
they  do  not  extend  for  more  than  about  dO°  on  either  side 
of  the  equator.  It  is  not  conditions  of  temperature  alone, 
however,  which  limit  their  distribution;  for,  within  this 
sone,  tiie  reef-builders  are  not  found  alive  at  a  gpreater 
depth  than  from  fifteen  to  twenty  fathoms,  while,  at  the 
equator,  an  average  temperature  of  68°  is  not  reached 
within  a  depth  of  100  fathoms. 

Not  only  heat,  then,  but  light,  and  probably  rapid  and 
effectual  aeration,  are  essential  conditions  for  the  activity 
of  the  reef -building  Aaiinonotu  But,  even  within  the  coral 
SBone,  the  distribution  of  the  reef -builders  appears  to  be 
singularly  capricious.  None  are  found  on  the  west  coast 
of  Africa,  very  few  on  the  east  coast  of  South  America,  none 
on  the  west  coast  of  North  America ;  while  in  the  Indian 
Ocean,  the  Pacific,  and  the  Caribbean  Sea,  they  cover 
thousands  of  square  miles.  It  is  by  no  means  certain,  how- 
ever, that  any  one  species  of  West  India  reef  coral  is 
identical  with  any  East  Indian  species,  and  the  corals  of 
the  central  Pacific  differ  very  considerably  from  those  of 
the  Indian  Ocean. 

Different  species  of  Corals  exhibit  great  differences  as 
to  the  rapidity  of  their  growth,  and  the  depth  at  which 
they  flourish  best ;  and  no  one  must  be  taken  as  evidence 
for  another  in  these  respects.  Certain  species  of  Perforata 
(Mad/reporid(B  and  PoritidoR)  appeal*  to  be  at  once  the  fastest 
growers,  and  those  which  delight  in  the  shallowest  waters. 
The  AMtrteida  among  the  Aporosa,  and  SerUxtopora  among 
the  TalnUaia,]iye  at  greater  depths,  and  are  probably  slower 
of  increase. 

Under  the  peculiar  conditions  of  existence  which  have 
just  been  described,  it  would  seem  easy  enough  to  compre- 
hend, d  priori,  the  necessary  arrangement  of  cot«1  tq^^. 


168       THE  ANATOMY  OF  INTBBTSBSATXD  ANDCALfi. 

As  the  Teet'hxnlding  Adinotoa  cannot  live  at  greater  depths 
than  twenty  fathoms,  or  thereabouts,  it  is  clear  that  no 
reef  can  be  originallj  formed  at  a  greater  depth  below  the 
surface,  and  such  a  depth  usually  implies  no  very  great 
distance  from  land.  Furthermore,  we  should  expect  that 
the  growth  of  the  coral  would  fill  up  all  the  space  between 
the  shore  and  this  furthest  limit  of  its  gprowth;  so  that 
the  shores  of  coral  seas  would  be  fringed  by  a  sort  of 
fiat  terrace  of  coral,  covered,  at  most,  by  a  very  few  feet 
of  water;  that  this  terrace  would  extend  out  until  the 
shelving  land  upon  which  it  had  grown  descended  to  a 
depth  of  some  twenty  fathoms;  and  that  then  it  would 
suddenly  end  in  a  steep  wall,  the  summit  and  upper  parts 
of  which  would  be  crowned  with  overhanging  ledges  of 
living  coral,  while  its  base  would  be  hidden  by  a  talus  of 
dead  fragments,  torn  off  and  accumulated  by  the  waves« 
Such  a  "fringing  reef"  as  this,  in  fact,  surrounds  the 
island  of  Mauritius.  The  beach  here  does  not  gradually 
shelve  down  into  the  depths  of  the  sea,  but  passes  into  a 
flat,  irregular  bank,  covered  by  a  few  feet  of  water,  and 
terminating  at  a  greater  or  lees  distance  from  the  shore  in 
a  ridge,  over  which  the  sea  constantly  breaks,  and  the 
seaward  face  of  which  slopes  at  once  sheer  down  into 
fifteen  or  twenty  fathoms  of  water. 

The  structure  of  a  fringing  reef  varies  at  different 
distances  from  the  land,  and  at  different  depths  in  its  sea- 
ward face.  The  edge  beaten  by  the  surf  is  composed  of 
living  masses  of  Forties,  and  of  the  coral-like  plant,  the 
Nullipore ;  deeper  than  this  is  a  zone  of  Aporosa  (AstrceidiB), 
and  of  Millepores  (Seriatopara) ;  while,  deeper  still,  all  living 
coral  ceases;  the  lead  bringing  up  either  dead  branches,  or 
showing  the  existence  of  a  flat  gently  sloping  floor,  the 
true  sea-bottom,  covered  with  fine  coral-sand  and  mud. 
Passing  from  the  edge  of  the  reef  landwards,  the  Foritidm 
cease,  and  are  replaced  by  a  ridge  of  agglomerated  dead 
branches  and  sand,  coated  with  Nullipore ;  the  floor  of  the 
shallow  basin,  or  "  lagoon,"  enclosed  between  the  reef  and 
the  land,  is  formed  by  a  conglomerate,  composed  of  frag- 


FBINOIKO  BEBF8.     ATOLLS.  16^ 

ments  of  coral  cemented  bj  mud ;  and,  on  tliis,  Meandrince 
and  FitnguB  rest  and  flourish,  exhibiting  the  most  gaudj 
coloration,  and  sometimes  attaining  a  great  size.  During 
storms,  masses  of  coral  are  hurled  on  to  the  floor  of  the 
lagoon,  and  there  gradually  increase  the  accumulation  of 
rocky  conglomerate ;  but  in  no  other  way  can  a  fringing 
reef,  which  has  once  attained  its  limit  in  depth,  increase 
in  size,  unless,  indeed,  the  talus  accumulating  at  the  foot 
of  its  outer  wall  should  esver  rise  sufficiently  high  to  afford 
a  footing  for  the  corals  within  their  prescribed  limits  of 
depth. 

Such  is  the  structure  of  a  fringing  reef;  but  the  g^reat 
majority  of  reefs  in  the  Pacific  are  very  different  in  their 
character.  Along  the  north-eastern  coasts  of  New  Holland, 
for  instance,  a  vast  aggregation  of  reefs  lies  at  a  distance 
from  the  shore  which  varies  from  a  hundlfed  to  ten  miles  ; 
forming  a  mighty  wall  or  barrier  against  the  waves  of 
the  Pacific.  At  a  few  hundred  yards  outside  this  "  barrier 
reef  "  no  bottom  can  be  obtained  with  a  sounding  line  of  a 
thousand  fathoms ;  between  the  reef  and  the  main  land,  on 
the  contrary,  the  sea  is  hardly  ever  more  than  thirty 
fathoms  deep.  Many  of  the  islands  of  the  Pacific,  again, 
are  encircled  with  reefs  corresponding  exactly  in  their 
character  with  the  barrier  reef;  separated,  that  is,  by  a 
relatively  shallow  channel  from  the  land,  but  facing  the 
sea  with  an  almost  perpendicular  wall  which  rises  from 
a  very  great  depth. 

Finally,  in  many  cases,  especially  among  the  single  reefs, 
which  taken  together  constitute  the  great  Australian 
barrier,  there  is  no  trace  of  any  central  island;  but  a 
circular  reef,  usually  having  an  opening  on  its  leeward 
side,  stands  out  in  the  midst  of  the  sea.  These  reefs, 
apparently  unconnected  with  other  land,  are  what  are 
called  "  Atolls." 

How  have  these  barrier  reefs,  encircling  reefs,  and  atolls 
been  formed  P  It  is  certain  that  the  fabricators  of  these 
reefs  cannot  live  at  a  greater  depth  than  in  the  fringing 
reefs.    How  can  they  have  grown  up,  then,  from  a  tbowsasA 


170       THB  ANATOMY  OF  INTBBTEBSATED  AKDCALS. 

fathoms  or  more?  Why  do  they  take  so  generally  the 
circular  form?  What  is  the  connexion,  finally,  between 
fringing  reefs  and  atolls  P  The  only  thoroughly  satis- 
factory answer  to  these  questions  has  been  given  by 
Mr.  Darwin,  from  whose  beautiful  work  on  Coral  Beefs 
I  have  borrowed  most  of  the  f or^;oing  details.  Consider 
for  a  moment  what  would  be  the  effect  of  a  slow  and 
gradual  submergence  of  the  island  of  Mauritius — a  sab- 
mergence,  perhaps,  of  a  few  feet  in  a  century  (at  any  rate, 
not  greater  than  the  rate  of  upward  growth  of  ooral) 
continued  for  age  after  age.  As  the  edge  of  the  fringing 
reef  sank,  new  coral  would  grow  up  from  it  to  the  surface ; 
and,  as  the  most  active  and  important  of  the  reef-buildera 
flourish  best  in  the  very  surf  of  the  breakers,  so  the  margin 
of  the  reef  would  grow  faster  than  its  inner  portion,  and 
the  discrepancy  would  increase  as  the  latter,  Rinking  deeper 
and  deeper,  became  further  removed  from,  the  iregion  of 
active  growth^  Nevertheless,  th^  sea-bottom  within  the 
reef  would  constantly  tend  to  be  raised  by  the  accumulation 
of  fragments,  and  by  the  deposit  of  fine  mud,  in  its  sheltered 
and  comparatively  calm  waters.  On  the  other  hand,  on  the 
seaward  face  of  the  reef,  no  possible  extension  could  take 
place  by  direct  growth ;  and  that  by  accumulation  must  be 
exceedingly  slow,  the  incessant  wash  of  tides,  waves,  and 
currents  tcoiding  incessantly  to  spread  any  talus  over  a  wider 
and  wider  area. 

Thus,  then,  the  edge  of  the  reef  imceasingly  compensates 
itself  for  the  depression  which  it  undergoes,  while,  inside 
the  reef,  only  a  partial  compensation  takes  place,  and, 
outside,  hardly  any  at  all.  Continue  the  sinking  process 
until  its  highest  peak  was  but  a  few  hundred  feet  above 
the  surface,  and  all  that  would  be  left  of  Mauritius  would 
be  an  island  surrounded  by  an  encircling  reef;  carry  on 
the  depression  further  still,  and  a  circular  reef,  or  atoll, 
alone  would  remain.  But  the  region  of  the  coral  reefs  is, 
for  the  most  part,  that  of  constant  winds.  During  the 
whole  process  of  growth  of  the  reef,  therefore,  one  of  its 
sides — ^that  to  windward — has  been  exposed  to  more  surf 


ANCIBirr  SEBFS.  171 

tlian  that  to  leeward.  Not  only  will  the  (greater  quantity 
of  debria,  therefore,  have  been  heaped  up  bj  stormB  upon 
the  windward  side,  but  the  coral  builders  tiiemselyes  will 
here  have  been  better  fed,  better  aerated,  and  conaequentlj 
more  active.  Hence  it  is  that,  other  things  being  alike, 
there  is  a  probability  that  the  leeward  side  of  the  reef  will 
grow  more  slowly,  and  repair  any  damages  less  easily,  than 
the  windward  side ;  and  hence,  again,  as  a  result,  the  known 
fact,  that  the  practicable  channels  of  entrance  into  encir- 
cling reefs  or  atolls  are  usually  to  leeward. 

The  winds  and  waves  are  singularly  aided  in  g^rinding 
down  the  oorals  into  mud  and  fragments,  by  the  Seari  and 
HiMhiuruB  which  haunt  the  reefs;  the  former  browsing 
upon  the  living  Polypes  with  their  hard  and  parrot-like 
jaws,  and  passing  a  fine  calcareous  mud  in  their  excrements ; 
the  latter,  more  probably,  swallowing  only  the  smaller  frag- 
ments and  mud,  and,  having  extracted  from  them  such 
nourishment  as  they  may  contain,  casting  out  a  similar 
product.  It  is  curious  to  reflect  upon  the  similarity  of  action 
of  these  wormlike  Holothurica  upon  the  sea-meadows  of 
coral,  to  that  which  the  Earthworms,  as  Darwin  has  shown, 
exert  upon  our  land  meadows ! 

In  the  FalsBozoic  period,  reefs  like  those  which  have  just 
been  described  appear  to  have  aboimded  in  our  own  lati- 
tudes ;  and  there  is  the  most  striking  superficial  resemblance 
between  the  ancient  beds  of  calcareous  rock  which  record 
their  existence,  and  the  masses  of  coral  limestone,  hard 
enough  to  clink  with  a  hammer,  which  are  now  being  formed 
in  the  Pacific,  by  the  processes  of  accumulation  of  coral- 
mud  and  fragments,  and  their  consolidation  by  percolating 
water.  Closer  examination,  however,  shows  an  important 
difference  in  the  nature  of  the  corals  which  compose  the 
two  reefs.  The  modem  limestones  are  made  up  of  Per- 
foraia,  Millepores,  and  Aporosa.  The  ancient  ones  contain 
MilleporeB,  but  usually  neither  Perforaia  nor  Aporo»a, — ^both 
these  groups  being  replaced  by  the  Bugoaa,  none  of  whose 
members  (with  some  doubtful  exceptions)  have  survived  the 
Palfldozoio  period.     On  the  other  hand,  Paksoc^elus  «xl<\ 


17:2   THE  ANATOMY  OF  IN VERTEBRATED  ANIMALS. 

Pleurodictyon  are  the  onlj  genera,  belonging  to  the  Aporosa 
or  PefforcUa,  which  have  jet  been  discoyered  in  strata  of 
greater  than  mesozoic  age. 

The  CteKophosa.* — These  are  freelj  swimming  marine 
animals,  which  never  give  rise  by  gemmation  to  componnd 
organisms,  and  are  always  of  a  soft  and  gelatinous  consist* 
ence,  their  chief  bulk  being  made  up  by  the  greatly  de- 
veloped mesoderm.  Many  are  oval  or  rounded  {Berde,  PUw 
rohrachia,  Fig.  31),  while  in  others  the  body  is  produced  into 
lobes  {Callianira),  or  may  even  be  ribbon-shaped  {Cegtwn) ; 
but,  whatever  their  form,  they  present  a  distinct  bilateral 
symmetry,  similar  parts  being  disposed  upon  opposite 
sides  of  a  median  plane,  which  is  traversed  by  the  axis 
of  the  body.  The  mouth  is  situated  at  one  end  of  this 
axis,  which  may  be  termed  the  oral  pole.  At  the  opposite, 
or  aboral  pole,  there  is  no  median  aperture,  but  usually, 
if  not  invariably,  a  pair  of  apertures  a  short  distance 
apart  The  faces  of  the  halves  of  the  body  present  four 
longitudinal  bands  of  long  and  strong  cilia,  disposed  in 
transverse  rows,  like  so  many  paddles ;  these  constitute  the 
chief  organs  of  locomotion.  Each  half  is  also  often  provided 
with  a  long  retractile  tentacle ;  and  lobed  processes  of  the 
body,  or  non-retractile  tentacula,  may  be  developed  on  its 
oral  face.  The  mouth  leads  into  a  wide,  but  flattened, 
gastric  sac,  the  aboral  end  of  which  is  perforated,  and  leads 
into  a  chamber  termed  the  infundihulwm.  From  the  aboral 
face  of  this,  a  canal  which  bifurcates,  or  two  canals,  lead  to 
the  aboral  apertures.  On  opposite  sides  of  the  inf  undibulum 
a  canal  is  given  off  towards  the  middle  of  each  half  of  the 
body,  which  sooner  or  later  divides  into  two,  and  these  two 
again  subdivide,  so  that  four  canals,  which  diverge  and 
radiate  towards  the  inner  faces  of  the  rows  of  paddles,  are 

*  Allman  (*  Monograph  of  the  part  from  the  conclusion  to  which 

Tubularian  Hydroida,'  1871,  p.  3)  i  woe  led  by  the  study  of  the 

conaidera  that  the  CUnaphora  are  structure  of  Fleurobrachioj  many 

more  properly  arranged  among  years  ago,  that  the  Ctenophora  are 

the  Jfytm^xoa.     I  confess,  how-  peculiarly  modified  Adinotoa^ 
ever,  that  I  tee  no  reason  to  de- 


THE  CIZMOPHOB^  173 

rentually  formed.     Having  readied   tKe    Borface,   eocli 

adiatiiig  can&l  enters  a  longitudinal  canal,  which  Tinderiiea 

he  row  of  paddles,  and  ma;  give  off  branches,  or  unite 

rith  the  o^er  longitudinal  canals  in  a  circular  canal  at  the 

boral  end  of  the  bodj.    In  addition,  two  other  canals,  which 

on  parallel  with  each  flat  face  of  the  gastric  sac,  open  into 

be  infundibulum.    And,  when  retractile  tentacnla  are  pre- 

ent.  their  cavities  also  communicate  with  the  unie  chamber. 

The  entire  Byatem  of  canals  is  in  free  communication  with 

he  gastric  cavity,  and  corresponds  with  the  enteroocele  of 

n  AMnia.    Indeed,  an  Actinia  with  onlj  eight  mesenteries, 

nd  these  exceedingly  thick,  whcrebj  the  intermesenteric 

hambera  would  be  reduced  to  canals;   with  two  nboral 

ores  instead  of  the  one  pore,  which  ciistg  in  Csreanlhtu ; 

nd   with   eight   bands   of    cilia    corresponding   with   the 

tduced    intermesenteric   chambers,   would   have    all   the 

sential  peculiarities  of  a  Ctcnophoran. 

The  question  whether  the  Clenophora  pOBsess  a  nervoua 

item  or  not  ia  still  under  debate.    Between  the  aboral 

irturea  there  ia  a  rounded  cellular  body,  on  which  there 

«at«d,  in  manj  ciiscs,  a  sac  cuntaining  solid  particles, 

one  of  the  lithocjeta  of  the  medusiform  Hydrotoa.     I 

10  reason  to  doubt  that  the  rounded  body  is  a  ganglion 

the  sac  a  rudimentary  auditory  oi^an.    Bands  which 

.te  from  the  ganglion  to  the  rows  of  paddles  may  be 

^ded  as  nerves;  though  they  may  contain  other  than 

ns  stmctnres.* 

ant  originally  cleicrihed 

■"       .Md  rid|t,  whei 


IfMiglion.    Aght- 
lon  hu    not  bpon    vcri-       hnnd,  htse  denied  ll 


UdbI  cordi  proceeiierl  in 
(_Plairolrracliia),  but  hi* 

BtwequflnC  inveelignlorB.  ii*«™nces  described  (lliough  thej 

f  laUIIne-KdnardBiful-  rcslly    eiiai)    are    jiiatly    Inter- 

otben  (among  vh-irn  1  prcled.     And  agiiQ,  Ihough   IV  - 

idamyicirhtbenerviua  bndf.defcrlhedu  an  otolithic  M 

Hului  of   a   gan[(lirin,  uiidoubLMl])' eiiiti  in  the  poiilii 


railed  whether  it  li  ui  Midllory 
Thtu  prablemt  1i«>t«  'bma  t«- 


174       TRX  UTATOHT  OV  imrXSTXBKATED  JiKHTAXB. 


Th«  on,  and  spennatozoa  ftre  dereloped  in  the  lateral 
walls  <^  the  longitudinal  canak,  which  oorreapond  with  the 
bees  of  the  meeenteriea  in  the  CoraUiggtta,  and  tlie  aezea 
are  nBoallf  united  in  the  «ame  individiuL 

The  deTelopment  of  the  CUnopkorxt  has  recentlj  been 
thorooghlj  investigated  hj  Kowalewakj  and  bj  A. 
Agatrn''  ('  Uemoirs  of  the  American  Aoademj  of  Arts  and 
Scienoee,'  1874). 

Fig.  31. 


IB  of  iU  bnndiM,  ill,  cual  nmnlng  bj  the  ^de  of  tli* 


The  laid  egg  is  contained  in  a  spacioaa  capenle,  and  con- 
aiats  of  an  external  thin  layer  of  protoplasm,  which,  in  lonie 
oanca,  ia  contractile,  inveeting  an  innv  venonlar  aobetaaoe. 


oeatl;  idnrcBllB^cd  with  (MM  nripUos  of  the  Darroiu  tytten 
tmttf  aod  br  the  lid  of  In*  M-  baa  alrtmdr  bcea  ^WUd  ('Ve> 
ftMd  metbodt  of  Mo4«ta  Ullo>      p.  64). 


Uifj,  by  D*.  EtaMC^  wboM  i— 


THE  OTBNOPHOKA.  175 

After  fecundation,  the  vitellas  thus  constitnted  divides  into 
two,  f onr,  and  finally,  eight  masses ;  on  one  face  of  each  of 
these  the  protoplasmic  layer  accumulates,  and  is  divided  off 
as  a  blastomere  of  much  smaller  size  than  that  from  which 
it  arises.  By  repeated  division,  each  of  these  gives  rise  to 
still  smaller  blastomeres,  which  become  distinctly  nucleated 
when  they  have  reached  the  number  of  thirty-two,  and  form 
a  layer  of  cells,  which  gradually  spreads  round  the  large 
blastomeres,  and  invests  them  in  a  complete  blastodermic 
sac.  At  the  pole  of  this  sac,  on  the  face  opposite  to  that  on 
which  these  blastoderm  ceUs  begin  to  make  their  appear- 
ance, an  ingrowth  or  involution  of  the  blastoderm  takes 
place,  which,  extending  through  the  middle  of  the  large 
yelk-masses  towards  the  opposite  pole,  gives  rise  to  the 
alimentary  canaL  This,  at  first,  ends  by  a  rounded  blind 
termination ;  but  from  it,  at  a  later  period,  prolongations 
are  given  off  which  become  the  canals  of  the  enterocoole. 

At  the  opx>osite  pole,  in  the  centre  of  the  region  corre- 
sponding with  that  in  which  the  cells  of  the  blastoderm  first 
make  their  appearance,  the  nervous  ganglion  is  developed 
by  metamorphosis  of  some  of  these  cdils. 

The  invaginated  portion  of  the  blastoderm,  which  gives 
rise  to  the  alimentary  canal,  appears  to  answer  to  the 
hyx)oblast,  while  the  rest  corresponds  with  the  epiblast. 
llie  large  blastomeres  which  become  enclosed  between  the 
epiblast  and  hypoblast  in  the  manner  described,  seem  to 
serve  the  purpose  of  a  food-yelk ;  and  the  space  which  they 
originally  occupied  is  eventually  filled  by  a  gelatinous  con- 
nective tiseue,  which  possibly  derives  its  origin  from  wander- 
ing cells  of  the  epiblast. 

Ib  those  Ctenophora  the  bodies  of  which  depart  widely 
from  tlie  globular  form  in  the  adult  state,  the  young 
undefgo  a  soH  of  metamorphosis  after  they  leave  the  egg, 
and  haive  acquired  all  the  essential  characters  of  the  group 
to  whidi  they  belong. 

As  might  be  expected  from  their  extreme  softness  and, 
perishable  natorey  no  fossil  Ctenophora  toe  known. 


176      THE  ANATOMT  OF  UfYEBTEBRATID  AJTIXALS. 


CHAPTER  IV, 

THE  TUBBELLABIA,  THE  BOTIFEBA,  THE  TBEMATODA, 

AND  THE  CE8TOIDEA. 

The  Tubbellabia. — The  animals  wluch  constitute  this 
gi'oup  inhabit  fresh  and  salt  water  and  damp  localities  on 
land.  The  smallest  are  not  larger  than  some  of  the  hifu* 
soria,  which  they  approach  very  closely  in  appearance, 
while  the  largest  may  attain  a  length  of  many  feet.  Some 
are  broad,  flattened,  and  discoidal,  while  others  are  extremely 
elongated  and  relatively  narrow.  None  are  divided  into 
distinct  segments,  except  the  genns  Alaurifia,  in  which  there 
are  four;  and  the  ectoderm,  which  constitutes  the  outer 
surface  of  .the  body,  is  everywhere  beset  with  vibratile 
cilia*  Bod-like  bodies,  similar  to  those  met  with  in  some 
Infusoria  and  in  many  Annelida,  are  often  embedded  in  its 
substance,  and  in  some  genera  (e.g,,  Microatomum,  Thy$anO' 
poon)  true  thread-cells  occur.  Stiff  sets  project  from  the 
ectoderm  in  some  species. 

The  aperture  of  the  mouth  is  sometimes  situated  at  the 
anterior  end  of  the  body,  sometimes  in  the  middle,  or  towards 
the  posterior  end,  of  its  ventral  face.  In  many,  the  oral 
apei*ture  is  surrounded  by  a  flexible  muscular  Up,  which 
sometimes  takes  on  the  form  of  a  protrusible  proboscis. 

A  deflnite  digestive  cavity  can  hardly  be  said  to  exist  in 
the  lowest  Turbellaria  (e.  g.  Convoluta)  in  which  the  endo- 
dermal  cells  are  not  arranged  in  such  a  manner  as  to  bound 
a  central  alimentary  cavity,  and  the  food  finds  its  way 
through  the  interstices  of  an  endodermal  parenchyma.  In 
the  higher  forms,  the  alimentary  cavity,  which  may  be  simple 
or  ramified,  provided  with  an  anal  aperture  or  without  one, 


THS  TUBBBUaAJUA.  177 

is  lined  by  the  endoderm,  between  which  and  the  ectoderm 
is  an  interspace  more  or  less  completely  occupied  by  the 
connective  and  mnsoolar  tissues  of  the  mesoderm*  Hence 
there  is  no  definite  perivisceral  cavity. 

The  TurbeUaria  possess  vessels  of  two  kinds.  1.  Waier 
veaseUf  which  open  externally  by  one  or  more  pores,  and  are 
cDiated.  When  these  vessels  are  present,  there  are  usually 
two  chief  lateral  trunks,  from  which  many  branches  are 
given  off.  It  is  probable  that  the  ultimate  ends  of  these 
branches  open  into  lacunar  interspaces  between  the  elements 
of  the  tissues  of  the  mesoderm.  2.  Faeud-luBmal  vessels, 
which  appear  to  form  a  closed  system,  usually  consisting 
of  one  median  dorsal  and  two  lateral  trunks,  which  anasto* 
mose  anteriorly  and  posteriorly.  The  walls  of  these  vessels 
are  contractile  and  not  ciliated,  and  their  contents  are 
dear,  and  may  be  coloured.  These  two  systems  of  vessels 
have  been  shown  by  Schulze  to  co-exist  in  TetrasteTiMMi, 
The  nervous  system  consists  of  two  ganglia  placed  in  the 
anterior  end  of  the  body,  from  which,  in  addition  to  other 
branches,  a  longitudinal  cord  extends  backwards  on  each 
side  of  the  body.  In  some  cases,  these  lateral  trunks 
exhibit  ganglionic  enlargements,  from  which  nerves  are 
given  off;  and  they  may  become  approximated  on  the 
ventral  side  of  the  body,  thereby  showing  a  tendency  to 
the  formation  of  the  double  ganglionated  chain  oharacter- 
istio  of  higher  worms.  Most  possess  eyes,  and  some  have 
auditory  sacs.  The  TwrheUaria  are  both  monoecious  and 
dicBcious,  and  the  reproductive  organs  vary  from  the 
utmost  simplicity  of  structure  to  considerable  complexity. 
In  most,  the  embryo  passes  by  insensible  gradations  into 
the  form  of  the  adult,  but  some  undergo  a  remarkable 
metamorphosis. 

The  TwrbeOMria  are  divisible  into  two  groups.  In  the  one, 
the  Aproda,  the  digestive  cavity  is  csBCfd,  having  no  anal 
aperture ;  in  the  other,  the  Proetueha,  it  is  provided  with  an 
anal  opening*  The  two  groups  form  parallel  series,  in.  each 
of  which  organisation  advances,  from  forms  which  are  little 
inore  than  gaatruke  provided  with  reproductive  OT^gBoi&v^ 


178       T0E  ANATOMY  OF  INYXBTIBBATSD  AjriMALS. 

animals  of  relatively  high  organiBation.  In  Uie  simplest  of 
the  Aprocia,  such  as  Macrotlomwm,^  the  oral  opening  is 
devoid  of  any  protrusible  mnscnlar  proboscis,  and  the  ali- 
mentary sac  is  a  siipple  straight  bag.  The  male  and  female 
generative  organs  are  tinited  in  the  same  individual,  and 
each  consists  of  a^i  aggpreg^tion  of  cells ;  which,  in  the 
former  case,  gradually  enlarge,  fil|  with  yelk-gprannles, 
and  become  ova ;  while,  in  the  latter,  they  are  converted  into 
spermatozoa.  The  generative  cells  are  contained  within  a 
sac,  which  opens  externally  by  a  median  pore  on  the  oral 
face  of  the  body,  the  male  apertore  being  posterior  to  the 
female.  The  margins  of  the  male  apertare>  are  produced 
into  a  curved  prominence,  the  penis. 

Those  2Vir5e{toria  which  resemble  if oorosfomtMfi  in  having 
a  straight,  simple  digestiye  cavity,  are  termed  Bhabdoctda, 
They,  for  the  most  part,  possess  a  buccal  proboscis,  which 
is  capable  of  being  protruded  from,  or  retracted  into,  a 
chamber  formed  by  the  walla  of  the  ciroum-oral  region  of 
the  body  (Fig.  32,  c). 

In  some  {e,g,  Protiowwn)  the  anterior  end  of  the  body  is 
provided  with  a  second  hollow  muscular  proboscidiform 
organ,  which  may  be  termed  theyroiiM  probototf. 

In  all  the  higher  rhabdocoelous  TwiMlaria^  the  female 
generative  apparatus  becomes  complicated  by  the  presence 
of  a  special  gland,  the  vUelUmwm  (Fig.  32,  m),  in  which  an 
accessory  vitelline  substance  is  formed.  There  is  a  single  or 
double  germarium  (Fig.  32,  Q,  having  tieariy  the  same  struc- 
ture as  the  ovary  of  MacrosUmwrn,  and  the  ova  are  formed 
in  it  in  the  same  way.  When  detached,  however,  they  con- 
tain no  vitelline  granules;  but  the  two  vitellaria,  which  are 
long  and  simple  or  branched  tubes,  open  into  the  oviduct ; 
and  the  vitelline  matter  which  they  secrete  envelopes  the 
proper  ovum,  and  becomes  more  or  lesb  fused  with  it,  as  it 
passes  into  the  uterine  continuation  of  the  oviduct  connected 
with  the  outer,  or  vaginal,  end  of  the  uterus.  There  is  usually 
a'  spermatheca,  or  receptacle  for  the  s^Uiinal  fluid  (IHg. 

^  E.  Van  Beneden, '  Recherches  tar  la  Coinpotition  et  la  Significa- 
tion ds  rCSnf,*  ld70»  p.  64^ 


a,  Jfc),Bnd  the  e;^,  after  impregnfttioii,  are  eaoloMd  within 

I  h»id  ahell  (Fig.  32,  n).    The  teatee  and  vaaa  defereutiA 

Fij.3a. 


Fig.  »i.—OpiMamiam  (ofW  8abulc«).— a,  OentnU  dsttoq*  t7it«m; 
mBiBvtiauof  ihemUr  vmmI*  waaeanolow  to  it|  A,ni)Mth;c, 
proboauii ;  d,  tNla ;  •,  ran  dalerentia ;  /,  vetianlm  umliulli ;  g, 
poili;  il,  tnafti Rpartnre ;  J,  v^^na;  4,tpennsthM>-,  i,gertD>riaiDi 
-■'-"—• —        -iterei  ■with  two  on,  aulowd  within  th^  bard 


(f^g.  8S,  d,  a)  geQerallj  hare  the  fonn  ot  two  long  tabes. 
The  peoia  is  often  evenible  and  corered  with  epinea  (Pi^. 

a  J). 


180       THS  AVATOMT  OV  nTYBBTXBBATSD  AVIVAL8. 

In  some  genera  a  difference  is  observed  between  the  eggs 
produced  in  summer,  which  have  a  soft  vitelline  membrane, 
and  those  produced  later.  These  so-called  winter  ova  have 
hard  shells. 

The  water-vascular  system  consists  of  lateral  trunks, 
which  open  by  a  terminal  pore,  or  by  many  pores,  and  give 
off  numerous  ramifications.  They  are  not  contractile,  but 
their  inner  surface  is  ciliated. 

Many  of  the  Bhahdoccsia  multiply  by  transverse  fission  ; 
and,  in  the  genus  Caienula,  the  incompletely  separated 
animals  produced  in  this  way  swim  about  in  long 
chains. 

The  vitellus  of  the  impregnated  ovum  undergoes  complete 
yelk-division,  and  the  embryos  pass  directly  into  the  form 
of  the  parent ;  but  the  precise  nature  of  the  steps  of  the 
developmental  process  require  further  investigation.  How- 
ever, there  seems  little  reason  to  doubt  that  the  ectoderm 
and  endoderm  are  formed  by  delamination. 

In  the  remaining  Aprocta,  termed  Dendrocceila,  the  diges- 
tive cavity  gives  off  many  ccBcal,  frequently  branched,  pro- 
cesses into  the  mesoderm,  one  of  which  is  alvrays  median 
and  anterior  (Fig»  38) ;  and  the  mouth  is  always  provided 
with  a  proboscis.  Some  (Proeoiyla)  have  a  frontfd  proboscis, 
and  others  (BdeUwra)  a  posterior  sucker.  The  Miimnla 
commonly  known  as  PlanaritB  belong  to  this  division.  Some 
are  marine,  some  fresh* water,  and  some  terrestrial. 

In  the  fresh-water  forms,  the  female  reproductive  appa- 
ratus has  a  distinct  vitellarium,  as  in  the  higher  Ehab- 
docoda,  and  there  is  only  one  common  genital  aperture. 
But,  in  the  marine  Plancma  (Fig.  33),  there  is  no  vitel- 
larimn ;  the  ovaries  and  testes  are  numerous,  and  scattered 
through  the  mesoderm,  being  connected  with  the  exterior 
by  ramifications  of  the  oviducts  and  of  the  vasa  def  erentia. 
A  ramified  gland,  which  secretes  a  viscid  albumen  or  en- 
velope for  the  eg^,  opens  into  the  vagina,  and  the  female 
is  distinct  from  the  male  'aperture,  Fkmtwia  dUnea  is 
oniseznaL 

In  some  of  the  PIonarMs  there  ure  distinct  water^vaaoalir 


THX  DIHDSOOdl^  181 

cuuJa  of  the  ordinuy  kind ;   but  in  the  land  PlanariuiB* 
two  nearlj  simple  oanalo,  ooonpied  by  a  spongj  tdirae,  and 


,   _, .      ...  ,    :,  cciopb*e»l  oriflce;  d,  itomaeb;  r, 

nmlfloatiom  or  gutrio  rnca;  /,  giDglia;  jr,  teiU*'.  A,  tbIcuIb> 
MBlwdot;  i,  male  ganllml  canal  and  peai*;  4,  ovidaota;  I,  ipSF' 
matbiwal  dlUtatioD  al  tbelrjuncllon  ;  n,  vulva. 

the  connexion  of  which  with   the  exterior  hu    not  been 
obwrred,  occapj  the  place  at  the  water  Teaaeb. 

*  Uemtr,  "  Oa  Un  Anatomy  and  Hlitolon  of  tha  Land  Fknariana 
^rCajiam.'^     (PUUnophloal  Transaclioni,  1873.) 


182       THE  ANATOMY  OF  niYSBTBBRATBD  AJTIMALS. 

The  fresh- water  PlanaricB,  like  the  Mhahdoecda,  undergo 
no  metamorphosis  in  the  coarse  of  their  development ;  and 
the  like  is  tme  of  some  of  the  marine  Dendroccela,  Kefer- 
stein  *  has  carefully  worked  ont  the  development  of  Le^Uh 
plana  (Polyeeli8)4  The  TiteUas  undergoes  division  first 
into  two  and  then  into  four  equal  blastomeree;  next,  from 
one  snrf ace  of  these  four  blastomeres,  four  small  segments 
are,  as  it  were,  pinched  off<  These  divide  rapidly,  and 
form  a  blastoderm,  which  grows  over  the  more  slowly 
dividing  large  segments,  and  eventually  encloses  them.  So 
far,  the  process  is  very  similar  to  that  which  has  been  de^ 
scribed  in  the  Ctenophora.  But  though  Kef  erstein  describes 
and  figures  the  various  stages  by  which  the  globular  ciliated 
embryo  attains  the  form  of  the  adult,  neither  his  descrip** 
tion  nor  the  figures  enable  one  to  say  whether  the  aliment 
tary  cavity  arises  by  delamination  or  by  invagination,  nor 
to  trace  the  mode  of  origination  of  the  buccal  proboscis, 
though  this  organ  is  one  of  the  first  to  make  its  appearance^ 
and  its  aperture  becomes  the  future  mouth* 

In  some  of  the  marine  Planariit,  however,  the  embryo, 
when  it  leaves  the  egg,  differs  very  widely  from  the  adult« 
Johannes  Miiller  described  such  a  larva,  in  which  the  body 
is  provided  with  eight  lobes  or  processes,  one  ventral 
and  median  in  front  of  the  mouth,  three  lateral,  and 
one  dorso-median«  The  edges  of  these  processes  are 
fringed  by  a  continuous  series  of  cilia,  which  pass  from 
one  process  on  to  another,  so  as  to  form  a  complete 
circlet  round  the  bodyi  The  successive  working  of  the 
cilia  forming  this  lobed  transverse  girdle  of  the  body 
produces  the  appearance  of  a  rotating  wheels  as  in  the 
Botifera.  The  eyes  are  situated  on  the  aboral  face  of  the 
embryo,  in  front  of  the  ciliated  circlet,  while  the  mouth 
opens  immediately  behind  it.  As  development  proceeds, 
the  lobes  disappear,  and  the  body  takes  on  the  ordinary 
Planarian  character. 


*  *  Beitrige  sur  Anatolnit  nnd  EntwickelongscMchichte  einiger  See- 
ranarien,'  186S. 


TKB  PBOCTUOKA.  163 

Aa  will  be    seen,  some  of   the  Pnehteha  ttRve  ]axvm 
Fig.  31. 


I,  Mntnl  canglla  of  thg  ngrroui 
c,  ftperture  through  which  the  prabaacii 

--■'—  of  proboscla  ;  e,  poster' 

,  '' /(  ?•   inleitine;   h,  ,__ 

tani  i,  wter-Twdi ;  k,  rh^thiuioaUy  contnoling  Teueii.  (Aflw 
BoIidIm.)  B.  Anterior  extremitv  of  the  everted  proUncis  of  Telra- 
Mimmii,  cihibitiDg  the  prindp*)  tad  the   reserve   atlleu.    (After 


0  the  pwieti 


nmilarlj  provided  with  a  pne-ond  ciUat«d  zone;  Mud  Lbx^» 


184   THE  ANATOMY  OF  INYSBTEBRATED  ANIMALS. 

of  ihe  same  fundamental  type  abound  among  the  poljchsB- 
tou8  Annelida,  the  Echinodermatat  and  the  MoUu9ca. 

The  lowest  ProcUiehti,  such  as  MierogtomMm,  have  no 
frontal  proboscis  (whence  they  are  termed  Arhynehia),  and 
they  differ  very  little  from  the  lowest  Bhabdocoday  save  in 
the  fact  that  there  is  an  anus,  and  that  the  sexes  are 
distinct.  But  all  the  other  Produoha  {Bhfnehoecela,  or 
Nemerteans)  are  provided  with  a  frontal  proboscis,  which 
sometimes  occupies  the  greater  part  of  the  length  of  the  body 
(Fig.  34),  It  has  special  retractor  mnscleB,  and  its  internal 
surface  is  either  merely  papillose,  or  may  possess  a  peculiar 
armature,  consisting  of  a  sharp  chitinoos  style  (Fig.  34,  B). 
There  is  no  buccal  proboscis,  but  the  month  leads  into  a  long, 
straight  intestine,  with  short,  lateral,  cnoal  dilatations.* 

The  Proctttoha  usually  present  only  ihe  pseud-hsmal 
vessels,  though,  as  has  been  mentioned  abore,  Schulze  found 
water-vessels  co-existing  with  them  in  Teiinutmnfna  (Fig.  34). 

The  nervous  system  of  the  Proetueha  is  like  that  of  the 
Aproeta;  but,  in  correspondence  with  the  often  extreme 
elongation  of  the  body,  the  backwardly-prolonged  cords 
are  very  stout.  Moreover,  the  ganglia  are  united  by  an 
additional  commissure  over  the  proboscis,  which  thus  tra- 
verses a  nervous  ring.  In  some,  the  lateral  cords  approach 
one  another  on  the  ventral  aspect  of  the  body,  and  gan- 
glionic enlargements  appear  where  the  nerves  are  given  off, 
thus  presenting  an  approximation  to  the  double  ganglio- 
nated  chain  of  higher  forms. 

In  addition  to  eyes,  almost  all  the  Proetueha  possess  two 
ciliated  fosses,  one  on  each  side  of  the  head  (Fig.  34,  55), 
which  receive  nerves  from  the  ganglia.  Occasionally  two 
otolithic  vesicles  are  attached  to  the  cerebral  ganglia. 

The  Proetueha  are  almost  always  dioBoious.  The  simple 
reproductive  glands  are  lodged  in  the  intervals  between  ihe 
saccular  dilatations  of  the  intestine,  and  the  ova  and  aper- 
matoKoa  nsually  make  their  vray  out  by  the  dehiscence  of 

*  For  the  organisatSon  of  the      toeh*s  elaborate  monogr^h  latelly 
Rhynchoooele      7\irbeUarkL     or      pabliahod  by  the  Bay  Society.   • 
Kemerteanii  set  Dr.  C  Mcln- 


I  rmaanaB^ 


185 


th«  mtegimiant.  In  gome,  howerer,  tbe  embrjoa  are 
derdoped  in  the  onu-iao  aaoa,  or  in  the  oaritf  of  the 
bodj.  Jn  mort  of  ^e  Proetueha,  the  egg,  after  pMsiiig 
through  the  moraU  stage,  aoqnires  an  alimentar;  caritji 
.    Fig  ST..  Fig.  37. 


TT,  Hiwij-tned  Semeneta. 

apgtirttaiij  by  deUminatioD,  and  paaHee,  without  other 
netuaorphoaiB  than  the  shedding  of  a  ciliated  outer 
inreatmaat,  into  the  form  of  the  adult. 


186      THI  AKATOMT  OV  IKTSBTSftftATSD  AVUIAUB. 

Professor  A.  Agassiz*  has  desoribed  a  free-swimming 
larva,  the  broad  anterior  end  of  the  body  of  which  is  sur- 
rounded by  a  zone  of  cilia,  immediately  ;behind  which  the 
mouth  opens ;  while,  around  the  anal  aperture,  at  the  narrow 
posterior  end,  is  a  second  circlet  of  cilia.  IThis  larra  exactly 
resembles  those  forms  of  polychsfftous  Annelidan  lanrsB 
which  are  called  Telatroeha,  As  in  these  Annelids^  the 
region  of  the  body  which  lies  between  the  two  ciliated  rings 
elongates  and  becomes  segmented,  while  a  pair  of  eyes  and 
two  short  tentacles  ore  developed  on  the  head  in  fix>nt  of 
the  prse-oral  ciliated  band.  But,  as  development  adyances, 
the  segmentation  becomes  obliterated,  the  dliated  bands 
and  the  feelers  vanish,  and  the  worm  assumes  the  characters 
of  a  NemerteaUif 

In  species  of  the  genus  Lineua,  the  ciliated  embryo  which 
leaves  the  egg  is  speedily  converted  into  a  body  like  a  helmet 
with  ear-lappets,  and  having  a  tuft  of  cilia  in  place  of  a 
plume  (Fig.  35).  The  lappets  are  fringed  with  long  cilia, 
and  between  them,  where  the  head  would  fit  into  a  helmet, 
is  the  aperture  of  a  mouth,  which  leads  into  a  c»cal  pouch- 
like alimentary  cavity.  This  larva  was  named  by  Miiller, 
who  discovered  it,  PUidium  gyrans.  On  each  side  of  the 
ventral  face  of  the  PUidiwm,  two  involutions  of  the  in- 
tegument take  place.  Aggregations  of  cells  in  relation 
with  these,  and  probably  forming  part  of  the  mesoblast, 
appear,  eventually  enclose  the  alimentary  canal  of  the 
Pilidiunif  and  give  rise  to  an  elongated  veiiniform  body, 
in  which  the  characteristic  features  of  a  Nemertean  soon 
become  discernible  (Fig.  36).  The  worm  thus  developed  be- 
comes detached  (Fig.  37)  and  falls  to  the  bottom,  canying 
with  it  the  alimentary  canal  of  the  Pilidivm,  and  leaving 
the  ciliated  integument  to  perish. 

In  this  remarkable  process  of  development  the  formation 

*  "  On  the  Young  Stages  of  a  an  anncctent  form  between  the 

few  Annelids."     (Annals  of  the  Turbellaria   and    oUier    groupa. 

j.yceum  of  New  York,  1864.)  See  Schneider,  "  Ueber  Baa  and 

f  It  is  very  probable,  however,  Entwickelung  von  Polygordins." 

that  this  larva  belongs  to  the  genus  C*Arohiv  t^i  Anau  mid  Pbytio- 

/'oJj|yo9tit«i,  which  appears  to  be  logic,'  1868.) 


TUE    ROTIFERA.  1^7 

of  the  Nemertean  body  may  be  compared,  on  the  one  hand, 
to  that  of  the  segmented  mesoblast  in  Annelida  and 
Ardkropoda^  and,  on  the  other,  to  that  of  an  Schinoderm, 
EthinuB,)  within  its  larva. 


The  Born^BBA. — ^The  "  wheel-animalcnles,"  as  they  were 
termed  bj  the  older  obserrers,  on  account  of  the  appearance 
of  rotation  produced,  as  in  many  Annelid  larvse,  by  the 
working  of  the  yibratile  cilia  with  which  the  oral  end  of  the 
body  is  provided,  were  formerly  included  among  the  Infu- 
mria,  Hoitevert  they  are  true  MetoKoa,  as  their  vitelluB 
undergoes  division  into  blastomeres,  and  the  tissues  of  the 
body  are  produced  by  the  metamorphosis  of  the  cells  into 
which  the  blastomeres  are  converted*  They  are  free  or  ad- 
herent, but  never  absolutely  fixed  animals,  and  they  do  not 
multiply  by  gemmation  or  fissioui  The  oral  end  of  the 
body  is  usually  broader  than  the  opposite  e^remity,  and 
presents  the  form  of  a  disk,  sometimes  produced  into  ten- 
tacle-like prolongations  (Fig.  39).  The  edges  of  this  troehai 
dUk  are  fring^  With  long  cilia,  but  the  general  surface  of 
the  body,  instead  of  being  ciliated,  as  in  the  TurheUaria,  is 
formed  by  a  dense,  genei^ally  chitinous,  cuticular  layer, 
which  is  sometimes  converted  into  a  kind  of  shell  and 
variously  sculptured*  Transverse  constrictions,  which  are 
slight  in  the  anterior  part  of  the  body,  but  may  become 
more  marked  towards  its  posterior  end,  give  rise  to  an  im- 
perfect segmentation.  The  segments  do  not  appear  to 
exceed  six,  and  the  divisions  are  less  marked  in  the  tubi- 
colous  than  in  the  free  Bot\fera,  The  mouth  is  a  funnel- 
shaped  cavity»  situated  in  the  middle,  or  on  one  side,  of  the 
troohal  disk.  The  walls  of  this  cavity  are  abundantly  cili- 
ated, and  at  the  bottom  is  a  muscular  pharjmx,  or  maHaa, 
provided  with  a  peculiar  armature*  Sometimes,  as  in 
8tephaMOcero9,  a  large  crop<*like  cavity  lies  between  the 
moatli  and  the  mastax,  and  the  aperture  of  communication 
between  this  crop  and  the  mouth  is  guarded  by  a  valve 
formed  by  two  broad  membranous  folds  which  project  into 
the  cavity  of  the  crop.     The  armature  of  the  maatax 


188       THE  ANATOMT  OF  IHYXBTBBKATSD  AKIMAUB. 

g^eraUj  consists  of  four  pieces — ^two  lateral,  the  mai 
and  two  central,  constituting  the  ineu$.  The  contract 
of  the  muscnlar  masses,  to  which  the  mallei  are  attach 
causes  the  free  ends  of  the  latter  to  work  backwarda  f 
forwards  upon  the  incus,  and  crush  the  prey  which 
taken  into  the  mouth.* 

A  short  oesophagus,  proyided  with  ciHa  or  -rihratile  mc 
branee,  leads  into  a  digestiye  cavity  bounded  by  the  eii( 
derm.  The  anterior  or  gastric  part  of  this  cayi^  is  usiu 
dilated,  and  giyes  off  a  large  csBcum  on  each  side.  1 
posterior,  narrower,  intestinal  part  usually  opens  externa 
by  a  cloacal  chamber;  but,  in  some  Rotifers  (e,g.  NoU 
nuUa),  the  alimentary  cavity  is  a  blind  sac,  devoid 
intestine  or  anus;  and  in  the  males,  so  far  as  they  i 
known,  the  whole  alimentary  canal  is  aborted  and  rep 
sented  by  a  solid  cord. 

A  spacious  perivisceral  cavity  occupies  the  inter 
between  the  walk  of  the  alimentary  canal  and  the  parie 
of  the  body.  The  latter  contains  circular  and  longitudi] 
muscular  fibres,  which  may  be  smooth  or  striated. 

Opening  into  the  cloaca  there  is  usually  a  large  th 
walled  vesicle  with  rhythmically  contractile  walls ;  and, 
connexion  with  this,  are  two  delicate  water- vessels,  whi 
pass  forwards,  often  giving  off  short  lateral  branches,  a 
eventually  break  up  into  numerous  ramifications  in  t 
trochal  disk.  The  branches  are  open  at  the  ends,  where 
the  cavities  of  the  water- vessels  are  in  communication  w: 
the  perivisceral  cavity  on  the  one  side,  and  with  the  m 
rounding  water  on  the  other.  Here  and  there,  in  the  con: 
of  the  main  trunks  and  at  the  ends  of  the  branches,  lo 
cilia,  which,  by  their  constant  undulation,  give  rise  tc 
flickering  motion,  are  situated. 

The  nervous  system  is  represented  by  a  relatively  lai 
single  ganglion  placed  on  one  side  of  the  body,  near  i 
trochal  disk.    One  or  more  eyespots  are  sometimes  seal 

*  See,  for  the  ▼arioui  forms  of  loguei  of  the  Mmuducating  A 
this  apperatuB,  Gone,  **On  the  raius  in  the  Matifera/*  (,' 
Straetore,  Fnnetioiia,  and  Homo-      Trans.  1855.) 


189 

on  the  gaoglion,  and  there  are  other  organs  which  appear 
to  be  sensor;.  Sncb  are  the  ciliated  pit  asd  the  spur-like 
proooM  (mfaor)  or  processes,  provided  at  the  end  with  a 
toft  of  Betas,  which  oooor  in  many  Rotifan,  and  are  more 
or  less  cloaelj  connected  with  the  ganglion.  In  Bome  there 
ia  a  sac  filled  with  caloareoos  matter  (otocjst  F)  attached  to 
the  ganglion. 

Fig.  38. 


Fig  3S.— fljnUiu  imla  (•ftgr  Cohn).— A,  tvaala:  a,   uin«;  i,  «Mi- 
tnetUa  *erielg;  «,  waUr  veMeli;  <,  avar;;/,  ganglion.    B,  mate; 
'>TMlola;  ^tMlli;/,gaD)!lton;9,MCigMMiiplt. 


Tb«  ararimn  and  the  testis  are  simple  glands  which  open 
into  Um  doaca,  and  are  always  plaoed  in  distinct  indifidnala. 
All  the  malea  at  present  knowa  difFer  from  the  fomalsB  in 
btttns  mnoh  sm^er,  uid  in  tJieir  digestive  ^^ft|  beins 
■rwited  in  it«  derrfopmait,    ThA  nulaa  cop^Qsite  m^^  ^bb 


190      THI  ANATOMY  OV  nTfSBTlBRATSD  AKIMAL8. 

females,  and  the  eggs  are  sometdmes   attached   to,  and 
carried  about  by,  the  latter — e.g,  Brachionut, 

In  some  Rotifers,  the  eggs  are  distinguishable,  as  in 
certain  TwrbeUaria,  into  wwnmer  and  tinnier  ova.  The 
latter  are  enclosed  In  a  peculiar  shelL  In  Laeimdaria,  it 
appeared  to  me  that  the  winter  oya  were  segregated  portions 
of  the  oyarium,  and  that  they  were  probably  dereloped 
without  impregnation.  Cohn,  on  the  contrary,  has  given 
reasons  for  believing  that  the  summer  ova  are  occasionally, 
if  not  always,  developed  without  fecundation,  and  that  it 
is  the  winter  ova  which  are  fecundated. 

The  egg  undergoes  complete  yelk«division,  and  the  embryo 
gradually  passes  into  the  adult  form.  The  blastomeres  are 
soon  of  unequal  sizes,  and  the  smaller,  as  an  epiblast,  invest 
the  larger,  which  form  the  hypoblast. 

Salensky's  *  recent  observations  on  Braehiontu  ureeolaris 
show  that  a  depresfdon  arises  on  one  face  of  the  epiblaqt  and 
that  the  antero-lateral  parts  of  this  depres^on  are  con- 
verted into  the  trochal  disk,  while  its  mediaii  posterior  part 
grows  out  into  the  "foot;"  and  he  points  out  the  resem- 
blance of  the  embryo  in  its  early  stages  to  that  of  some 
Gasteropoda. 

An  involution  of  the  epiblast  at  the  bottoqi  of  the  depres- 
sion gives  rise  not  only  to  the  oral  chamber,  but  also  to  the 
mastax;  eventually  communicating  with  the  gastro-intes- 
tinal  division,  which  is  developed  out  of  the  hypoblast. 
The  ganglion  is  a  product  of  the  epiblast, 

Some  of  the  modifications  of  the  general  structure  thus 
described  which  occur  in  the  different  groups  of  the  Boti* 
fera  are  of  considerable  interest. 

Thus,  in  the  tubicolous  forms,  the  body  is  elongated  and 
terminated  posteriorly  by  a  discoidal  surface  of  adhesion. 
The  animals  (of  which  a  number  are  often  associated 
together),  fixed  by  this  disk,  enclose  themselves  in  cases,  the 
foundation  of  which  is  a  gelatinous  secretion.  The  intestine 
is  bent  upon  itself  (Laeinularia,  Fig.  39, 11.),  and  opens  upon 
the  face  of  the  body  opposite  to  that  upon  which  the 

•  «2«ltieMft  mt  WiM.  ZoobsiV  1871 


TBI  BOTIFB&l.  191 

ganglion  ia  plaoed.  Tha  p«tdiinole  of  attaohment  ia  theraf ore 
a  prooeaa  <rf  the  uaonl  face  of  the  bod^.  In  these  Bot^wa 
the  troohal  disk  ia  sometimes  prodaced  into  long  ciliated 
t«nt«cala,  vhioh  surround  the  month  symnietricallj  (iSfe- 
phoMOMrM — Pig,  39,  V.)  or  ita  edges  njay  be  provided  with 
two  oireleta  of  ailia,  one  in  front  of,  and  the  other  behind, 
the  ani  aperture ;  and  it  may  be  bilobed  or  horaeshoe-ehaped, 
aa  in  Jfalieorfa  and  ZooHMtlarM*  (Fig.  39, 1.  II.). 

In  the  free  Botifers,  the  bod^  ma^  be  rounded,  sao-like, 
and  deroid  of  appandagea,  aa  in  the  genas  Ai^anehna, 

rig. ». 


which  haa  neither  anas  nor  inteatine.  In  Albtrtia  and 
latuUm,  on  the  other  hand,  the  bodj  ia  elongated  and  venni- 
foim.  Koat  of  the  free  Sot^ferv  (Fig.  38)  are  provided  with 
a  Mgouotad  and  sometimes  telescopicsUj-jointed  "  foot," 
nsnallj  terminated  b;  two  stj'lee,  which  can  be  approximated 
or  dirarioated  like  pincers,  and  serve  to  anchor  the  body. 
Thia  toot  is  »  median  proceaa  of  that  face  of  the  body  which 
ia  o^oaite  to  that  on  which  the  ganglion  ia  placed,  ao  that 


',  LaetnloHn  nttallM.    {TnumeOaat 


F  tiM  MlGiaaeaftcBV 


192       THE  AHATOKT  OV  INYXBTBBBATKD  UriMAUB. 

it  is  not  the  homologae  of  the  peduncle  of  the  tubiooloui 
forms. 

Polyarthra  and  Triarthra  possess  long,  sjmmetricaUy 
arranged,  movably  articulated  set»;  and  PedoHon  has 
median  appendages  proceeding  from  both  the  neural  and 
the  opposite  faces  of  the  body,  as  well  as  lateral  appendages. 

In  most  of  the  free  Botifers  the  trochal  disk  is  large;  it 
may  be  bilobed  or  folded  upon  itself  (Fig.  39,  in.)»  or  its 
surface  may  give  rise  to  ciliated  processes  (Fig.  39,  lY.).  In 
Alberiia  and  Notommata  tardigradot  however,  the  trochal 
disk  is  reduced  to  a  small  ciliated  lip  around  the  oral  aper- 
ture; and  there  is  no  trochal  disk  in  ApBUuB,  Lindia, 
Taphrocampa,  and  Bal<Uro,  Some  few  Botif era  are  parasitic. 
Thus  Alberiia  is  an  entoparasite,  and  Balairo  an  ectopara- 
site, upon  oligochffitous  Annelids. 

Under  the  name  of  Oasterotritha,  Metschnikoff  and 
ClaparMe  *  include  the  curious  aquatic  genera  ChoBtonoUu, 
Ichthydium,  ChoBiura,  Cephalidiwn,  DoBydUis,  TurhaneUa, 
and  Hemddatys,  the  last  of  which  alone  is  marine.  These 
^Tiinri<t1a  haYC  been  united  with  the  BoHfera,  bnt  they  differ 
from  them  in  the  absence  of  a  mastax  and  in  the  disposi- 
tion of  the  cilia,  which  are  restricted  to  the  yentral  surface 
of  the  body.  It  appears  probable  that  they  form  an  annectent 
group  between  the  Botif  era  and  the  TurbeUaria,  which  last 
approach  the  Botifera  by  such  forms  as  DinophUtu. 

The  free  Botifers  present  marked  resemblances  to  the 
telotrochous  larvse  of  Annelids.  The  joxmg  LacinuUmtif  for 
example,  has  a  circular  prsD-ora]  disk  proyided  with  two 
eye-spots  and  a  second  circle  of  cilia  behind  the  month,  and 
is  wonderfully  like  an  Annelid  lanra  (Fig.  39, 1.).  The  ap- 
pendages of  TViarihra  and  Polyarthra  may  be  compared  to 
the  lateral  bundles  of  long  set®  of  the  lairs  of  8pio  and 
Nerine,  and  the  pharyngeal  armature  is  essentially  Anne- 
lidan.  On  the  other  hand,  in  the  sessile  tubicolous  BoUfera, 
the  trochal  disk  assumes  the  characters  of  the  lophophore  in 
the  Pohftoa,  and  of  the  tentacular  circlet  of  the  G^hyiean 

•  ClapsrMe  and  Metsohnikoff,  'Beitrigs  mr  KenntnlM  der  Eat- 
wiokelnngigeicbiohts  der  Chsetopods^*  ISCa, 


THX  TBBMATODA. 


193 


Phonmia,  Many  years  ago  I  drew  attention  to  the  points 
of  resemblance  between  the  BoHfera  and  the  larrse  of 
Echinoderms  ("On  Lcusinvlaria  soeiaXU**  I.  c.)  Of  any 
SQch  close  and  direct  relations  with  the  Crugtaeea,  I  see  no 
evidence ;  but  Pedalion,*  with  its  jointed  setose  appendages 
and  cnrious  likeness  to  some  Nauplitu  conditions  of  the 
lower  Orutieicea,  suggests  that  connecting  links  in  this 
direction  may  yet  be  f onnd-f  In  fact,  the  BotifercL,  aa  low 
Metazoa  with  nascent  segpnentation,  naturally  present  re- 
semblances to  all  those  groups,  which,  in  their  simpler 
forms,  converge  towards  the  lower  Metaxoa, 

The  Tbbkatoda. — These  are  all  parasitic,  either  upon 
the  exterior  (ectoparasites)  or  in  the  internal  organs  (endo- 
parasites)  of  other  animals.  Many  are  microscopic,  and 
none  attain  a  leng^  of  more  than  an  inch  or  two.  Most 
have  a  broad  and  flattened  form,  one  face  being  yentral 
and  the  other  dorsal,  and  the  body  is  never  segmented. 

In  the  adult,  the  ectoderm  is  not  ciliated,  but  its  out<?r- 
most  layer  is  a  chitinous  cuticula.  In  most  Tremaioday  one 
or  more  suckers  are  developed  upon  the  ventral  surface  of 
the  body,  behind  the  mouth.  These  are  sometimes  armed 
with  chitinous  spines  or  hooks;  and  setaB  of  the  same 
character  may  be  developed  in  other  parts  of  the  body, 
especially  in  the  region  of  the  head. 

The  mouth  is  usually  terminal,  but  is  sometimes  ventral 
and  sub-central;  it  is  ordinarily  placed  in  the  centre  of 
a  muscular  sucker,  rarely  proboscidif  orm.  The  alimentary 
canal  is  never  provided  with  an  anus.    Sometimes  a  simple 


*  Hudaon,  "  On  a  Vew  Ro- 
tifer." (*  Monthly  MicroBCopical 
Journal,'  1871.) 

t  The  lingular  marine  genas 
Eekimodere*  (I>i:gardin)  is  perhaps 
such  a  link.  These  are  minute 
wormlike  animals,  with  a  rounded 
head,  followed  by  a  number  (10 
or  11)  of  distinct  segments,  the 
last  of  which  is  bifurcated. 
Thara  are  no  limba,  but  the  head 


is  provided  with  recurved  hooks, 
and  the  body  segments  with 
paired  sete.  The  nervouM 
system  appears  to  be  represented 
by  a  single  ganglion,  which  lies 
in  the  head  and  presents  eye- 
spots.  The  development  of 
£chinoderei  is  unknown.  (See 
Greef,  *Archiv  fiir  Naturge- 
schichte/  186^.) 


O 


194       THE  ANATOMY  OF  UnTEBTEBRATED  ANIMALS. 

sac,  it  is  often  bifurcated,  and  occasionaUj  branched,  like 
that  of  the  dendrocoele  TurheUaria.  Sometimes  {AmphUina^ 
Amphiptyches)  the  alimentary  canal  is  absent ;  and,  accord- 
ing to  Yan  Beneden,  it  becomes  aborted  in  the  adnlt  Distama 
JUicolle,  The  interval  between  the  endoderm  and  the 
ectoderm  is  occupied  hj  a  cellular  or  reticulated  mesoderm, 
in  which  abundant  muscular  fibres  are  developed.  The 
peripheral  muscular  fibres  form  an  external  circular  and 
on  internal  longitudinal  layer. 

The  water-vascular  system  is  well  developed,  and  may 
consist  of — (1)  a  contractile  sac,  which  opens  externally 
and  communicates  with  (2)  longitudinal  vessels  with  con- 
tractile non-ciliated  walls,  from  which  proceed  (3)  non-con- 
tractile and  ciliated  branches  which  ramify  through  the 
body  and  the  ultimate  ramifications  of  which  probably  end 
by  open  mouths,  as  in  the  Botifera, 

Thei«  is  no  pseud-heemal  system.  The  nervous  system 
has  not  been  discovered  in  all ;  but,  when  it  exists,  it  has 
the  same  arrangement  as  in  the  aproctous  TurbeUaria, 
Eye-spots  have  been  observed,  but  no  other  sense-organs. 
With  rare  exceptions,  the  Tremaioda  are  hermaphrodite, 
and  the  reproductive  organs  are  constructed  upon  the  same 
type  as  in  the  rhabdocoele  TurbeUaria,  a  large  vitellarium 
being  always  present.  The  accessory  vitellus  is  included, 
in  the  form  of  numerous  pellets,  along  with  the  primitive 
ovum,  and  is  absorbed  pari  passu  with  the  development  of 
the  embryo. 

Aspidogaster  conchicola  (Fig.  40)  inhabits  the  pericardial 
cavity  of  the  fresh-water  mussel ;  it  is  a  very  convenient 
subject  for  examination  on  account  of  its  small  size,  and 
the  ease  with  which  it  can  be  rendered  sufficiently  trans- 
parent for  the  display  of  the  arrangement  of  its  internal 
organs,  by  the  judicious  use  of  the  compressorium.  The 
flat  oval  body,  rounded  posteriorly,  is  produced  in  front 
into  a  truncated  cone,  on  the  face  of  which  the  mouth 
opens.  The  ventral  sucker  is  very  large,  and  its  surface 
is  Bubdiyided  into  rectangular  areas.  There  is  no  peri- 
visceral cavity,  its  place  being  occupied  by  a  mass  of 


ASPID0OA8TEB 


195 


gpaagj  ceUnlar  tjaaiie.  Th«  oral  cavitj  leads  into  an 
oral,  thiclc-walled,  maacnlar  phaijngeal  bnlb,  whence  an 
eIoiigftt«d  pjrriform  sac,  which  conHtitutea  the  rest  of  tbe 
alimentarf  canal,  ia  continned.  This  occnpiea  a  grent 
part  ot  Ute  bodj,  and  extends  nearly  to  ita  posterior 
end ;  bnt  there  is  no  anne.  A  contractile  racDole  placed 
at  the  hinder  extremitr  of  the  body  opens  outwards  b; 
Fig.  40. 


Fig.  40. — AmiJogmItT  anichicob.—A..  amngemei 
uid  reproductlre  organt ;  prcifile  or  the  •alTiiat  ii 
b,  tniucnlar  phujnx ;  c,  glonu)! ;  d,  gennaiiuni : 


or  the  alimcntiu^' 
lutliae.  s.oiDDlb: 
T,  iaienul  viadefc- 


a  small  pore  (Fig.  41,  a),  and  gives  off  two  lateral  con- 
tractile non-ciliated  canals  (b),  which  pass  to  the  anterior 
end  of  the  Tentrsl  Backer  and  there  end  blindly ;  bnt  before 
reaching'  thia  termination  each  givee  off  a  non-contractile 
ciliated  Teasel,  (Fig.  41,  e)  which, on  arriTing  at  the  pbarTni, 
tnnia  bat^wards  and  ramifies  through  the  body.  The  cilia 
"    '  '  h  towmrds  the  extremitiea  of  these  vesBeU, — &e  Vet- 


196       THB  AMATOKT  Or  IRTBBTIBKA^D  AITQULS. 

minationa  of  the  corraspoadrng  canals  in  the  Botiftra  being, 
on  the  contrary,  richly  ciliated.  No  nerrei  have  aa  jet 
been  found  in  JfpidtKfasfar. 

As  in  most  Tromatoda,  the  genitalia  (Figs.  40  and  43.)  fonn 
a  loi^  part  of  the  TiBcera,  and  the  strncture  of  the  com- 
plex hermaphrodite  apporatoB  is  in  some  respects  so  pecu- 
liar, that  it  is  needful  to  describe  it  in  detail.  It  consiats 
of~l.  The  Kermarium.  2.  Theritellariuni.  3.  Theoviduct. 
4.  The  ntcrus  and  vagina.  5.  The  common  Teatibule.  6. 
The  testis.    7.  The  Tasa  deferentia,  internal  and  eit«maL 

Fig.  41. 


,  ..  ._.or«l  ollikled  tnuki, 

that  of  (he  Icrt  tidH  shaded  ;  d,  dilaUtioi  of  this  trunk ;  B,  oua  of 
larger,  and  C,  one  of  the  uoatler,  ciliated  Tneele, 

8.  The  penis  and  ita  sac.  The  ovary  (d)  is  the  anterior  of 
two  rounded  maases  lying  in  the  sucker.  At  first  sight  it 
appears  to  be  oval,  but  it  is,  in  fact,  pyrifarm,  the  larger 
end  being  anterior,  while  the  posterior  narrower  extremity 
is  bent  backwards  beneath  the  anterior  end.  Before  it 
reaches  the  anterior  extremity  of  the  mass,  however,  it  is 
bent  sharply  back  again,  parallel  with  itself,  and  so  passes 
into  the  oviduct  (Fig.  40,  t).  The  ovary  is  eurrounded  by 
u  delicate,  but  sbwng,  coat,  enclosing  a  maae  of  tranapa- 
Tvat  protoplaam.  At  the  anterior  end  of  the  ovary  miunte 
granules  are  scattered  throngh  this  subotance,  and  are  oc- 


A8PIDOOA8TSB  CONCHICOLA.  197 

casionallj  surrounded  by  a  faint,  clear  area  (Fig.  48,  A  1). 
These  are  the  radimentary  germinal  spots  and  Tesicles  of  the 
fatore  OTa,  the  coarse  of  whose  derelopment  may  be  readily 
traced  by  working  from  the  anterior  to  the  posterior  ex- 
tremity of  the  ovary.  The  germinal  spots  become  larger, 
and  gradnally  assume  the  appearance  of  resicular  nuclei ; 
while  the  clear  area  around  them  in  like  manner  becomes 
larger,  and  acquires  more  and  more  the  appearance  of  a 
cayity.  While  this  cavity  is  small,  it  has  no  distinct  wall, 
but,  as  it  enlarges,  the  contour  of  the  wall  becomes  dis- 
tinctly marked  (Fig.  43,  A  2,  3,  4).  On  examining  the  ovary 
close  to  the  commencement  of  the  oviduct,  a  division  of 
the  homogeneous  protoplasmic  basis  or  matrix  of  the  ovary 
into  areas  surrounding  each  germinal  vesicle  becomes 
obvious.  On  the  application  of  pressure,  the  matrix  breaks 
up  into  masses  corresponding  with  these  areas  in  size, 
which  are  very  flexible,  but  when  left  to  themselves  assume 
a  rounded  or  oval  form,  and  have  all  the  appearance  of 
perfect  ova,  except  that  they  possess  no  vitelline  mem- 
brane, and  that  the  yelk,  instead  of  being  granular,  is 
clear,  and  comparatively  small.  These  primary  ova,  as 
they  may  be  termed,  become  detached,  and  pass  into 
the  oviduct.  Here  they  are  fecundated,  and,  becoming 
surrounded  by  a  great  mass  of  accessory  yelk,  and  a  shell, 
gradually  acquire  the  appearance  of  the  complete  ova. 

The  accessory  yelk  is  the  product  of  the  vitellarium — a 
large  double  gland  consisting  of  a  number  of  oval,  pyri- 
form,  or  irregular  granular  masses  placed  on  each  side,  at 
the  junction  of  the  sucker  with  the  body  (Fig.  40,  g). 

These  masses  appear  to  be  quite  independent  of  one 
another ;  nor  do  they  at  first  present  any  obvious  commu- 
nication with  the  genitalia ;  but  if  the  oviduct,  just  after  it 
becomes  free  from  the  ovarium,  be  examined,  it  will  be  found 
to  receive  a  short  duct  (Fig.  42,  /),  filled  with  strongly  re- 
fracting granules  of  the  same  nature  as  those  in  the  vitol- 
larinm.  Tliis  duct  is  enlarged  posteriorly,  and  then  divides 
into  two  ducts  filled  with  the  same  matter,  which  take  a 
direction  towards  the  vitellarium,  but  can  be  trac^  tlq 


198       THE  AN4T0HT  OV  IBTBBTBBKATBD  AmUHa. 

fur^cr  than  tbej  contain,  grannlea  (Fig.  42).  Bj  the 
carefnl  application  of  pressure,  howerer,  the  grannlea  maj 
be  forced  from  the  Titellarinm,  through  ut  anleriw  and 
posterior  branch  npon  eaoh  side,  into  these  dncta. 

The  OTidnct  (Fig.  42.  i)  is  richly  ciliated  intemallyi  it 
is  at  first  applied  to  the  under  surface  of  the  orarinm, 
und  when  it  becomes  free  it  receives  a  canal  (e),  which 
nMy  be  traced  back  to  the  testis,  and  which  would  appear 

Fig.  *a. 


TH  darereoi  ia  leco  behind  lbs  viteUu')4D  ducu. 

to  correspond  with  the  internal  vas  deferens  of  other 
Tremaloda  described  by  Ton  Siebold.*  This  canal,  how- 
ever, presents  no  dilatation,  or  internal  vesicnla  seminalia. 
The  oviduct  next  receives  the  duct  of  the  vitellarium,  and 
then  becoming  much  convoluted  (k],  and  rapidly  widen- 

■  The  ceDneetion  or  thli  duct  Aipidagiuler,  but  I  bsTS  hsd  no 

witb  tb«  teitla  ia  th«  Trtmatala  oppoHuulty  of  re.eumlniiig  tbl> 

hu    rscentlv    been    denied    by  uiimsl  rince  tfae  DubllcslloD  of 

Rlleds  ('  HQlter't  ArehlT,'  1871).  Stleds't  paper. 

1  hul  DO  doubt  of  Its  er' ' 


ASPIDOOASTEB  CONCHICOLA.  199 

ing,  passes  into  the  uterus  (2),  a  wide  tube,  which  nms 
forwards,  disposed  in  many  undulating  curves  (Fig.  40,  Q, 
to  terminate  on  the  left  side  of  the  anterior  part  of 
the  body,  close  to  the  male  organs.  Posteriorly,  the  walls 
of  the  uteiois  are  thin;  but  in  its  anterior,  or  vaginal, 
part  they  become  thick  and  muscular.  The  genital  vestibule 
into  which  the  vagina  opens  is  very  small. 

The  testis  (m)  is  an  oval  body  of  the  same  size  as  the 
ovarium,  and  situated  just  behind  it.  Minute  water- vessels 
ramify  upon  it,  as  upon  the  ovarium ;  and  it  contains  a 
granular  and  cellular  mass,  but  no  spermatozoa.  The 
external  vas  deferens  (Figs.  40  and  42)  is  a  delicate  duct, 
which  passes  forwards  and  comes  into  contact  with  the 
ovarium,  without,  however,  so  far  as  I  could  observe,  com- 
municating with  it  or  with  the  oviduct;  it  then  bends 
backwards  and  upwai-ds,  passing  between  the  anterior  vi- 
tellarian  masses  into  the  fore  part  of  the  body.  Here  it 
suddenly  becomes  about  twice  as  wide  as  before,  and  runs 
forwards,  as  an  undulating  thick  tube,  to  the  penis  (Fig. 
40,  p),  a  shoi*t-and  conical  body,  occupying  the  bottom  of  a 
large  pyrif  orm  sac,  which  opens  in  common  with  the  uterus. 
The  spermatozoa  are  linear. 

The  development  of  the  ova  presents  many  very  interest- 
ing peculiarities  (Fig.  43).  Above  the  junction  of  the  duct 
of  the  vitellarium  with  the  oviduct  the  contents  of  the  latter 
were  pale  and  clear,  and  presented  no  formed  particles 
beside  the  primary  ova  which  had  just  been  detached  from 
the  ovarium  (Fig.  43,  C).  Below  the  insertion  of  the  vitel- 
larian  duct,  however,  the  oviduct  was  full  of  granules  like 
those  in  the  vitellarium,  mixed  up  with  ova  in  a  more  ad- 
vanced state.  In  the  smallest  of  these  (Fig.  43,  D),  the 
shell  of  the  ovum  had  commenced,  but  was  incomplete  at  one 
end.  At  the  opposite  extremity,  it  enclosed  a  mass  of  irre- 
gularly aggregated  vitelline  granules,  which  covered  almost 
one-half  of  a  round  pale  mass,  not  larger  than  one  of  the 
primary  ova;  in  which,  however,  three  nuclei  (two  of  which 
were  very  close  together,  as  if  they  had  just  divided)  were  to 
be  distinguished.    In  more  advanced  ova  the  sheU.  ^^^^ 


200       THE  ANATOKT  OV  INTBBTXBBATBD  ANIMALS. 


complete,  but  either  colourless  or  of  a  yerj  pale  brown  hue. 
In  some  of  these  the  primary  ova  contained  many  nadei 
and  were  imbedded  in  and  surrounded  by,  a  confused  mass 
of  accessory  yelk  granules ;  while  in  others  these  grannies 
were  aggregated  into  a  number  of  regular  spheroidal  masses 
(Fig.  43,  B). 

As  development  proceeds,  the  accessory  yelk-maases  gra- 
dually disappear ;  the  primitive  ovum,  now  become  the  ho- 


Fig.  43. 


^ 


Fig.  43,—Atpidogaster  conchicola.—A,  section  of  the  ovary ;  I,  its  an- 
terior end ;  :^,  germinal  spot  surrounded  by  a  distinct  wall ;  S,  4,  a 
complete  germinal  vesicle  and  spot;  C,  a  primary  ovum;  D,  young 
state  of  a  oomplete  ovum :  the  primary  ovum  partially  surrounded 
by  yelk  granules  and  a  shell ;  B,  complete  ovum,  with  the  accessory 
yelk  aggregated  into  spheroids;  £,  vacuolated  embryonic  mass; 
F,  embryo. 

mologuc  of  the  blastodermic  disk  or  vesicle  in  other  animals, 
to  all  appearance  increasing  at  their  expense.  At  the  same 
time,  clear  rounded  vacuoles  in  various  numbers  appear  in 
its  substance;  but  the  nnclei  of  the  germ,  though  Tery 
minute,  can,  with  proper  care,  be  readily  detected  between 
these.  In  the  final  stages  the  shell  becomes  browner,  the 
▼aonoles  and  granules  disappear,  and  the  substance  of  the 
embryo  i^pears  homogeneous.    But  if  carefully  examined, 


THS  BBTBLOPMENT  OF  ABPIDOOASTSB.  201 

tbe  mintite  nuclei  become  -risible,  especially  if  water  be 
allowed  to  act  on  the  tissue,  and,  if  the  shell  be  burst, 
and  its  contents  poured  out,  thej  readily  break  up  into 
small  but  well-marked  cells,  each  with  its  nucleus. 
At  the  same  time,  the  embryo  takes  on  a  form  not  very 
distantly  resembling  that  possessed  by  the  adult;  into 
which  it  eventually  x>a8Be8  without  any  metamorphosis.* 

Thus  it  appears  that,  in  Aspidogcuter,  the  ovarium  gives 
rise  to  primary  ova,  which  pass  down  the  oviduct  and 
become  fecundated,  either  by  the  spermatozoa  conveyed 
by  the  internal  vas  deferens,  or  by  those  received  by  the 
vagina  when  copulation  with  another  individual  or,  pos- 
sibly, self -impregnation,  occurs;  that,  next,  the  essential 
part  of  the  process  of  "yelk-division"  takes  place,  the 
germinal  spot  dividing  and  subdividing,  and  the  primary 
ovum  becoming  in  this  way  converted  into  the  spheroidal 
blastoderm;  that,  contemporaneously,  the  blastoderm  be- 
comes invested  by  the  accessory  yelk  granules  poured  in  by 
the  vitellarian  duct,  and  by  a  shell ;  that  the  accessory  yelk 
arranges  itself  into  spheroidal  majBses,  which  probably 
supply  the  blastoderm  with  the  means  of  its  constant  en- 
largement ;  and  that,  finally,  the  accessory  yelk  disappears, 
and  the  blastoderm  becomes  converted  into  the  embryo. 

The  modifications  exhibited  by  other  Trematoda  concern 
the  number  of  the  suckers,  of  which  there  are  usually 
several  in  the  ectoparasites,  but  not  more  than  one  in  the 
endoparasites ;  their  support  on  a  chitinous  framework,  or 
the  addition  to  them  of  spines  or  booklets,  similar  to  those 
of  Cettoidea  or  Acardhccephala :  the  bifurcation  of  the  intes- 
tinal canal,  and  the  ramification  of  its  branches,  so  that  the 
forms  of  the  alimentary  apparatus  repeat  the  two  extremes 
observed  in  the  aproctous  TurbeUaria;  the  existence  of 
two  nervous  ganglia  with  a  single  transverse  commissure 

*  The  tabstsnce    of  this  ac-  Beneden    has    recently    thrown 

eoant  of  the  structure  and  de-  much  light  on  the  mode  in  which 

velmmwiit  of  Atpittoga$Ur,  with  the  ova  of   the    Trematoda  are 

the  illuttimtive  figures,  was  pub-  formed    and    developed    in    his 

lished  hi   1S56  in    The  Medical  ^Recherches  sur  la  composition 

Timm  and  Omttite,    M.  £.  van  et  la  signification  de  VQE.ut? 


202       THE  ANATOKT  OV  nffYSBTSBBJLTSD  AHIICALS. 


in  many ;  and  the  occasional  presence  of  sensory  organs 
(eye-spots).  The  non-contractile  canals  of  some  genera  are 
destitute  of  cilia,  except  at  their  inner  terminations. 

The  variations  of  the  reproductiTe  organs  are  rather 
of  position  than  of  stmctore.  Dioecioos  Trematodes 
are  very  rare,  the  most  important  being  the  formidable 
Bllharzia,  the  male  of  which  is  the  larger  and  retains  the 
female  in  a  gynceeophore,  or  canal,  which  is  fonned  by  the 

Fig.  44. 


Pig.  44. — A,  B,  Monottomum  mutabile ;  A,  the  ciliated  embryo  (a) 
.  enclosing  the  sooid,  (b,)  represented  free  in  B  (after  SieboJd) ;  C« 
BediOf  or  lying's  yellow  worm  of  Distoma  patificvm^  oont^ning 
germs  of  other  RedUe  ;  D,  Redia  containing  CercancB  (a) ;  £,  Ctr" 
carta;  F,  JJittomoy  which  results  from  the  metamorphosii  of  the 
Cercaria,    (After  Steenstrup.) 

infolding  of  the  margins  of  the  concave  side  of  the  body. 
BlViarxiahBa  neither  intromittent  organ  nor  seminal  pouch, 
and  the  history  of  its  development  has  not  been  traced  be- 
yond the  escape  of  a  ciliated  embryo  from  the  ovum.  This 
parasite  is  found  in  the  blood  vessels  of  man,  chiefly  in 
those  of  the  urinary  organs,  the  ova  escaping  from  the 
body  through  the  ulcerated  surfaces  to  which  the  parent 


THB  BEYSLOPMEKT  OV  THS  TBSMATODA,  203 

gives  rise.  In  the  ectoparasites,  the  embryo  passes  into 
a  form  identical  with  or  closelj  resembling  that  of  the 
parent  while  still  within  the  egg^  as  in  Aapidogaster,  When 
this  happens  {e.g,  Distoma  variegaium,  D.  tereticoUe),  the 
one  end  of  the  embryo  is  often  provided  with  spines,  and 
it  is  capable  of  slow  creeping  movements.  But,  in  most 
of  the  endoparasites,  the  embryo  leaves  the  parent  as  a 
morula,  which  is  usually  ciliated.  Thus,  in  Distoma  lanceo- 
latum,  D.  hepc^Hcum,  and  Monogtomum  mutahile,  the  embryo 
which  escapes  from  the  egg  has  a  ciliated  investment,  which 
propels  it  rapidly  through  the  water,  and  may  be  provided 
with  eyespots  and  water- vessels  (Fig.  44,  A).  On  becoming 
attached  to  the  animal  upon  which  it  is  parasitic,  the  embryo 
of  Monostomnm  gives  exit  to  a  larva,  having  the  form  of  a 
cylindrical  sac  with  two  lateral  prolongations  and  a  taper- 
ing taiL  The  Bedia,  as  this  form  is  called  (Fig.  44,  B,  C),  has 
a  mouth  and  a  simple  csecal  intestine,  but  no  other  organs. 
In  its  cavity  a  process  of  internal  gemmation  takes  place, 
giving  rise  to  bodies  resembling  the  parent  in  shape,  but 
destitute  of  reproductive  organs,  and  furnished  with  long 
tails,  by  which  they  are  propelled.  These  creatures,  called 
Cercarice  (Fig.  44,  E),  escape  by  bui^sting  through  the  Bedia, 
and,  after  a  free  swimming  existence,  penetrate  the  body 
of  some  other  animal,  their  tails  dropping  off.  They 
then  become  encysted,  and,  under  suitable  conditions, 
assume  the  adult  form,  and  develope  reproductive  organs 
^Fig.  44.  F). 

The  cycle  of  forms  through  which  Distoma  mUitare  passes 
has  been  nearly  completely  traced,  and  may  be  briefly  stated 
as  follows.  1st.  The  parent  form,  whose  habitat  is  the  in- 
testines of  water-birds,  bears  on  its  anterior  extremity  two 
alternating  circles  of  larger  and  smaller  booklets,  and  a 
few  others,  irregularly  disposed.  Rings  of  papillsB  give  the 
centre  of  the  body  an  annulated  aspect.  The  mouth,  abnost 
terminal,  leads  into  the  long  straight  digestive  caecum. 
The  generative  organs  are  similar  to  those  of  Aspidogaster ; 
the  testes  are,  however,  double,  and  lack  the  internal 
TAB  deferens.    The  ova  are  few,  eight  or  ten  in  ii.umV>^ic. 


204       THE  JLNATOICT  OF  INYBBTSBBATSD  ANIMALS. 

2nd.  From  each  oyum  issues  a  ciliated  larva,  showing  the 
rudiments  of,  3rd,  a  Bedia,  but  the  mode  of  derelopment  of 
the  latter  has  not  been  f uUj  traced.  The  perfect  Bedia  is 
found  attached  to  the  body  of  a  water  snail  (Paludina), 
the  cUiated  inyestment  having  disappeared.  It  consists  of 
a  sac,  within  which  is  suspended  a  tubular  bag,  containing 
coloured  masses,  probably  alimentary.  Anteriorly,  the 
head  is  represented  by  a  kind  of  crown,  in  which  no  (bso- 
phagus  exists  as  yet,  and  not  far  from  the  posterior  ex- 
tremity the  two  lateral  projections,  characteristic  of  Disto- 
matous  BedicR,  appear.  During  the  rapid  growth  of  the 
zooid,  the  head  becomes  marked  off  by  a  constriction,  and 
a  mouth  and  gullet,  with  a  pharyngeal  dilatation,  admit 
aliment  to  the  digestiye  sac.  In  the  body  cavity,  external 
to  this  sac,  vesicles  appear,  rapidly  increase,  and  take  the 
form  of  Cercarice ;  the  Bedia  bursts,  and  these  new  zooids 
are  set  free.  4th.  The  Cercaria  has  a  long  tail  with  lateral 
membranous  expansions,  by  means  of  which  it  swims  after 
the  fashion  of  a  tadpole.  The  pharyngeal  bulb  is  fol- 
lowed by  an  oBsophagus,  which,  opposite  the  ventral  sucker, 
divides ;  the  two  branches  ending  in  a  csscum  on  either 
side  of  the  contractile  vacuoles  of  the  water-vascular 
system.  These  are  median,  the  terminal  quadrate  chamber 
opening  into  an  anterior  ciixjular  one,  whence  are  given 
off  the  two  main  canals  which  traverse  the  body  longi- 
tudinally, and  are  then  lost.  5th.  After  swimming  about 
freely  for  a  while,  the  Cercaria  fixes  itself  upon,  or  bores 
its  way  into,  a  Patuditia ;  the  tail  dropping  off,  and  the 
body  coating  itself  with  a  structureless  cyst,  in  which  it 
remains  quiescent,  but  undergoes  some  further  advances 
in  development,  the  coronal  booklets  making  their  appear- 
ance. 6th.  When  a  Paludinat  thus  infested,  is  swallowed  by 
a  water  bird  and  digested,  the  cysts  are  set  free  in  the 
alimentary  canal  of  the  bird ;  sexual  organs  appear  within 
the  included  Distoma ;  the  body  elongates  and  narrows  an- 
teriorly ;  the  sucker  moves  nearer  the  head,  and  the  coronal 
circlets  reach  their  full  development.  The  Distoma  gra^ 
dually  assumes  the  form  of  the  parent,  attaches  itself  by 


TBI  DBTBLOmUIT  OT  THX  TBIIUTODA, 


205 


hookleta  to  the  mtestmal  walls,  and  aoqnires  oomplete 
ml  orgaiiB.*  Thua  the  deTelopmeotal  stages  of  Ditlcma 
Uar*  maj  be  sninmed  up,  as :  1.  Ciliated  larrA.  2.  Badia. 
Oareorta.  4.  Cerearia,  tail-less  and  encysted,  or  incom- 
baDUloma.    5.  Perfect  I>utofna. 

^be  stages  of  tranntioa  vary  in  different  genera.    Thna, 
Bnl  generatioBB  of  Bedim  maj  intervene  between  the 
Fig. «. 


lit,  —  Bmefphalm  votymorphut  of  the  freih-water  musvel-  A, 
iBdIIed  ■poroc;>t;  B,  portion  of  the  mme  more  uimgniBed,  a, 
iCer  cokt,  b,  inner-,  c,  d,  f^m  mutes  in  coune  of  d*v«lopmeat ; 
,  one  of  the  germ  muaes  more  highly  miignified ;  D,  BucriAaiut, 

h,  mcken ;  c,  cleu  uvily ;  d,  caudal  ippendageg. 

rd  and  fourth,  stages ;  or  the  mature  animal  ma;f  appear 
lie  close  of  this  stage,  baTing  undergone  no  Cercarian 
xunorphosis. 

Q  Bncephahu  ipohfmoTphm,  a  parasite  of  the  fresh-water 
Mel  (IHg.  45),  two  candal  appendages,  which  seem  to 
respond  with  the  tail  of  the  ordinaiy  Cerearia,  become 
•  Vmi  Bentden, '  BUmoire  eur  lei  Ten  Intettlokox ' 


206       THE  AKATOICY  OF  nTYSBTSBBATED  JLVmALS. 

enormously  elongated.  They  are  converted  into  ramified 
tubes  called  tporoeytts,  which  sometimes  occupy  all  the 
interspaces  of  the  viscera  of  the  musseL  These  develope 
new  BueephaXi  by  internal  gemmation.  The  Trematode 
condition  appears  to  be  the  genus  Qasterofdomwn,  which 
inhabits  fresh-water  fishes. 

The  Sporocysts,  BedisB,  and  Cercarise,  free  or  encysted, 
are  found  almost  exclusively  in  invertebrated  animals, 
while  the  corresponding  adult  Trematodes  are  met  with  in 
the  vertebrated  animals  which  prey  upon  these  Inveriebrata. 

The  singular  double-bodied  Diplonoon  pcaradooeum  has 
been  shown  by  Von  Siebold  to  result  from  a  sort  of  conju- 
gation between  two  individuals  of  a  Trematode,  which,  in 
the  separate  state,  has  been  named  Diporpa.  The  Diporpce, 
when  they  leave  the  egg,  are  ciliated  and  provided  with  two 
eyespots,  with  a  small  ventral  sucker  and  a  dorsal  papilla. 
After  a  time  the  Diparpoe  approach,  each  applies  its  ventral 
sucker  to  the  dorsal  papilla  of  the  other,  and  the  coadapted 
parts  of  their  bodies  coalesce.  They  acquire  fully  developed 
sexual  organs  only  after  this  union.* 

Cryrodactylus  multiplies  agamically  by  the  development  of 
a  young  Trematode  within  the  body,  as  a  sort  of  internal 
bud.  A  second  generation  appears  within  the  first,  and 
even  a  third  within  the  second,  before  the  young  Oyro* 
ddctylus  is  bom. 

The  Cestoidea. — The  Tape- worms  are  all  endoparasites, 
and,  in  their  adult  condition,  infest  the  intestines  of  verte- 
brated animals. 

The  simplest  form  known  is  CaryophyUcBus^f  found  in 
fishes  of  the  Carp  tribe.  It  has  a  slightly  elongated  body, 
dilated  and  lobed  at  one  end,  so  as  to  resemble  a  dove, 

*    Zeller,     **  Untersuchangen  indebted  for  information  reepeet- 

iiber     die     Entwickelung     des  ing    thi4  and    other  genera  of 

Diplozoon  paradoxum."    (*Zeit-  C*stndea  which  have  nol  fallen 

schrift  f&r  WiM.  Zoologie,'  1872.)  under  my  own  observation.   Alio 


t  See  the  *  Memoire  sur  lea  Yen      Leurlcarr,     *  Die    Menschlichen 
IntesUnauz,'  1858,  by  M.  P.  J.      Parasiten,' 
van  Beneden,  to  whion  I  am  maoh      *  Entoaoa.' 


TKK  CBSTOmXA. 


207 


wlienoe  tlie  name  of  the  genns.  In  atmctnre  it  reaembleB 
a  l^emaitode,  devoid  of  any  trace  of  an  alitnentarjr  canal, 
bat  prorided  witli  the  characteristic  water-rascnlar  ajatem 
and  with  »  single  set  of  hermaphrodite  reprodnotiTe  organs. 
In.  lagula,  the  bodj  is  much  elongated,  and,  at  the 
head  end,  eshibite  two  lateral  depresnons.  It  ia  not 
dWided  into  aegment«,  bnt  there  are  nnmerona  aets  of 

Fig. «. 


Flf.  M.—Diagrmin  of  tbe  Btrucluie  of  >  Ceatoid  worm,  nilb  only  one 
kiinL  Tba  pomtion  of  the  iiooki  of  &  Tmia,  and  of  one  of  Ifas  pro- 
Vaoidei  of  ft  Trtrarhynchai  ie  ladicaied.  A,  hesd  Mid  neck ;  B, 
Mgment  of  the  body  correjponding  with  ■  pmglotlU  ;  a,  nulrj/sn  ,- 
b,  iHtellar  iidnei  (  Tmia);  c,  <f.  e",  Bpinose  evenibla  pmboacis 
(  TttmHiftiduu];  d,  sucker;  t,  KanKlioD  (?) ;  /,  laleral,  and  g,  circular 
wmter  veuel ;  A,  ramificalioni  of  the  water  vessels ;  *,  anastoinoainj^ 
tmnk;  i,  eontraelile  varuole;  I,  genila!  Testibule;  n,  penia  and  vas 
defereni;  a,Taglna,  o, commoa  avity  ^nd  erMieula  trmiiuilit  interior ; 
p.  orarj;  q,  nt^Tu;  r,  vitetlarisn  duct, 

Mxnal  organs  arranged  in  longitudinal  series.  The  open- 
inga  of  the  genital  glands  are  situated  in  the  middle  line  of 
the  body.  These  parasites  inhabit  Fiabes  and  Amphibians, 
M  weD  H  wat^  bird>i,  but  thej  attain  their  sexual  state 
(mly  im  Um  Utter. 

ta  the  JXKxn  typical  Cetfoidea  the  body  is  do&gate^,  «ii^ 


^» 


208       THE  ANATOICY  OF  niYBBTBBSATBD  AKIMALS. 

presents,  at  one  end,  a  liead  provided  with  suckers,  and  veiy 
generally  with  chitinons  hooks,  either  disposed  circularly 
around  the  summit  of  the  head,  or  upon  proboscidiform 
tentacles,  which  can  be  retracted  into,  or  protruded  from, 
the  head.  Sometimes  the  head  is  produced  into  lobes ;  and 
very  generally,  when  lobes  or  tentacles  exist,  they  are  four 
in  number,  and  are  disposed  symmetrically  round  the  head. 
A  short  distance  beyond  the  latter,  the  slender  body  widens 
and  becomes  transversely  grooved,  so  as  to  be  marked  out 
into  segments.  Longitudinal  water-vessels  run  parallel 
with  one  another  through  the  body,  and  are  connected  by 
transverse  trunks  in  each  s^^ent,  and  by  a  circular  vessel 
in  the  head.  In  Bothriocephalus  lotus,  the  principal  trunks 
are  occupied  by  a  spongy  reticulated  tissue. 

In  most  of  the  tape- worms,  innnmerable,  solid,  strongly 
refracting  corpuscles  are  scattered  through  the  substance 
of  the  body  (Fig.  48,  A).  It  is  probable  that  these  are  more 
or  less  calcified  connective  tissue  corpuscles.  Similar  bodies 
which  occur  in  some  Trematoda  were  found  by  Clapar^e 
to  be  lodged  in  dilated  ends  of  the  water- vessels,  but  it  would 
appear  that  they  arc  not  so  situated  in  the  Cestaidea,^ 

The  distance  between  these  transverse  grooves,  and  their 
depth,  increase  towards  the  hinder  end  of  the  body ;  and  each 
segment  is  eventually  found  to  contain  a  set  of  male  and 
female  organs.  The  genital  organs  are  constructed  upon  the 
same  general  plan  as  those  of  the  Trematoda,  but  the  uterus, 
as  it  fills  with  ova,  usually  takes  the  form  of  a  ramified  sac. 
At  the  extreme  end  of  the  body,  the  segments  become 
detached,  and  may  for  some  time  retain  an  independent 
vitality.  In  this  condition  each  segment  is  termed  a  pro- 
glottis ;  and  its  uterus  is  full  of  ova. 

The  embryo  is  developed  in  these  ova  in  the  same  way  as 
iu  the  Trematoda ;  and,  as  in  the  latter  group,  it  may  either 
be  ciliated  (as  in  Bothriocephalus)  or  non-ciliated,  which 

*  Sommer  and  Landois,  '^Ueber  logie,*  1872.)  Lcuckart,  however, 

den  Bau   der   geschlechtareifeii  maintains  the  contrary  opinion, 

Glieder  tou  Boihrhcephalu*  la-  *Die  Menschlichen  Parasiten,'  p. 

tus:*  C  Zeitschrift  fur  Win.  Zoo-  175. 


THE  CBSTOIDBA. 


209 


last  is  the  more  usual  case.  The  embryo  is  a  solid  morula, 
on  one  face  of  which  four  or  six  chitinous  hooks,  disposed 
sjmmefcrically  on  either  side  of  a  median  line,  are  deve- 
loped. 

If  the  egg  is  placed  in  appropriate  conditions,  the  hooked 
embrjo  emerges  from  the  shell,  and  rapidly  increases  in 
size.  After  a  time,  a  cayitj  appears  in  the  midst  of  the 
cella  of  which  the  momla  is  composed,  and  a  chitinous 
cuticula  is  developed  upon  the  outer  surface  of  the  embrjo. 
Bamified  water- vessels  make  their  appearance  in  the  wall 

Fig.  47. 


Fig.  47. — Dimgrams  illustrative  of  the  relation  between  Tttnia,  (^ati- 
cercuMj  Cetnunut^  and  JSchinococcus.—AL^  B,  young  Tctnia  in  the  ScoUt 
stage,  the  latter  with  an  enlarged  recejakaadnm  ScolicUy  into  which 
the  head  and  neck  are  withdrawn  in  C,  Cy^ticercu* ;  D,  CanttruM ; 
£,  hjpothetical  condition  of  Echmooocauy  in  which  ^  Tttnia  heads ' ' 
are  developed  only  on  the  inner  surface  of  the  primary  cyst;  F, 
Eekimoeoeeus  with  secondary  cysts ;  G,  embryo  Tcmia  (afier  Stein). 

of  the  spheroidal  sac  thus  formed,  and  in  some  cases  open 
by  an  external  pore.  There  is,  therefore,  a  very  close 
resemblance  between  this  cestoid  embryo  and  the  sporocyst 
of  a  Trematode. 

When  the  saccular  embryo  has  attained  a  certain  size,  a 
tiiiokening  and  invagination  take  place,  usually  at  one 
(Tcenia),  sometimes  at  many  {CcenuruSy  Echinococcus),  points 
of  its  walL  The  invagination  of  the  wall  elongates  inwards, 
and  becomes  a  cecum,  the  cavity  of  which  opens  outwards. 
At  the  bottom  of  the  interior  of  this  csDcum,  and  thecetoT^ 


210 


or  iimKTXBfti.nD  axwals. 


on  what  is  morphologically  if«  external  anrface,  the  hooks 
of  those  Bpecies  which  poweas  them  are  developed,  whilo. 
upiiu  the  aide-walla,  elerationa  ariae,  which  become  con- 
verted into  anckers.  The  cscnm  ia  next  evaginated  or  tnmed 
inside  out,  aild  the  embiyo  has  the  form  of  a  phiiU,  u( 

Fig.  48. 


Vlg.4B,—  Eclimiinifeutrftermmm.—\,  "Tenta  hekd,"  or  Stvltii  a, 
hDoka;  b,  gucken;  c,  cilia  In  w&tervewela;  d,  onal,  ilmiglj  nfnel- 
Ing  pvllclea,  B,  ilDgle  hooka;  C,  portion  of  Ibe  elailic  cyM,  a; 
with  ihe  inner  membrmnou*  primary  eyit, t ;  eand  *,  Scolka  derelup- 
ing  from  ici  inaaraurface;  li,  a  Beoondary  eyat. 

which  the  evaginated  cfficom  forma  the  neck.  Round  its 
apex  are  the  hooka,  and  below  these  the  enckera,  forming  s 
complete  Ceatoid  head ;  while  the  sac  answers  to  the  bodj 
of  the  phiaL  The  original  hooks  of  the  embijo  are  cast 
off  in  tlie  o&orae  of  this  process. 


THE  DBYELOPMENT  OF  THE  GESTOIDEA. 


211 


If  the  eggs  of  the  Tape- worm  have  passed  into  the  alimen- 
tary canal  of  an  animal  in  which  the  worm  is  nnable  to 
attain  its  sexual  condition,  the  hooked  embryo,  as  soon  as 
it  is  hatched,  bores  its  way  through  the  walls  of  the  alimen- 
tary canal,  and  eyentnally  becomes  lodged  in  the  connective 
tissue  between  the  muscles,  or  in  the  liver,  or  in  the  brain 
or  eye.  Here  it  goes  through  the  changes  which  have  been 
described,  and,  generally,  the  sac  undergoes  very  great  dila- 
tation. The  region  of  the  wall  of  the  sac  to  which  the 
cestoid  head  is  attached  becomes  invaginated,  and  thuR 
is  enclosed  within  a  chamber,  the  parietos  of  which  are 
really  constituted  by  the  outside  of  its  own  body.  In  thin 
condition,  the  animal  is  what  is  termed  a  Cystic  worm,  or 
bladder- worm ;  and  when  there  is  only  one  head  it  is  a 
CysHeercus.  In  the  genera  Ccenvrus  and  Eehinoeoecus  the 
cystic  worm  has  many  heads ;  and,  in  Echinocoeeus,  the  struc- 
ture of  the  cystic  worm  is  still  further  complicated  by  its 
proliferation,  the  result  of  which  is  the  formation  of  many 
bladder- worms  enclosed  one  within  the  other,  and  contained 
in  a  strong  laminated  sac  or  cyst,  apparently  of  a  chitinons 
nature,  secreted  by  the  parasite  (Fig.  48). 

In  the  Cystic  condition,  the  Tape-worms  never  acquire 
sexual  organs ;  but,  if  transported  into  the  alimentary  canal 
of  their  appropriate  hosts,  the  heads  become  detached  from 
the  cysts,  and,  rapidly  growing,  give  rise  to  segments,  which 
become  sexxisl  proglottides.  The  Tape- worms  are  rarely  met 
with  in  both  the  cystic  and  cestoid  conditions  in  the  same 
animal ;  but  the  cystic  form  is  found  in  some  creature  which 
serves  as  prey  to  the  animal  in  which  the  cestoid  form 
occurs.    Thus : — 


Ctstic  Fobm. 

Cysticercus  celluioscB, 
(Muscles  of  the  Fig) 

Cysticercus f 

(Muscles  of  the  Ox) 
Oystieercus  pisiformis. 
(Liver  of  the  Babbit) 


Cestoid  Form. 

Tasnia  solium, 

(Man) 

Tcenia  inedMcansUata. 

(Man) 

T^jenia  serrata, 

(Dog,  Fox) 


212       THE  ANATOMY  OF  INTKBTBBSATBD  AJmCALS. 


Cystic  Fobm. 

Cystieercua  JasciolarU, 

(Liyer  of  Bats  and  Mice) 

Ccenurus  eerebralis, 

(Sheep's  bram) 

Echinocoeetu  veterinorum. 

(Liver  of  Man  and  of 

domestic  Ungolata) 


Cbbtoid  Form. 

Tcenia  erauicoUls. 

•    (Oat) 

TcBwia  ecenwrus, 

(Dog) 

Tcenia  Echinoeoeeus, 

(Dog) 


The  embryo  of  Tcenia  cucumerina  passes,  in  the  body  of  the 
Dog-louse  (Trichodeetea  eanis),  into  a  OyaHcereoid,  or  minute 
unjointed  and  sexless  Teenia,  without  anj  terminal  dilata- 
tion. The  dog  devours  the  louse  and  the  Gjsticerooid 
becomes  a  Tcenia  cticvmerina  in  his  intestine.  The  eggs  of 
the  Tcenia,  contained  in  fsBces  adherent  to  the  hair  of  the 
dog,  are  in  turn  devoured  by  the  louse,  and  thus  the  "  vicious 
circle  "  of  parasitism  is  maintained. 

The  cystic  Tetraphyllidea  frequent  osseous  fishes,  their 
sexual  maturity  being  attained  in  the  bodies  of  Flagio- 
stomes.  The  head  is  provided  with  four  suckers,  or  lobes, 
which  may  be  stalked  and  unarmed,  as  in  Echeneibothrium, 
or  furnished  with  booklets  as  in  Acanthohothriwm ;  while,  in 
Teirarhtfnchus,  four  proboscidiform  tentacles,  thickly  set 
with  booklets,  are  retracted  into  sheaths  alongside  of  the 
suckers  (Fig.  46). 

The  DiphyUidea  have  two  suctorial  disks,  two  armed 
rostellar  prominences,  and  a  collar  of  booklets  on  the  neck. 

The  migrations  of  the  Psettdophyllidea  are  chiefly  from 
fishes  and  amphibians  to  water  birds,  one  genus  (Bothrich 
cephalus)  containing  species  which  enter  the  human  body, 
probably  in  the  flesh  of  fresh- water  fishes.  The  head  has 
neither  suckers  nor  lobes,  but  is  deeply  grooved  on  either 
side.  In  Bothriocephdlvs  the  genital  apertures  are  in  the 
middle  of  each  segment.  The  embryo  is  ciliated,  and  swims 
actively  in  water.  Becent  experiments  tend  to  show  that 
the  development  of  the  embryo  in  this  genus  may  take 
place  directly,  or  without  the  intervention  of  a  CysHeercue 
stage. 


THB  CE8TOIDEA. 


213 


It  is  obyions  that  the  Cestoidea  are  very  closelj  related 
to  the  Trematoda,  In  fact,  inasmuch  as  some  of  the  latter 
are  anenteroos,  and  some  of  the  former  are  not  segmented, 
it  is  impossible  to  draw  anj  absolute  line  of  demarcation 
between  the  two  groups.  It  would  appear  that  the  Ceatoidea 
are  either  Trematodes  which  have  undergone  retrogressive 
metamorphosis  and  have  lost  the  alimentary  canal  which 
they  primitiYely  possessed ;  or  that  they  are  modifications 
of  a  Trematode  tjrpe,  in  which  the  endoderm  has  got  no 
further  than  the  spongy  condition  which  it  exhibits  in 
ConvohUa  among  the  TwrbeUaria,  and  in  which  no  oral  aper- 
ture has  been  formed;  or  lastly,  it  is  possible  that  the 
central  cavity  of  the  body  of  the  embryo  Tcsnia  simply 
represents  a  blastocoele. 

If  the  Cesioidea  are  essentially  Trematodes,  modified  by 
the  loss  of  their  digestive  organs,  some  trace  of  the  diges- 
tive apparatus  ought  to  be  discoverable  in  the  embryo  tape- 
worm. Nevertheless,  nothing  of  the  kind  is  discernible, 
unless  the  cavity  of  the  saccular  embryo  is  an  enterocoele. 
And  if  this  cavity  is  a  blastoccele,  and  not  an  enteroccele, 
it  may  become  a  question  whether  the  tape- worms  are  any- 
thing but  gigantic  morulse,  so  to  speak,  which  have  never 
passed  through  the  gastrula  stage. 


214       THE  AHATOMY  OF  HmSTUBiLTBD  AJKHUlLB. 


CHAPTER  V. 

THE    HIBUDINEA,    THE    OLIOOCHiBTA,     THE    POLYCHiBTA, 

THE  OEPRTBEA. 

The  Hibudinea. — The  Leeches  are  aquatic  or  fcerrestrial, 
more  or  less  distinctlj  segmented,  vermiform  animals,  most 
of  which  suck  blood,  though  some  deyour  their  prej.  The 
ectoderm  is  a  cellular  layer,  covered  extemallj  bj  a  chiti- 
nous  cuticula,  and  except  in  Malaeobdella,  devoid  of  cilia. 
Yerj  commonly  it  is  marked  by  transverse  constrictions 
into  rings,  which  are  more  numerous  than  the  true  »omite$f 
as  indicated  by  the  ganglia  and  the  segmental  organs ;  and 
simple  glands  may  open  upon  its  surface.  One  or  more 
suckers,  which  serve  as  organs  of  adhesion,  are  developed 
upon  it.  In  some  (Acanthobdella)  bundles  of  sets  are  pre- 
sent; in  others  (Branchellian)  the  sides  of  the  body  are 
produced  into  lobe-like  appendages;  but  none  have  true 
limbs,  unless  the  lateral  appendages  of  HisiriohdeUa  are 
to  be  considered  as  such ;  nor  are  the  anterior  segments 
of  the  body  so  modified  as  to  give  rise  to  a  distinct 
head. 

The  mouth  is  generally  situated  at  the  anterior  end  of 
the  body ;  the  anus  at  the  opposite  extremity,  on  the  dorsal 
side  of  the  terminal  sucker.  The  buccal  cavity  may  be  armed 
with  several  serrated  chitinous  plates,  as  in  the  Medicinal 
Leech,  where  there  are  three  such  teeth.  By  their  aid  the 
Leech  incises  the  skin  and  gives  rise  to  the  well-known 
triradiate  mark  of  a  leech-bite.  The  buccal  cavity  usually 
opens  into  a  muscular,  sometimes  protrusible,  pharynx,  from 
which  a  narrow  oesophagus  leads  into  a  stomach,  which  is 
frequently  produced  into  lateral  csdca.    In  the  Medicinal 


TBW  HQtTmniEA. 

Leech  (Fig.  49),  for  example,  Uiere 
are  eleven  paira  of  each  cnca,  in- 
creaaing  in  length  and  capacity 
from  before  backirardB.  From  the 
stomach  a  narrow  intestine  le«ds 
to  the  anna.  In  Malaeobdtlla  the 
alimentaiy  canal  is  a  aimple  tnbe 
bent  sereral  times  npon  itself.  The 
alimentary  canal  ia  lined  bj  the 
cella  of  the  eadoderm,  and  the 
space  between  tbem  and  the  ecto- 
derm iaoccnpied  by  the  mesoderm, 
which  contains  abandant  connec- 
tive and  mnacnlar  elements,  and 
is  excavated  by  the  blood-chaimela, 
which  sometimes  have  the  form  of 
wide  sinnsee,  bat  in  other  cases 
are  comparativelj  narrow  vessels  a* 
with  definite  wslls.  '   ^ 

In  the  lower  Himdinea,  as  Clep-  Z 
tine,  the  einnses  and  vessels  appear 
tu  form  one  continnoas  sj-atem  of 
cavities  containing  a  fluid  which 
must  be  regarded  aa  blood.  Bat 
in  the  Leech,  a  distinct  paendhn- 
mal  vaacnlar  sjstem  has  attained 
a  great  degree  of  deBnition  and 
compleiitf :  it  consists  of  (1)  a 
median  dorsal  trunk  ;  (2)  a  median 
ventral  tnmk,  in  which  the  gan- 
glionic nerve-chain  lies ;  (3,  4)  two 
wide  lateral  longitndinal  tmnks 
{Tig.  50).  These  anastomose  with 
one  another,  and  give  off  nnmerous 
branches,  which  open  into  a  rich 
capiUaij  net-work,  sitaated  in  the 
moscolar  layer  of  the  mesoderm, 

*  *  Dia  Mentchlloben  Fanslten.' 


Ji 


rm 


216       THl  AKATOVT  OV  IWBKTXBKATKD  AHnULS. 

and  on  tbe  segmental  and  reprodnctiTe  orgaiu.    The  fluid 
contomcd  within  these  veeeeU  has  a  red  ooloor,  and  con- 
tains no  corpoHcleB. 
More  or  fewer  of  the  aegments  of  the  bodf  are  piorided 

Fig.  SO. 


■urfMeaf  ■  portion  of  one-half  of  the  bodv  i*  deplctedi  a,  a,  tli* 
venlraJ  trunk  ;  t,  (■,  (•  the  \mXen\  trank  and  id  brincha ;  /,/',  Um 
donal  trunk  and  iu  bnneho )  g,  the  slender  tiaoiccrH  tmnkt 
which  branch  out  at  each  end ;  h,  i,  the  trsniTene  rantral  bnm^M 
of  the  Uteral  tniak ;  4,  I,  the  brancb  to  (he  («ti>  (c),  and  tha  Mg- 
menlal  orjian  (rf)  -,  «,  branch  from  the  dilatation  on  th<  teadi  to  tba 
parietal  plainaea  ;  b,  b,  va*  defereni. 

with  what  are  termed  tegmttdai  organt.  Theae  are  tnbei 
which  open  extemalljr  on  the  ventral  wall  of  the  bodj, 
while  at  their  other  extremitiea  they  either  open  into  the 
nnnaw  bj  ciliated  monUia  (CIspMMtf),  or  form  a  closed 


THB  HIBIJDIirBA.  217 

and  more  or  less  reticulated  non-oiliated  coil  (JETirudo). 
These  obviouslj  answer  to  the  ciliated  water-yessels  of  the 
TwrheUaria  and  Trematoda. 

The  nerrous  system  consists  of  a  cerebral  mass  in  front 
of  the  month,  proceeding  from  which,  on  each  side,  is 
a  oommissure  connecting  it  with  a  ventral  cord  on  which 
ganglia,  corresponding  in  number  with  the  somites  of  the 
bodj,  are  developed.  In  MaiacobdeUa,  these  cords  are  lateral 
and  wide  apart,  but,  in  all  the  other  Hirudinea,  they  come 
close  together  behind  the  month,  and  occupy  the  middle  line 
of  the  ventral  face  of  the  body.  In  the  Leech,  according  to 
Leackart,  there  are  originally  thirty  pairs  of  post-oral  gan- 
glia, but  the  seven  posterior  and  the  three  anterior  'pam 
coalesce,  so  that  only  twenty-three  pairs  are  distinguishable 
in  the  adult.  Nerves  are  given  off  to  the  pharynx  and 
intestines,  and  the  former  develope  special  ganglia. 

Simple  eyes  are  usually  present  on  the  anterior  or  oral 
segment,  and  receive  nerves  from  the  supraoesophageal 
ganglia.  In  the  Leech  these  eyes  are  situated  in  the  fii'st 
three  segments.  Cup-shaped  depi'essions  of  the  integu- 
ment of  the  anterior  segments  of  the  body,  lined  by  peculiar 
glassy  cells  and  in  relation  with  nerves  which  tenninate  in 
fine  filaments,  have  been  discovered  by  Leydig  in  several  of 
the  Hirudinea,* 

The  elongated  spindle-shaped  muscle-cells  of  the  body 
are  abundant,  and  are  disposed  in  a  superficial  circular, 
and  deep  longitudinal  layer,  while  dorso-ventral  bands 
pass  from  the  dorsal  to  the  opposite  body- wall. 

Malacobddla  and  Sistriobdella  are  dioBcious,  but  the  other 
Hirudinea  are  hermaphrodite.  The  male  organs  consist  of 
numerous  testicular  sacs,  situated  on  each  side  of  the  body, 
and  connected  by  a  vas  deferens,  which  usually  opens  into 
a  sac,  terminating  in  an  eversible  penis.  The  spermato- 
zoa are  often  enclosed  in  a  case  or  spermcUophore,  The 
female  organs,  much  smaller  than  the  male,  consist  of 
ovarieB,  with  ovidticts  opening  into  a  vagina.  The  vaginal 
orifice  is  behind  that  of  the  penis.  In  the  Leech  the  eggs 
*  *  Archiv  fur  Anatomie  uud  Phyttiologie,'  1861. 


218       THE  AKJlTOVY  OF  IHyXBTBBKATBD  ▲KIMALB. 

are  enclosed  in  a  sort  of  cocoon,  formed  bj  a  yiscid  secre- 
tion of  the  integument. 

The  observations  of  Bathke  and  Lenckart  on  the  de- 
velopment of  Nepheli8f  Clepnne,  and  Hirudo  show,  that, 
after  the  division  of  the  vitellus  into  a  few  equal-sized 
large  blastomeres,  small  blastomeres  are  separated  from 
the  large  ones  (as  in  the  Ctenophora  and  Polycelis),  and  the 
rapidlj  multiplying  small  blastomeres  form  an  investment 
to  the  slowly-dividing  large  ones.  This  investment  is  the 
epiblast,  and  becomes  the  ectoderm,  while  the  included 
larger  blastomeres  are  eventually  converted  into  the  cells 
of  the  endoderm.  At  one  end  of  the  body  the  oral  aperture 
appears,  in  some  cases  {e.g,  Nephelis)  surrounded  by  a 
raised  lip,  as  in  the  embryo  Planarian ;  and  the  embryo 
passes  into  the  G^trula  stage.  The  body  now  elongates 
and,  on  the  ventral  face,  the  mesoblast  makes  its  appear- 
ance as  a  layer  of  cells,  sometimes  divided  into  two  longi- 
tudinal bands,  separated  by  a  median  interval.  Three  pairs 
of  segmental  organs,  which  have  only  a  temporary  existence 
and  have  been  regarded  as  primordial  kidneys,  are  developed 
at  the  posterior  end  of  the  body.  The  mesoblast  next 
becomes  divided  transversely  into  the  number  of  somites 
of  which  the  body  is  eventually  composed;  the  division 
first  making  its  appearance  on  the  ventral  face  of  the  body. 
A  pair  of  ganglia,  probably  derived  from  the  epiblast,  is 
developed  in  each  segment. 

Thus,  in  the  Leeches,  the  segmentation  of  the  body  is 
the  result  of  the  segmentation  of  the  mesoblast,  which 
becomes  the  mesoderm  of  the  adult.  And  it  is  this  seg- 
mentation of  the  mesoblast,  and  consequently  of  the  meso- 
derm, which  constitutes  the  most  important  difference  be- 
tween the  Leech  on  the  one  hand,  and  the  Turbellarian  and 
Trematode  on  the  other. 

On  the  other  hand,  in  the  development  of  a  mesoblast 
which  undergoes  division  into  segments,  the  Leeches 
exhibit  the  fundamental  character  of  all  such  segmented 
Livertebrates  as  the  chsetophorous  Annelida  and  the  Arthro- 
poda. 


THE  OLIOOGHJBTA.  219 

The  OLioooHiBTA. — ^The  Earthworm  {Lumbriew)  and 
fresh-water  worms  (Nais,  TuhifeXf  Chostogcuier),  which  are 
included  under  this  name,  are  closelj  allied  with  the  Leeches 
in  the  essential  points  of  their  structure  and  development, 
much  as  they  differ  from  them  in  habit  and  appearance. 

They  have  elongated,  rounded,  segmented  bodies,  often 
divided  by  many  superficial  transverse  constrictions  into 
rings,  which,  as  in  the  Leeches,  maybe  more  numerous  than 
the  proper  somites.  There  are  no  limbs,  but  each  segment 
is  usually  provided  with  two  or  four  sets  of  longer  or 
shorter  chitinous  setee,  which  are  developed  and  lodged 
in  integumentary  sacs.  The  outermost  layer  of  the  ecto- 
derm is  a  non-ciliated  chitinous  cuticle. 

The  mouth  is  situated  close  to  the  anterior  end  of  the 
body,  but  a  "cephalic  lobe*'  not  unfrequently  projects 
beyond  it  on  the  dorsal  side.  The  anus  is  at  the  opposite 
extremity  of  the  body,  and  the  straight  alimentary  tract 
which  connects  the  two  and  is  lined  by  the  endoderm,  is 
usually  divided  into  a  pharyngeal,  cesophageal,  and  gastro- 
intestinal portion,  the  latter  often  being  produced  laterally 
into  short  ceeca.  The  mesoderm  presents  well-developed 
transverse,  longitudinal,  and  dorao- ventral  muscular  fibres, 
as  in  the  Leeches.  It  is  excavated  by  a  spacious  perivisceral 
cavity,  which  contains  a  colourless  corpusculated  fluid,  and 
is  divided  by  thin  but  muscalar  mesenteries,  which  stretch 
from  the  intestine  to  the  parietes,  and  thus  break  up 
the  perivisceral  cavity  into  partially  separate  chambers. 
Li  addition,  there  is  a  system  of  pseud-hflsmal  vessels,  like 
those  of  the  Leeches,  provided  with  contractile  walls,  and 
containing  a  red  non-corpusculated  fluid.  No  communi- 
cation has  been  ascertained  to  exist  between  these  vessels 
and  the  perivisceral  cavity ;  but  there  can  be  little  doubt 
that,  as  in  the  case  of  the  Leeches,  they  must  be  regarded 
as  a  specially  differentiated  part  of  the  general  system 
of  the  perivisceral  cavity. 

In  the  majority  of  the  segments  there  are,  as  in  the 
HtrudineOf  paired  segmental  organs;  these  are  ciliated 
and  their  inner  ends  open  into  the  perivisceral  chamb^T. 


220       THB  ANATOMY  OF  HrYXBTSBSATSD  AHIKALS. 

The  nervous  sjstem  consiBts  of  proB-oral  or  cerebral 
ganglia,  continued  backwards,  on  the  Tcntral  aspect  of  the 
bodj,  bj  commissures  on  each  side  of  the  oasophagas  into 
a  double  chain  of  closelj  united  post-oral  ganglia. 

Large  tubular  fibres  are  imbedded  in  the  neurilemma  of 
the  ganglionic  chain  on  its  dorsal  face.  In  the  Earthworm 
there  are  three  of  these — one  median  and  two  lateral — ex- 
tending along  the  whole  length  of  the  ventral  end,  but  not 
into  the  oesophageal  commissures.*  The  nature  of  these 
structures  is  unknown. 

These  animals  are  hermaphrodite.  The  generative  organs 
are  situated  in  the  front  part  of  the  bodj,  the  male  organs 
being  anterior  to  the  female.  In  the  aquatic  Oligoehaia 
(NaU,  Tubifex)  the  genital  glands  have  no  proper  ducts,  but 
the  segmental  organs  of  the  segments  in  which  they  are 
contained  convey  the  generative  products  outwards.  In 
the  terricolous  forms  {Lumbricuti)  the  vasa  deferentia  are 
continuous  with  the  testes,  which  are  very  large.  The 
ovaries,  on  the  other  hand,  are  minute  solid  bodies  attached 
to  one  of  the  mesenteries,  and  the  oviducts  are  separate 
tubes  with  funnel-shaped  mouths,  which  open  into  the 
cavity  of  the  segment. 

In  Nats  and  Ch/Btogaster,  agamic  multiplication  occurs 
by  the  development  of  posterior  segments  of  the  body 
into  zooids,  which  may  remain  associated  in  chains  for 
some  time,  but  eventually  become  detached  and  assume 
the  parental  form.  Schulze  has  observed  that  when  a 
Naia  has  divided  into  an  anterior  and  posterior  zooid, 
the  last  somite  of  the  former  gradually  enlarges,  and 
becomes  divided  into  new  somites,  the  anterior  of  which 
give  rise  to  a  head.  A  new  zooid  is  thus  developed 
between  the  previously  existing  ones.  This  process  is 
repeated  in  what  was  the  penultimate,  but  is  now  the 
ultimate  somite  of  the  anterior  zooid;  and  again  in  the 
penultimate  somite  when  it  has,  in  the  same  way,  become 
terminaL 

*  Claparede,  *  HiBtologitohe  Untenttchungen  uber  den  RegcjUKurmy* 
1869. 


THB  8TBUCTT7BX  OF  THX  XABTHWOBK.  221 

Ls  the  Earth-worm  ia  a  very  accessible  subject,  it  maj  be 

ifal  to  the  stadent  to  be  famished  with  an  acconnt  of 

ae  of  the  chief  points  of  its  organisation  more  in  detaiL 

rhe  exterior  of  the  body  of  an  Earthworm  (Lwrnhrieut 

'e&tru,  rvbeUus  or  communis)  shows  a  namber  of  dose-set 

nsverse  grooyes  which  divide  its  body  into  nnmerons 

now  rings  or  segments.*    The  most  anterior  segment  is 

all  and  conical,  and  presents,  on  its  under  surface,  a 

xrestion  which  is  the  oral  aperture.    The  anus  is  at  the 

poeite  end  of  the  body.    Behind  the  mouth,  the  successire 

;ments  rapidly  attain  their  average  size ;  but,  in  a  full- 

)(wn  worm,  a  part  of  the  body  into  which  more  or  fewer 

tlie  segments  between  the  twenty-fourth  and  thirty* 

fch  indusively  (29  P-^,  L.  terregirit ;  24-29  P,  L,  rvbeUw ; 

•32,  L*  eommunis)  enter,  is  swollen,  of  a  different  colour 

«n  the  rest,  provided  with  abundant  cutaneous  glands, 

I  veoeires  the  name  of  eingulum  or  cUteUvm, 

u  the  dorsal  median  line  there  is  a  series  of  small  aper- 

m  o>r  pores,  one  for  each  segment  except  the  most  anterior, 

th  lead  into  the  perivisceral  cavity;  while  upon  the 

ral  surface  of  the  anterior  part  of  the  body  the  eight 

;ures  of  the  organs  of  generation  are  situated.    Of 

,  four,  situated  two  on  each  side,  between  the  ninth 

mth,  and  the  tenth  and  eleventh  segments,  are  the 

igs  of  the  receptaeula  seminU.    The  openings  of  the 

fiducts  are  on  the  fourteenth    segment;   those  of 

>  vasa  def erentia  on  the  fifteenth.    Besides  these,  all 

l^ents,  except  some  of  the  most  anterior,  exhibit 

of  minute  openings  appertaining  to  the  segmental 

and    they  are  further  perforated    by   the  four 

inal  double  rows  of  setae,  which  project  slightly 

he  surface  of  the  integument,  and  offer  a  certain 

9  when  the  worm  is  drawn  from  tail  to  head 

he  fingers. 

ly  is  invested  in  a  thin  and  transparent  but  dense 

ettSon   how   far   all     of  the  development  of  the  Earth- 
ite  represent  somites      worm  is  in  favour  of  their  being 
open.    The  history     true  somitet. 


222   THE  ANATOMY  OF  INTXSTEBBATXD  ANIMALS. 

euticula,  perforated  by  excessively  minute  vertical  canals. 
Within  this  lies  a  thicker  layer,  consisting  of  a  regulated 
nucleated  protoplasm,  the  meshes  of  which  are  filled  with 
a  transparent  gelatinous  substance.  This  layer  probably 
represents  both  the  dermis  and  epidermis,  and  has  been 
termed  the  hypodermis.  Internal  to  it  lies  a  thick  layer 
of  circular  muscular  bands,  in  the  interstices  of  which 
pigment  granules  occur ;  and,  still  more  internally,  is  a 
much  thicker  coat  of  muscular  fibres,  which  are  disposed 
longitudinally. 

The  cavity  circumscribed  by  this  longitudinally  fibrous 
muscular  layer  is  lined  by  a  kind  of  connectiye  tissue. 
Corresponding  with  the  divisions  between  every  pair  of 
segments  (except  in  the  most  anterior  part  of  the  body), 
this  connective  tissue  is  continued  transversely  towards  the 
axis  of  the  body,  and  passes  into  that  which  forms  the  wall 
of  the  intestine ;  while,  on  the  ventral  side,  it  forms  an 
arch  over  the  ventral  nervous  cord,  and  the  vessels  which 
accompany  it.  In  the  interior  of  each  of  these  mesenteric 
septa,  radiating  and  circular  muscular  fibres  are  abundantly 
developed,  and  the  former  are  connected  externally  with 
the  superficial  layer  of  transverse  muscles. 

The  perivisceral  cavity  is  thus  divided  into  nearly  as 
many  short  chambers  as  there  are  segments ;  each  chamber 
communicates  with  the  exterior,  directly  by  the  dorsal 
pore  and  indirectly  through  the  segmental  organs,  while 
fluid  may  pass  from  one  to  the  other  by  the  supra-neural 
archways. 

The  short  and  curved  setse  project  much  further  into  the 
interior  of  the  body  than  they  do  on  to  its  exterior.  The 
free  apices  of  each  pair  are  situated  close  together,  while 
their  inner  ends  diverge  from  one  another.  Each  is  enclosed 
in  a  sac  in  which  it  is  developed,  and  to  which  the  muscles, 
by  which  it  is  protruded,  are  attached.  There  are  eight 
setsB  to  each  somite,  one  pair  not  far  from  the  ventral 
median  line  on  each  side ;  and  the  other  pair  placed  in  the 
same  transverse  line,  but  further  outwards. 

The  mouth  leads  into  a  muscular  pharynx,  with  a  com- 


THB  BTBUCTUBX  OF  THE  XABTHWOSM.  223 

paratirelj  small  internal  cavity,  which  reaches  as  far  back 
as  the  seventh  segment.  From  this  a  narrow  OBsophagas  is 
oontinned  as  far  back  as  the  fifteenth  or  sixteenth  segment ; 
and  presents  three  pairs  of  lateral  glandular  diverticula, 
which  contain  a  calcareous  matter,*  in  the  region  of  the 
twelfth  and  thirteenth  segments.  Posteriorly,  the  gullet 
opens  into  a  crop,  which  is  succeeded,  about  the  eighteenth 
segment,  by  a  thickened  and  muscular  gizzard. 

Upon  this  follows  the  intestine,  which  has  the  appearance 
of  a  simple  tul>e ;  but  is  in  reality  complicated  by  the  invo- 
lution of  its  wall,  along  the  dorsal  median  line,  into  a  thick 
fold,  which  projects  into  the  interior  of  the  intestinal  cavity, 
and  is  the  so-called  typhlo8ole.  The  exterior  of  the  intestine 
and  the  cavity  of  the  typhlosole  present  a  coating  of 
yellowish-brown  cells. 

The  MegmentcU  organs  are  greatly  convoluted  tubes,  situated 
one  on  each  side  of  every  segment  except  the  first,  and 
attached  to  the  posterior  mesenteric  septum  of  the  segment. 
Each  canal  communicates  internally,  by  a  wide  funnel- 
shaped  ciliated  aperture,  with  the  perivisceral  cavity,  while 
externally,  it  opens  by  a  minute  pore,  which  is  usually  dose 
to  the  internal  pair  of  setse.t 

A  colourless  fluid,  containing  colourless  corpuscles,  and 
answering  to  the  blood  of  other  invertebrated  animals,  occu- 
pies the  perivisceral  cavity ;  but,  in  addition  to  this,  there  is 
a  deep  red|fluid,  devoid  of  corpuscles,  which  fills  a  very  largely 
developed  system  of  pseud-hsamal  vessels.  These  consist  of 
longitudinal  and  transverse  principal  trunks,  and  of  very 
numerous  branches  which  proceed  from  them  and  ramify 
in  aU  parts  of  the  body,  except  the  cuticle  and  hypo- 


The  longitudinal  trunks  are  three :  one  eupra-irUegtinal, 
which  lies  along  the  dorsal  aspect  of  the  alimentary  canal ; 
<nie    wb'inietiinal,  which   corresponds  with  this  on  the 

*  Hie  nature  of  this  substance  tale,'  1873.^ 

has    recently  been  discussed  by  t  Gegenbaur, ''Ueberdiesoge- 

M.  E.  Perrier,  "  Etude  sur  un  nannten  Respirationsorgane  des 

genre  noaveao  des  Lombriciens.'*  Regenwurms. '    (*  Zeitsohrift  fur 

(•Axohivet  de  Zoologie  ezp^men-  Wits.  Zoologiey'  1852.) 


224       THE  ANATOlfY  OF  INYBSTXBBATXD  AHIXALS. 

ventral  aspect  of  that  canal ;  and  one  tub^neural,  which  lies 
beneath  the  ganglionic  cord. 

The  supra-intestinal  and  sub-intestinal  vessels  are  con- 
nected in  the  greater  number  of  the  segments  bj  pairs 
of  eommismral  transverse  trunks,  which  embrace  the  in- 
testine, and  give  off  numerous  branches  to  it.  The  supra- 
intestinal  and  sub-neural  vessels  give  off  transverse  trunks 
into  the  mesenteric  septa,  which  branch  out  into  the  mus« 
cular  layers,  and  some  of  which  anastomose  so  as  to 
form  a  second  set  of  transverse  communications.  More- 
over, the  sub-neural  trunk  and  the  sub-intestinal  trunk 
respectively  3end  branches  to  each  segmental  organ,  upon 
which  they  are  distributed,  and,  anastomosing,  give  rise 
to  another  series  of  communications  between  the  longi- 
tudinal trunks. 

In  the  seven  most  anterior  segments,  the  longitudinal 
vessels  break  up  into  a  network,  and  there  are  no  distinct 
transverse  commissural  vessels.  Behind  these,  and  in  the 
region  of  the  generative  apparatus,  the  commissural  vessels 
are  greatly  dilated,  and  form  from  five  to  eight  pairs  of 
so-called  hearts  which  are  attached  to  the  anterior  faces 
of  as  many  mesenteries.  These  contract  from  the  dorsal 
towards  the  ventral  side. 

The  nervous  system  consists  of  two  cerebral  ganglia 
lodg^  above  the  pharynx  in  the  third  segment,  and  united 
by  commissural  cords  with  the  anterior  ganglia  of  the 
chain,  which  extends  through  the  whole  length  of  the 
body  on  the  ventral  wall  of  the  perivisceral  cavity. 

There  are  no  eyes,  nor  are  any  other  organs  of  special 
sense  known. 

The  Earthworm  is  hermaphrodite.  The  testes  are  two  pairs 
of  large  sacs,  each  of  the  anterior  pair  being  bilobed. 
The  testes  of  opposite  sides  are  united  in  a  common  median 
reservoir,  situated  in  the  tenth  and  eleventh  segments,  from 
which,  on  each  side,  ducts  take  their  origin.  The  two 
ducts  of  the  testes  of  the  same  side  unite  into  a  single  vas 
deferens,  and  these  two  vasa  deferentia  open  externally  on 
the  ventral  aspect  of  the  fifteenth  segment    The  ovarii 


THE  DETSLOPMBKT  OF  THE  EABTHWOSM.  225 

are  two  minute  solid  bodies,  not  more  than  -^^  of  an  inch 
long,  attached  to  the  posterior  face  of  the  mesenteric 
septum  which  separates  the  twelfth  and  thirteenth  segments. 
Thej  therefore  lie  in  the  cavity  of  the  latter.  The  ovidncts 
are  quite  distinct  from  the  oyaries,  and  open  internally 
by  wide  funnel-shaped  apertures,  situated  in  the  cavity  of 
the  thirteenth  segment.  From  these  funnel-shaped  ends 
the  oviducts  are  continued,  as  slender  tub^^  through  the 
mesenteric  septum  which  separates  the  thirteenth  from 
the  fourteenth  segment,  and  open  on  the  ventral  face  of 
the  latter. 

Four  globular  spermathecse,  or  receptacles  of  the  sper- 
matozoa, are  situated,  two  on  each  side,  in  the  tenth  and 
eleventh  segments,  and  open  on  the  ventral  face  between 
the  ninth  and  tenth,  and  the  tenth  and  eleventh  segments 
respectively.  These  are  filled  when  copulation  takes  place, 
during  which  process,  the  two  worms  are  said  to  be  bound 
together  by  a  tough  secretion  of  their  clitella. 

The  development  of  the  Oligochcsta  has  recently  been 
carefully  investigated  by  Kowalewsky.  The  eggs  of  the 
Earthworm  are  laid  in  chitinous  cocoons  or  cases,  which 
are  probably  secreted  by  the  clitella.  In  addition  to  the 
eggs,  the  cocoons  enclose  an  albuminous  fluid,  and  packets 
of  spermatozoa.  The  viteUus  is  invested  by  a  membrane, 
and  contains  a  germinal  vesicle  and  spot.  Complete  yelk- 
division  takes  place,  and  eventually  the  blastoccele  becomes 
reduced  to  a  mere  cleft.  The  blastomeres  are  disposed  in 
two  layers — one  consisting  of  small,  and  the  other  of  large 
blastomeres.  The  embryo  thus  formed  becomes  concave 
on  the  side  formed  by  the  large  blastomeres,  until  it 
assumes  the  form  of  a  sac,  ciliated  externally,  with  an 
opening,  the  future  mouth,  at  one  end ;  the  cavity  of  the 
sac  being  the  primitive  alimentary  canal,  and  the  layer  of 
large  blastomeres,  the  hypoblast.  Between  the  two,  a 
mesoblastic  layer  appears,  but  the  exact  manner  of  its 
origin  is  not  known.  On  one  face  of  the  saccular  embryo 
the  mesoblast  becomes  divided  into  a  series  of  quadrate 
masses,  like  the  protovertebne  of  a  vertebrate  envbrj^^ 


226       THB  AKATOlfY  OF  nTYBSTEBRATSD  AHIMALS. 

disposed  gymmetrically  on  each  side  of  a  median  line, 
which  corresponds  with  the  future  ventral  median  line 
of  the  body.  Along  this  line,  the  epiblast  becomes  thick- 
ened inwards,  and  the  thickening  is  converted  into  the 
ganglionic  chain.  At  the  same  time,  each  quadrate  mass 
of  the  mesoblast  is  excavated  bj  the  development  of  a 
cavity  in  its  interior,  whereby  it  becomes  converted  into 
a  sort  of  sac.  The  adjacent  anterior  and  posterior  walls 
of  successive  sacs  unite,  and  give  rise  to  the  mesenteric  septa, 
while  their  cavities  become  the  chambers  of  the  perivisceral 
cavity.  The  segmental  organs  commence  as  cellular  out- 
growths from  the  posterior  face  of  each  septum  thus  formed, 
and  only  subsequently  become  excavated  and  communicate 
with  the  exterior. 

The  development  of  tlie  Earthworm,  therefore,  closely 
resembles  that  of  the  Hirudinea,  and  more  especially  that  of 
the  Medicinal  Leech,  in  which  the  digestive  cavity  of 
the  embryo  would  seem  to  be  formed,  as  in  the  Earthworm, 
by  a  process  which  is,  in  a  sense,  invagination.  It  would 
appear  that  the  first  formed  aperture  is  the  mouth ;  while 
the  anus  is  a  secondary  perforation ;  and  the  segmentation 
of  the  body  commences  in  the  mesoblast. 

In  the  fresh- water  Oli^ochcetay  Euaaees  and  Tubifem^  the 
vitellus  also  becomes  divided  into  large  and  small  blasto- 
meres.  The  latter  extend  over  the  larger  blastomeres,  and 
form  the  epiblast  ( =  ectoderm).  A  mesoblast  ( =  mesoderm), 
divided  into  two  broad  longitudinal  bands,  is  developed,  and 
the  oral  cavity  is  said  to  be  formed  by  invagination  of  the 
epiblast  between  the  anterior  ends  of  the  two  bands  of  the 
mesoblast.  In  this  case,  the  mouth  in  these  genera  is  a 
secondary  formation.  The  innermost  layer  of  large  blasto- 
meres becomes  the  hyx)oblast  ( -  endoderm).* 

The  PoLTCHiETA. — ^Except  that  the  PolychoBta  are  almost 
invariably  dioBcious  and  marine,  while  the  Oligochceia  are 

*  Kowmlewikv,  <*  Embryologische  Studien.*'  (*  Hem.  de  PAcad.  de 
St  Petenboorg/  1861.) 


POLTKOE  SQITAMATA.  227 

moiioBcioQS,  and  inhabitants  either  of  land  or  fresh  water,  it 
is  hard  to  say  what  absolute  characters  separate  these  two 
groups.  The  lowest  forms  of  the  Polyclueta,  such  as  CapUella 
and  PolyophthalmuSy  might  be  regarded  as  marine  dioecious 
Naidoe,  But,  in  the  higher  Polychceta,  each  segment  of  the 
body  developes  lateral  processes — the  parapodia,  or  rudi- 
mentary limbs,  which  are  usually  provided  with  abundant 
strong  setsB ;  a  distinct  cephalic  segment,  the  prcMtomium, 
appears  in  front  of  and  above  the  mouth,  and  bears  eyes  and 
tentacles ;  while  those  parapodia  which  lie  in  the  vicinity  of 
the  mouth  may  be  specially  modified  in  form  and  direction, 
foreshadowing  the  jaws  of  the  Arthropoda,  Ciliated,  some- 
times plumose,  processes  of  the  dorsal  walls  of  more  or  fewer 
of  the  segments  may  perform  the  office  of  external 
hranchice ;  and,  occasionally,  the  dorsal  surface  gives  rise 
to  flat  shield-like  processes,  the  so-called  elytra. 

The  following  detailed  description  of  a  very  common 
species  of  Polyrwe,  will  give  a  fair  conception  of  a  poly- 
chsetous  Annelid,  in  which  the  highest  degree  of  complexity 
of  organisation  known  in  the  group  is  attained : — 

Polynoe  aquamaia  is  an  elongated  vermiform  animal,  about 
an  inch  long,  the  body  of  which  is  divided  into  a  succes- 
sion of  portions,  for  the  most  part  similar  and  equivalent 
to  one  another,  but  presenting  peculiar  modifications  at 
the  anterior  and  posterior  extremities.  Each  such  portion 
is  properly  termed  a  somite;  while  the  term  "segment" 
may  be  retained  to  indicate  generally  a  portion  of  the  body, 
without  implying  its  precise  equivalency  to  one  somite  or 
to  many.  Thus,  then,  the  body  of  the  Polynoe  is  composed 
of  a  series  of  twenty-six  "  somites,"  terminated  anteriorly 
by  a  "segment,"  the  proestomiumi  (* Kopf-lappen,*  Grube) 
and  posteriorly  by  another,  the  pygidium,  which  may  or 
may  not  represent  single  somites. 

If  one  of  the  somites  from  the  middle  of  the  body  (Fig.  51, 
0,  D)  be.  examined  separately,  it  will  be  found  to  be  trans- 
versely elongated,  so  as  to  be  about  three  times  as  broad  as 
it  is  long,  and  to  be  slightly  convex  above  and  below,  prc- 
MOting   a  deep,  median,  longitudinal  groove  inien.ot\3« 


228       THE  AITATOICT  OT  nmBTIBKATBD  AHIMiUB. 

Laterally  tlie  somite  is  prodaced  into  two  thick  proceaaes, 
the  "parapodia." 

Bacb  parapodiom  diridea  attta  esbremity  into  twopoiliona, 

a  anperior  and  an  inferior,  which  may  be  denominated  r«- 

Fig.  51. 


Fig.  il.—Fol^r  tqatuniOa. 

A.  Vleved  from  above  ■ad  enlarged  :   a,  b,  r,  etc.  u  Id  Fig.  53  B ;   r, 
elytra ;  /.  apace  lefl  between  the  two   potCerloT   elytra ;  g,  febe 

and  fimbria  of  the  elytra. 

B.  Poaterior  extremity,  inferior  Hei 
tubercle ;  c,  c",  notopodlal  and  neoropodii 

C.  Section  of  half  a  aomlte  with  elyr 


pygidial  drri;  h,  iDferfor 
DOtopodium;  t,   unriv 


apectively  the  notopodaim(Fig,Sli)aixdiheneiiirop<>ditim(k), 
the  one  ooonpTisg  the  "  hemal,"  or  dorsal,  the  other  iho 
■'  neonl "  or  rentral  aspect,    The  latter  ia,  in  thia  ap«ciea 


FOLYKOE  8QIXAMATA«  229 

SO  much  the  larger,  that  the  notopodinin  appears  like  a  mere 
tubercle  projecting  from  its  tipper  surface.  In  other  An* 
nelidOf  however,  and  in  the  young  state  of  Polynoe,  the 
notopodium  is  as  large  as  the  neuropodium.  Both 
divisions  of  the  parapodia  are  armed  with  peculiar  stiff 
hair-like  appendages  (g),  composed  of  chitin,  and  developed 
within  diverticula  of  the  integument,  or  irichophores,  in  which 
their  bases  always  remain  enclosed.  These  can  be  pro- 
truded and  retracted  by  muscles  attached  to  their  sacs,  and 
they  vary  exceedingly  in  form.  Three  distinct  kinds  are 
observable  in  Polynoe  alone.  The  notopodium  and  the 
neuropodium  carry  each  a  single,  sharp,  style-like  aciefUum, 
the  greater  part  of  the  length  of  which  is  imbedded  in  the 
parapodium  and  its  divisions,  while  the  point  just  projects 
at  about  the  centre  of  the  latter.  The  neuropodial  is  very 
much  longer  than  the  notopodial  aciculum. 

Superiorly,  the  notopodium  carries  two  transverse  rows 
of  more  slender  organs  of  a  similar  nature,  the  $eUB :  the 
proximal  set  are  much  shorter  than  the  distal,  but  even 
the  latter  do  not  attain  a  length  of  more  than  -^  of  an  inch 
(Fig.  62,  G). 

The  proximal  set  are  somewhat  knife-like  in  shape  if 
viewed  in  profile,  consisting  of  a  comparatively  short, 
straight  **  handle,"  by  which  they  are  imbedded  in  their 
sacs,  and  of  a  thick,  rounded,  curved  blade,  tapering  to  a 
fine  point  at  its  extremity.  Close-set  transverse  ridges, 
finely  serrated  at  their  edges,  and  inclined  obliquely  to  the 
stirface  of  the  blade,  traverse  its  convex  anterior  circum- 
ference, leaving  the  back  free.  The  distal  set®  (Fig.  52,  G) 
have  a  very  similar  sbructure,  but  they  are  much  elongated 
and  very  slender.  The  handle  is  longer ;  and  the  blade,  little 
curved  and  simply  set  on  at  an  angle  with  the  handle,  is 
produced  at  the  end  into  a  long  and  delicate  filament.  The 
base  of  the  blade  (E)  is  beset  with  incomplete  ridges,  like 
those  of  the  short  setee,  but  towai*ds  the  middle  (F)  these 
ridges  appear  to  encircle  the  blade  completely,  assuming  the 
aspect  of  so  many  closely  imbricated  concentric  scales,  before 
finally  becoming  obsolete  upon  the  extremity  of  the  seta. 


230       THE 


or  IHTXBTKB&A.TED  AXUCAXS. 


The  nenropodial  actculnm  needs  no  special  notice,  except 
that  the  eitremitj  of  it»  trichophore  projects  as  a  sort  ai 
papilU,  less  obviooB  in  fnll-grown  apecimens,  which  dindes 
the  neoropodium  into  an  upper  and  a  lower  portion,  the 
former  containing  about  half  as  manj  eeta  aa  the  latt«r. 

Fig.  52. 


Tig-iO—Polyndt    , 

A^t jtron  viewed  from  »bov( 
G,  F,  parts  of  the  blute  of 
fr«e  (Xlremlty  of  knotopodi 


The  apertures  of  the  tricfaophores  are  placed  between  lobe- 
like  prolongations  of  the  neuropodinm,  to  which  the  special 
term  of  kUna  (Gmbe)  may  be  applied.  In  this  species 
&eij  present  no  remarkable  pecoliaritj  beyond  their  in- 
eqnali^. 


POLYKOB  BQITAMATA.  231 

The  neuropodial  set®  (Fig.  52,  C,  D),  although  at  first 
sight  very  different  from  the  notopodial  setsB,  are,  in 
tmth,  constructed  on  essentially  the  same  plan,  the  blade 
being  short,  while  the  handle  is  proportionally  elon- 
gated. The  blade  is  subcylindrical  at  its  base,  pointed 
and  slightly  curved.  Eight  or  nine  transverse  ridges  ex- 
tend around  about  two-thirds  of  the  circumference  of  its 
proximal  half;  the  basal  ridges  are  narrow,  and  merely 
serrated,  but  towards  the  apex  the  ridges  become  deeper, 
and  the  serrations  pass  into  strong  teeth ;  at  the  same  time, 
one  side  of  the  ridge  is  elongated  into  a  strong  point. 

Attached  to  the  under  surface  of  the  parapodium  by  a 
somewhat  enlarged  base,  with  which  it  is  articulated,  is  a 
smooth,  conical,  very  flexible  filament, —  the  neuropodial 
cirrus  (Pig.  51,  c') ;  it  hardly  reaches  to  the  end  of  the  neuro- 
podium.  Again,  springing  from  the  neural  surface  of  the 
somite,  close  to  the  parapodium,  there  is  a  small  pyriform 
tubercle  (h),  divided  by  longitudinal  grooves  into  about 
eight  segments.  This  is  possibly  connected  with  the  repro- 
ductive function. 

The  appendage  of  the  notopodium  or  rather  of  the  noto- 
podial side  of  the  parapodium  and  somite,  varies  according 
to  the  particular  somite  which  may  be  examined.  In  some 
somites  this  appendage  is  a  cirrus  (Fig.  51,  D,  c)  similar  to 
the  neuropodial  cirrus,  but  much  larger,  equalling  the  semi- 
diameter  of  the  body  in  length,  and  presenting  an  enlarged 
pigmented  bulb  of  attachment  to  which  the  filament  of 
the  cirrus,  which  is  cylindrical  for  about  two-thirds  of  its 
length,  and  then  becomes  enlarged  and  suddenly  tapers  to 
its  extremity,  is  articulated. 

In  the  other  somites  the  notopodial  appendage  is  a  large, 
thin,  oval  plate — the  elytron  (Fig.  51,  0,  c).  It  is  attached 
by  a  thick  peduncle,  and  has  its  long  axis  directed  obliquely 
outwards  and  backwards.  The  surface  of  the  elytron 
(Fig.  52,  A)  is  covered  with  an  ornamentation  of  larger  or 
smaller  tubercular  prominences,  granulated  and  ridged 
upon  their  surface.  A  part  of  the  inner  and  anterior  edge 
of  each  elytron  overlaps  or  is  overlapped  by  its  fellows  for 


232       THE  AKATOMT  OF  niTBBTEBRATXD  ANIMALS. 

a  certain  extent  of  its  oircnmference,  which  is  so  far 
smooth,  but  in  the  rest  of  its  extent  it  is  fringed  with 
coarse  brownish  filaments  or  fi/mbruB,  which  arise  from  the 
npper  snrface  just  within  the  edge,  and  are  obviouslj 
oatgrowths  of  the  same  order  as  the  tubercles. 

Such  is  the  structure  of  one  of  the  middle  somites  of 
Polynoe  agrtiamaia.  The  anterior  and  posterior  somites,  with 
the  exception  of  the  first  and  second,  present  only  minor 
differences,  as  in  the  proportions  of  the  setsB,  or  in  the 
figure  of  the  elytra.  The  first  somite,  which  contains  the 
mouth,  is  the  peridofnium  (**  mund-segment "  of  Grube). 
The  parapodia  of  this  somite  are  narrow  and  elongated 
(Fig.  63,  B,  C,  m);  they  are  obscurely  divided  at  their 
extremity  into  a  rudimentary  neuropodium  and  notopo* 
dium,  and  give  attachment  to  a  pair  of  large  peristomial 
ciiri  (c'  e)  ("  cirrhes  tentaculaires,"  Audouin  and  Milne- 
Edwards  ;  "  Fiihler-cirren,'*  Grube),  of  the  same  structure 
as  the  notopodial  cirri,  which  stretch  forwards  by  the  sides 
of  the  mouth. 

The  apex  of  a  single  small  aciculum  issues  rather  aboye 
the  point  of  division  of  the  peristomial  parapodium,  and 
two  minute  curved  setsB  accompany  it.  These,  have  been 
generally  overlooked  ;  *  but  they  seem  to  demonstrate,  in 
a  very  interesting  manner,  the  nature  of  the  appendages 
of  the  peristomial  segment. 

The  second  somite  differs  from  the  rest  only  in  the  great 
elongation  of  its  neuropodial  cin*us,  which  is  directed  for- 
wards and  applied  against  the  mouth. 

The  peristomium  and  the  pnestomium  together  are  ordi- 
narily confounded  under  the  common  term  of  "  head.'*  The 
latter  (Fig.  53,  B,  G,  I)  is  an  oval  segment  flattened  supe- 
riorly, placed  altogether  in  front  of  and  above  the  month, 
presenting  on  its  postero-lateral  edges  four  dark  spots,  the 
ejes,  and  possessing  hve  cirriform  appendages,  two  pairs 
and  a  single  median  one.    The  latter  (a),  or  the  prcestomial 

*  At    lesst,   in    the   descrip-  valuable  paper,  *'Ueber  die  Ent- 

tions  of  the  adult  Fofyn6§,  'Ihey  wickelung  und  Metamorphose  der 

are  particularly  mentioned,  how-  Polynoen."  Q  M filer's   Arohiv,' 

ever,    by   Max   MCOler    in    hit  1851.) 


FOLTHOI  B4ITAIU.TA.  233 

feiUaofe  ("  antenne  mMiane,"  Milne-Edwftrds)  is  eimilar  in 
Btmctnre  to  an  ordinorj  ciiroe.  Of  the  other  t^pend^es, 
th«  upper  one  apoa  each  aide  (sapero-lsteral  pnestomial 
eirnw,  "  antanne  mitojenne  ")  also  reeemblee  an  ordinal; 
cirnu  (b) ;  but  the  lower  (infero-lateral  pmBtomial  cirmB, 
'antenne  extome")  {V)  ia  mach  larger,  and  ia  capable  of 
extreme  elongation  and  contraction,*  while  the  ordinary 
Fig.  S3. 


Fig.  Sa.—Polfn6t  tjuamala. 

A.  Pnlerlor  eitremltj;  from  sbove:  c,  Dotopodiml  clrma  of  tut 
■otnite  :  df  pjgidiftL  cirri  ;  r,  BtiUA. 

B.  Anterior  eitremltj  from  kbove:  a,  pneitoml^  tenUole;  b,  *u- 
poior  and  6' inferior  pittatomial  cimw;  c,  c',  natopodial  uid  neuro- 
podlal  cirri;  e,  peduncle  of  first  elytron  :  /,  prKilomium :  a,  par*' 
podium  of  periKomluni.  C.  Inferior  view  of  anterior  extremity, 
lettan  u  before. 

cirri  are  merely  flexible.  Although  at  first  sight  probable, 
jet  it  would  appear  from  Max  Muller's  accoant  of  the  deve- 
lopment of  Polynoe,  that  these  two  appendages  do  not,  like 
the  two  periatomial  cirri  which  tbej  essentially  resemble, 

•  I  have  never  olwerved  any 
InvaginalioD  aurli  ■■  ii  alaled  to 
seeur  by  Audouin   and   Uilae-      p.  10.) 


Edward*.  IBM.  ('Blittrir*  Natn- 
relle  du  Littoral  de  la  Fiance,' 


234   THE  ANATOMY  OF  IHYBBTEBBATED  ANIMALS. 

correspond  with  the  notopodial  and  nenropodial  cirri  of  a 
single  parapodium,  inasmuch  as  they  arise  from  perfectly 
distinct  portions  of  the  prsDstomium.  It  is  yery  possible 
that  each  represents  the  appendage  of  a  somite,  and  in  this 
case  the  prsBstomium  would  be  composed  of  at  least  two 
somites.  Whether  the  prsBstomial  tentacle  indicates  another, 
or  whether  it  is  merely  an  appendage  of  such  a  nature  as 
the  labrum  or  the  rostrum  of  a  Crustacean,  there  is  no 
evidence  at  present  to  show. 

It  is  highly  interesting  to  remark,  that  thus,  in  the 
Polynoe,  as  in  the  Arthropoda,  the  "  head "  results  from 
the  modification  of  a  number  of  somites,  some  of  which 
lie  in  front  of,  and  others  behind,  the  mouth.  The  move- 
ments and  evident  extreme  sensitiveness  of  the  inferior 
prsBstomial  cirri  during  life  indicate  that  they  perform 
the  functions,  as  well  as  occupy  the  position,  of  an- 
tennae. 

The  hindermost  segment  of  the  body,  or  pygidium  (Fig. 
51  6,  Fig.  53  A),  is  narrow,  and  divided  at  the  end  into 
two  supports  for  the  pygidial  (d)  cirri,  which  are  as  long  as 
the  three  last  somites,  and  resemble  the  notopodial  cirri  in 
form  and  structure.  They  extend  directly  backwards, 
almost  parallel  with  one  another  and  with  the  notopodial 
cirri  of  the  last  somite,  which  are  thrown  backwards  and 
downwards  (Fig.  53,  A,  c).  It  seems  probable  that  the 
pygidium  represents  only  a  single  somite. 

The  anus  is  not  terminal;  as  in  many  Annelids,  but  is 
seated  in  the  middle  of  a  strongly  raised  papilla  (Fig.  53, 
A  x\  which  projects  from  the  dorsal  surface  of  the  penulti- 
mate somite ;  its  sides  are  produced  into  about  fourteen 
folds.  The  two  last  elytra  have  their  edges  excavated, 
80  as  to  leave  a  space  over  the  anus  (Fig.  51,  A/). 

The  notopodial  cirri  and  the  elytra  do  not  coexist  upon 
the  same  somites;  and  the  order  of  arrangement  of  the 
elytrigerous  and  cirrigerous  somites  is  very  curious.  The 
Ist  or  peristomial  somite  is  cirrigerous,  and  so  are  the  3rd, 
6th,  8th,  10th,  12th,  14th,  16th,  18th,  20th,  22nd,  24th,  25th, 
and  26th;   while  the  2nd,  4th,  5th,  7th,  9th,  11th,  13th, 


THX  POLYCHiBTA.  235 

15tli,  17th,  19th»  2 let,  and  23rd  somites  bear  elytra,  making 
twelve  pairs  in  all. 

In  no  polychsBtoos  Annelid  is  the  stmctiire  of  a  somite 
more  complex  than  in  Polynoe ;  and  there  are  but  very  few 
parts  not  found  in  Polynoe  to  be  met  with  in  other  Annelida. 
The  careful  study  of  this  species,  therefore,  furnishes  us  with 
an  almost  complete  nomenclature  for  the  external  organs  of 
the  whole  group ;  and  it  will  be  found  that  the  other  forms 
of  Annelida  differ  mainly  in  the  greater  or  less  development 
and  modification  of  the  organs  which  have  just  been  de- 
scribed. A  large  proportion  of  the  Polychceta  are  like 
Polynoe,  free  and  actively  locomotive  animals,  which  rarely 
fabricate  tubular  habitations,  and  are  therefore  termed 
ErranHa ;  they  possess  a  prsestomium,  usually  provided  with 
eyes  and  feelers,  and  have  many  parapodia,  which  are  not 
confined  to  the  anterior  region  of  the  body.  They  very 
generally  have  a  proboscis,  provided  with  chitinous  teeth. 

The  singular  genus,  Tomopteris,  is  a  transparent  pelagic 
Annelid,  with  numerous  parapodia,  each  terminated  by  two 
lobes  representing  the  neuropodium  and  notopodium, 
but  with  setae,  two  of  which  are  very  long,  only  in  the 
cephalic  region. 

The  sedentary  Annelids  (Tubicola)  fabricate  tubes,  either 
by  gluing  together  particles  of  sand  and  shells,  or  by  secret- 
ing a  chitinous  or  calcified  shelly  substance,  in  which  they 
remain  (e.  g.  ProtuUit  Fig.  54).  The  prsestomium  is  small 
or  wanting;  none  have  a  proboscis;  there  are  no  cirri; 
and  the  parapodia  are  short  or  rudimentary.  The  branchise 
are  developed  only  on  the  anterior  somites,  and  the  latter 
are  often  markedly  different  from  those  which  constitute 
the  posterior  part  of  the  body. 

In  some  (SerptUidcB)  a  tentacle  is  enlarged  and  its  end 
secretes  a  shelly  plate  which  serves  as  an  operculum,  and 
shuts  down  over  the  mouth  of  the  calcareous  tube  inhabited 
by  the  animal,  when  it  is  retracted.  The  dilated  end  of 
the  opercular  tentacle  sometimes  serves  as  a  chamber  in 
which  the  young  undergo  their  development,  (species  of 
8pirorbi»). 

The  alimentary  canal  of  the  polychsetoufi  AntieUda  x^x^-^ 


Fig.  b4.—Pmiila  Dyitcn.  A,  the  lexnat,  mabire  lalinal,  extracted 
lirom  III  calcanou*  tube;  a,  bredcUai  plamca-  b,  hood-Uke  u- 
pantion  of  the  tntecior  end  of  the  body:  c,  the  month;  4,  the 
■tumach:  *,  the  uiiu;  /,  (he  t«atei:  f,  the  oTk.  B.  «  PrvMa  in 
dmnearproUfamaoa;   i, ttaebnnoliueof theiaoid.. 


THB  POLYCHJBTX.  287 

presents  any  marked  distinction  into  stomach  and  intestine, 
and  is  almost  always  of  the  same  length  as  the  body,  ex- 
tending, without  folds  or  convolutions,  from  its  anterior  to 
its  posterior  extremity ;  but  in  Siphonostomum  {Chlorasma), 
PeeHnaria  and  others,  it  is  more  or  less  convoluted.  It  is 
attached  by  membranous  bands,  or  more  complete  mesen- 
teries, to  the  walls  of  each  somite,  and  very  commonly 
presents  a  dilatation  between  eveiy  pair  of  mesenteries. 
In  most  PolychcBia,  the  intestine  acquires  in  this  way 
merely  a  moniliform  apx>earance,  but  in  Polynoe,  Aphro^ 
dUe,  ^aUon,  and  their  allies,  long  csca  are  given  off  upon 
each  side  of  the  alimentary  canal,  and,  sometimes  becoming 
more  or  less  convoluted,  terminate  at  the  upper  part  of 
each  segment  (Fig.  51,  D)  close  beneath,  or  in  the  branchiee, 
where  such  organs  exist. 

The  anterior  portion  of  the  alimentary  canal  is,  in  a 
gpreat  number  of  the  Polychosta,  in  fact  in  all  the  typical 
ErrarUia,  so  modified  as  to  constitute  a  distinct  muscular 
pharynx,  the  anterior  portion  of  the  wall  of  which  can  be 
everted  like  the  finger  of  a  glove,  from  the  aperture  of  the 
mouth,  and  the  posterior  portion  protruded,  so  as  to 
form  a  proboscis.  In  Polynoe  squamata,  the  proboscis  is 
one-fourth  as  long  as  the  body,  and  its  walls  are  very 
thick  and  muscular.  At  its  anterior  extremity  it  is  sur- 
rounded with  a  circle  of  small  papillae,  immediately  behind 
which  are  four,  strong,  pointed  and  curved  homy  teeth, 
implanted  in  the  muscular  wall  (Fig.  52,  B).  Each  tooth 
has  a  little  projection  upon  its  convex  edge,  which  is  con- 
nected by  a  short  strong  ligament  with  the  corresponding 
projection  of  another  tooth ;  and  the  one  pair  of  teeth, 
thus  connected,  works  vertically  against  the  opposite  pair. 
In  Nereis,  there  are  two  iK)werful  teeth  which  work  horizon- 
tally, besides  minute  accessory  denticles.  In  SyUie,  the 
chitinous  lining  of  the  pharynx  is  produced  into  a  circle  of 
sharp  teeth  anteriorly,  and  there  is,  in  addition,  a  much 
stronger  triangular  median  tooth.  In  Olycera,  which  pos- 
sesses a  pair  of  teeth,  the  extremity  of  the  protruded 
proboscis  is  covered  with  very  remarkable  papillaa.    Th;^ 


238       THE  ANATOMY  OV  UrTEBTKBRATED  ANIMALS. 

most  complex  arrangement  of  teeth,  however,  ia  that  pre- 
sented by  the  EunicidoB,  In  Euniee,  there  are  altogether 
nine  distinct  pieces :  two  large,  flat,  more  or  less*  calcified 
portions  united  together  below,  and  three  cutting  and 
tearing  teeth  on  the  right  side  working  against  four  on  the 
left.  As  has  been  already  stated,  the  tubicolar  Annelids 
possess  neither  proboscis  nor  teeth. 

No  special  hepatic  gland  appears  to  exist  in  the  Annelida, 
unless  the  intestinal  cseca  perform  that  function,  and  the 
secretion  of  the  bile  is  doubtless  effected  by  the  glandular 
tract,  which  extends  for  a  greater  or  less  distance  in  the 
walls  of  the  aHmentary  canal.  A  pair  of  glandular  caeca, 
the  function  of  which  is  not  known,  is  appended  to  the 
base  of  the  proboscis  in  Nereis, 

The  general  cavity  of  the  body,  or  periyisceral  carity. 
which  is  included  between  the  parietes  of  the  alimentary 
canal  and  those  of  the  body,  is  filled  with  a  fluid  which 
contains  corpuscles,  which  are  usually,  as  in  the  Inveriebrata 
in  general,  colourless.  They  are  red,  howcTer,  in  Olyeera, 
and  in  a  species  of  Apnewmea  (De  Qaatrefages).  The  para- 
podia,  the  cirri,  the  branchisB,  and  all  the  other  important 
appendages  of  the  Polychceta  contain  a  cavity  continuous 
with  the  perivisceral  cavity,  and  are  therefore  equally  filled 
with  the  blood.  The  circulation  of  this  fluid  is  effected  partly 
by  the  contraction  of  the  body  and  its  appendages,  partly 
by  the  vibratile  cilia,  with  which  a  greater  or  less  extent  of 
the  walls  of  the  perivisceral  cavity  is  covered. 

In  a  great  number  of  the  Polychceta  no  part  of  the  body  is 
specially  adapted  to  perform  the  function  of  respiration, 
the  aeration  of  the  blood  probably  taking  place  wherever 
the  integument  is  sufficiently  thin;  and,  even  when  dis- 
tinct biunchisB  ordinarily  exist,  members  of  the  same  family 
may  be  deprived  of  them.  In  Polynoe  sqvamatcty  ciliated 
spots  which  appear  to  represent  branchis,  may  be  discovered 
on  the  dorsal  side  of  the  bases  of  the  parapodia,  at  any 
rate,  in  young  specimens.  In  some  species  of  Polynoe 
the  parapodia  give  rise,  at  oorresponding  points,  to  large, 
richly  ciliated,  malleif  orm  toberdes,  in  which  the  csdca  of 


THE  POLYCH.STA.  239 

the  alimentary  canal  terminate.  In  Sigalion,  a  filiform, 
ciliated  branchia  depends  from  the  upper  part  of  the  somite, 
beneath  the  elytron ;  and  besides  this,  curious  little  ciliated 
palettes  are  arranged  upon  the  dorsal  surface  of  the  para- 
podia,  and  upon  the  sides  of  the  anterior  somites.  But 
the  best  developed  branchise  among  these  Annelids  are  pos- 
sessed by  the  AmphinomidoB,  and  the  EunicidcB  among  the 
Erraniia;  the  TerehellidoB,  and  the  SerpulidcB  among  the 
Tubicola,  In  the  three  former  families  the  branchiffi  are 
ciliated  branched  plumes,  or  tufts,  attached  to  the  dorsal 
surface  of  more  or  fewer  of  the  somites.  In  the  last 
(Fig.  54)  they  are  exclusively  attached  to  the  anterior  seg- 
ment of  the  body,  and  present  the  form  of  two  large  plumes, 
each  consisting  of  a  principal  stem,  with  many  lateral 
branches.  The  stem  is  supported  by  a  kind  of  internal 
skeleton,  of  cartilaginous  consistence,  which  sends  off  pro- 
cesses into  the  lateral  branches. 

I  have  been  unable  to  find  any  pseud-hsemal  vessels  in 
Polynoe  squamatay  and  as  Claparede  *  could  discover  none  in 
the  transparent  P.  lunulatay  it  is  safe  to  assume  their  non- 
existence. Clapai*ede,  in  fact,  denies  them  to  the  whole  of 
the  AphroditidcB, 

When  it  is  present,  the  pseud-Lsemal  system  varies  very 
much  in  the  arrangement  of  its  great  trunks;  but  they 
commonly  consist  of  one  or  two  principal  longitudinal 
dorsal  and  ventral  vessels,  which  are  connected  in  each 
somite  by  transverse  branches.  Where  branchise  exist, 
loops  or  processes  of  one  or  other  of  the  great  trunks 
enter  them.  The  dorsal  and  the  ventral  trunks  are  usually 
rhythmically  contractile,  and  contractile  dilatations  at  the 
bases  of  the  branchiae  (Etmice),  in  x>ortions  of  the  lateral 
trunks  {Arenicola),  or  in  those  which  supply  the  proboscis 
(Eunice,  Nereis)^  have  received  the  name  of  "  hearts."  The 
direction  of  the  contractions  is  usually  sach  that  the 
blood  is  propelled  from  behind  forwards  in  the  dorsal 
vessel,  and  in  the  opposite  direction  in  the  ventral  vessel ; 
but  the  course  which  it  pursues  in  the  lateral  trunks 

*  •  Ann^lides  Chetapodes  da  Golfe  de  Millet,'  1868,  p.  65. 


240       THE  AHATOMT  OF  IHYBBTBBIU.TBD  AKIMALS. 

is  probably  verj  irregular.  In  ChlaroBma,  in  wliicli  eyen 
the  smallest  ramifications  of  the  vessels  are  contractile,  I 
have  observed  csecal  branches  depending  into  the  peri- 
visceral cavity  in  which  the  contained  fluid  underwent 
merely  an  alternate  flux  and  reflux.  Ramified  csBca 
of  a  similar  kind  appear  to  exist  in  the  oligochsetous 
genera,  Euaxes  and  Lumhriculus.  The  principal  trunks 
give  off  a  great  number  of  branches,  which  ramify  very 
minutely  in  some  Annelids  {Eunice)  and  may  give  rise  to 
retia  mirabilia  (Nereis) ;  but  in  many  {e.g.  Protula),  there 
are  hardly  any  branches  and  no  minute  capillary  ramifi- 
cations. 

In  many  Polycliceta  no  segmental  organs  have  yet  been 
discovered,  and  in  others  they  appear  to  be  represented  by 
mere  openings  in  the  parietes  of  the  body.  I  have  observed 
short  ciliated  canals  opening  externally  upon  the  ventral 
surface  at  the  bases  of  the  parapodia  in  Phyllodoce  viridis, 
and  there  are  indications  of  the  existence  of  similar  organs 
in  SyUis  vitttUa.  True  segmental  organs  have,  however, 
been  found  by  Ehlers  and  ClaparMe  in  many  Polychata,  In 
some  cases  their  walls  are  thick  and  glandular,  and  they 
probably  have  a  renal  function.  In  addition,  they  frequently 
play  the  part  of  oviducts  and  spermiducts.  Whether  the 
ciliated  canal  extending  along  the  ventral  surface  of  the 
intestine,  which  I  have  described  in  Proitda^  is  a  structure 
of  the  same  order  or  not,  I  am  not  prepared  to  say. 

The  nervous  system  of  the  Polychceta  usually  consists  of 
a  chain  of  ganglia, — one  pair  for  each  somite,— connected 
together  by  longitudinal  and  transverse  commissural  bands, 
which  diverge  between  the  cerebral  ganglia  and  the  suc- 
ceeding pair,  to  allow  of  the  passage  of  the  oesophagus. 
The  most  important  differences  presented  by  the  nervous 
systems  of  the  Polychcsta,  result  from  the  varying  length 
of  the  transverse  commissures.  In  Vermilia,  SerptUa,  SabeUa, 
these  commissures  are  very  long,  so  that  two  distinct  and 
distant  series  of  ganglia  appear  to  run  through  the  body, 
while,  in  Nepihys,  the  two  series  of  ganglia  are  fused  into 
a  single  cord  enlarged  at  intervals.    Every  transitional 


THE  POLTCHiETA. 


241 


ccmdition  between  these  is  observable  in  Tcrchellay  Aonia^ 
Glycera,  Phyllodoce,  and  Aphrodite.  In  most  Folychceta  a 
▼erj  extensive  series  of  visceral  nerves  supplies  tlie  alituen- 
tary  canal. 

The  recog^sable  organs  of  sense  in  the  Annelida  are  eyes 
and  auditory  vesicles.  The  former  are  usually  very  simple, 
consisting  qf  an  expansion  of  the  extremity  of  the  optic 

Fig.  55. 


—c 


Fig.  55. — A.  Anterior  end  of  tlie  nervous  Bystcm  of  Polynbe  squanmta 
(after  De  Quatrefoges)  :  ct,  cerebral  ganglia ;  6,  oesophageal  commis- 
■ures ;  c,  longitudinal  commissures  of  the  ventral  ganglia. 

B.  Anterior  end  of  the  nervous  system  of  SabeUa  fiabeUata  (after 
De  Quatrefages):  a,  cerebral  ganglia;  h,  oesophageal  commissures ;  r, 
longitudinal  commissures  of  the  ventral  ganglia.  Those  of  opposite 
tides  are  uuited  by  long  transverse  commisburcs. 

nerve,  imbedded  in  pigment,  and  provided  occasionally,  but 
not  invariably,  with  transparent  spheroids  or  cones.  Aleiope 
and  Torrea  have  very  well  developed  and  large  eyes.  The 
eyes  are  usually  confined  to  the  anterior  extremity  of  the 
body,  and  to  the  prsestomium  where  it  exists ;  but,  in  the  re- 
markable genus  PolyophthalmtiSf  De  Quatrefages  discovered^ 


-1-        THE    ANATOiMY    OF    INVKRTKBRATED    ANIMALS. 


—  I 


]>odide8  the  ordinarj  cephalic  eyes,  a  double  series  of  addi- 
tional visual  organs,  one  pair  being  allotted  to  each  somite. 
In  Branehiommat  eyes  are  situated  at  the  ends  of  the  bran- 
chial plumes.  Ehrenberg  has  described  two  caudal  eyes  in 
Amjphieorat  and  De  Quatrefages  has  shown  that  similarly 
placed  eyes  exist  in  three  other  species  of  PolyehoBta,  two  of 
which  are  closely  allied  to  Amphicara,  while  ^he  other  is 
an  errant  form,  related  to  Lumbrinereis.  These  curious 
worms  are  said  to  swim  about  with  the  caudal  extremity 
forwards. 

Auditory  sacs,  containing  many  otoliths,  have  been  ob- 
served upon  each  side  of  the  oesophageal  ring  in  Areni- 
cola,  and  similar  organs  have  been  noticed  in  other  Tubicola ; 
but  hitherto  their  existence  has  not  been  certainly  deter- 
mined  in  the  ErratUia. 

The  genitalia  of  the  polychstous  Annelida  are  exces- 
sively simple  in  their  structure;  indeed,  special  repro- 
ductive organs  can  hardly  be  said  to  exist  in  most,  the 
generative  products  being  merely  developed  from  some 
part  of  the  walls  of  the  perivisceral  cavity,  in  which  they 
eventually  freely  float,  making  their  way  out  in  a  manner 
which  is  not  quite  understood  at  present ;  probably,  how- 
ever, through  temporary  or  permanent  apertures  at  the 
bases  of  the  parapodia.  In  many,  the  segmental  organs 
appear  to  serve  as  excretory  ducts.  As  a  rule,  the  poly- 
chsetous  Annelids  are  dioecious ;  but  some  {e.g.  ProitUaf  Fig. 
54)  are  hermaphrodite.  The  ova  undergo  their  development 
within  the  body  of  the  parent  in  some  species  of  Eunice ; 
in  pouches  attached  to  the  body  in  Ikoogone ;  in  masses  of 
gelatinous  matter  which  adhere  to  the  tubes  of  the  vermi- 
dom  in  Protula ;  beneath  the  elytra  in  Polynoe  cirraia ; 
in  the  cavity  of  the  opercular  tentacle  in  some  Spirarhee ; 
while,  in  other  cases,  they  appear  to  become,  almost  imme* 
diately,  free  ciliated  embryos. 

The  vitelluB  undergoes  division,  and  is  converted,  as  in  the 
case  of  the  Oligocha^  and  Hirttdinea,  into  blastomeree  of 
two  kinds.  This  contrast  between  the  two  components  of 
tlie  emibiyo  commences  with  the  division  of  the  vitellos  into 


THB  DEYBLOPMBNT  OV  THE    POLTCH.£TA.  243 

two,  inasmuoli  as  the  first  fiflsnre  is  usually  so  directed  as  to 
divide  the  yelk  into  unequal  portions.  Both  subdivide, 
hat  the  smaller  much  faster  than  the  larger ;  so  that  the 
former  becomes  converted  into  very  small  blastomeres, 
which  gradually  envelope  the  larger  blastomeres  resulting 
from  the  subdivision  of  the  latter.  The  larger  included 
Uastomeres  are  destined  to  form  the  alimentary  tract; 
the  smaller  peripheral  ones,  on  the  other  hand,  give  rise 
to  the  ectoderm,  and  to  the  nervous  ganglia.*  As  in  the 
OUffochada  and  Hirvdineay  again,  the  mesoblast  forms  a 
thick  band  on  each  aide  of  the  median  ventral  line,  and 
ita  transverse  division  originates  the  segmentation  of  the 
body.  But,  generally,  the  development  of  the  proiosomites, 
as  these  segments  might  be  called,  does  not  occur  until 
some  time  after  the  embryo  has  been  hatched.  The  somites 
increase  in  number  by  tibe  addition  of  new  ones  between 
the  last  and  the  penultimate  somite. 

The  embryos  of  the  PolychcBta  differ  from  those  of  the 
OligochcBia  and  Hirudinea  in  being  ciliated.  In  some  cases, 
the  cilia  form  a  broad  zone  which  encircles  the  body, 
leaving  at  each  end  an  area,  which  is  either  devoid  of  cilia, 
or,  as  is  frequently  the  case,  has  a  tuft  of  long  cilia  at  the 
cephalic  end.    Such  larvsB  are  termed  Atroeha. 

In  other  embryos  the  cilia  are  arranged  in  one  or  more 
narrow  bands,  which  surround  the  body.  A  very  common 
arrangement  is  one  in  which  a  band  of  cilia  encircles  the 
body  immediately  in  front  of  the  mouth,  the  region  in 
front  of  the  band  bearing  eyes,  and  becoming  the  prsesto- 
mium  of  the  adult  (e.g,  Polynoe).  In  such  embryos,  there 
is  very  commonly  a  second  band  of  cilia  around  the  anal 
end  of  the  embryo,  and  a  tuft  of  cilia  is  attached  to  the 
centre  of  the  prsestomium.  These  larvse  are  called  Telotrocha, 
In  other  cases,  one  or  many  bands  of  cilia  surround  the 
middle  of  the  body,  between  the  mouth  and  the  hinder 
extremity.    These  are  Mesoirocha. 

In  the  telotrochous  larva  of  PhyUodoee  a  shield-shaped, 

*  ClaparMe  and  MeUcbnikoff,  *  Beitrige  sur  Kenntnifs  der  £nt- 
wickeluugsgeichiohte  der  Cbaetopoden,'  1^68. 


244       THE  ANATOMY  OF  INYESTBBBATBD  ANIMALS. 

mantle-like,  elevation  of  the  integument  covers  the  dorsal 
region  of  the  body  behind  the  prsB-oral  ciliated  ring.  In 
the  larvae  of  the  Serpulidce  a  process  of  the  integument 
grows  out  behind  the  mouth,  and  surrounds  the  anterior 
part  of  the  body  of  the  larva  like  a  turaed-back  collar.  It 
persists,  as  a  kind  of  hood,  in  the  adult. 

Some  lai*v8B  are  provided  with  set®  of  a  different  cha- 
racter from  those  which  are  possessed  bj  the  adult,  and 
which  are  cast  off  as  development  advances. 

Many  PolychcBta  multiply  by  a  process  of  zooid  develop- 
ment, which,  in  some  cases,  appears  to  be  a  combination  of 
fission  with  gemmation ;  in  others,  to  approach  very  nearly 
to  pure  fission  or  pure  gemmation.  The  result  is,  not  infre- 
quently, the  formation  of  long  chains  of  connected  zooids. 

The  method  of  multiplication  which  De  Quatrefages  ob- 
served in  Syllis  prolifera,  is  nearly  simple  fission,  the  animal 
dividing  near  its  middle,  and  the  posterior  division  ac- 
quiring a  new  head. 

In  Myrianida,  Milne-Edwards  has  described  the  occur- 
rence of  a  sort  of  continuous  budding  between  the  ultimate 
and  penultimate  segments,  in  which  region  new  segments 
are  formed  until  the  zooid  has  attained  its  full  length. 

Frey  and  Leuckart  and  Krohn  have  shown  that  Autolytus 
prolifer  multiplies  in  a  somewhat  similar  manner;  but, 
instead  of  each  new  zooid  being  formed  at  the  expense  of 
an  entire  somite,  it  is  developed  from  only  a  portion  of  one. 
Finally,  I  found  in  Protula  Dysteri  that,  when  the  Proiula 
had  attained  a  certain  length,  all  the  somites  behind  the 
sixteenth  became  eventually  separated  as  a  new  zooid ;  but 
the  development  of  the  latter  is  not  mere  fission,  inasmuch 
as  one  of  the  earliest  steps  in  the  process  is  the  enlarge- 
ment of  the  seventeenth  somite,  and  its  conversion  into 
the  head  and  thorax  of  the  bud  (Fig.  54,  B).  Sars  has 
described  a  similar  mode  of  multiplication  in  his  FUograna 
impUxa,  a  very  closely  allied  form. 

In  SyUis  and  in  Proiula,  the  producing  and  the  produced 
zooids  alike  develope  generative  products,  but  in  Autolytus, 


AOAMOGBKBSIS  AMONG  POLTOHJETA.  245 

Krohn  has  shown  that  the  primary  producing  zooid  remains 
sexless,  the  secondary  produced  zooids  having  a  somewhat 
different  form,  and  sdone  giving  rise  to  ova  and  sperma* 
tozoa. 

In  some  species  of  the  genus  Nereis,  the  worm,  after  the 
development  of  its  genital  organs  has  taken  place,  takes 
on  the  characters  of  what  was  formerly  considered  a 
distinct  genus,  Heteronereis ;  and  the  males  and  the  females 
of  the  same  species  of  Nereis  have  even  been  regarded  as 
different  species  of  Heteronereis,* 

The  series  of  forms  represented  by  the  TurbeUaria,  the 
Hirudinea,  the  Oligoehceta,  and  the  Folychasta,  illustrates 
the  manner  in  which  a  type  of  organisation,  which,  in  its 
simplest  condition,  exhibits  but  little  advance  upon  a  mere 
GJastrula,  passes  into  one  in  which  the  body  is  divided  into 
many  segments,  each  provided  with  a  pair  of  appendages 
or  rudimentary  limbs^ 

The  segmentation,  or  serial  repetition  of  homologous 
somites,  extends  to  the  nervous  system,  and,  more  or  less, 
to  the  vascular  and  reproductive  organs,  in  the  higher  forms 
of  these  "  Annulose  "  animals ;  from  which  a  further  exten- 
sion of  the  same  process  of  segmentation,  with  a  fuller 
development  of  the  appendages  and  a  more  complete  appro- 
priation of  some  of  tbem  to  manducatory  pui*po8es,  leads 
ud  to  the  Arthropoda, 

The  Gbphtbea. — These  are  marine  vermiform  animals 
without  distinct  external  segmentation  or  parapodial  ap- 
pendages. The  ectoderm  has  a  chitinous  cuticle,  and  is 
often  provided  with  tubercles,  hooks,  or  setae  of  chitiu 
(EehiuruSf  Stemaspis).  No  calcareous  skeleton  is  found  in 
any  of  the  Gephyrea,  The  integument  frequently  contains 
numerous  simple  glands,  the  apertures  of  which  perforate  the 
cuticle.  In  one  genus  {Stemaspia),  two  shield-shaped  plates, 
fringed  with  set®,  are  developed  upon  the  hinder  part  of  the 

*  Ehlen,  "Die  Gatiung  UeteronertUr    (^Gdttingen  Nachrichten/ 
1867.) 


246       THE  ANATOICT  OV  INYBRTBBIULTED  ANIMALS. 

Tentral  surface  of  the  body.  There  are  external  circular, 
and  internal  longitudinal  muscular  fibres  beneath  the  ecto- 
derm. An  inner  layer  of  circularly  disposed  muscular 
fibres  may  be  added.  The  oral  end  of  the  body  may 
haye  the  form  of  a  retractile  proboscis  {Priapulus),  or  be 
provided  with  tentacular  appendages.  These  may  be 
arranged  in  a  circle  round  the  mouth,  and  short  {Sipun- 
cuius.  Fig.  56,  I.  t),  or  long  {Phoronis),  or  there  may  be 
a  single  long,  sometimes  bifurcated  and  ciliated,  tenta- 
cular appendage  {Bonellia).  Filamentous  appendages, 
which  are  probably  branchiie,  are  g^ven  off  at  the  hinder 
end  of  the  body  in  Stenuupis  and  Priapulus,  The  endo- 
derm  is  usually  ciliated  throughout.  The  intestine  is 
straight  in  most  genera,  but  is  coiled  and  bent  upon 
itself,  so  as  to  terminate  in  the  middle  of  the  body,  in 
Sipunculus  (Fig.  56,  I.).  In  PhorowU  the  anus  is  close  to 
the  mouth.  The  anal  aperture  is  always  situated  upon  the 
dorsal  aspect  of  the  body.  There  is  a  spacious  perivisceral 
cavity  undivided  by  mesenteries,  which  in  some  cases  {Prui- 
pulus,  8ipuneiUu8)  opens  externally  by  a  terminal  pore.  In 
EehiuruSf  Bonellia,  Thalcissema,  a  pair  of  tubular,  some- 
times branched  organs,  which  are  ciliated  internally,  and 
communicate  by  ciliated  apertures  with  the  perivisceral 
cavity,  open  into  the  rectum.  These  appear  to  represent 
the  water- vessels  of  the  Botifera  and  the  respiratory  tubes 
of  the  HolothuricB. 

A  pseud-hsBmal  system  exists  in  most  {8ipunculu8,  Sier- 
nntpisy  Bonellia^  EchiuruSy  and  Phoronia),  and,  when  fully 
developed,  consists  of  two  longitudinal  trunks — one  dorsal, 
or  supra-intestinal,  the  other  ventral,  with  their  terminal 
and  lateral  communications.  The  pseud-hsemal  fluid  is 
colourless,  or  may  have  a  pale  reddish  tinge,  in  most.  In 
Plwronis  it  is  said  to  contain  red  corpuscles.  In  8ipwi- 
cuius,  the  cavities  of  the  tentacles  communicate  with  a 
circular  vessel  provided  with  csecal  appendages ;  and  this 
circular  vessel  is  said  to  open  into  the  pseud-hsmal  vessels. 

The  nervous  system  presents  a  collar,  which  surrounds 
the  ooeophagus,  and  from  which  a  simple  or  ganglionated 


FiE.  M.— S'>niinJ«  nxihi  (kfter  Kefe-steia  ud  Ehlera;  ■ 
1.  lln  uimkl  lalil  open  lunsitudiully -)  n.s.  T;  (entkoln;  r,  the 
four  TCtraclOT  muielti  of  ihe  probaicis  ;  r,  the  pilnia  ■[  which  th«j 
*cra  attsched  tu  the  walls  of  tba  bodj;  a,  cetophaput;  i,  Intei- 
tlne;  a,  anui;  J,  J',  loop>  of  [he  intestine ;  i,  jr,  ippanduM  of  the 
rveluin;  i,  fuilform  mmcla;  w,  ciliated  gronve  on  the  inner  tide 
of  tb«  tnt«atine ;  q.  anil  muaclea ;  i,  ueol  eUndi ;  (,  cKca  which 
open  on  each  aide  of  the  nervoua  cord,  anil  are  general/;  eoutidered 
to  be  lealea  j  p,  pore  at  the  hinder  end  of  ihe  biidy ;  x,  nervoui  cord, 
which  end*  in  a  liibed  ganglionic  matt,  cline  to  the  mouth,  and 
preaenia  an  enlargement,  ^,  ai  its  posterior  end ;  m,  m',  ■■',  miUBlei 

U.  AlarvalKipunculuiatKiul^ofaoinchlong.— a,  moulh;  a.galiet; 
(,  cecal  gUnd;  >,  intettlne  wiib  musea  of  faltj'  cell>;  ",  anu>;  ir, 
ciliated  groovfl  of  (ho  Iniealine;  g,  hraJn  with  two  pair*  of  red  eye- 
■poKi  a,  nervout  curd,  p,  pore;  (,  (,  aa-called  teatei;  W  W,  circlet 
of  Cilia. 

giving  off  lateml  branches.    The  ventral  cord  containB  it 
•  'Zoologiiche  Beitnisc,'  ISIil. 


24&       THE  ANATOMY  OF  IMYBRTBBEATED  ANIMALS. 


t 


central  canal,  and  the  collar  usually  presents  a  cerebral 
ganglionic  enlargement.  Budimentcurj  eyes  are  sometimes 
connected  with  the  cerebral  ganglion. 

The  sexes  are  distinct,  and  the  reproductive  elements  are 
developed  either  from  the  parietes  of  the  perivisceral  cavity 
or  in  simple  caocal  glands.  In  8ipunculu8,  the  ova  and 
spermatozoa  float  freely  in  the  perivisceral  cavity. 

The  actively  locomotive  embryo  of  Sipunculua  (Fig.  56,  EI) 
is  surrounded  by  a  circular  band  of  cilia  placed  immediately 
behind  the  mouth  (w,  w),  and  resembles  a  Rotifer  or  a 
mesotrochal  Annelidan  larva.  As  development  advances  it 
loses  this  apparatus,  and  passes  gradually  into  the  adult 
form.  In  Phoronis,  the  embryo  is  also  mesotrochal,  but  it 
has  two  ciliated  bands,  one  circular,  round  the  anus,  and  the 
other  immediately  behind  the  mouth.  The  post-oral  band 
of  cilia  is  produced  into  numerous  tentaculiform  lobes,  and 
fringes  the  free  edge  of  a  broad  concave  lobe  of  the  dorsal 
side  of  the  body,  which  arches  over  the  mouth.  In  this 
state  the  embryo  is  the  so-called  Actinabrocka.*  An  invagi- 
nation of  the  ventral  integument  of  the  larva  connects 
itself  with  the  middle  of  the  intestine,  and  then,  becoming 
evaginated,  pulls  the  intestine,  in  the  form  of  a  loop,  into 
the  ventral  process  thus  formed,  which  gives  rise  to  the 
body  of  the  Phoronis,  while  the  tentacles  of  the  larva  grow 
into  those  of  the  adult.  Schneider  has  suggested  that 
the  bell-shaped  larva,  with  long  setfle,  termed  MUraria  by 
Miiller,  is  the  embryo  of  Stemaspia, 

The  affinities  of  the  Gephyrea  with  the  Turhellaria,  with 
the  Annelida,  and  with  the  Bati/era,  are  unmistakable. 
In  fact,  it  may  be  doubted  whether  Siemtupia  should  not  be 
associated  with  the  Polychcdta,  and  BoneUia  is  in  many  re- 
spects comparable  to  a  colossal  Rotifer.  Their  usually 
assumed  connexion  with  the  Echinodermaia  is  more  ques- 
tionable. The  circular  canal  which  communicates  with  the 
cavities  of  the  tentacles  in  Sipunculua  has  been  compared 
to  the   ambulacral  system  of  the  Echinoderms,  but  the 

*  Schneider,  **  Uehor  ilio  Metamorphoie  der  Actinotrocha  branehiuta^** 
C  Axchiv  tur  Aiiat./  1862.) 


THE  OBFHYBBA. 


249 


manner  of  its  development  is  not  yet  safficientlj  nnderetood 
to  justify  the  expression  of  an  opinion  on  this  subject. 
Krohn  has  described  a  bilobed  organ  on  the  ventral  face 
of  the  gullet  of  the  larva  of  Sipunculus,  which  opens 
extemallj  in  front  of  the  ciliated  band  by  a  narrow  ciliated 
duot  *  (Fig.  56,  II.  s).  It  has  a  striking  similarity  to  the 
"  water-vessel "  of  the  larva  of  Bcdanoglosmu,  which,  how. 
ever,  lies  on  the  opposite  side  of  the  body. 

•  ** Ueber  die  Larve  des  Stpunculut  nudus**    C  Archiv  fQr  Anat.,* 


250       THE  ANATOMY  OV  nTYSBTSBBATBD  ANIMALS. 


CHAPTER  VI. 


THE  ABTH&OPODA. 

The  segmentation  of  the  body,  that  is,  its  division  into  a 
series  of  somites,  each  provided  with  a  pair  of  lateral 
appendages,  which  is  so  characteristic  a  feature  of  the 
higher  Annelids,  is  exhibited  in  a  still  more  marked  degree 
by  the  Arihropoda.  In  these  animals,  moreover,  the  appen- 
dages themselves  are  usually  divided  into  segments,  while 
one  or  more  pairs  of  the  appendages  in  the  neighbourhood 
of  the  mouth  are  modified  in  form  and  position  to  sub- 
serve manducation.  Segmental  organs,  at  least  in  their 
Annelidan  form,  are  wanting  in  the  ^r^ropoda,  and  neither 
in  the  embryonic  nor  the  adult  condition  do  they  ever 
possess  cilia. 

The  process  of  yelk-division  may  be  complete  or  incom- 
plete, but  no  known  Arthropod  ovum  gives  rise  to  a  vesicu- 
lar morula,  nor  is  the  alimentary  cavity  ordinarily  formed 
by  invagination.*  The  precise  mode  of  origin  of  the  meso- 
blast  has  yet  to  be  worked  out,  but  the  perivisceral  cavity 
appears  always  to  be  developed  by  its  splitting.  In 
other  words  it  is  a  9ch%zoccele. 

As  with  Annelids,  the  segmentation  of  the  body  results 
from  the  subdivision  of  the  mesoblast  by  transverse  con- 
strictions into  protoaomUes ;  and  there  is  every  reason  to 
believe  that  the  ganglionated  nervous  chain  arises  from  an 
involution  of  the  epiblast. 


*  The  recent  observations  of 
Bobretzky  on  the  dt-velopment 
of  OnUcuttLnd  AHaeu* {Hofmiknn 
and  Schwalbe,  *  Jahresbericiite/ 
Bd.  ii.,  1875J  however  tend  to 


show  that  the  hypoblast  arises 
by  a  sort  of  modified  invagination 
of  the  primitive  blastoderm. 
And  in  other  Arthropoda  there  are 
indications  of  a  similar  process. 


THE  ABTHBOPODA.  251 

The  neural  face  of  the  embryo  is  fashioned  first,  and  its 
anterior  end  terminates  in  two  rounded  expansions — the 
proeephdlie  lobes — which  are  converted  into  the  sides  and 
front  of  the  head.  The  appendages  are  developed  as  paired 
outgrowths  from  the  neural  aspect  of  each  somite,  and  what- 
efver  their  ultimate  form,  they  are,  at  first,  simple  bud-like 
processes.  Very  generally,  a  broad  median  prolongation  of 
the  sternum  of  the  somite  which  lies  in  front  of  the 
mouth,  g^ves  rise  to  a  labrum ;  while  a  corresponding,  but 
often  bifid  median  elevation,  behind  the  mouth,  becomes 
a  meioHoma, 

In  many  Arthropods,  the  hsmal  or  tergal  face  of  the 
body  grows  out  into  lateral  processes,  which  may  either  be 
fixed,  or  more  or  less  moveable.  The  lateral  prolongations 
of  the  carapace  in  the  Crustacea  and  the  wings  of  Ineecta 
are  structures  of  this  order. 

In  a  number  of  Insects  belonging  to  different  orders  of 
the  class,  an  amnionic  investment  is  developed  from  the 
extra-neural  part  of  the  blastoderm  by  a  method  similar 
to  that  which  gives  rise  to  the  amnion  in  the  higher  Verte- 
brcUa, 

In  aU  the  higher  Arthropods,  a  certain  number  of  the 
somites  which  constitute  the  anterior  end  of  the  body 
coalesce  and  form  a  head,  distinct  from  the  rest  of  the 
body;  and  the  appendages  belonging  to  these  confluent 
somites  undergo  remai'kable  modifications,  whereby  they 
are  converted  into  organs  of  the  higher  senses  and  intc» 
jaws.  In  many  cases,  the  somites  of  the  middle  and 
posterior  parts  of  the  body  become  similarly  differentiated 
into  groups  of  polysomitic  segments,  which  then  receive 
the  name  oithorax  and  abdomen.  The  somites  entering  into 
each  of  these  groups  may  remain  distinct  or  may  coalesce. 
The  tergal  expansions  of  the  somites  of  the  head,  or  of  both 
head  and  thorax,  may  take  the  shape  of  a  broad  shield,  or 
carapace.  This  may  constitute  a  continuous  whole  (e.g, 
Apu9,  Astacus) ;  or  its  two  halves  may  be  moveably  connected 
by  a  median  hinge,  like  a  bivalve  shell  (Cypris,  Limnadia) ; 
or  finally,  the  tergal  processes  of  each  side  may  remain  dis- 


252       THE  ANATOMY  OV  IinrBSTEBSATBD  ANIMALS. 

tinct  from  one  another  and  freely  moveable  on  their  respec- 
tive somites  (wings  of  Insects). 

Limbs,  or  appendages  capable  of  effecting  locomotion, 
are  always  attached  either  to  the  head  or  to  the  thoraX,*  or 
to  both.  Thej  may  be  present  or  absent  in  the  abdominal 
region.  In  adult  Ar<ichnida  and  Inseda,  there  ^re  no 
abdominal  limbs,  unless  the  accessory  organs  of  gedStation, 
the  stings  of  some  insects,  and  the  peculiar  appendages  of 
the  abdomen  in  the  Tkyaanwra  and  CoUembola  be  such. 

The  alimentary  apparatus  presents  very  wide  diversities 
in  form  and  structure,  and  in  the  number  and  nature  of 
its  glands.  The  anus,  which  is  very  rarely  absent,  is  situated 
in  the  hindermost  somite. 

In  like  manner,  the  blood-vascular  system  varies  from  a 
mere  perivisceral  cavity  without  any  heart  (Ostraeoda,  Cirri- 
pedia)  up  to  a  complete,  usually  many-chambered  heart  with 
well-developed  arterial  vessels.  The  venous  channels,  how- 
ever, always  have  the  nature  of  more  or  less  definite 
lacunse.  The  blood  corpuscles  are  colourless,  nucleated 
cells. 

Special  respiratory  organs  may  be  absent,  or  they  may 
take  one  of  the  following  forms. 

1.  BranchuB,  Externally  projecting  processes  of  the  body 
or  limbs,  supplied  with  venous  blood,  which  is  thus  brought 
into  contact  with  the  air  dissolved  in  water. 

2.  TrackecR.  Tubes  which  traverse  the  body  and  gene- 
rally open  upon  its  exterior  by  apertures  termed  stigmata, 
and  thus  bring  air  into  contact  with  the  blood  and  the 
tissues  generally.  Saccular  reservoirs  of  air  are  often 
formed  by  dilatations  of  these  tubes. 

The  so-called  Tracheo-hranchicB  of  some  aquatic  Insect 
larv8B  are  usually  laterally  projecting  processes  of  more 
or  fewer  of  the  thoracic  or  abdominal  somites,  containing 
abundant  trachese,  which  communicate  with  those  which 
traverse  the  body  {Ephemenda,  Ferlaridas),  They  are  in 
no  sense  branch!®,  but  simply  take  the  place  of  stigmata. 
The  exchange  of  constituents  between  the  air  contained 

*  The  extinct  TrUohiUt  possibly  fonn  en  exception  to  this  rale. 


THB  ABTHBOPODA.  253 

in  the  traclieee  of  these  aTiimalfl  and  that  of  the  anrrounding 
medium,  is  effected  indirectly,  by  diffusion  through  the 
waDa  of  the  tracheo-branchise,  instead  of  directly,  through 
the  stigmata,  as  in  other  cases. 

In  the  aquatic  lanrsB  of  many  Dragon-flies  {Libelliilid<B)t 
the  function  of  the  tracheo-branchisB  is  performed  by  folds 
of  the  lining  membrane  of  the  rectum,  which  contain  abun- 
dant trachesB.  Water  is  drawn  into,  and  expelled  from,  the 
c&yitj  of  the  rectum  by  rhythmical  contractions  of  its  walls, 
80  as  to  secure  the  exchange  of  gaseous  constituents  between 
the  air  which  it  contains  and  that  which  fills  the  trachese. 

3.  Pulmonary  sacs.  These  are  met  with  only  in  some 
Aradmida.  They  are  involutions  of  the  integument,  the 
walls  of  which  are  folded  in  such  a  manner  as  to  expose 
a  hirge  surface  to  the  air,  which  is  alternately  taken  into, 
and  expelled  from,  their  apertures.  The  blood  is  brought 
to  these  sacs  by  venous  channels. 

The  exact  mode  by  which  the  separation  of  the  nitro- 
genous products  of  the  waste  of  the  tissues  from  the  blood 
is  effected  in  Arthropods  requires  further  elucidation.  In 
many  however,  such  products,  notably  uric  acid,  have  been 
found  to  abound  in  the  corpus  adiposum — a  cellular  mass 
which  lies  in  the  walls  of,  and  more  or  less  fills,  the  peri- 
visceral cavity — and  in  the  Malpighian  glands.  In  the 
latter  case,  they  are  conveyed  out  of  the  body  by  the  intes- 
tine. 

The  nervous  system  consists  primitively  of  a  pair  of 
ganglia  for  each  somite,  but  the  number  of  ganglia  dis- 
coverable in  the  adult  depends  on  the  extent  to  which 
these  primitive  ganglia  coalesce.  There  is  usually,  if 
not  always,  a  well-developed  system  of  gauglionated  vis- 
ceral nerves,  connected  with  the  cerebral  ganglia  and 
distributed  to  the  gullet  and  stomach. 

Eyes  are  usually  present ;  and,  when  they  exist,  they  are 
almost  always  situated  in  the  head  and  are  connected 
with  the  cerebral  ganglia.  Among  the  Crustacea,  however, 
Euphausia  has  eyes  in  some  of  the  thoracic  limbs,  and  in  some 
abdominal  somites.    The  eyes  may  be  simple  or  compound. 


254       THE  ANATOMY  OV  IKYB&TEBSATED  ANIMALS. 

In  the  latter  case  there  are,  in  correspondence  with  the 
namber  of  parts  into  which  the  transparent  corneal  con- 
tinuation of  the  chitinous  cuticula  over  the  eje  is  divided, 
a  namber  of  elongated  bodies  which  lie  between  the  ont^r 
surface  of  the  ganglionic  expansion  of  the  optic  nerve  and 
the  inner  face  of  the  cornea.  These  bodies  consist  of 
two  parts :  an  external  transparent  crystalline  cane  and  an 
internal  prismatic  rod.  The  broad  end  of  the  cone  is 
external,  and  is  applied  to  the  inner  surface  of  the  corneal 
facet ;  its  narrow  end  is  continuous  with  the  outer  extremity 
of  the  prismatic  rod,  which,  by  its  inner  end,  is  connected 
with  the  ultimate  ramifications  of  the  optic  nerve.  Each 
of  these  crystalline  cones  and  prismatic  rods  is  separated 
from  the  rest  by  a  pigmented  sheath.* 

Distinct  auditory  organs  have  been  observed  in  Crus- 
taceans and  Insects.  They  are  not  exclusively  confined 
to  the  head.  In  the  opossum  shrimp  (Mysis),  for  example, 
they  are  placed  in  the  appendages  of  the  last  somite  of  the 
abdomen.  And  in  Insects,  the  only  organs  to  which  the 
auditory  function  can  be  certainly  assigned  are  situated 
in  the  thorax  or  in  the  legs. 

There  is  some  reason  to  think  that  the  antenns  of  Insects 
are  the  seat  of  the  olfactory  function,  but  no  certain 
information  on  this  head  has  been  obtained.  The  very  fine 
setffi  to  the  bases  of  which  nerves  can  be  traced,  which 
abound  on  the  antennary  organs  of  Insecta  and  Crustacea, 
but  are  found  in  other  regions  of  the  body,  are  probably 
partly  tactile  and  partly  auditory  organs. 

As  a  general  rule,  all  the  muscles  of  the  Arthropoda,  even 
those  of  the  alimentary  canal,  are  striated.  Those  of  the 
body  and  limbs  are  often  attached  by  chitinised  tendons  to 
the  parte  which  they  have  to  move.  As  the  hard  skeleton 
is  hollow  and  the  muscles  are  inside  it,  it  follows  that  the 
body,  or  a  limb,  is  bent  towards  that  side  of  its  axis,  which 

*  Leydig, '  Das  Auee  der  GUe-  eye  of  the  lobster,  accompttnied 

derthiere,'  1864.     Schulxe,  *  Un-  by  full  references  to  the  liten- 

tersoohungen/  1868.    Mr.  £.  T.  tare  of  the  subject,  in  the  *Quar- 

Newton  ham  given  a  vary  eood  terly  Journal  of   Microscopical 

aeoouat  of  the  stracture  of  the  Bcienee'  for  1875. 


THE  ABTHBOPODA.  255 

is    opposite  to  that  on  whicli  a  contracting    muscle  is 
ntaated. 

Sounds  are  produced  bj  many  Insects;  but  in  most 
oases,  they  cannot  be  properly  referred  to  a  voice,  in  the 
sense  in  which  that  term  is  applied  to  the  sounds  pro- 
duced in  the  higher  animals,  by  the  vibrations  of  the 
atmosphere  arising  from  the  impact  of  a  current  of  air 
upon  the  free  edges  of  membranes  bounding  the  aperture  of 
exit  of  the  current.  The  chirping  and  humming  of  Insects 
often  arise  from  the  friction  of  their  hard  parts  against 
one  another,  or  from  the  rapid  vibration  of  their  wings :  in 
some  instances,  however,  recent  investigations  render  it 
probable  that  they  are  produced  by  the  action  of  expiratory 
currents  on  tense  membranes  which  bound  the  stigmata. 

Agamogenesis  is  veiy  common  among  some  groups 
of  the  Arihropoda,  such  as  the  Onuicicea  and  the  Insecta, 
but  has  not  yet  been  observed  in  the  Myriapoda  or  the 
Arachnida.    It  may  be  effected  in  one  of  two  ways : 

1.  Either  individuaLs  which  are,  by  their  structure,  incap- 
able of  being  impregnated  and  are  therefore  physiologically 
sexless,  though  it  may  happen  that  they  more  or  less  ap- 
proximate females  moi'phologically,  give  rise  to  offspring 
{Cecidomyia  larvse.  Aphis) ; 

2.  Or  individuals  which  are  capable  of  being  impregnated, 
and  are  thus  both  morphologically  and  physiologically  true 
females,  give  rise  to  eggs  which  develope  without  impreg- 
nation. (The  queen  bee,  so  far  as  the  production  of  drones 
is  concerned ;  many  Lepidoptera.) 

The  cases  of  Apus,  Daphnia  and  Cypris  would  belong 
to  the  latter  category,  if  it  were  certain  that  the  very  same 
females  which,  for  a  certain  period,  produce  young 
agamogenetically,  at  another  time  undergo  fecundation. 
Multiplication  by  fission  or  external  gemmation  is  not 
known  to  take  place  in  any  Arthropod.  Hermaphrodism 
occurs  as  a  rule  in  some  few  Arthropods  {e,g.  the  Cirripedia 
and  Tardigrada),  and  as  an  abnormal  'sport'  in  sundry 
CruHaeea  and  in  many  Irueeta. 


256       THE  ANATOMY  OF  INYBSTEBBATBD  ANIMALS. 

In  absolute  number  of  species,  the  Arihropoda  far  exceed 
all  the  rest  of  the  animal  kingdom  put  together.  Thus 
Grerataecker,*  while  allowing  60,000  species  for  the  latter, 
estimates  the  number  of  species  of  Arihropoda  as  rather 
above  than  below  200,000 ;  by  far  the  larger  proportion  of 
these,  probably  more  than  150,000,  being  Insects. 

The  Arihropoda  are  commonly  divided  into  the  Crustojoea^ 
the  Araehnida,  the  Myriapoda,  and  the  Inseeta ;  and  though 
it  is  impracticable  to  give  a  definition  which  shall  absolutely 
separate  the  first  two  groups,  it  is  perhaps  not  worth  while 
to  disturb  an  arrangement  which  has  much  practical  con- 
venience. But,  for  purely  morphological  purposes,  it  may 
be  instructive  to  regard  them  from  another  point  of  view. 

The  Arihropoda  may,  in  fact,  be  divided  into  two  series. 
One  of  these  consists  almost  wholly  of  air-breathing  forms, 
which,  if  they  possess  8x>ecial  respiratory  organs,  have  either 
pulmonary  sacs  or  tracheee,  or  both  combined ;  while  the 
other  includes  a  corresponding  predominance  of  water- 
breathing  animals,  which,  if  they  possess  respiratory  organs, 
have  branchiffi.  The  latter  series  contains  the  Crustacea  ; 
the  former  comprises  the  Arachnida,  Myriapoda,  and 
Inseeta. 

In  the  course  of  the  development  of  the  higher  Arihropoda, 
there  is  a  stage  in  which  the  body  begins  to  be  segmented, 
but  the  appendages  are  not  developed.  This  is  foUowed  by 
a  stage  in  which  appendages  make  their  appearance,  but 
the  antennary  and  manducatory  appendages  (gnathites)  are 
like  the  other  limbs :  and,  finally,  there  is  a  stage  in  which 
the  gnathites  are  completely  converted  into  jaws.  Now, 
among  the  water-breathing  Arihropoda,  no  trace  of  limbs 
has  yet  been  certainly  discovered  among  the  Trilohita ;  in 
the  Merostomata  {Eurypterida  and  Xiphosura)  the  gnathites 
are  completely  pediform;  while,  in  the  Entomostraea  and 
Ma^lacoHraea,  more  or  fewer  of  the  gnathites  are  so  modified 
B8  to  subserve  manducation  and  no  other  function. 

•  Bronn't  '  KlAMen  und  Ordnungen  des  Thierreiohs,*  vol.    ▼.  p. 
S78.    1866. 


THX  0&0UP8  OF  THE  ABTHBOPODA. 


267 


In  the  air-breathing  series,  no  completely  apodaJ  forms 
are  known.  The  Tardigrctda  and  the  PewUutomida  appear 
to  have  no  jaws ;  but  the  presence  of  oral  stilets  in  the 
former,  and  the  position  of  the  hooks  which  represent  the 
limbs  in  the  latter,  throw  some  doubt  upon  this  point. 

In  the  Arciehnida  and  the  Peripatidea  the  gnathites  are 
completely  pediform.  But,  in  the  Myriapoda,  and  still 
more  in  the  Iruecta,  the  gnathites  lose  the  character  of  legs, 
and  are  completely  converted  into  manducatory  organs. 
Thus  we  arrive  at  the  following  arrangement  of  the  Arthro^ 
poda: — 

Abthsopoda. 

J.  Without  Onathiiea. 

Tbilobita.      Tabdiosada  (P)      Pentastomida  (P) 

JJ.  With  Pediform  Onathites, 


Mebostomata. 


Abachnida. 


Pebipatidea. 


III.  With  Maxilliform  Gnathites, 


Ektomostbaca. 

Maulcostbaca. 

% ^ ' 

Water-breathers. 


Mtbiapoda. 
Iksbcta. 

Air-breathers. 


For  the  most  pait. 


Of  the  four  great  groups,  the  Crustacea  are  those  which 
present  the  greatest  and  the  most  instructive  variations 
upon  the  fundamental  type  of  structure ;  while  the  modifi- 
cations of  the  Insecta^  Arachnida,  and  Myriapoda,  are  less 
extensive,  and  may  be  regarded  as  of  secondary  morpho- 
logical importance.  The  Crustacea  will  therefore  be  treated 
of  at  some  length,  while  the  other  groups  will  be  passed 
over  more  lightly. 


268>      THE  UTATOMT  OF  nrVBBTBBBJLTED  AHDCALS. 


THS  OSUSTAOEA. 

The*  TftiLOBiTA. — These  ancHent  Arthropods,  which  have 
been  extmct  sibce  the  latter  part  of  the  Palseozoic  epoch, 
occur  in  the  fossil  state  in  great  nnmbers,  and  in  conditions 
yerj  favourable  for  their  preservation ;  but,  up  to  this  time, 
no  certain  indications  of  the  existence  of  appendages, 
nor  even  of  any  hard  sternal  body-wall,  have  been  dis- 
covered, though  a  shield-shaped  labmm,  which  lies  in  front 
of  the  mouth,  has  been  preserved  in  some  specimens.  The 
body  consists  of  a  eephoMe  shield  (Fig..  57,  A) ;  of  a  variable 
number  of  movably  articulated  thoracic  «omife«  (Fig.  57,  B) ; 
and  of  a  pygidiwm,  composed  of  a  variable  number  of 
the  somites  which  succeed  tne  thorax,  united  together 
(Fig.  57,  0). 

Each  thoracic  somite  presents  a  median  portion,  convex 
from  side  to  side,  termed  the  axis  or  tergvmi,  and  two 
flattened  lateral  portions,  i}iQ  pleura.  The  former  overlap 
one  another  largely  wh^i  the  body  is  extended ;  the  latter, 
when  it  is  flexed ;  and  the  freedom  of' motion  permitted  by 
this  arrangement  is  so  great,  that  many  Trilobites  were 
able  to  roll  themselves  up  like  woodlice,  and  are  found 
fossilised  in  that  condition.  At  the  lateral  edge  of  each 
pleuron,  the  cuticular  substance  of  which  it  is  composed 
folds  inwards,  and  can  be  traced  on  the  ventral  or  sternal 
side  for  some  distance.  But  in  the  middle  of  the  ventral 
region  no  indication  of  a  sternum  is  discoverable.  It  may 
therefore  be  concluded  that  the  sternal  region  of  the 
somite  was  of  a  soft  and  perishable  nature ;  and  that  the 
thoracic  somite  of  a  Trilobite  resembled  one  of  the  abdo- 
minal somites  of  a  crab  in  this  and  in  some  other  respects. 

The  glahellum  (Fig.  57,  4),  or  central  raised  ridge  of 
the  cephalic  shield,  is  a  continuation  of  the  thoracic  axis, 
the  lobation  of  its  sides  perhaps  referring  to  the  number 
of  primitive  somites  it  represents.  The  limb,  or  lateral 
area  on  either  side,  answers  to  a  thoracic  pleuron;  its 
ihickeiMd  margin  (Fig.  57,  i)  is  produced  into  two  longer 


TBM  TSIIiOBITA. 


259 


or  shortOT  posterior  angles  (g) ;  inferiorlj,  the  marginal 
twnd  ia  reflected  inwards  tor  a  short  distance,  as  the 
tM^fnNUnJ /oM,  the  remaining  eternal  area  being  inooniplete. 
A  median  moreable  plate  answers  to  the  labnun  of  Apttt 
Mtd  Limubu.     On  the  occipital  or  lateral  margin  of  the 

Fig.  sr. 


Fig.  S7— Diagram  of  Dalmanita  (after  Piotet)— A,  head ;  !,  margi- 
nal band;  2,  marglnsl  groove,  mternal  to  (he  band;  3,  ocdpftal 
•Cfment;  4,'glabe11uni ;  5,  great  lulure;  6,  eves;  a,  fixed  gena;  b, 
■eparable  gcnaj  ,o,  genal  anglej  B,  Ihoru;  T,  aiii  or  tetgiun;  P, 
pleoion ;  C,  pjgidium ;  9,  tei^l ;  10,  pl«anl  portiooi  of  the  pjrgl- 


Umba  eature  (Fig.  57,  5)  commences,  and  passing  between 
the  e^e  and  the  glabellam.  meets  that  of  the  oppoaite  side 
either  in  front  of  the  latter,  or  on  the  margin  of  the  limb, 
or  on  the  snbf  rontal  fold,  and  is  connected  with  the  I&bral 


260   THE  ANATOMY  OV   INTBBTBBKATBD  AKIHALS. 

suture  by  one  or  two  sutures.  The  limb  is  thus  divided  into 
two  parts — one  fixed  (the  fixed  gena,  Fig.  57,  a),  attached 
to  the  glabellum ;  the  other  separable  (thie  moveable  gena. 
Fig.  57,  h),  on  which  the  eye  is  placed.  The  eyes  are  absent 
in  some  genera.  In  others,  they  occur  as  isolated  ocelli ;  or 
in  groups,  their  interspaces  being  occupied  by  the  common 
integument ;  or  they  may  resemble  the  compoxmd  eyes  of 
other  Arthropods. 

M.  Barrande  *  has  succeeded  in  tracing  out  the  develop- 
ment of  some  species  of  Trilobites.  He  finds  that  the 
smallest,  and  therefore  yoxmgest,  forms  are  discoidal  bodies, 
without  any  clear  evidence  of  segmentation.  The  division 
into  somites  takes  place  by  degrees,  the  number  increasing 
up  to  the  adult  condition.  It  is  possible  that  still  yoxmger 
conditions  may  have  escaped  f  ossilisation,  but  the  analogy 
of  Limulus  suggests  that  these  small  discoidal  forms  reaUy 
represent  the  condition  in  which  the  Trilobite  left  the  egg. 

The  MBBOSTOMATA.f — ^The  only  existing  representative 
of  this  division  of  the  Cmdcuxa  is  the  genus  Limuku  (the 
King  Grabs  or  Horse-shoe  Grabs),  the  various  species  of 
which  are  found  in  America  and  in  the  Moluccas.  They 
are  usually  classed  as  a  distinct  order  of  the  Crustacea, 
termed  Xiphosura  or  PcBcUopoda. 

The  body  of  Limulus  (Fig.  58)  is  naturally  divided  into 
three  parts,  which  are  moveably  articulated  together.  The 
most  anterior  is  a  shield- shaped  portion,  curiously  similar 
in  form  to  the  head  of  a  Trilobite.  Its  convex  dorsal 
surface  is  similarly  divided  into  a  median  and  two  lateral 
regions;  its  edges  are  thickened,  and  its  posterior  and 
external  angles  are  produced  backwards.  At  the  anterior 
end  of  the  median  region  two  simple  eyes  are  situated, 
and  at  its  sides  are  two  large  compound  eyes.  The  sternal 
surface  presents,  anteriorly,  a  flattened  subJrofUal  area, 

*  *Sv8t^e  Silorien  da  centre  graph  of  the  Britbh  fossil  Cms- 

deBoheme.'TomeL    Trilobites.  Uoes   belonging   to  the    order 

1851  Msrostometa,'  1866. 

t  H*  Woodward,   'A    Mono- 


THX  KIBOBT0IU.TA.  ^61 

bdund  whicli  it  ta  deeply  excavated,  bo  tliat  tbe  labrom  and 
llie  ^ipendageB  ore  hidden  in  a  deep  canty  formed  bj  itc 
■ludring  waJlB.  The  middle  diviaion  of  the  body  of  iFtmtiiut 
exliibita  markingB  which  indicate  that  it  iB  composed  of,  ab 
teweatiSixcoaleacedBoimtes;  its  margin*  are  epiaoae,  and  its 
excaT&t«d  itemal  face  lodges  the  appendages  of  this  region. 

Fig.  as. 


FIb-  58,— a,  Limului  aolxninta  (doraal  vi«w).     B,  L.  n.  

(Tantnl  view),  (mfter  Milne- Ed wtnli)  :  a,  Mleriat,  b,  middle  diiiiien 
of  tha  bod;;  c,  te1»inj  d,  gubfroDlal  area;  e,  mntennolMi/,  uiten- 
XB  i  9t  optrcDlum ;  h,  bnaohireraui  appcndigM. 

The  temtinai  diTieiou  is  a  long,  pointed,  and  latemlly 
serrated  spine,  which  ia  termed  the  telion. 

The  month  is  placed  in  the  centre  of  the  sternal  anrface 
of  the  anterior  division;  the  anus  opens  on  the  same  8nr< 
face,  at  the  jonction  between  the  middle  division  and  the 
teleon.  A  moveable,  eacntcheon-shaped,  labnun  projects 
backwards  in  the  middle  line,  immediately  behind  the  snb* 


262       THB  ANATOMY  OV  nfYBBTBBBATED  ANIMALS. 

frontal  area  (<2) ;  and,  on  each  side  of  it,  is  a  three-jointed 
appendage,  the  second  joint  of  which  is  prolonged  in  snch 
a  manner  as  to  form  with  the  third,  a  pincer  or  chela.  The 
attachment  of  this  appendage  is  completely  in  front  of 
the  labmm,  which  separates  it  from  the  mouth. 
.  In  each  of  the  next  five  pairs  of  appendages,  the  basal 
joint  is  enlarged ;  and,  in  the  anterior  four,  its  inner  edge  is 
beset  with  numerous  moveable  spines.  The  attachment  of 
the  basal  joint  of  the  foremost  of  these  appendages  (the 
second  of  the  whole  series)  is  in  front  of  the  mouth ;  but 
its  prolonged,  spinose,  posterior  and  internal  angle  may  be 
made  to  project  a  little  into  the  oral  cavity.  The  basal  joints 
of  the  following  three  appendages  are  articulated  at  the 
sides  of  the  mouth,  and  the  inner  angle  of  each  is  pro- 
vided with  a  spinose  process  which  projects  into  the  oral 
cavity.  The  second,  third,  fourth,  and  fifth  appendages  in 
the  females  are  chelate;  in  the  males  of  most  species, 
the  second,  and  sometimes  the  third,  are  not  chelate.  The 
large  basal  joint  of  the  sixth  appendage  is  almost  devoid 
of  spines,  and  bears  a  curved,  spatulate  process,  which  is 
directed  backwards  between  the  anterior  and  middle  divisions 
of  the  body.  The  fifth  joint  of  this  limb  carries  four  oval 
lamellae.  The  appendages  which  form  the  seventh  pair, 
very  unlike  the  rest,  are  short,  stout,  and  single-jointed. 

The  eighth  pair  of  appendages,  again,  are  of  a  totally 
different  character  fi*om  those  which  precede  them.  They 
are  united  in  the  middle  line  into  a  single  broad  plate, 
which  forms  a  sort  of  cover,  or  operculum,  over  the  succeeding 
appendages,  when  the  animal  is  viewed  from  the  sternal 
side.  On  the  dorsal  face  of  this  plate  are  seated  the  two 
apertures  of  the  reproductive  organs. 

From  the  inner  face  of  the  anterior,  or  sternal,  wall  of  each 
half  of  the  operculum  a  strong  process  arises,  and  passes 
upwards  to  be  attached  to  a  corresponding  process  of  the 
tergal  wall  of  the  anterior  division  of  the  body.  By  far 
the  greater  part  of  the  large  levator  muscle  of  the 
appendage  arises  from  the  tergal  wall  of  the  anterior 
divisioii  of  the   body,   and   the  nerve    which    supplies 


THB  MBB08TOMATA.  263 

the  limb  is  derived  directly  from  the  posterior  paart  of 
the  multiganglionate  cord  which  surroxmds  the  gaUet  and 
supplies  the  appendages  which  lie  in  front  of  the  operculnm. 

The  five  pairs  of  apx>endages  which  remain  resemble 
the  opercolnm  in  their  general  form,  and  have  ascending 
processes,  which  are  connected  with  inward  prolongations 
of  the  tergal  wall  of  the  middle  division  of  the  body. 
Their  nerves  are  derived  from  the  g^anglia  which  lie  in  this 
region  of  the  body. 

Thus  there  are  altogether  thirteen  pairs  of  appendages^ 
eight  of  which  are  connected  with  the  anterior,  and  five 
with  the  middle  division  of  the  body ;  and  the  apx>endages 
in  the  region  of  the  mouth  are  essentially  ordinary  limbs, 
the  basal  joints  of  some  of  which  are  so  modified  as  to 
subserve  manducation. 

The  determination  of  the  homologies  of  the  parts  hither- 
to spoken  of  as  the  anterior  and  middle  divisions  of  the 
body,  and  of  their  appendages,  is  a  matter  of  some  difficulty ; 
but,  on  comparing  the  disposition  of  the  limbs  and  their 
nervous  supply  with  what  obtains  in  the  higher  Crustacea, 
it  seems  hardly  doubtful  that  the  first  pair  of  appendages 
answer  to  the  antennules ;  the  second,  to  the  antennse ;  the 
third,  to  the  mandibles ;  the  fourth  and  fifth,  to  the  maxillsB ; 
and  the  sixth,  seventh,  and  eighth,  to  the  mazillipedes  of 
Aataeus  or  Homarus ;  and>  in  this  case,  the  anterior  division 
is  a  cephalo-thoraz.  If  the  position  of  the  genital  openings 
marks  the  hinder  boxmdary  of  the  thorax,  the  middle 
division  of  the  body  represents  an  abdomen,  composed  of 
five  somites.  But,  on  the  other  hand,  it  may  be  that  the 
genital  organs  open  in  front  of  the  hinder  extremity  of 
the  thorax,  as  in  female  Podophthahnia,  and  that  the  five 
somites  which  form  the  middle  division  correspond  with 
the  remaining  five  somites  of  the  thorax  of  a  PodophthaJ- 
mian.  In  this  case,  the  region  which  corresponds  with  the 
abdomen  in  the  higher  crustaceans  is  xmdeveloped. 

The  alimentary  canal  of  Limuhu  is  very  peculiarly  ar- 
ranged. The  gullet  passes  directly  forwards  and  upwards, 
and  gradually  widens  into  the  stomach,  the  walls  of  which 


264       THE  ANATOMY  OF  INYSBTBBBATBD  AKDIALS. 

ar6  proTided  with  mauj  longitudinal  f olda.  The  pjloroB 
is  prolonged  into  a  narrow  tube  which  projects  into  the  intes- 
tine. The  two  biliary  ducts  on  each  side  are  far  apart, 
and  branch  out  into  minute  tubules,  which  form  a  mass 
occupying  the  greater  part  of  the  cavity  of  the  body.  The 
rectum,  a  slender  canal  with  plaited  wtdla,  and  very  short, 
opens  into  a  sort  of  cloaca  situated  between  the  telson  and 
the  sternal  wall  of  the  abdomen. 

The  heart,  in  Limultu  polyphemus,  is  an  elongated  mus* 
cular  tube,  divided  into  eight  chambers,  and  having  as  many 
pairs  of  lateral  valvular  apertures.  It  lies  in  a  large  peri- 
cardial sinus,  which,  in  its  abdominal  portion,  presents  on 
each  side  five  apertures,  the  terminations  of  the  branchial 
veins.  The  branchisB  consist  of  numerous  delicate  semi- 
circular lamellse,  attached  transversely  to  the  posterior  faces 
of  the  five  post-opercular  appendages,  and  superimposed 
upon  one  another  like  the  leaves  of  a  book. 

The  nervous  system  appears,  at  first  sight,  to  be  very  con- 
centrated, its  principal  substance  being  disposed  in  a  ring, 
embracing  the  oesophagus ;  but,  on  closer  inspection,  it  is 
found  to  consist  of  an  anterior  mass,  representing  the  prin- 
cipal part  of  the  cerebral  ganglia  in  most  other  Crastaeea, 
and  of  two  ganglionic  cords  which  proceed  from  the  outer 
and  posterior  angles  of  that  mass,  and  extend  as  far  as  the 
interval  between  the  last  and  penultimate  pairs  of  appen- 
dages. These  cords  are  thick,  and  lie  on  each  side  of  the 
Cdsophagpis,  around  which  they  converge,  so  as  to  come  into 
close  union  and  almost  confluence,  immediately  behind  it. 
In  front  of  this  point,  however,  they  are  connected  by  three 
or  four  transverse  commissures,  which  curve  round  the  pos- 
terior wall  of  the  (Bsophagus,  and  become  gradually  shorter 
from  before  backwards. 

The  first  of  these  commissures  unites  the  two  cords  oppo- 
site the  origin  of  the  nerves  to  the  third  pair  of  appendages, 
which  I  regard  as  the  homologuee  of  the  mandibles.  In 
front  of  this  point,  the  cerebral  ganglia  give  off,  from  their 
anterior  edges,  the  nerves  to  the  ocelli,  eyes,  and  frontal 
TQgion;  and*  from  their  posterior  and  xmder  surfaces,  those 


THE  MSB08T0MATA.  265 

to  the  antennules.  The  nerres  to  the  anteniUB  arise  from  the 
cord  close  to  the  oater  and  posterior  angles  of  the  cerebral 
ganglia,  and  some  distance  in  front  of  those  to  the  mandibles. 
Close  behind  the  latter,  arise  the  large  nerves  to  the  fifth 
and  sixth  cephalo-thoracic  appendages. 

The  nerves  to  the  rudimentary  seventh  pair  of  appendages 
are  slender,  and  arise  rather  from  the  xmder  part  of  the 
post-casophageal  ganglia;  those  which  supply  the  eighth 
pair  of  appendages,  constituting  the  operculum,  are  also 
slender,  and  seem  to  come  off  from  the  two  longitudinal 
commissural  cords,  which  connect  the  post-cesophageal 
ganglia  with  those  which  are  situated  in  the  second  division 
of  the  body,  though  they  are,  in  truth,  only  united  in  one 
sheath  with  them  for  a  short  distance,  and  can  be  readily 
traced  to  the  post-oBsophageal  ganglia,  internal  to  the 
nerves  of  the  seventh  pair  of  appendages.  The  longitu- 
dinal commissures  are  very  long,  and  are  enclosed  in  a 
continuation  of  the  same  sheath ;  they  pass  back  into  the 
second  division  of  the  body,  and  there  present  four  gan- 
glionic enlargements,  whence  the  nerves  of  the  post- 
opercular  appendages  proceed.  The  last  of  these  ganglia 
is  much  larger  than  the  others,  and  appears  to  consist  of 
several  confluent  masses.  The  nerves  diverge  from  it  in 
such  a  manner  as  to  resemble  a  ccmda  equina. 

The  reproductive  organs  of  both  sexes  consist  of  a  mass 
of  glandular  ceeca,  which  ramify  through  the  body  amidst 
the  hepatic  tubules,  and  eventually  open  on  papill®  situated 
on  the  posterior  face  of  the  operculum.  The  males  are 
much  smaller  than  the  females,  and  present,  in  many 
species,  an  external  sexual  distinction  in  the  peculiarity  of 
their  second  and  third  appendages  already  referred  to. 

The  young  of  Limulus  acquires  all  its  chai'acteristio 
features  while  still  within  the  eg^.  The  interesting  obser- 
vations of  A.  Dohm  *  have  shown  that,  in  an  early  stage^ 

*  *'  Unteraachungen  uber  Baa  tions  of  Lookwood  and  Paokard, 

und  Eatwickelung  der  Arthropo-  '  American   Nataraliit,'  vol.  iv. 

den."     (<Jenai8die  Zeitachrift/  1871,  vol.  vii.  1873,  and  *  Memoirs 

Bd.  vi.)    See  alao  the  obaerva-  of  the  Boston  Society  of  Natural 


266     THE  AjfATomr  ov  nryxBTiBBATBD  ahucals. 

the  embryo  is  proyided  with  the  nine  anterior  pairs  of  ap- 
pendages, and  is  marked  out  into  fourteen  somites  by  trans- 
yerse  grooves  upon  its  sternal  face.  The  body  has  tiie  form 
of  a  thick  ronnded  disk,  divided  into  an  anterior  shield 
composed  of  six  somites,  and  a  posterior,  likewise  shield- 
shaped  region,  formed  by  the  union  of  eight  somites.  The 
telson  has  not  made  its  appearance.  In  this  condition,  its 
resemblance,  apart  from  the  limbs,  to  snch  a  Trilobite  as 
TriniAcleus  is,  as  Dohm  points  out,  most  remarkable. 

The  Xiphosura  were  represented  in  the  Carboniferous 
epoch  (BeUinwrus), 

The  Eurypterida  (Fig.  59)  are  extinct  Crustacea  of  Palseo- 
zoic  (Silurian)  age,  which  sometimes  attain  a  very  large 
size  and  in  many  respects  resemble  LimtUus,  while,  in  others, 
they  present  approximations  to  other  Crustacea,  especially 
the  Copepoda.  An  anterior,  eye-bearing,  shield-shaped  divi- 
sion of  the  body  is  succeeded  by  a  number  (12  or  more)  of 
free  somites,  and  the  body  is  ended  by  a  broad,  or  narrow 
and  spine-like,  telson.  IHve  pairs,  at  most,  of  limbs,  pro- 
vided with  toothed  basal  joints,  are  attached  to  the  sternal 
surface  of  the  shield,  and  the  mouth  is  covered,  behind 
them,  by  a  large  oval  plate  which  appears  to  represent  a 
metastoma  (Fig.  59,  B  g,).  Some  of  the  anterior  limbs  are 
frequently  chelate  {Fterygotus) ;  the  terminal  joints  of  the 
most  posterior  pair  are  generally  expanded  and  paddle-Hke. 
The  integument  often  presents  a  peculiar  sculpture,  simu- 
lating minute  scales.  The  sternal  surface  of  one  or  more 
of  the  anterior  free  somites  is  occupied  by  a  broad  plate, 
with  a  median  lobe,  and  two  laterally-expanded  side-lobes 
(Fig.  59,  B  h),  having  a  remote  resemblance  to  the  oper- 
culum of  Limuhu, 

The  Entomostbaca. — All  the  remaining  Crustacea  have 
completely  specialised  jaws ;  and  as  many  as  six  pairs  of 
appendages  may  be  converted  into  gnathites. 

Hisloff7,'187a;  with  the  diteot-  Lmmhu  by  E.  van  Beneden, 
tfan  or  Um  wjtUmstin  plaoe  of      <  Journal  de  Zoologies'  1872. 


IBM  INTOKOBTBACA.  267 

In  Ute  EtUoTMdraea,  if  the  body  poarwiep  an  tbdanuai 

(reckoning  aa  Bnch  the  eomitea  which  tie  behind  the  genitftl 

apertnre),  its  Monites  are  devoid  of  appendage*.     HoreoTer, 

Fig.  S9. 


B,  ventnl  aapect.    ClJi,  Oie  cephalo-thorwlo  ibleld  b         „    , 
vjtt,  and  b,  e,d,  t,f,  the  looomotlva  limba;  T,  talton;;,  the  meta- 
nomk;  k,  liieMa'aal  pUtaof  the  uiterioT  f^MMmlM*. 

the  Bomitee,  coantiog  Uiat  which  bears  the  eyes  ae  the  first, 
are  more  or  fewer  than  twenty.  There  are  never  more  than 

*  'Der  EurypttTHt  Ttwtipa,  ia»  dan  abarrilnrlMhaii  SoUeUni  dir 
ludOaiaL'    1B». 


268       THB  AJIATOXY  OF  UfYESTSBSATED  AJIIMALS. 

three  pairs  of  gnathites.  The  embryo  almoBt  always  leaves 
the  egg  in  the  condition  of  a  Navplitis ;  that  is,  an  oval  body, 
provided  with  two  or  three  pairs  of  appendages,  which  be« 
come  converted  into  antennary  organs  and  gnathites  in 
the  adult.  The  division  of  the  Entomostnica  comprises  the 
Copepada,  the  ^istoa,  the  Branchiapoda,  the  Ostraeoda,  and 
the  Pectostraea, 

The  CoPEPODA. — In  these  Ewtomostraca,  which  come 
nearest  to  the  Evrypterida,  the  cephalic  shield,  which  is  dis- 
coidal  and  not  folded  longitudinally,  is  succeeded  by  a 
certain  number  of  free  thoracic  and  abdominal  somites. 
The  antennules  and  antennsB  are  large,  and,  as  in  the 
Eurifpterida,  are  organs  of  locomotion  and  sometimes  of 
prehension.  The  anterior  thoracic  members  are  converted 
into  foot  jaws ;  the  posterior  serve  as  paddles,  the  limbs  of 
each  pair  being  often  united  together  in  the  middle  line, 
as  in  Limulus.    The  embryo  leaves  the  egg  as  a  Navplius, 

The  various  species  of  the  genus  Cyclops,  which  abound 
in  fresh  water,  afford  excellent  illustrations  of  the  struc- 
ture of  the  Copepodd, 

The  minute  animal  (Fig.  60)  is  shaped  something  like  a 
split  pear,  the  larger  end  corresponding  with  the  head,  and 
the  convex  side  with  the  dorsal  surface.  The  anterior  third 
of  the  body  is  covered  by  a  large  carapace,  which,  at  the 
sides,  extends  downwards  as  a  free  fold  over  the  bases  of  the 
appendages,  but  is  hardly  at  all  free  posteriorly.  Anteriorly, 
in  the  middle  line,  it  curves  forwards  and  downwards,  and 
is  produced  into  a  short  rostrum,  on  each  side  of  which  a 
considerable  excavation  lodges  the  base  of  the  long  anten- 
nule,  by  the  vigorous  oar-Uke  strokes  of  which  the  animal 
darts  through  the  water.  At  the  anteiior  boundary  of 
the  head,  the  double,  black,  median  eye,  which,  xmless  very 
closely  examined,  appears  single,  shines  through  the  cara- 
pace, and  at  the  sides  of  the  latter,  two  coiled  tubes  with 
dear  contents,  the  so-called  shell-glands,  are  seen. 

Pour  distinct  and  moveable  somites  succeed  the  carapace, 
and  gndually  diminish  in  diameter.    The  body  then  sud< 


THX  COPKFOD^  269 

denl^  enlarges,  and  becomes  divided,  in  the  fenude,  into 
tonr  segments,  the  last  of  wMoh  girea  attachment  to  two 
long  setose  etjlea,  vHch  possibly  represent  another  somite. 
There  is  a  well-developed  and  prominent  labrom  (or  con- 
joined epistoma  and  labnun)  in  front  of  the  month,  and 
behind  it  is  a  bilobed  metastoma.  The  first  pair  of  appen> 
Fig.  60. 


Fig.  60.—Cyekpt.—Blia  Tlew  of  ta  adult  fanile  cwninga  , 
OTiaaei,  and  veotnl  ii>w  of  tbe  hosd,  (bowing  the  labnun,  niBia- 
■toD»  ud  appendsgra  of  tbe  left  dde.  V,  eja,  II',  tnteuniile.  III', 
antenna,  IV ',  mandible,  V,  flrtt  MulUs,  Vl',  woond  muilla  (erro- 
nea(uljmark«l  VII'),a,oaUr,A,  iauerdlvitioii.  I,9^S,4,A,thoi«do 
limb*.  B,  roMium  ;  A,  labruia ;  aU,  mtUitODUu 

dages  are  tbe  long  and  manj-jointed  anUnnviei,  which  ore 
the  chief  organs  of  locomotion.  These  are  encceeded  by 
the  short  and  few-jointed  antennn.  The  third  pair  of 
append^es,  or  first  pair  of  gnathitee,  differs  from  the  cor- 
responding limb  in  JAimdvt  in  the  redaction  of  the  greater 
part    of   the    appendage  to   a  ndiment  terminated    by 


270       TH«  AJIATOMY  OF  INTBBTBBRATSD  ANIMALS. 

• 

setfiB,  while  the  strong  basal  part  is  the  principal  gnathite 
or  ma/ndible.  The  second  pair  of  gnathites  are  strong  and 
incurved ;  following  upon  these  is  a  third  pair  of  appen- 
dages, each  divided  into  two  portions,  an  inner  and  an 
outer.  The  latter  is  by  far  the  larger,  and  is  so  constructed, 
that  the  three  distal  articulations  can  be  bent  back  upon 
the  proximal  ones,  and  opposed  to  the  internal  division, 
constituting  a  prehensile  organ,  the  "hand"  of  Jurine.* 
Thus  the  gnathites  of  Cyclops  are  a  pair  of  mandibles 
followed  by  two  pairs  of  maxills.  At  some  distance  be- 
hind the  third  pair  of  gnathites  the  first  pair  of  thoracic 
apx>endage8  is  attached  to  the  hinder  part  of  the  cephalo- 
thorax.  Each  consists  of  a  two-jointed  baeal  part  {protopo- 
diie),  terminated  by  two  three-jointed  divisions  {eoBopodUe  and 
endopadUe).  Three  similar  pairs  are  appended  to  the  three 
anterior  free  somites,  while  a  fifth  rudimentary  pair  is 
connected  with  the  next  and  smallest  of  these  somites. 
The  suddenly  enlarged  following  segment  of  the  body 
carries  the  apertures  of  the  reproductive  organs  in  the 
female,  and  supports  the  ovisacs.  It  is  commonly  regarded 
as  the  first  abdominal  somite ;  but,  according  to  Glaus,  it  is 
composed  of  two  distinct  somites,  which  become  united  only 
after  the  last  moult. 

The  alimentary  canal  is  straight  and  simple,  and  without 
any  distinct  liver.  There  is  no  heart  nor  any  special 
respiratory  organ. 

The  single  ovary,  situated  in  the  thorax,  is  provided  with 
two  oviducts,  which  open  on  the  sides  of  the  coalesced  first 
and  second  abdominal  somites.  On  the  ventral  face,  between 
the  apertures  of  the  oviducts,  is  the  median  aperture  of  a 
colleterial  gland  which  secretes  the  viscid  matter  which 
forms  the  coat  of  the  ovisac.  Short  lateral  ducts  connect 
the  gland  with  the  extremities  of  the  oviducts. 

•  That  these  are  two  divisions  ppden.'    Wunburg    Natorwiss. 

of  the  third  gnathite,  and  not  two  Zeitschrift,  1862.)    Under  these 

separate  appendages,  has  been  de-  oircomstances  1  do  not  know  why 

monstrated  by  tracing  ont  their  they  shoold  be  termed  **  nuudlli- 

development.  (Glaus,  *  Organisa-  pedes.*' 
tkm  and  Verwindfachaft  der  Cope- 


THE  OOPBPODA.  271 

The  male  is  much  smaller  than  the  female,  and  the  two 
enlarged  somites  of  the  abdomen  remain  distinot.  There 
is  a  single  testis  provided  with  two  vasa  deferentia.  A 
specially  glandular  portion  of  the  latter  secretes  the  material 
of  the  spermatophores,  or  cases  in  which  the  spermatozoa 
are  enclosed.  The  antenna  are  thickened,  and  provided 
with  a  peculiar  hinge-joint,  by  means  of  which  the  male 
firmly  seizes  the  fourth  pair  of  swimming  legs  of  the  female 
during  copulation,  and  then  bending  up  his  abdomen, 
deposits  two  of  the  spermatophores  on  the  median  opening 
of  the  colleterial  gland,  into  which  the  spermatozoa  pass  on 
their  way  to  the  oviducts.  The  gland  thus  plays  the  part 
of  a  spermatheca.  The  eggs  are  carried  about  in  the 
ovisacs  xmtil  they  are  hatched. 

The  vitellus  undergoes  complete  division,  and  a  morula 
results,  the  blastomeres  of  which  soon  become  differen- 
tiated into  a  superficial  epiblast,  surrounding  a  deeper- 
coloured  mass,  which  gives  rise  to  the  hypoblast  and 
mesoblast.  The  whole  embryo  then  becomes  divided  by 
two  constrictions  into  three  segments,  and  the  hypoblast 
arises  by  delamination  aroxmd  a  central  cavity,  whicl 
becomes  the  alimentary  canal.  There  is  a  large  labrum  on 
the  ventral  side  of  the  first  segment  in  front  of  the  mouth. 
The  eye  appears  on  the  tergal  aspect  of  the  most  anterior 
segment,  as  two  pigment-spots  which  soon  coalesce  into  one ; 
and  a  pair  of  jointed  setose  limbs  grows  out  of  each  segment. 
In  this  Naupliu8'Bta,te  the  yoxmg  Cyclops  leaves  the  egg. 

The  posterior  part  of  the  body  elongates  and  becomes 
divided  into  the  somites  of  the  thorax  and  abdomen,  from 
which  their  respective  appendages  bud  out;  and  these 
changes  are  accompanied  by  exuviation  of  the  cuticle.  The 
three  pairs  of  appendages  of  the  Nauplitis  are  converted 
into  the  antennules,  antennse,  and  mandibles  of  the  adult. 

There  are  a  few  other  fresh-water  and  many  marine 
genera  of  Copepoda.  Among  the  latter,  the  PonteUidw  are 
remarkable  for  the  separation  of  that  part  of  the  head 
which  bears  the  antennules  and  the  antennse,  from  the  rest, 
a  peculiarity  to  which  a  parallel  can  be  found  only  among 


272       THE  ANATOMY  OW  nr^BBTEBKATBD  AKOfALS. 

the  Stomcdopoda,  CoryecBus  has  two  large,  more  or  lees  lateral 
eyes  in  addition  to  the  median  eye,  sabchelate  antennas, 
and  a  rudimentary  abdomen.  The  beautifully  iridescent 
Sctpphirina  has  an  extremely  depressed  body,  short  fili- 
form antennffi,  two  eyes,  and  rudimentary  gnathites.  A 
short  thoracic  heart  is  present  in  some  genera. 

The  Epizoa. — ^Insensibly  connected  by  such  genera  as 
Ergcuilu8  and  Caligus  with  the  typical  Gopepods,  are  a  great 
number  of  very  singular  Crustacea,  which,  from  their  habit 
of  living  parasitically  upon  aquatic  animals  (whence  their 
vulgar  name  of  "fish-lice"),  have  received  the  title  of 
Epizoa.  ChondracarUhtu  ffibhaafu,  commonly  found  in  great 
abundance  on  the  walls  of  the  branchial  chamber  of  the 
Fishing-frog  {Lophiu8  piscatoriua),  may  serve  very  well  as 
an  illustration  of  the  most  remarkable  peculiarities  of  this 
aberrant  group. 

The  female  (Fig.  61)  is  not  more  than  half  an  inch  long, 
but,  posteriorly,  two  long  slender  cylindrical  filaments,  (Hke 
the  rest  of  the  animal,  of  a  whitish  or  yellowish  colour,)  are 
attached  to  its  body,  which  is  broad  and  flattened,  and  as 
it  were  crimped  at  its  edges,  so  as  to  present  two  principal 
transverse  folds.  The  angles  of  the  folds  are  elongated 
into  lateral  processes  (h,  t,/),  and  similar  processes  {d,  e) 
proceed  from  the  middle  line  of  the  body,  which  by  these 
outgrowths  and  foldings  becomes  singularly  distorted ;  and 
the  grotesqueness  of  the  animal's  appearance  is  not  a  little 
enhanced  by  the  bowing  motion,  accompanied  by  a  flapping 
backwards  and  forwards  of  its  gouty  limbs,  which  it  exe- 
cutes when  detached  from  the  integument  of  the  Lophiut, 

The  head  is  expanded  into  a  sort  of  hood,  the  convex 
anterior  margin  of  which  bears  the  antennules  and  antenme, 
the  latter  being  metamorphosed  into  the  strong  curved 
hooks  by  which  the  ChondraMifUhtu  is  securely  anchored  to 
the  infested  animal.  A  subquadrate  labrum  overhangs 
the  mouth,  but  does  not  enclose  the  mandibles  and  form 
a  guotorial  apxmratus,  as  it  does  in  some  EpiMoa, 

The  mandibles  and  the  two  pairs  of  maxillffi  resemble 


THB  IPIEOA. 


carved  booVe  or  daws.    Two  pairs  of  appendagea  (Pig. 
61,  b  e),  composed  each  of  a  protopodite,  terminated  by  an 


Tig.Sl.—  Chowlracantkiugitbona.—Ytmtlv:  A,  lateral  view.  B,  tbd- 
tim)  view,  enlu-ged.  a,  lind  ;  b,  c,  tpptndmgea  ;  d,  medlui  dsmi 
pTooen ;  i,  msdlui  ventral  proceuM ;  /,  i,  A,  lateral  proceuee ;  t, 
tenninkl  legment,  (,  male  ;  g,  avIwMa ;  ■•,  n,  medlo-danat  ovuian 
tabes ;   p,  bteral    OTarian    lubes ;    o,  ovidact.     1,    3,  anleiinulei ; 

endopodite  and  exopodite  and  exbibiting  haidly  any  tsuft 


274   THE  AKATOMY  OP  INYEBTEBBATBD  ANIMALS. 

of  articulation,  are  attached  to  the  anterior  'port  of  the 
body  behind  the  head. 

The  body  ends  in  a  rounded  segment,  situated  in  the 
deep  notch  between  the  hindermost  marginal  processes,  and 
bearing  the  two  projecting  vulvae.  Above  each  of  these 
is  a  small  triangular  papillose  lobe  (Fig.  62,  tr),  probably  a 
modified  appendage,  to  which,  as  we  shall  see,  the  male 
attaches  himself,  while  below  them  are  two  other  rudi- 
mentary appendages  (Fig.  62,  y).  The  alimentary  canal  is 
a  straight  tube  running  from  the  mouth  to  the  opposite 
extremity  of  the  body.  No  heart  is  discoverable,  and  the 
nervous  system  and  organs  of  sense  (if  any)  are  equally  un- 
distinguishable.  The  interspace  between  the  alimentary 
canal  and  the  walls  of  the  body  is  almost  wholly  occupied 
by  the  ovarium,  which  consists  of  four  tubes,  situated  on 
each  side  of  the  intestine,  and  giving  off  ramified  caeca,  in 
which  the  ova  are  developed.  Anteriorly,  each  pair  of  tubes 
opens  into  the  oviduct  of  its  side,  which  passes  down  along 
the  side  of  the  body  to  terminate  at  the  vulva.  The  lower 
part  of  the  oviduct  contains  a  clear  gelatinous  substance, 
and  is  very  similar  in  aspect  to  the  cement  duct  of  a  cirri- 
pede ;  this  substance  is  secreted  by  the  walls  of  the  oviduct, 
and  forms  the  walls  of  the  ovigerous  sac.  The  latter,  as 
has  been  stated,  has  the  form  of  a  long  cylindrical  fila- 
ment, the  upper  end  of  which  is  firmly  held  between  the 
prominent  lips  of  the  vulva  (Fig.  62,  «). 

The  male  Chondracanthus  does  not  attain  to  a  twelfth 
the  length  of  the  female,  and  looks,  at  first,  like  a  papilla 
upon  her  body  near  the  vulva.  On  close  examination,  how- 
ever, he  is  seen  to  be  firmly  fixed  by  his  antennary  hooks  to 
one  of  the  two  triangular  lobes  described  above.  The  hooks 
are  doubtless  at  first  attached  to  the  lobe  by  muscular 
contraction ;  but  the  connexion  once  effected  seems  indis- 
soluble— at  least  maceration  in  caustic  soda  does  not  cause 
the  male  to  become  detached.  It  does  not  appear  that 
more  than  one  male  is  attached  to  a  female. 

The  body  of  the  male  (Fig.  62)  is  pyriform,  and  exhibits 
indications  of  a  division  into  six  segments  beside  the  head. 


CHOMSKlCAHTHUa  QIBBOBUS. 


275 


The  anterior  extremity  presents  a  black  eje-apot  imbedded 
in  its  substance,  and  gives  origin  to  a  pair  of  radimentary 
antennoles,  and  to  the  strong,  hooked,  prehensile  antenUEB. 
Behind  and  below  them  is  a  large  labram  and  three  pairs 
of  hook-like  gnathitea.  These  are  sncceeded  bj  two  pairs 
of  enbcjlindrical  appendages,  which  apparently  represent 
ambnlatorj  limba. 

The  caudal  extremity  ia  terminated  by  two  styles,  and 
there  are  two  prominent  tubercles  on  the  ventral  surface  of 
the  penaltimat«  somite,  in  which  the  genital  apertorea  are 
seated.    The  alimentary  canal  ia  a  delicate,  irregular  tube, 


Fig.  63.— C.  Male  CAonrframntAiu,  in  tif,  m 
temsle  ;  v,  tri*ngut*r  papillose  lobrg;  q,  ■ 
cje-ipol:  (,  tt«ti»;  «,  vu  defwena ;  b, 
rudimentUT  appeadagei  of  Ihi  feoule  ;  y,  ot 


r,    tuItib   of 

inllal  aperture;  y, 


having  many  brownish  granules  imbedded  in  its  walls,  A 
wide  cBaophagna  is  connected  with  its  anterior  extremity ; 
but  the  opposite  end  appears  to  be  rounded,  and  to  be  united 
with  the  ventral  surface  of  the  integument  only  by  connec- 
tive tissue.  A  complex  muscular  system,  composed  of 
atriped  fibres,  ia  visible  through  the  integument,  and  the 
eye-spot  seems  to  be  connected  with  a  subjacent  gan- 
glionic mass.  The  body  is  sufficiently  transparent  to 
allow  the  pulsations  of  a  heart  to  be  seen,  but  none  can 
be  discovered.    The  testis  is  a  large  oval  bilobed  n 


il 


276       THE  ANATOMY  OF  IKYEBTEBBATED  ANIMALS. 

lying  like  a  saddle  upon  the  anteiior  part  of  the  intestine. 
From  this  body  a  thick  yas  deferens  runs  back  upon  each 
side  of  the  intestine,  and  dilates  in  the  penultimate  and 
antepenultimate  somites  into  a  thick  walled  pyriform  sac 
— a  soH  of  yesicula  seminalis.  The  embryo  leaves  the  egg 
as  a  Naupliu8,  like  that  of  Cyclops. 

There  are  many  genera  of  these  parasites,  some  of  which, 
such  as  the  almost  completely  vermiform  Lemcece,  deviate 
even  more  widely  than  Clwudracanthiis  from  the  ordinary 
form  of  CruslcLcea,  while  others,  such  as  Ergasilus  and  Noto^ 
delphys,  differ  but  little  from  the  free  Copepoda. 

In  CaliguSt  the  labium  and  metastoma  are  elongated  and 
united  into  a  tube  in  which  the  sharp  styliform  mandibles 
are  enclosed ;  and  from  the  prevalence  of  this  suctorial  form 
of  mouth  in  some  of  the  best  known  species  of  parasitic 
Copepoda,  they  are  frequently  termed  "  suctorial "  crus- 
taceans. Suctorial  disks  for  attachment  are  developed  from 
the  coalesced  posterior  pairof  thoracic  members  in  Achtheres ; 
and,  in  this  genus,  the  head,  as  a  distinct  part,  becomes 
almost  entirely  obsolete. 

Arguhis,  the  parasite  so  common  on  the  Stickleback,  is 
worthy  of  notice  as  one  of  the  most  curious  modifications 
of  the  epizoic  type.*  It  is  extremely  flattened,  and  is  com- 
posed of  an  anterior  cephalo-thoracic  disk,  behind  which 
lies  a  very  short  and  broad,  notched,  abdomen.  A  median 
styliform  weapon  lies  in  a  sheath  in  front  of  the  mouth,  and 
the  small  mandibles  and  maxillsB  are  enclosed  in  a  short  tube 
formed  by  the  labrum  and  the  metastoma.  Six  pairs  of 
appendages  lie  behind  the  mouth,  the  anterior  being 
metamorphosed  into  suckers,  the  next  pair  into  strong 
limbs  with  a  toothed  second  joint,  and  the  four  others 
constituting  biramous  swimming  feet.  There  are  two 
pairs  of  antennary  organs,  and  two  compound  eyes.  Ac- 
cording to  Leydig,  the  males  are  provided  with  cups  on  their 

*  Clans  (*  Ueber  die  Entwic*  of  Argultu  with  the   Copepoda, 

kelung,  Organization  nnd  syste-  bnt  proposes  to  regard  it  as  the 

matisdie  Stellung  der  Arguliden,'  type  of  a  special  group,  the  Bnm* 

1875)  has  proved  the  close  affinity  dUicra. 


THB  BBANOHIOPODA.  277 

penultimate  swimming  feet ;  and,  during  copulation,  these 
are  filled  with  the  senunal  fluid,  which  is  thus  transferred 
to  the  Yulva  of  the  female,  and  thence  to  the  spermatheca. 
The  eggs  are  laid,  and  not  carried  about  in  ovisacs.  The 
larva  is  provided  with  two  pairs  of  principal  8¥mnming 
appendages,  the  future  antenuBB  and  the  mandibular  palps, 
the  latter  eventually  entirely  disappearing.  There  is  a  pair 
of  small  antennules,  a  pair  of  strong  legs  in  the  place  of  the 
suckers,  and,  behind  them,  the  rudiments  of  the  prehensile 
legs  and  the  first  pair  of  biramous  appendages,  the  others 
being  rudimentary. 

Notodelphys,  which  may  be  found  very  commonly  in  the 
branchial  sac  of  Asddians,  closely  resembles  an  ordinary 
Copepod,  except  that  it  becomes  much  distorted,  and  that  it 
carries  its  ova  in  a  chamber  formed  by  the  dorsum  of  the 
carapace. 

However  strangely  modified  the  adult  form  may  be  (and 
it  must  be  remembered  that  it  is  always  the  female  which 
undergoes  the  greatest  amount  of  change),  the  larvae  of  all 
these  epizoic  parasites  resemble  those  of  the  ordinary  free 
Copepoda  in  possessing  only  two  {Achtheres,  Trachelitistea)  or 
three  pairs  of  appendages,  (which  appertain  to  the  anterior 
region  of  the  head) ;  and  they  are  endowed  with  considerable 
powers  of  locomotion. 

The  Beanchiopoda. — The  genera  Nehalia,  Apus,  Bran- 
chipus,  lAmnetis,  Daphnia,  and  their  allies,  are  usually 
divided  into  two  orders,  the  Phyllopoda  and  the  Cladocera ; 
but  these  pass  into  one  another  so  gradually,  and  have  so 
many  structural  peculiarities  in  common,  that  the  subdivi- 
sion of  the  group  of  Branchiopoda  appears  to  me  to  be  a  step 
of  doubtful  propriety.  Closely  resembling  the  lower  Pod- 
ophthalmia^  such  as  Mysis,  in  some  respects,  these  Crusta- 
ceans are  invariably  distinguished  from  them  by  the 
possession  of  a  greater  or  less  number  of  somites  than 
twenty;  Nehalia,  which  most  nearly  approximates  the 
higher  Onutacea,  having  twenty-two  somites.  Furthermore 
the  thoracic  and  abdominal  appendages  of  the  BraucKvygo^ 


278   THE  ANATOMY  OF  INYEBTEBBATED  ANIMALS. 

are,  in  the  majority  of  cases,  more  or  less  foliaceoos,  re- 
sembling, in  many  respects,  the  anterior  maxillipede  of  an 
AstacuSy  and  being  constructed  on  essentially  the  same  plan. 

Aptis  glacialis  (Fig.  63)  presents  an  elongated  vermiform 
body,  terminated  by  two  long,  multiarticulate,  setose  styles, 
and  covered  anteriorly  by  a  gi*eat  shield-like  carapace,  deeply 
excavated  behind.  The  posterior  three-fifths  of  the  carapace 
are  free,  and  merely  overlap  the  segments  of  the  body;  the 
anterior  portion,  on  the  contrary,  is  united  with,  and  forms 
the  tergal  surface  of  the  corresponding  region  of  the  head ; 
the  free  portion  of  the  carapace  shelves  away  laterally  from 
a  median  ridge,  on  each  side  of  which  a  curious  concentric 
marking,  indicating  the  position  of  the  shell  gland,  (Fig.  63, 
B,  SB,)  is  visible.  This  gland  is  a  coiled  tube  with  clear 
contents,  which,  according  to  Clans,  opens  on  the  base  of 
the  first  pair  of  thoracic  appendages,  immediately  behind 
the  second  maxillaa.  Where  the  free  joins  the  fixed  portion 
of  the  carapace,  the  ridge  is  abruptly  terminated  by  a  trans- 
verse depression.  A  little  distance  in  front  of  this  is  another 
deeper  transverse  groove,  close  to  which,  in  the  middle  line, 
are  the  two  reniform  compound  eyes,  converging  towards 
one  another  anteriorly  (Fig.  63,  B,  i). 

The  ventral  siQ-face  of  the  anterior  division  of  the  carapace 
(Fig.  63,  C),  presents  a  flattened,  semilunar,  subfrontal 
area,  as  in  Limulusy  behind  which  it  slopes  upwards  on 
all  sides  into  the  posterior  division,  thus  forming  a  wide 
chamber,  in  which  the  anterior  thoracico-abdominal  seg- 
ments are  lodged.  In  the  middle  line,  the  subfrontal  plate 
sends  back  a  long  and  wide  process,  moveably  articulated 
with  it,  and  rounded  at  its  free  end — the  labrum ;  above  and 
behind  which  the  mouth  and  gnathites  are  situated.  Behind 
these  follow  twenty-six  spinulose  thoracico-abdominal  seg- 
ments; the  anterior  twenty  of  which  bear  the  swimming 
feet,  while  the  twenty-sixth,  much  larger  than  the  others,  is 
produced  into  an  incurved  point  posteriorly,  and  carries  the 
anus  and  the  terminal  setae. 

The  compound  eyes,  as  has  been  said,  are  seated  upon  the 
npper  surface  of  the  anterior  division  of  the  carapace.    On 


THE  BSAKCHIOPODA.  279 

the  under  surface,  just  above  and  behind  tbe  posterior 
boundary  of  tbe  subfrontal  area,  and  on  each  side  of  tbe 
labrum  (Fig.  63,  0,  lb) yia  a  delicate  jointed  filament — tbe 
antennule  (Fig.  63,  C,  ii').  Bebind  tbis,  Zaddacb  found  in 
some  specimens  of  Apus  cancriformia,  a  second  very  small 
filament,  tbe  rudiment  of  tbe  antenna,  wbicb  in  tbe  larva 
is  so  large  and  important  an  organ;  but  I  bave  observed 
notbing  of  tbe  kind  in  A,  glacialis.  On  eacb  side  of  tbe 
labrum  is  a  large,  convex,  strong,  tootbed  mandible,  and 
tbe  aperture  of  tbe  moutb  is  bounded  posteriorly  by  a  pro- 
foundly divided  plate,  tbe  metastoma.  Succeeding  tbis  are 
two  pairs  of  small  maxillse,  tbe  second  pair  being  f  oliaceous, 
and  almost  rudimentary.  Bebind  tbese  appendages,  a  cer- 
vical fold  marks  off  tbe  boundary  between  tbe  bead  and 
tbe  tborax,  and  at  tbe  same  time  corresponds  witb  tbe 
commencement  of  tbe  free  portion  of  tbe  carapace.  Wbetber 
tbe  carapace  is  also  to  a  certain  extent  attacbed  to  tbe 
first  tboracic  somite,  as  Grube  states,*  or  wbetber  it  is 
entirely  cepbalic,  as  Milne-Edwards  considers,  is  a  point 
upon  wbicb  I  bave  been  able  to  come  to  no  very  clear  de- 
termination ;  indeed,  it  is  a  question  ratber  for  tbe  embryo- 
logist  tban  tbe  anatomist. 

Of  tbe  twenty  pedigerous  segments,  tbe  first  eleven  bave 
eacb  one  pair  of  appendages;  but,  bebind  tbe  eleventb,  eacb 
segment  gives  attacbment  to  a  gi*adually  increasing  number 
of  limbs,  so  tbat  tbe  twentietb  carries  five  or  six  pairs. 
Altogether  twenty-eigbt  pairs  of  appendages  are  attacbed 
to  tbese  nine  posterior  tboracic  segments ;  tbese,  added  to 
tbe  eleven  preceding,  make  tbirty-nine  appendages  in  all. 
Wbile  eacb  of  tbe  anterior  eleven  segments  must  be  regarded 
as  single  somites,  tbe  nature  of  tbe  posterior  ones  is  open 
to  doubt;  tbey  may  be  single  terga,  tbe  sterna  and  ap- 
pendages of  wbicb  bave  multiplied;  or,  more  probably, 
tbey  eacb  represent  a  number  of  coalesced  terga. 

Eacb  appendage  consists  of  tbree  divisions — an  endopo- 
dite,  exopodite,  and  epipodite,  supported  on  a  protopodite  or 
basal  division  (Fig.  63,  D,  E,  F).   Tbe  latter  consists  of  tbree 

*  *  Bemerkangen  uber  die  Phyllopoden,'  p.  81 « 


THI  AHATOMT  OT  tNVBBTSB&l.TEI>  AHIKALB. 
Fig.  61. 


THB  BIKANOHIOPOD^.  281 

Fig.  6^—Apu$  glacialu,—Ky  lateral  view,  with  the  right  half  of  the 
carapace  cut  away.  B.  Dorsal  view.  C.  Anterior  part  of  the  body, 
ventral  aspect.  D,  one  of  the  anterior,  £.  one  of  the  (middle, 
and  F,  one  of  the  pa«terior  limbs,  without  their  ooxopodites.  x,  con- 
voluted "  shell  gland  "  in  the  carapace ;  y,  caudal  filament ;  &, 
labrum.  1,  2,  3,  4,  Endopodite.  6.  Exopodite.  7.  Epipodite  or 
branchia.    I',  eye ;  IT,  antennule ;  IV',  labrum ;  V,  YI',  maxillfe. 

joints — a  coxopodite  produced  intemallj  into  a  strongly 
setose  prominence  (not  represented  in  the  figures),  a  basi- 
podite,  and  an  ischiopodite,  the  latter  elongated  internally 
into  a  lanceolate  process,  and  bearing  on  its  outer  side  two 
appendages,  of  which  the  proximal  —  the  epipodite  or 
branchia  (Fig.  63,  D,  E,  7) — is  pyriform  and  yesioular  in 
specimens  preserved  in  spirit.  The  distal  appendage, 
which  appears  to  represent  the  exopodite  (6),  is  a  large 
flat  plate,  provided  with  long  setsB  on  its  margin. 

The  endopodite  consists  of  four  joints,  the  two  proximal 
ones  berng  much  the  longer,  and,  like  the  penultimate,  giving 
off  internally  a  long  process.  Finally,  the  terminal  joint  is 
claw-like  and  serrated  on  its  concave  edge. 

The  avei'age  form  of  these  appendages  is  represented  by 
(E)  taken  from  the  middle  of  the  series;  anteriorly  the 
limbs  become  more  slender  and  leg-like  (D);  posteriorly, 
on  the  other  hand,  they  ai'e  completely  foliaceous,  as  (F) ; 
but  the  same  elements  are  recog^nisable  throughout. 

The  eleventh  pair  of  appendages  alone  depart,  in  any 
important  respect,  from  the  rest  of  the  series,  each  of 
these  being  modified  so  as  to  serve  as  a  receptacle  for 
the  ova.  To  this  end  the  joints  of  the  endopodite  are 
greatly  expanded,  and  converted  into  a  hemispherical 
bowl;  the  exopodite,  metamorphosed  into  another  such 
bowl,  shuts  down  over  the  endopodite;  and,  into  the 
box  thus  formed,  the  ova  are  conducted  by  means  of  the 
oviduct,  which  opens  into  it. 

On  the  dorsal  surface  of  each  side  of  the  terminal  segment 
of  the  body  there  is  a  tubercle  produced  into  five  spines 
anteriorly,  and  carrjdng,  posteriorly,  a  long  and  delicate 
setigerous  filament  (Fig.  63,  B,  g). 

The  alimentary  canal  of  Apva  is  very  simple,  couKifl^xw^ 


282       THE  ANATOMY  OF  INVSBTBBRATED  ANIMALS. 

of  a  vertically  ascending  (Bsophagus,  which  bends  back  into 
the  small  stomach,  situated  immediately  behind  the  com- 
pound eyes,  in  the  middle  of  the  region  bounded  by  the  two 
transverse  furrows  on  the  dorsum  of  the  carapace ;  from  the 
hinder  end  of  the  stomach  the  straight  intestine  passes  back 
to  the  anus,  which  is  seated  beneath  the  terminal  segment. 
The  liver  consists  of  caeca,  which  branch  off  from  the 
stomach  and  lie,  on  each  side  of  it,  in  the  head.  Zaddach 
describes  a  pair  of  glands  which  he  regards  as  salivary, 
placed  above,  and  opening  into,  the  stomach  itself,  like  the 
salivary  glands  of  the  Scorpion. 

The  heart  occupies  the  tergal  region  of  the  eleven  anterior 
thoracic  somites,  presenting  as  many  chambers,  with  lateral 
venous  apertures. 

The  nervous  system  consists  of  a  quadrate  cerebral  mass, 
placed  immediately  under  the  compound  eyes,  and  giving 
off  large  nerves  to  them  and  to  the  remains  of  the  single  eye 
of  the  larva,  which  lies  in  front  of  their  anterior  extremities. 
Commissures  pass  downwards  and  backwards  on  either  side 
of  the  oesophagus,  and  connect  the  cerebrum  with  a  chain 
of  numerous  ganglia  placed  on  the  median  line  of  the  ventral 
surface.  It  is  worthy  of  remark,  that  the  antennary  and 
antennulary  nerves  are  given  off  from  the  commissures,  far 
behind  the  chief  cerebral  mass. 

In  the  female,  the  ova  are  developed  in  the  csecal  branches 
of  two  long  tubes,  situated  one  on  each  side  of  the  body, 
and  opening,  as  above  described,  in  the  eleventh  pair  of 
appendages.  Apus  usually  propagates  agamogenetically, 
and  the  examination  of  thousands  of  individuals,  extending 
over  more  than  thirty  years,  failed  to  reveal  to  Von  Siebold 
the  existence  of  a  male  fonn.  In  1856,  however,  Kozubow- 
ski  *  discovered  a  small  proportion  of  males  (16  in  160), 
among  the  specimens  taken  in  the  neighbourhood  of  Cracow ; 
and  near  Rouen,  in  1863,  Sir  John  Lubbock  found  the 
largest  proportion  of  males  to  females  yet  known,  viz., 
33  in  72.    On  the  other  hand,  between  1857  and  1869,  Von 

•  "  Ueber  den  mannlichen  Apus  cancriformis.'*     (*  ArchlF  flir  Natur- 
geschichte,'  1857.) 


THE  BBANCHIOPODA. 


283 


Siebold  examined  many  thousands  of  specimens  of  the 
Bavarian  Apus  without  finding  a  single  male.* 

The  testis  is  similar  to  the  ovary  in  form,  and  its  duct 
opens  upon  the  eleventh  pair  of  appendages,  as  in  the  case 
of  that  of  the  female  organs.  The  spermatozoa  are  oval  aud 
without  motion. 

The  young  Apus  {cancriformis),  when  just  hatched,  is  a 
Nauplius,  The  body  is  oval,  indistinctly  divided  into  a  few 
segments,  and  entirely  destitute  of  appendages,  except  a 
shorter  anterior,  uniramous,  and  a  longer  posterior,  biram- 
ous,  pair  of  oar-like  organs,  situated  at  the  anterior  extremity, 
on  either  side  of  the  single  median  eye.  The  carapace  is 
rudimentary,  and  there  are  no  caudal  filaments.  The  little 
animal  soon  casts  its  skin,  and  the  mandibles,  which  are 
provided  with  long  palps,  make  their  appearance.f  With 
successive  ecdyses,  the  larva  assumes  more  and  more  the 
form  of  the  adult,  and  acquires  the  pair  of  compound  eyes ; 
the  anterior  pair  of  appendages  being  converted  into  the 
antennules,  the  posterior  pair  disappeai-ing,  or  remaining 
as  rudimentary  antennae,  and  the  mandibular  palps  also 
vanishing. 

Singular  and  highly  instructive  modifications  are  exhibited 
by  the  other  genera  of  the  BranchiopocUiy  such  as  Nehcdia, 
Branchipus  (Cheirocephalus),  lAmnetis,  and  Daphnia. 

In  Daphnia  and  its  allies  (Fig.  64),  the  thoracic  members 
are  reduced  to  six,  five,  or  even  four  pairs,  some  or  all  of 
which  may  take  the  form  of  ordinary  limbs ;  the  abdomen  is 
rudimentary ;  the  heart  is  short ;  and  the  carapace  presents 
a  posterior  division  (omo8tegite)y  obviously  developed  from 
the  anterior  thoracic  somites,  the  lateral  halves  of  which 
are  deflexed  so  as  to  resemble  a  bivalve  shell,  into  which  the 
hinder  part  of  the  body  can  be  withdrawn.  The  anterior 
division  of  the  carapace  (cephalogtegite)  in  Daphnia  has,  on 
the  contrary,  the  same  structure  as  the  corresponding  part 

*  Beitrage     zur    Partheno-  t  According  to  Claus*8  recent 

?;ene8i8  der  Arthropoden,*  1871.  investigations,  this  third  pair  of 

t  appears  that,  in  Apus,  the  im-  appendages  is  present  from  the 

pregnated  ova  alone  give  rise  to  time  the  young  Apus  leaves  the 

males.  egg. 


284       THE  ATU.TOMT  Or  IIITEBTXBK1.TSD  AHIHAU. 

of  the  canLpac«  of  Aptu,  but  tlie  compound  ejw,  repn- 
sented  by  a  smgle  maBB.are  eitnated  at  tbe  anterior  extremis 
of  tbe  bead,  ratber  tban  on  its  upper  sorface,  and  tbe  BUigle 
eye  is  quite  diBtinct,  and  far  posterior  to  tbem  (Fig.  64,  B, 
t,  u").  Tbe  antennnles  (Fig.  64,  A.  ii*)  are  small,  radi- 
mentary,  and  placed  at  the  sides  of  tbe  produced  frontal 

Fig.  64. 


CI,  cephaloitegitc,  or  that  part  of  the  carap»ce  which  a 
heM;    Ml,  oDiDsteeite,  or    thoracic    portioa  of  the  can,         ,      . 
llMrt;    •(.   eeniCBl    depretiion;   III,   labriUD ;    1',    compound  eye; 
U',   almple   eye;    t,   we  ' Bhell-glanil,'  wbloh  opens  Dchipd  tbe 


rostrum,  but  tbe  antennffl  are  very  large,  and  congtitute 
tbe  principal  locomotive  organs.  The  posterior,  or  second, 
maiillEe  are  obsolete.  In  Evadne,  Polyphemvs,  Sida  and 
other  genera,  sucker-tike  organs  of  adhesion  are  situated 
OD  the  anterior  region  of  the  carapace.  Tbe  eggs  are  de- 
veloped in  the  cavity  of  tbe  carapace,  and  tbe  embijoe  pass 


THE   BSANCHIOPODA.  285 

directly  into  the  form  of  the  parent,  except  in  Leptodorut 
where  they  are,  at  first,  Natiplius-Mke, 

Idmneiia  and  Estheria  present  a  DaphniaAike  carapace, 
though  more  completely  bivalire,  combined  with  the  nmne- 
roxLB  segments  of  the  body  and  the  f  oliaceons  appendages 
of  the  typical  Phyllopods  (Fig.  65). 

Nehalia  has  a  large  carapace,  provided  with  a  moveable 
rostrum,  like  that  of  Squilla,  and  arising  entirely  from 
the  head,  which  is  remarkable  for  its  very  slight  sternal 
flexure.  In  this  genus,  the  eyes  are  large  and  peduncu- 
lated ;  there  are  well-developed  antennules,  antennse,  man- 
dibles, and  two  pairs  of  maxillse,  the  anterior  of  which  ends 
in  a  long  palp. 

Branehipus,  finally,  developes  no  carapace  either  from 
the  head  or  the  thorax,  the  segments  of  the  latter  being 
entirely  free,  while  the  former  is  similar  in  shape  to  that 
of  an  Insect,  or  Edriophthalmous  Crustacean,  and  carries 
two  large  stalked  eyes,  two  antennules  (singularly  modified 
in  the  male),  two  antennae,  a  pair  of  mandibles,  and  two 
paira  of  maxillse. 

In  Eatheria  and  Limnetis,  the  males  are  met  with  in  full 
proportion  to,  and  may  be  even  more  numerous  than  the 
females.  No  males  are  known  in  Limnadia  gigas,  although 
thousands  have  been  examined,  while,  in  L,  Stanleya/na, 
more  males  than  females  have  been  found.  In  Branchipus, 
males  are  fewer  than  females;  in  Artemia,  they  occur 
only  at  rare  intervals.  In  Daphnia,  the  males  are  few,  and 
appear  only  at  certain  seasons  of  the  year.  But  notwith- 
standing the  rarity  or  absence  of  the  males  in  many  of 
these  genera,  reproduction  proceeds  with  great  rapidity. 
The  ova  are  capable  of  development  without  fecundation ; 
and  isolated  females  of  the  genus  Daphnia  will  thus  go 
on  producing  broods  for  generation  after  generation,  with- 
out any  known  limit. 

Under  certain  circumstances,  however,  bodies  of  a  different 
nature  from  these  "  agamic  ova,"  as  they  have  been  well 

*  "Ueber  die  Gattongen  Estheria  and  Limnadia:*  ('Arcbiv  fur 
NAtargeichichte,'  1854.) 


286       THE  ANATOHT  Or  IHTIBTEBEATKD  AHIIUX8. 

termed  by  Sir  Jolm  Lubbock,*  are  dereloped  within  tl 
QYKrj,  the  Bubstance  of  which  acqairee  an  accninvilation  < 
strongly  refracting  gnuinlea  at  one  spot,  and  forms  a  dai 
maas,  the  BO-called  "  ephippial  ovum."  When  fnlly  fonne 
two  of  these  bodies  pass  into  the  dorsal  chamber  of  the  oar: 
pace,  the  walls  of  which  have,  in  the  meantime,  becoa 


Fit.  ei.~LimiKlit  limdymM  <ftfI«T  Grubc).— The  appet  lefUku 
figure  ia  tlie  male,  tbe  other  the  femsle ;  one  tbIvb  of  the  carapai 
in  each  caaebda|  removed.  A'.  Antennules.  A'.  AntaoDte.  J 
Toiing  larva.  B.  The  umB  further  adranccd.  c.  Head.  o.  E; 
d.  Carapace,  if.  Uody.  A'.  AntennK,  M.  Maodibles.  a*.  Gtei 
plate  (labnun  ?)  which  coven  the  minitb. 

altered.  The  outer  and  inner  layera  of  the  int^omei 
acquire  a  peculiar  stmctnre,  a  brown  colonr,  and  a  moi 
firm  consistency,  over  a  large  saddle-like  area.    When  tl 


epblpplni 
BoyalSo 


THE   OSTBACODA.  287 

next  moult  takes  place,  these  altered  portions  of  the  integu- 
ment, constituting  the  "  ephippium,"  are  cast  off,  together 
with  the  rest  of  the  carapace,  which  soon  disappears,  and 
then  the  ephippium  is  left,  as  a  sort  of  double- walled  spring 
box  (the  spring  being  formed  by  the  original  dorsal  junction 
of  the  two  halves  of  the  carapace),  in  which  the  ephippial 
ova  are  enclosed.  The  ephippium  sinks  to  the  bottom,  and, 
sooner  or  later,  its  contents  give  rise  to  young  DaphnicB. 

Jurine*s  and  Sir  J.  Lubbock's  researches  have  proved 
that  the  development  of  the  ephippial  ova  may  commence 
without  the  influence  of  the  male,  and  they  seem  to  indicate 
that  these  ova  may  even  be  fully  formed  and  laid  without 
the  male  influence.  On  the  other  hand,  there  appears,  under 
ordinary  circumstances,  to  be  a  certain  relation  between 
the  complete  development  of  ephippial  ova  and  the  presence 
of  males ;  and,  as  yet,  no  ephippial  ova  produced  by  virgin 
females  have  been  directly  observed  to  produce  young. 
The  question,  therefore,  seems  to  stand  thus,  at  present : 
the  agamic  ova  may  certainly  he  produced,  and  give  rise 
to  embryos,  without  impregnation;  the  ephippial  ova 
may  certainly  be  produced  without  impregnation;  but 
whether  impregnation  is  or  is  not  absolutely  necessary  for 
their  further  development,  there  is,  at  present,  no  evidence 
to  show. 

The  great  majority  of  the  Branchiopoda  inhabit  fresh 
waters.  Artemia,  however,  delights  in  brine  pools.  The 
genus  Estheria  is  of  Devonian  age,  and  it  seems  probable 
that  the  Silurian  Hymenocaris  and  its  allies  were  related 
to  Apv^. 

The  OsTBACODA. — This  group  contains  several  genera 
of  both  recent  and  fossil  Crustacea,  for  the  most  part 
of  very  small  size,  and  distinguished  by  their  hard, 
often  calcified,  and  completely  bivalve  shell,  provided  with 
a  distinct  hinge.  The  valves  of  this  shell  consist  of  the 
lateral  moieties  of  the  carapace;  they  are  commonly 
unequal  and  unsymmetrical,  and  present  a  peculiar  orna- 
mentation.   The  shell  gland  is  very  small.    The  Ofl^ooodA 


288   THE  ANATOMY  OF  INYEBTEBSATED  ANIMALS. 

are  also  remarkable  for  the  extremely  mdimental  condition 
of  their  abdomen,  and  for  the  paucity  of  their  thoracic 
appendages,  which  instead  of  being  f  oliaceons,  are  strong 
and  snbcjlindrical,  like  the  ambulatory  legs  of  the  higher 
Crtutacea. 

The  cephalic  flexure  is  as  well  marked  as  in  the  highest 
Crustacea,  so  that  the  eye,  obscurely  diyided,  and  median  in 
Cypris  (Fig.  66,  A),  but  double  and  lateral  in  Cyihere  (B),  is 
situated  in  the  upper  part  of  the  anterior  region  of  the 
body.  The  antennules  and  antennse,  attached  to  their 
respective  somites,  the  sterna  of  which  constitute  the  an- 
terior boundary  of  the  body,  arc  similar  in  form  and  func- 
tion to  ambulatory  limbs.  The  ducts  of  a  peculiar  gland 
open,  according  to  Zenker,  at  the  end  of  the  strong  spine 
with  which  the  antenna  of  Cythere  is  provided.  Thelabmm 
is  conspicuous,  and  the  mandibles  are  strong,  and  possess 
a  well-deyelox>ed  palp.  The  first  maxilla  is  provided  with 
a  large  foliaceous  setose  appendage  (epipoditeP)  The 
second  maxilla  in  Cythere,  is  represented  by  the  first  of  the 
three  pairs  of  ambulatory  limbs  (Fig.  66,  B,  e,  e,  e),  present 
in  this  genus.  In  Cypris,  which  possesses  a  second  pair  of 
maxillsB,  there  are  only  two  pairs  of  ambulatory  limbs  (Fig. 
66,  A,  p,  I.  II.).  The  apertures  of  the  reproductive  organs, 
provided  in  the  male  with  a  wonderfully  complex,  homy, 
copulatory  apparatus  (described  with  great  minuteness  by 
Zenker),  are  situated  between  the  last  pair  of  thoracic 
members  and  the  large  caudal  hooks. 

Strong  adductor  muscular  bundles  pass  from  one  yalve  of 
the  carapace  to  the  other,  and  leave  impressions  discernible 
from  without,  the  form  and  arrangement  of  which  furnish 
valuable  systematic  characters. 

The  alimentary  canal  of  the  Ostracoda  is  provided 
anteriorly  with  an  apparatus  of  hard  parts,  resembling  in 
many  respects  the  gastric  armature  of  the  Isopodti,  and 
gives  origin  to  two  hepatic  cseca.  Cypris  and  Cythere  have 
no  heart;  but,  in  Cypridina,  Conchoecia  and  Halaerypti9 
there  is,  according  to  Glaus,  a  short  saccular  heart  with 
one  anterior   and   two  lateral  apertures.     The  nervous 


THE  OSTBACODA. 


289 


system  is  difficnlt  to  make  ont;  but,  in  Cythere  lutea, 
the  same  observer  found  a  large  cerebral  ganglion  in  front 
of  the  mouth,  whence  filaments  passed  to  an  ophthalmic 
ganglionic  mass,  and  to  the  antennaxy  organs.  A  double 
ganglion,  behind  the  mouth,  supplies  the  gnathites ;  three 
ganglia,  situated  in  the  thorax,  send  filaments  to  its  append- 
ages, and  a  terminal  ganglion  supplies  the  caudal  appendage 
and  genitalia.  In  the  female,  the  ovaries  lie  in  the  valves 
of  the  carapace,  and  terminate  in  oviducts  which  open  by 
distinct  apertures  in  front  of  the  caudal  appendage. 
Immediately  anterior  to  them  are  the  openings  of  two 

« 

Fig.  66. 


Fig.  66.— A.  Cypris.—A.  i.  ii.  Antennules  and  Anteimee.     M.  i.  ii. 

ni.     Mandibles  and  Maxillas.     P.   i.  n.  Thoracic   members,     c. 

Caudal  extremity,     b.   Mandibular  palp.    o.  Eye.    B.  Maxillary 

appendage. 
B.  Cythere. — o.  Eye.    a,  Antennule.    b.  Antenna,    c.  Mandible,    d. 

First  maxilla,     e.  e.  e.  Second  maxilla  and  two  thoracic  members. 

/*.  Caudal  extremity.    (After  Zenker.)* 

homy  canals,  called  vaginsB  by  Zenker,  each  of  which  is 
continued  into  a  long  convoluted  transparent  tube,  and 
eventually  terminates  in  a  large  vesicle,  the  spermatheca, 
into  which  the  spermatozoa  of  the  male  are  received. 

In  the  males,  the  antennae,  the  second  maxillse,  or  some  of 
the  thoracic  limbs,  are  modified  in  such  a  manner  as  to  enable 
them  to  seize  and  hold  the  females.  The  testes  are  elon- 
gated csBca  in  Cypris,  globular  vesicles  in  Cythere,  and 
communicate  with  a  long  vas  deferens,  which  opens  into 

•  M  Monographie  der  Ostracoden."    (*  Archiv  fur  Naturgesehichte, 
1854.J 


290       THE  AKATOMT  OV  IHTEBTBBBATED  ANIICALS. 

the  copnlatoiy  i^paratos.  In  Cypris,  a  very  singalar  cylin- 
drical mncotis  gland  is  connected  with  the  Yas  deferens ;  but 
perhaps  the  most  remarkable  peculiarity  abont  the  genital 
apparatus  in  the  male  consists  in  the  size  of  the  spenna- 
toeoa,  which  in  Chfpris  ovum  are,  according  to  Zenker, 
more  than  three  times  as  long  as  the  body.  Thej 
possess  a  spirally-wound  coat,  and  are  totally  deprired  of 
mobility. 

The  Odracoda  either  attach  their  eggs  to  aquatic 
plants,  or  carry  them  about  between  the  yalves  of  the 
carax>ace. 

Glaus  *  has  worked  out  the  development  of  Cyprxs,  which 
passes  through  nine  successive  stages,  dlsting^aiBhed  from 
one  another,  not  merely  by  the  shape  of  the  carapace,  but 
by  the  number  and  form  of  the  limbs.  An  ecdysis  of  the 
chitinous  cuticle  of  the  body  and  carapace  terminates  each 
stage  of  development.  When  the  CjfprU  leaves  the  egg,  it 
resembles  a  ^oicpZttM,  in  possessing  a  single  median  eye  and 
only  three  pairs  of  limbs  (the  future  antennules,  antenn®, 
and  mandibles);  but  none  of  these  are  divided  into  two 
branches.  The  body  is  laterally  compressed  and  has  a 
bivalve  carapace. 

The  changes  undergone  by  the  marine  (htracoda  after 
they  leave  the  egg  are  much  less  marked. 

Fossil  Ottracoda  abound  in  strata  of  all  ages,  from  the 
older  paJsBozoic  formations  onwards;  and,  so  far  as  the 
characters  of  the  carapace  furnish  evidence,  the  most 
ancient  forms  differed  very  little  from  those  which  now 
exist. 

The  PSCTOSTBACA  (Bhizoeephala  and  Cirripedia)  leave  the 
egg  as  a  Nauplitu,  provided  with  three  pairs  of  limb-like 
appendages,  of  which  the  anterior  pair  are  simple,  while 
the  two  posterior  pairs  are  bifurcated  (Fig.  68,  A).  An 
additional  pair  of  filiform  appendages  subsequently  makes 

*  *  Eiitwiok«lii]ig8geeehicht«  von  Cjpris'  (IS68);  sad 'Qrond- 
svlge,'p.487. 


THB  PBOTOSTSACA.  291 

its  appearance  in  front  of  the  nndiyided  pair  of  members, 
in  most  caaes ;  and  there  is  a  disooidal  carapace,  the  antero- 
lateral angles  of  which  usually  become  greatly  produced. 
Subsequently,  the  carax>ace  becomes  biTalve  (as  in  many 
PhyUopoda,  and  in  the  Cladoeera  and  (htreieoda),  and  the 
anterior  undivided  pair  of  limbs  are  converted  into  re- 
latively large,  jointed  appendages,  provided  with  a  sucker- 
like organ.  The  thorax  grows  and  usually  developes  six 
pairs  of  appendages. 

Finally,  the  bivalve-shelled  larva  fixing  itself  by  the 
suckers  of  its  anterior  limbs,  the  prsB-oral  region  of  the 
head  becomes  enlarged,  and  is  converted  into  the  base,  or 
peduncle,  in  ordinary  Cirripedes;  while  it  gives  off  the 
root-like  processes  which  grow  into  the  tissues  of  the 
animals  on  which  the  Bhi%oceplvala  are  parasitic.  The 
Peefof^rooa  are  almost  all  hermaphrodite,  a  condition  which 
is  very  exceptional  among  Arthropods.  They  possess  no 
heart. 

The  CiBSiPEDiA. — It  can  hardly  be  a  matter  of  reproach 
to  the  older  naturalists  if  they  failed  to  discover  the  aflSnity 
connecting  the  sedentary  "  Acom-ehells  "  of  a  rocky  coast 
with  the  active  Shore-crab  which  runs  amongst  them;  or  if 
they  classed  the  Barnacles  with  MciOusea,  instead  of  ad- 
mitting them  to  that  place  amidst  the  Crustacea  which  is 
now  assigned  to  them  by  every  naturalist  of  competent 
judgment.  Nothing,  in  fact,  at  first  sight,  is  less  suggestive 
of  a  Orustacean  than  a  Balanus,  or  a  Lepas;  the  former 
firmly  fixed  by  the  base  of  its  multivalve  conical  shell,  the 
latter  by  its  fleshy  and  contractile  peduncle ;  the  only  sign 
of  life  in  either  being  the  alternate  protrusion  and  retraction 
from  the  valvular  opening  of  the  animal's  case  of  a  bundle 
of  curved  filamentous  cirri,  which  sweep  with  a  brushing 
motion  through  the  water,  and  scoop  the  floating  nutritive 
matters  towards  the  mouth. 

The  valves  through  which  the  cirri  make  their  egress 
are  strengthened,  in  both  BalawM  and  Lepa$,  by  four  cal- 
cified pieces,  two  on  each  side ;  those  of  each.  ba2kl  \)fisai% 


292       THE  ANATOMY  OF  INYEBTEBBATSD  AKIKAIiflL 

united  together  by  an  oblique  suture,  or  by  a  regular  articu- 
lation ;  while  the  two  pieces  of  opposite  sides  are  connected 
only  along  one  margin,  either  immediately  (Balanus)^  or  by 
means  of  an  intermediate  piece  {Lepas). 

The  upper,  or  distal,  pieces  are  termed  the  tergcL,  the 
lower,  or  proximal,  pieces  the  scuta,  the  intermediate  piece 
is  the  carina.  In  Lepas,  there  are  no  other  hard  external 
pieces ;  but,  in  Balanus,  the  conical  shell,  into  which  the 
valves  can  be  more  or  less  completely  retracted,  is  com- 
posed of  six  portions  or  compartments.  Of  these,  one  is 
situated  on  the  same  side  as  the  opening  between  the  valves 
and  another  at  the  precisely  opposite  point,  or  on  the  same 
side  as  the  line  of  union  of  the  valves.  The  latter  is  the 
homologue  of  the  intermediate  piece,  or  carina,  in  Xepof ; 
the  former,  in  Balanus,  consists  of  three  pieces  united 
together,  the  median  rostrum  and  the  two  rostro-lateral  com- 
partments. On  each  side  of  the  carina  is  a  compartment 
termed  carino-lateral,  and  between  them  and  the  complex 
rostrum  lies  a  lateral  compartment. 

If  the  shell  consisted  of  its  eight  typical  pieces  (as  it  does 
in  the  genus  Octameris),  it  would  be  found  that  each 
presented  a  triangular  free  middle  portion  and  two  lateral 
wings.  The  former  is  always  termed  the  paries,  but  the 
latter  receive  different  names,  according  as  they  overlap  or 
are  overlapped  by  others.  In  the  former  case,  they  are 
termed  radii,  in  the  latter,  alee.  Thus,  typically,  the  carina! 
and  the  rostral  compartments  are  overlapped  on  both  sides, 
and  their  wings  are  consequently  both  alse ;  the  lateral  and 
carino-lateral  compartments  are  overlapped  on  one  side, 
and  overlap  on  the  other,  hence  they  have  an  ala  on  one 
side,  a  radius  on  the  other ;  while  the  rostro-lateral  com- 
partment overlaps  on  both  sides,  and  hence  its  wings  are 
both  radii.  In  Balanus,  however,  the  rostrum  and  rostro- 
lateral  compartments,  being  replaced  by  a  single  compart- 
ment formed  by  their  confluence,  this  piece  has  radii  on 
both  sides. 

Different  as  is  the  appearance  of  Lepas  from  that  of 
Balanus,  they  closely  resemble  one  another  in  essential 


THX  OIBBIPBDIA*  293 

structure.  Thus,  to  commence  with  Lepas,  On  cutting  away 
the  scutum  and  tergum  of  one  side  (Fig.  67,  B),  the  hinder 
part  of  the  body  of  the  animal  is  seen  within  the  sac  of 
the  eapUndum,  formed  by  the  valves  of  the  shell,  to  which 
it  is  attached  only  on  the  rostral  side  and  inf  eriorly  by  a 
comparatively  narrow  isthmus.  Immediately  behind  iJiis 
point  the  body  widens,  to  constitute  what  Mr.  Darwin*  has 
termed  the  prosoma,  but  the  thoracic  segments,  which 
succeed  the  prosoma,  gradually  taper  posteriorly.  Six 
pairs  of  appendages  (a)  are  attached  to  the  thorax,  each 
limb  consisting  of  a  basal  joint  (protopodite),  terminated 
by  two  long  multi-articulate  cirri,  the  representatives  of 
the  endopodite  and  exopodite ;  and  a  rudimentary  abdominal 
segment,  terminated  by  two  short  caudal  appendages, 
succeeds  the  thorax,  and  is  produced  in  a  long  setose  an- 
nulated  penis  (/).  Filamentous  appendages  depend  from 
some  of  the  thoracic  somites,  and,  projecting  from  the  inner 
wall  of  the  sac  on  each  side,  is  a  triangular  process,  the 
ovigerous  frcBniMn  (m). 

The  mouth  is  situated  at  the  posterior  part  of  a  pro* 
tuberant  mass,  seated  on  the  rostral  face  of  the  prosoma. 
This  is  principally  composed  of  a  large,  bullate  labrum, 
behind  which  are  a  pair  of  mandibles  with  large  and  setose 
palps,  and  two  pairs  of  maxillse.  Anteriorly,  the  prosoma 
passes  by  a  narrow  isthmus  into  the  rostral  part  of  the 
peduncle,  into  which  it,  as  it  were,  expands;  while  the 
posterior  margins  of  the  peduncle  become  continuous  with 
the  walls  of  the  sac. 

The  extremity  of  the  peduncle  is  fixed  by  a  peculiar  ce- 
menting substance  to  the  body  to  which  the  Lepas  adheres ; 
but,  if  it  be  carefully  detached,  there  will  be  found  connected 
with  the  rostral  portion  of  the  surface  a  pair  of  very 
minute,  singular-looking,  organs,  consisting  of  two  proxi- 
mal joints,  succeeded  by  an  articulation  which  is  dilated 
into  a  sucker,  and  terminated  by  an  elongated  setose  joint 
(Fig.  67,  A,  B,  I).  These  are  the  remains  of  the  anterior 
appendages  of  the  larva. 

•  *  Monograph  of  the  Clrripedia,'  185l«  1854. 


294       THB  ANATOKT  Ot  IBTERTBBBATBD  AITHCALB. 

Froro  what  has  been  said,  it  foUows  that  the  fixed  end  i 
the  peduncle  is,  in  fact,  the  anterior  eitremity  of  the  boe 
ef  the  Lepat,  and  that  a  B&macle  ma;  be  said  to  be 
Crustacean  fixed  bj  its  head,  and  kicking  the  food  into  i 
month  with  ite  l^a. 

Fig.  07. 


.{  LqMU.—a 


Fig.  67.— A.  Diigmnmatic  section  of  Bate 
,  plKsd  In  the  cavity  of  the  nc.  and  lieiavei  um  iBuium;  a, 
C  carint;    c,    I,  eariDO-lmtenl    compartnieDt ;    I,   lateral 
menl ;   r,    nntruiD ;    i,    ■culiun ;     (,   tergum ;    /,   pmii,    ,.  . 
fnrmed  glind  ;  h,  duct  cODneelinff  (Ms  willi  i,  i,  cement  duU 
gt*nda ;  f,  anleiiDK;    i,  peduneulmr    or  anriu  tabulei 
garoul  fnenum  ;  if,  aniu. 


The  mouth  in  Lepat  looks  towards  the  posterior  eztremit 
of  the  bodj,  and  leads  into  a  tubular  awopha^s,  whic 
passes  forwards,  and  opens  bj  a  wide  superior  eitremit 
into  the  globular  stomach.    From  this  point,  the  alimentai 


TBI  CIBItlPBBIA..  295 

canal  bends  back  upon  itself,  and  gradually  narrows  into 
the  intestine,  which  terminates  in  the  anus,  situated  at  the 
extremity  of  the  abdomen,  on  the  tergal  side  of  the  penis. 
Two  considerable  branched  coca,  probably  hepatic,  proceed 
as  diverticula  from  the  stomach,  corresponding  very  closely 
in  position  with  those  of  Dapknia.  No  heart  or  other 
circulatory  organs  are  known  to  exist ;  and  it  may  be  doubted 
if  the  ovigerous  frssna  of  Lepas  exert,  as  they  have  been 
supposed  to  do,  a  branchial  function. 

The  nervous  system  consists  of  a  pair  of  cerebral  ganglia 
situated  in  front  of  the  oesophagus,  and  connected  by  long 
commissures  with  the  anterior  of  five  pairs  of  thoracic 
ganglia,  whence  nerves  are  given  off  to  the  limbs.  In  the 
middle  line,  the  cerebral  ganglion  gives  off  two  slender 
nerves,  which  run  parallel  with  one  another  in  front  of  the 
stomach  and  enlarge  into  two  ganglia,  whence  they  are 
continued  to  a  double  mass  of  pigment,  representing  the 
eyes.  From  the  outer  angles  of  the  cerebral  ganglion  arise 
the  large  nerves  which  proceed  into  the  peduncle  and 
supply  the  sac.  These  appear  to  correspond  with  the 
antennary  and  frontal  nerves  of  other  Crustacea  ;  and  Mr. 
Darwin  describes  an  extensive  system  of  splanchnic  nerves. 

Lepas,  like  the  minority  of  the  Cirripedia,  is  hermaphrodite. 
The  vesiculsB  seminales  are  readily  seen  in  fresh  specimens, 
as  white  cords  distended  with  spermatozoa,  which  run  from 
the  canal  of  the  penis,  into  which  they  open,  forwards,  on 
each  side  of  the  body,  to  the  prosoma,  where  they  end  in 
dilated  extremities,  which  are  connected  with  a  multitude 
of  ramified  cseca  forming  the  proper  testis. 

The  ovaries  are  ramified  tubes  provided  with  cseeal 
dilatations,  and  lodged  in  the  peduncle.  The  oviducts  pass 
into  the  body,  and,  according  to  Krohn,  terminate  in  aper- 
tures situated  on  the  basal  joint  of  the  first  pair  of  cirri.* 
Two  '  gut-f oimed '  glands,  as  they  are  termed  by  Darwin, 
lie,  one  on  each  side  of  the  stomach,  and  are  probably 

*  The  position  of  these  aper-      to  the  thell-glands  in  Umnadia 
tnict  eoiresponds  with  that  of  the      snd  Aput, 
openiiigty  fuppoMd  to  appertain 


296       THE  AKATOMT  OV  DnTBBTBBBATBD  AHIMALS. 


accessory  glands  of  the  reprodnctiye  organs,  analogous  to 
those  which  secrete  the  walls  of  the  ovisac  in  the  Ccpepoda. 

The  mode  of  exit  of  the  ova  from  the  ovary  is  not  oeitainl j 
known,  nor  is  the  place  of  their  impregnation  ascertained; 
bat  they  are  eventually  f  oilnd  cemented  together  by  chitin 
into  large  lamellse,  which  adhere  to  the  ovigerous  frsBna, 
and,  ordinarily,  at  once  strike  the  eye  when  the  capitolnm 
of  a  Girripede  is  opened. 

Yelk  division  is  complete,  and  the  embryo  attains  to  its 
earliest  larval  condition  within  the  egg.  li  a  series  of  the 
fresh  ovigerous  lamelbe  be  taken  and  pulled  to  pieces  with 

Fig.  68. 


Fiff.  68,— A.  Larva  of  Balantu  bafanoidet  on  leaving  the  esg  (after 
Spence-Bate).  B.  Attached  pupa  of  Lepas  amtrali*  (after  Darwin) : 
»,  antennarv  apodemes;  f,  gut-formed  gland,  with  cement  duct 
running  to  the  antenna. 

needles  in  a  watch-glass  full  of  sea-water,  one  is  pretty 
sure  to  be  found  whence  a  number  of  active  little  NauplwM' 
like  animalcules  are  set  free  (Fig.  68,  A).  Each  presents 
a  somewhat  triangular  body,  produced  in  the  middle  line 
posteriorly  and  at  its  anterior  lateral  angles.  The  mouth 
is  situated  on  a  proboscidiform  projection  placed  nearly  in 
the  centre  of  the  body,  and  in  the  midst  of  three  pairs  of 
natatory  limbs,  of  which  the  two  posterior  pairs  have  bifid 
extremities.  In  front  of  the  mouth,  either  in  this  stage,  or 
after  one  or  two  moultings,  two  filaments  are  often  deve* 
loped.     A  single  eye-spot  is  situated  in  front  of  the  bases 


THB  DBTBLOPMBKT  OF  THB  OIBBIPBDLA.*         297 

of  the  anterior  appendages.  After  moulting  several  times^ 
tlie  larva  assumes  a  new  form,  passing  into  its  second 
stage.  The  carapace  is  now  oval  and  compressed,  so  as 
more  nearly  to  resemble  that  of  a  Daphnia  or  Cypris. 
There  are  two  eyes.  The  first  pair  of  swimming  appendages 
of  the  Nauplitu  are  converted  into  antennif  orm  organs,  each 
provided  with  a  sucker,  and  the  rudiments  of  the  six  pairs 
of  cirri  make  their  appearance  behind  the  mouth.* 

In  the  third  stage,  the  larva  is,  as  Mr.  Darwin  states, 
"much  compressed,  nearly  of  the  shape  of  a  Cypria  or 
mussel-shell,  with  the  anterior  end  the  thickest,  the  sternal 
surface  nearly  or  quite  straight,  and  the  dorsal  arched. 
Almost  the  whole  of  what  is  externally  visible  consists  of 
the  carapace;  for  the  thorax  and  limbs  are  hidden  and 
enclosed  by  its  backward  prolongation;  and,  even  at  the 
anterior  end  of  the  animal,  the  narrow  sternal  surface  can 
be  drawn  up,  so  as  to  be  likewise  enclosed."  The  larva,  in 
this  stage,  is  provided  with  two  large  compound  lateral 
eyes,  while  the  median  eye  is  arrested  in  its  development. 
The  oral  tubercle  exhibits  all  the  gnathites  of  a  Oirripede, 
but  they  are  covered  by  an  imperforate  integument,  so 
that  this  "locomotive  pupa,"  as  Mr.  Darwin  terms  it,  is 
unable  to  feed.  There  are  six  pairs  of  legs,  and  the  thorax 
ends  in  an  abdomen,  consisting  of  three  somites  terminated 
by  two  caudal  appendages.  There  is  no  penis.  The  most 
remarkable  structures  in  the  pupa,  however,  are  the  **  gut- 
formed  glands,"  which  are  already  well  developed,  and 
from  which  the  cement  ducts  can  be  traced  to  the  disks  of 
the  antenniform  organs,  on  the  faces  of  which  they  open. 
The  pupa,  after  swimming  about  for  awhile,  at  length 
selects  its  permanent  resting-place,  to  which  it  adheres, 
at  first,  only  by  the  action  of  the  suctorial  disks.  The 
temporary  attachment,  however,  is  speedily  converted  into 
a  persistent  one,  the  cement  pouring  out  from  its  excre- 

*  According  to  Clans  (*  Grand-  case  the  antennaiy  organs  repre- 

ziigeder  Zoologie,'  3te  Auflage,  p.  sent  antennules,  and  Uie  limbs  of 

460),  the  second  pair  of  appen-  the    Cirripede   Nauplhu    corre- 

dtkfpea  disappears,  and  the  third  spond  with  those  of  the  Gopepod 

gives  rise  to  the  mandibles*  In  this  and  Branchiopod  Aowpfiai. 


298       THE  ANATOMY  OV  Iir7BBTSBRATSD  AITIMALS. 

toiy  apertures  on  the  disks,  and  firmly  gluing  them  and 
the  anterior  end  of  the  body  down  to  the  surface  on  which 
they  rest. 

Goincidently  with  these  changes,  several  other  important 
alterations  take  place,  during  the  passage  of  the  locomotive 
pupa  into  the  fixed  young  Cirripede.  The  compound  eyes 
are  moulted,  and  with  them  the  antennary  apodemes,  fur- 
nished by  the  integument  of  the  deep  fold  which  separates 
that  part  of  the  body  of  the  pupa  which  corresponds  with  the 
beak  of  a  Daphma^  or  of  a  LimnetU,  from  the  prosoma.  The 
fold  is  thus  enabled  to  straighten  itself;  and,  as  a  oonse- 
quence,  the  carapace  of  the  Cirripede,  instead  of  remaining 
more  or  less  parallel  with  the  surface  of  attachment,  be- 
comes perpendicular  to  it.  Again,  in  the  pupa,  the  axis  of 
the  carapace  and  that  of  the  body  are  identical  in  direction  > 
but,  during  the  last  moult,  the  chamber  of  the  carapace 
extends  forwards  far  more  on  the  tergal  than  on  the  sternal 
side,  separating  the  tergal  part  of  the  prosoma  from  the 
**  beak,'*  with  which  it  was  at  first  continuous,  and  thus 
allowing  the  body  of  the  Cirripede  to  take  its  final  position, 
which  is  nearly  transverse  to  the  axis  of  the  carapace. 

The  terga  and  scuta  now  appear  as  homy  thickenings, 
and,  afterwards,  as  calcifications  in  the  wall  of  the  capi- 
tulum.  The  frssna  and  the  penis  make  their  appearance, 
and  the  genitalia  become  developed  in  the  prosoma  and  in 
the  peduncle,  which  is  produced  by  the  gradual  elongation 
of  the  "  beak  "  of  the  pupa. 

With  the  assumption  of  its  perfect  form,  the  Cirripede 
ceases  to  moult  its  carapace,  ecdy sis  being  hereafter  confined 
to  the  inner  lining  of  the  sac,  and  to  the  integument  of  the 
contained  body. 

Such  is  the  structure  and  development  of-  a  typical  pe- 
dunculate Cirripede.  In  other  genera,  such  as  PoUieipe$, 
calcareous  plates  are  developed  on  the  peduncle,  f  oreahadow- 
ing  the  compartments  of  the  sessile  forms.  The  latter,  of 
which  Bakmus  may  be  regarded  as  the  type,  differ  in  struc- 
ture from  Lepas  in  no  very  essential  particular.  The 
peduncle,  yery  short  and  broad,  instead  of  slender  and  elon- 


THB  CIBBIFBDIA.  299 

gated,  is  encased  by  its  compartments,  and  is  sometimes 
fixed  by  a  shelly  basis.  The  arrangement  of  the  layers 
of  cement  is  often  extremely  complicated ;  the  scnta  and 
terga  are  articnlated  together ;  the  frsna  are  mnch  larger 
organs,  and  possibly  subserve  the  respiratory  function; 
the  thoracic  ganglia  are  concentrated  into  a  single  mass ; 
and  the  cementing  apparatus  is  much  more  complicated. 

The  pedunculate  and  sessile  Cirri^ecUa,  taken  together, 
constitute  by  far  the  largest  of  the  three  great  gp*oups 
which  Mr.  Darwin  recognises ;  namely,  the  Thoraeiea,  cha- 
racterised by  having  limbs  attached  to  the  thoracic  somites, 
while  the  abdomen  is  rudimentary. 

The  second  group,  the  Ahdominalia,  contains  only  one 
genus,  Cryptophialus,  (Fig.  69,  5,  6)  which  has  no  thoracic 
limbs,  but  is  provided  with  three  pairs  of  abdominal  ap- 
pendages. The  larva  is  very  imperfect  in  its  first  and 
second  changes,  which  are  undergone  within  the  sac  of  the 
parent. 

The  third  group,  Apoda,  likewise  contains  only  one  genus, 
the  remarkable  Proteolepas  (Fig.  69,  7),  which  is  devoid  of 
either  thoracic  or  abdominal  limbs;  it  has  a  vermiform 
body,  and  a  rudimentary  peduncle,  represented  by  two 
threads  terminated  by  the  characteristic  antenniform 
organs. 

In  the  great  majority  of  the  Cirripedia  the  sexual  appa- 
ratus is  disposed  as  in  Lepas,  but  Cryptophialus  and  Alcippe 
are  unisexual,  the  male  differing  veiy  widely  in  form  and 
size  from  the  female  (Fig.  69,  3,6). 

The  BdUmidcB,  or  sessile  Cirripedes,  all  present  the  normal 
serual  relations ;  but  the  other  division  of  the  Thoraeica,  the 
LqMididcB,  contains  two  genera,  Ibla  and  Scalpellum,  which 
not  only  possess  species  having  the  sexes  in  distinct  indi- 
yiduaJs,  but  others  presenting  the  unique  combination  of 
males  with  hermaphrodites.  Thus,  ScalpeUwm  vulgare  is 
hermaphrodite,  possessing  well-developed  male  and  female 
organs.  Nevertheless,  on  the  inner  side  of  the  occludent 
margin  of  its  scutum  there  is  a  fold,  over  which  and  im- 
bedded in  the  spinose  chitinous  border  of  the  scutum,  a 


300       THK  AHATOXT  OF  nnnEBTBBRi.TXD  ABUtAIA. 

minato,  otbI,  aac-Uke  creature  is  commonly  fonnd,  firmly 

Fig.  65. 


Fig.  69.— 1.  Alcif^e  lampai ;  female.    3.  The  H 
H.  Horny  dl»k  of  BtMchment;  in  1,  the  male 
iprcki  on  either  ride  of  the  upper  part  of  the  s 
)b1t  of  cirri,     i,  I.  n.  Three  leginentg  uf  the  thorax  « 
the  atber  three  legmenM,  bearing  the  three  pain  of  terminal  ol 
e  very  short.    3.  Male  Alclppr.     a.   Anlennaty  appendage*. 


«IT.    A.  1 

withoDt  d 


Ve.icii 
Penli. 


..  Eje.  . 
oF  Akippi  in  a  portioi 


.    i.  Orifice  of  the  aao. 
of  a   " 


.  aboTB  IdIo  the  rim  of  the  apeit 
a,  b,  I.  n.  Abdominal  cirri,  i.  Appendsgea  of  anknown  natn 
6.  Male  CrypltfAiahu.  7.  J'rotfolrpat  birfiirta.  m.  Mouth,  g. 
Peduncie  and  antenna,  i.  i.  Veelcula  uminillt  and  penii.  (Af 
Darwin.) 

tached  by  cement  which  covera  the  characteriatic  anteimiL 


THX  OntBIPBDIA..  901 

of  a  Oirripede.  Witliin  the  sac  is  a  thorax,  with  f  onr  pairs 
of  rudimentary  appendages  terminated  by  a  short  abdomen. 
There  is  neither  mouth,  alimentary  canal,  nor  gnathites, 
the  cavity  of  the  body  being  pidncipally  occupied  by  a  great 
seminal  yesicle ;  and  no  trace  of  female  organs  exists.  This 
is,  therefore,  an  accessory,  or  "  complemental "  male.  In 
Scalpellum  omatwn,  the  individuals  are  males  and  females, 
two  of  the  former  being  lodged  in  cavities  of  the  scuta 
of  one  of  the  latter,  as  in  the  preceding  species,  and  in 
8.  rwtilwn.  The  males  have  no  mouth.  8.  rostratum  has 
complemental  males,  provided  with  alimentary  organs  at- 
tached to  the  interior  of  the  sac  of  the  hermaphrodite,  while 
8.  Peronii  and  vUlosum  have  still  more  perfect  complemental 
males  fixed  in  a  like  position.  In  Ibla  Cwningii,  the  female 
has  a  vermiform  male,  provided  with  well-developed  ali- 
mentary organs,  attached  within  her  sac ;  but,  in  the  only 
other  species  of  this  genus,  I,  quadrivaUns,  a  similarly 
constructed,  but  here  only  complemental  male,  is  lodged 
in  a  relatively  large  hermaphrodite  form. 

With  regard  to  the  habits  of  the  Cirripediay  the  ma- 
jority are  merely  cemented  to  foreign  bodies.  Anelasma 
and  Ihtbicinella,  however,  partially  bury  themselves  in  the 
integuments  of  the  shark  and  whale,  and  thus  prepare  us 
for  the  completely  boring  habit  of  Cryptophialtis,  Lithoirya, 
and  Alcipp€f  the  latter  of  which  (Fig.  69,  i,  2,  3)  burrows 
in  dead  shells  on  our  own  coasts. 

Proteolepas  lives  within  the  sac  of  AUpas  comtUa,  and 
appears  to  be  truly  parasitic  upon  it,  sucking  the  nutritive 
juices  from  the  soft  prosoma  of  the  animal  which  it  infests. 

The  Cirripedia  are  almost  exclusively  marine,  only  a  few 
species  tolerating  even  brackish  water.  The  Thoracica 
alone  have  yet  been  found  in  the  fossil  state.  The  oldest 
known  genus,  Pollicipes,  occurs  in  the  lower  oolite ;  there 
18  a  single  cretaceous  species  of  Verruca,  but  the  sessile 
Oirripedes  become  numerous  only  in  the  tertiary  epoch. 

The  Bhizocephala  {Peliogader,  SacctUina)  are  small 
and  parasitic;  usually  upon  the  abdomen  of  other  Ctuk. 


302       TEX  AXUOXT  or  BTSKmSAXBD  AMXKUJL 

(lOM  'PodopdUfculaia^.  ^e  body  is  Eke  •  «e  «r  di^  nd 
dcToid  of  KgineiiUiion  aad  at  limb*.  Tbr  ^ertm»  of  As 
^  ifl  fiiiinel-ahap«d  and  mpported  hj  k  nng  of  cUUb. 
nie  cmTamteraice  of  the  tunnel  give*  off  k  nimibtr  «f 
Toot-like  rmrrnim.  vhich  bnach  vMt  thrao^  tfae  boctf  rf 
tke  infested  »«i»n»l  The  alimeatarj  aaal  ia  ofcaoleta^  ud 
tbere  mie  no  Manent  glkndi.    Tltey  : 


Fig.  70.— A.  A'mrp/Hu-itiiBe  nf  Sacixliiui  imi pinia  :  ai,  nnfuet. 

B.  QTiTM-stdgc  of  Lenutoditcmi  paretOons.     C.  AdiUt  wmdlrtmi  «f 

Pthogailer  paguri :  a,  anlcrlor  ead  of  tbe  body  ;  b,  Kpertoie  i  e,  nwt- 

lik>  proc««M.     (After  F.  Hilllcr.) 

the  joong,  like  those  of  the  other  Peeie^raca,  pus  throngh 
a  Savpliv*  and  a  C^prit  stage.* 

The  Halacostbaca. — The  groops  of  Otulacea  known 
as  the  Fod^hlhahnia,  the  Cuntaeea,  the  SdnopMhoImia, 
and  the  Btomatopoda  are  here  inclnded  under  this  head. 

*TlwtanDQ7n-ii-iUeg,  nnull;  Imply    any  (peolftt  ■flfadty  with 

ap]di«d  to  that  condition  of  tho  the  Oitracitda.    On  Ui*  oontrmiy, 

Uttb  of  the  AEtoMrona  Id  wblel)  the  lena  In  the  CWiMtueli 

"    *     '-k  *  kCI-.        ^ I.  . _i It ffT-  ^^^^"  ^j 


THB  PODOPHTHALMIA.  903 

The  body  consists  of  twenty  somites  (counting  that  which 
bears  the  eyes  as  one),  and,  of  these,  six  (bearing  the  eyes, 
antennnles,  antennsB,  mandibles,  and  two  pairs  of  mazillffi) 
oonstitate  the  head ;  eight  enter  into  the  thorax,  and  bear 
the  foot-jaws  and  ambulatory  limbs;  and  six  form  the 
abdomen  and  swimming  limbs.  In  some  few  instances 
the  number  of  somites  is  reduced,  but  they  never  exceed 
twenty. 

The  Na/uplius-iorm  of  the  free  embryo  is  rare,  bat  occurs 
in  some  cases  {Peneus).  In  others  (Myns)  it  is  represented 
only  by  a  temporary  condition  of  the  embryo,  during  which, 
however,  a  chitinous  cuticula  is  formed  and  subsequently 
shed ;  and  what  appear  to  be  remains  of  such  a  transitory 
record  of  an  original  Ncnipliue  state,  are  seen  in  many 
Amphijpoda  and  laopoda,  which  nearly  attain  their  adult 
form  within  the  egg.  In  most  PodophthainUa,  the  embryo 
leaves  the  egg,  not  as  a  Natiplitu,  but  as  a  Zoma,  which 
has  thoracic,  but  no  abdominal,  appendages,  and  in  many 
respects  resembles  a  Copepod. 

The  Cvmacea  take  an  intermediate  position  between  the 
jfodopMhalmia  and  the  Edriophthahnia  on  the  one  hand, 
and  the  PhyUopoda  {Nebalia)  on  the  other.  They  thus 
serve  to  connect  the  MalacosUraca  with  the  Entomottraea, 

The  PoDOPHTHALMiA. — It  wiU  be  convenient  to  com- 
mence the  study  of  the  Malacostraea  with  the  Podoph' 
ihoUmia,  and,  as  excellent  examples  of  this  division  of 
convenient  size  are  readily  obtainable  in  the  fresh-water 
Crayfish  {Astacua  fiuviatilU)  and  the  Lobster  (^onutriM 
vvlgafrig\  and  as  they  furnish  a  very  intelligible  guide  to 
the  general  plan  of  structure  of  the  higher  Arihropod>ay  the 
organisation  of  Adobcus  will  be  described  at  length.  With 
some  unimportant  modifications,  what  is  said  about  it  will 
be  found  to  apply  to  the  Lobster. 

The  upper  and  anterior  portion  of  the  dense  and  more 
or  less  calcified  exoskeleton,  which  covers  the  body  of 
AdaeiUt  has  the  form  of  a  large  expanded,  shield-like  plate, 
tlfte  oan^aoe,  produced  into  a  strong  frontal  sgiiift  \»^* 


304       THE  ANATOMY  OF  IKYBBTBBRATBD  ASTMAXA 

tween  the  eyes,  and  bent  down  at  the  sides,  so  as  to  reach 
the  bases  of  the  legs.  The  posterior  division  of  the  body, 
on  the  other  hand,  presents  a  very  different  aspect,  being 
divided  into  a  series  of  distinct  moveable  somites.  This 
is  called  the 'abdomen,  while  the  anterior  division,  covered 
by  the  carapace,  corresponds  with  the  head  and  thorax  of 
other  Arthropoda,  and  receives  the  name  of  cephalo- 
thorax. 

On  taming  to  the  ventral  surface  of  the  Crayfish,  a  great 
number  of  limbs  or  appendages,  twenty  pairs  in  all,  are 
seen  to  be  attached  to  the  cephalo-thorax  and  abdomen,  six 
pairs  belonging  to  the  latter,  and  fourteen  pairs  to  the 
former  region  of  the  body. 

The  six  pairs  of  abdominal  appendages  are  commonly 
known  as  the  "false"  or  "swimming"  feet;  and  it  will 
be  observed  that  they  are  attached  to  the  six  anterior 
segments  of  the  abdomen  only,  the  seventh  being  unpro- 
vided with  any  such  organs.  Of  the  fourteen  pairs  of 
cephalo-thoracic  appendages,  the  five  posterior  are  called 
the  *' ambulatory "  legs,  being  the  organs  by  which  the 
Crayfish  is  enabled  to  walk.  Strictly  speaking,  however, 
the  anterior  of  the  five  pairs  is  not  more  ambulatory  than 
prehensile,  being  so  modified  as  to  constitute  the  great 
claws  or  "  chelie." 

Of  the  six  next  pairs  of  appendages,  passing  from  behind 
forwards,  five  are  not  at  first  sight  apparent,  the  posterior 
pair,  which  are  applied  over  the  mouth  and  cover  the  others, 
being  alone  visible.  These  and  the  two  pairs  which  lie  im- 
mediately  under,  or  in  front  of  them,  are  called  mcuBiUu 
pedes,  or  '*  foot-jaws."  The  next  two  pairs,  delicate  and 
foliaceous,  are  the  maxillsB;  while  beneath  or  rather  in 
front  of  them,  are  two  strong,  toothed  organs,  the  mandi- 
bles. These,  the  maxillae  and  the  maxillipedes,  thus  con- 
stitute six  pairs  of  gnathites. 

The  remaining  three  pairs  of  appendages  occupy  the  sides 
of  the  fore-part  of  the  cephalo-thorax,  in  front  of  the 
mouth.  The  most  posterior  pair,  or  the  long  feelers,  are 
the  antennsB;  the  next,  or  the  short  feelers^  are  the  anten* 


nuls ;  while  the  most  anterior  pair  are  the  moveable  stalks, 
which  support  the  eyes  upon  their  extremities ;  the  "  oph- 
thalmic peduncles,"  or  "  ophthalmites.** 

To  arrive  at  an  understanding  of  the  composition  of 
this  complex  body,  with  its  multiform  appendages,  we 
must  first  detach  and  study  carefully  one  of  the  abdominal 
segments — say  the  third.  Such  a  segment  is  nearly  semi- 
circular in  vertical  section,  the  dorsal  wall,  or  tergum, 
being  very  convex,  and  where  it  reaches  the  level  of  the 
almost  straight  ventral  wall,  or  sternum,  sending  down 
a  flattened  lobe,  which  is  reflected  at  its  free  edges  into 
a  corresponding  prolongation  of  the  ventral  wall,  so  that 
each  inf  ero-lateral  angle  of  the  s^pnent  is  prolonged  into 
a  hollow  process,  the  pleuron.  Near  the  outer  extremities 
of  the  straight  ventral  portion  of  the  segment  two  rounded 
articular  cavities,  which  receive  the  basal  joints  of  the  ap- 
pendages, are  situated.  A  transverse  groove  will  be  seen 
on  the  tergum,  separating  rather  more  than  the  anterior 
third  of  its  surface,  as  a  smooth,  convex,  lenticular  facet, 
which  is  completely  overlapped  by  the  posterior  margin 
of  the  preceding  segment,  when  the  abdomen  is  extended, 
and  is  left  uncovered  only  in  complete  flexion.  This  is 
the  iergai  facet,  A  corre8x>onding  flattened  and  rather 
excavated  surface  upon  the  anterior  half  of  the  pleuron, 
which  is  similarly  overlapped  by  the  preceding  pleuron, 
and  is  left  imcovered  only  in  complete  extension,  may  be 
termed  the|?2ettraZ/acei.  It  will  be  observed  that  there  is  a 
close  correspondence  between  the  skeleton  of  an  abdominal 
somite  of  a  Oray-fish,  and  that  of  a  thoracic  somite  of  a 
Trilobite;  except  that,  in  the  latter,  the  sternal  region  is 
not  calcified. 

The  appendages  of  the  segment  (Fig.  71,  E)  are  very 
simple,  consisting  of  a  cylindrical  basal  portion,  divided 
into  two  joints,  a  shorter  proximal,  and  a  longer  distal, 
to  the  latter  of  which  two  terminal  many-jointed  filaments 
are  articulated.  The  inner  of  these  is  distinguished  from 
the  outer  by  possessing  a  more  elongated  and  wider  basal 
joini.    The  whole  basal  division  of  the  appendages  is  tjx^ 


THX  liri.TOICT  OF  nmSTIBKATID 
FIr.  71. 


t*"^ 


ASTACUB  VLITYIATILIS.  807 

Fig.  71.— Astactu  fluvkaUii.  A.  Mandible,  a,  (,  endopodite ;  o.  its 
tenninal  joints  constituting  the  palpus  of  the  mandible.  B.  first 
maxilla.  C.  Second  maxilla.  D.  First  maxillipede.  £.  Second 
maxilllpede.  F.  Third  maxillipede.  All  the  preceding,  except  B. 
are  left  limbs.    6.  Ambulatory  leg.    H.  Appendage  of  first,  and 

1,  of  second  abdominal  somite  in  the  male.  K.  Appendage  of  third 
abdominal  somite.  L.  Sixth  abdominal  somite,  with  its  appen- 
dages and  telson.  a,  b.  Endopodite.  e.  Exopodite.  d.  Epinodite. 
e.  Setaceous  filaments  attached  to  coxopodite.  x.  Teigum  m  sixth 
abdominal  somite,    y,  z.  The  two  divisions  of  the  tebon.     In  6 1 

2,  basipodite ;  3,  ischiopodite ;  4,  meropodite  ; .'),  carpopodite ;  6,  pro- 
podite ;  7,  dactylopodite.  In  A.  d  marks  the  tendon  of  the  adductor 
muscle,  and,  in  K,  the  joints  of  a  fr,  and  e  are  not  sufliciently 
numerous.  M.  Transverse  section  of  half  a  thoracic  somite  (a). 
b,  Coxopodite.  c.  Basipodite.  d.  Ischiopodite.  A.  Brandiiferous 
epipodite.  /*,  p.  Branchiae,  e.  Filiform  appendage.  N.  One  of 
the  branchi^rous  epipodites.  a.  Its  point  of  attachment.  6.  Basal 
enlargement,    c.  Branchial  filaments,    d.  Terminal  lobes. 

proiopocUte ;  while  the  internal  and  external  terminal  fila- 
ments are  the  endopodite  (a  h)  and  exopodite  (e). 

An  abdominal  segment,  or  somite,  then,  is  composed 
of  a  tergum,  two  pleura,  and  a  sternum ;  but  it  must  be 
remembered  that  these  terms  rather  indicate  regions  than 
anatomical  elements,  the  whole  segment  being  continuously 
calcified,  and  no  sutures  or  other  absolute  demarcations 
separating  one  portion  from  another.  Furthermore,  the 
somite  carries  two  appendages,  each  divided  into  a  proximal 
portion  or  protopodite,  tei*minated  bj  two  branches,  the 
endopodite  and  exopodite. 

The  whole  exoskeleton  of  the  Adacus,  however  Tariou» 
may  be  the  appearance  of  its  different  parts,  consists  of 
somites  and  appendages  essentially  similar  to  those  which 
have  just  been  described,  but  which  are  more  or  lesa 
masked  by  the  connation,  the  coalescence,  the  abortion, 
or  the  extreme  modification  of  their  primitive  elements. 

If,  in  the  first  place,  we  follow  out  these  modifications  in 
the  posterior  somites,  we  find  the  fourth,  fifth,  and  sixth 
abdominal  somites  to  be,  in  all  essential  respects,.  «iTwiln.r  to 
the  third;  but  the  appendages  of  the  sixth  (Fig.  71,  L) 
are  singularly  changed,  the  protopodite  being  represented 
by  a  single  strong,  short  joint,  and  the  exopodite  and 
endopodite  having  the  form  of  wide  oval  setose  plates. 
The  exopodite  is  again  divided  into  two  poxtiona  V^*^  ^ 


308       THE  ANATOMY  OV  INYXBTBB&ATBD  AJriMAI.8. 

transverBe  joint.  The  seventh  division  of  the  abdomen 
(Fig.  71,  L,  y^  z)  is  the  teUan.  This  telson  bears  no  appen- 
dages ;  dorsallj  it  is  completely  calcified,  bnt  is  divided  by 
a  transverse  suture  into  two  portions,  the  posterior  of  which 
is  moveable  upon  the  other ;  ventrallj,  on  the  contrarj,  it 
is  onlj  the  posterior  part  which  is  f ullj  calcified,  the  middle 
of  the  anterior  portion,  in  which  the  anus  is  situated,  being 
completely  membranous,  and  the  sides  only  being  strength- 
ened by  calcareous  plates  extending  inwards  from  the 
dorsal  hard  skeletal  element,  or  aelerodemUte. 

The  x>owerful  tail-fin  of  the  Astacus  is  formed  by  the 
telson,  combined  with  the  two  distal  divisions  of  the  sixth 
abdominal  appendages  on  each  side.  The  other  abdominal 
appendages  can  have  very  little  influence  on  locomotion. 
In  the  female,  however,  they  play  an  important  part,  as 
the  carriers  of  the  eggs;  and,  in  this  sex,  there  is  nothing 
worthy  of  special  notice  about  the  first  and  second  ab- 
dominal somites  or  their  appendages,  except  that  those  of 
the  first  are  rudimentary.  In  the  male,  the  appendages 
of  these  two  somites  have  undergone  a  very  interesting 
metamorphosis,  whereby  they  are  fitted  to  subserve  copula- 
tion. Those  of  the  second  somite  (Fig.  71, 1)  are  enlarged, 
and  the  protopodite  and  basal  joint  of  the  endopodite  are 
much  elongated ;  the  latter  being  produced  internally  into 
a  plate  rolled  upon  itself,  and  thence  concave  outwards 
and  forwards.  It  is  as  long  as  the  rest  of  the  endopodite 
(which  like  the  exopodite  is  many-jointed)  and  serves  aa  a 
sort  of  sheath  for  the  reception  of  the  appendage  of  the 
first  abdominal  somite  (Fig.  71,  H)  which  consists  of  a 
single  plate  rolled  upon  itself  in  a  similar  manner,  so  as 
to  resemble  a  grooved  style.  These  organs,  doubtless,  help 
to  convey  the  spermatophores  from  the  male  g^enital  aper- 
tures to  the  body  of  the  female. 

The  compact  and  firm  cephalo-thorax  seems  at  first  to 
difEer  widely  from  the  flexible,  many-jointed  abdomen;  bat 
the  most  posterior  of  its  somites  offers  an  interesting  transi- 
tion from  the  one  to  the  other.  This  somite  is,  in  fact,  only 
vnited  bymiembruia  to  that  whioh  precedes  it, and  is  henoe. 


▲STACirS  VLUniTILIS.  d09 

to  a  certain  extent,  moveable.  Ite  sternal  portion  is  com- 
pletely calcified,  bat  the  epimera^  are  only  partially  cal- 
cified. 

The  appendages  of  this  somite  differ  widely  from  those 
of  the  abdomen,  representing  (as  their  development  shows) 
only  the  protopodite  and  endopodite  of  the  latter.  Each 
is  a  long  firm  leg,  composed  of  seven  joints,  the  proximal 
one  being  thicker  than  any  of  the  rest,  while  the  terminal 
joint  is  narrow,  curved  and  pointed.  To  these  seven  joints, 
Milne-Edwards  has  applied  the  following  terms  (Fig,  71, 
G).  The  proximal  one  which  articulates  with  the  somite, 
is  the  oomopodUe  (1),  the  next,  small  and  conical,  is  the  haai- 
podiie  (2),  the  third  cylindrical,  short,  and  marked  by  an 
annular  constriction,  is  the  ischiopodUe  (3).  Next  comes 
a  long  joint,  the  meropodUe  (4),  then  the  earpopodUe  (5)  and 
propodUe  (6),  and,  finally,  the  terminal  daetylopodite  (7).  f 

The  next  four  somites,  proceeding  anteriorly,  have  a 
similar  general  character  to  that  which  has  just  been  de- 
scribed,  but  they  cease  to  be  moveable  upon  one  another, 
partly  by  reason  of  the  calcification  of  the  interepimeral 
and  interstemal  membranes,  partly  on  account  of  the 
development  of  these  membranes  by  a  folding  inwards,  or 
involution,  into  processes,  the  apodemea,  which  project 
inwards  and  unite  with  one  another  in  the  cavity  of  the 
thorax.  In  an  Aiiacua  which  has  been  macerated,  or, 
better,  boiled  in  caustic  alkali,  the  floor  of  the  thoracic 
cavity  is  seen  to  be  divided  into  a  number  of  incomplete 
cells,  or  chambers,  by  these  apodemal  partitions,  which  will 
be  observed,  on  careful  examination,  to  arise  partly  from 
the  interstemal,  partly  from  the  interepimeral  membrane 
connecting  every  pair  of  somites.  The  former  portion  of 
each  apodeme  is  the  endostemite,  the  latter  the  endoplewite 
of  Milne-Edwards.    As  a  general  inile,  each  endostemite  is 

*  The  tenn  epimeron  is  here  sppendage  and  the  plearon. 

•mployed  In  a  more  special  sense  f  Probably  the  coxo-  and  basi- 

thaa  that  oomnioDly  used,  to  de-  podite   together   answer  to  the 

note  that  part  of  the  lateral  wall  protopodite    of   the    abdominal 

of  a  somite  which   is  situated  appendages,  the  remaining  j<tott 

between  the  articulation  of  the  representing  the  endo^g'Qidl^A* 


310      THE  ANATOMY  09  DrYEBTKBRATBD  ANIMAL8. 

distingoisliable  into  three  apopTiyses — tlie  aHhrodial^  which 
passes  outwards  and  unites  with  the  descending  diyiaion  of 
the  endopleurite  to  form  one  boundary  of  an  artioiilar 
cavity  for  a  limb ;  the  mesophragmal,  which  is  directed  in- 
wards, uniting  with  its  fellow,  and  forming  an  arch  over 
the  passage  left  in  the  middle  line  between  each  pair  of 
endostemites — the  so-called  sternal  canal ;  lastly,  the  para* 
phragmal  division  is  a  small  process,  which  passes  forwards, 
upwards,  and  outwards,  and  unites  with  the  anterior  division 
of  its  own  endopleurite,  and  with  the  posterior  division  of 
the  endopleurite  in  front  of  it. 

The  endopleurite,  likewise,  divides  into  three  apophyses, 
one  descending  or  arthrodial,  and  two  which  pass  nearly  hori- 
zontally inwards  :  the  anterior  horizontal  ax>ophyBis  Tiniting 
with  its  own  paraphragmal  apophysis,  the  posterior  with  the 
paraphragmal  of  the  antecedent  endostemite.  The  posterior 
horizontal  apophysis,  therefore,  crosses  the  space  between 
every  pair  of  apodemes  diagonally,  whence  the  appearance 
of  a  double  row  of  longitudinal  cells  opening  above,  on  each 
side  of  the  sternal  canal.  It  will  be  understood,  however, 
that  these  cells  are  veiy  incomplete,  communicating  with 
one  another  anteriorly  and  posteriorly,  by  the  largo 
apertures  left  between  the  endostemites  and  endopleurites; 
and,  laterally,  by  the  spaces  between  the  endostemites, 
through  which  each  series  opens  into  the  sternal  canal ;  while 
above,  they  are  in  free  communication  with  the  thoracic 
cavity.  The  apodemes  give  attachment  to  the  muscles 
of  the  appendages,  while  the  chain  of  ganglia  and  the 
sternal  artery  lie  in  the  sternal  canal. 

The  appendages  of  the  penultimate,  resemble  those  of  the 
last,  thoracic  somite,  but  the  three  preceding  pairs  difEler 
from  them  by  being  chelate,  that  is,  by  having  the  posterior 
distal  angle  of  the  propodite  produced  so  as  to  equal  the 
dactylopodite  in  length,  and  thus  constitute  a  sort  of 
opposable  finger  for  it  (Fig.  71,  G,  6,  7).  The  first  ambulatory 
or  prehensile  limb,  again,  is  remarkable  for  its  greai,  size 
and  strength,  and  for  the  ankylosis  of  its  badpodite  with 
the  ischiopodite. 


▲8TACV8  VLUTIATILIB.  811 

The  four  anterior  pairs  of  ambtilatory  limbs  differ  from 
the  last  pair  in  possessing  a  long  curved  appendage  (Fig. 
71,  N),  which  ascends  from  the  coxopodite,  with  which  it  is 
articulated,  and  passes  into  the  branchial  <^iamber,  in  which 
it  lies.  This  is  the  epipodUe ;  its  relation  to  the  function 
of  respiration  will  be  adverted  to  presently. 

The  sterna,  which  are  wide  in  the  three  hindmost  thoracic 
somites,  become  verj  narrow  and  almost  linear  in  the 
anterior  ones.  They  and  their  apodemes,  however,  remain 
perfectly  recognisable. 

The  sternal  regions  of  the  three  maxillipedary  somites 
have  the  same  characters,  their  appendages  and  articular 
cavities  becoming  smaller ;  while,  by  the  contemporaneons 
excessive  narrowing  of  the  interarticular  regions  of  the 
sterna,  these  cavities  are  closely  approximated. 

The  stemxun  of  the  next  anterior  somite  (bearing  the 
second  pair  of  maxillsB),  on  the  other  hand,  though  very 
narrow  from  before  backwards,  has  a  considerable  width, 
and  its  articular  cavities,  already  much  larger  than  those 
of  the  anterior  maxillipedary  somites,  are  consequently 
thrown  outwards.  Hence  results  a  sudden  widening  of 
the  second  maxillary,  as  compared  with  the  first  maxilli- 
pedary somite;  and,  as  a  consequence,  we  find  a  deep 
fold  or  depression  on  the  sides  of  the  body,  where  these  two 
somites  join.  This  fold  is  directed  upwards  and  backwards 
on  the  flanks  of  the  body,  parallel  with  an  important  im- 
pression on  the  carapace,  the  eervieal  groove.  Not  only  on 
this  ground,  but  because  the  fold  really  represents  a  true 
neck,  or  separation  between  the  head  and  thorax,  it  may 
approximately  be  termed  the  eervieal  fold.  The  scapho- 
gnathite,  (Fig.  71,  C,  e,  d,)  an  important  appendage  of  the 
second  maxilla,  lies  in  this  cervical  fold. 

The  appendages  of  the  three  maxillipedary  somites  (Fig. 
71,  D,  £,  F)  are  highly  interesting,  inasmuch  as  they  afford 
transitional  forms  between  the  ambulatory  limbs  and 
the  gnathites.  Each  maxillipede  is  composed  of  three 
diTirions,  articulated  with  a  stout  protopodite.  The 
outermost  of  these  divisions  is  a  curved,  elongated  lamina 


812       THX  AKATOXT  OF  U  f  IMaBKlMID  AKDCALS. 

(<!),  preciselj  resembling  the  epipoctite  of  tbe  pooterior 
thoracic  limbs  in  the  two  hinder  maxillipedes  (£«  F) ;  bnt^ 
in  the  anterior  (D)  not  modified  so  as  to  nerve  as  a  branehiat 
and  rather  approaching  the  scaphognathite  in  form. 

The  middle  division  of  each  maxillipede  (c),  answering  to 
the  exopodite,  is  long,  slender,  manj-jotnted,  andpalpiform» 
while  the  inner  division,  or  endopodite,  (a,  h,)  not  ontf 
corresponds  with  one  of  the  ambulatory  limbs,  bnt  in  the 
posterior  maxillipede  (Fig.  71,  F)  very  closely  resembles 
one,  and  contains  the  same  number  of  joints.  In  the  next 
maxillipede,  however  (Fig.  71,  E),  the  endopodite  is  pro- 
portionally shorter,  and  in  texture  and  form  rather 
approaches  the  foliaceous  endopodite  of  the  anterior 
maxillipede  (Fig.  71,  D),  in  which  a  flat  plate  is  applied  to 
the  posterior  surface  of  the  slender  exopodite.  A  perfect 
transition  is  thus  produced  between  the  corresponding 
divisions  of  the  second  maxillipede  and  of  the  second 
maxiUa. 

The  intermaxillary  apodeme,  or  that  developed  from  the 
connecting  membrane  of  the  two  maxillary  somites,  is  very 
remarkable  for  its  stoutness  and  for  the  great  size  and 
expanded  form  of  the  mesophragmal  processes,  which  unite 
into  a  broad  plate,  whence  prolongations  are  sent  forwards 
and  outwards,  in  front  of  the  tendon  of  the  great  adductor 
mandtbuUE  muscle  on  each  side.  These  prolongations  appear 
to  be  the  calcified  posterior  horizontal  apophyses  of  the 
mandibulo-maxillaiy  apodeme,  which  elsewhere  remains 
membranous. 

The  second  maxilla  (Fig.  71,  C)  much  resemUes  the  an- 
terior maxillipede,  but  the  epipodite  (d)  and  exopodite  (c) 
appear  to  be  combined  into  a  wide  oval  plate,  the  seajpfto- 
gnathite,  of  which  mention  has  already  be^  made.*  In  the 
first  maxilla  (Fig.  71,  B)  the  epipodite  and  exopodite  appear 
to  be  undeveloped,  and  the  joints  of  the  endopodite  are 
completely  foliaceous.     The  somite  which  supports  the 

*  Until    the   development    of      of  the  homologies  of  their  psrCs 
ihete     Appendages     has     been      must  be  reganted  as  provisional. 
woilBad   oat,  the  detemiaatioa 


ASTACmi  WLUTUSUM,  813 

mandibles  is,  to  a  greafc  eztent»  memlHranoiis  in  its  sternal 
region;  it  is  united  with  the  corresponding  region  of  the 
first  maYJllary  somite,  itself  represented  merslj  bj  a 
narrow,  distinctly  calcified,  band,  in  front  of  the  second 
maYJllary  sternum,  by  monbrane  only.  In  this  mem- 
branoos  space  the  elongated  apeitnre  of  the  mouth  is 
sitoated. 

On  each  side  of,  and  behind,  the  mouth  are  two  little 
elongated  oval  calcified  plates,  between  which,  an  oval 
process,  setose  at  its  extr^nity,  proceeds  downwards  and 
forwards,  and  lies  in  close  apposition  with  the  x>osterior 
face  of  the  mandible  of  its  side.  This  is  one^ialf  of  what 
is  termed  by  most  authors  the  lahiwnf  but,  to  avoid  con- 
fusion with  the  labium  of  Inseeta,  from  whioh  it  is  wholly 
different,  it  may  be  called  the  metcuioma  (Fig.  72,  f).  It 
obviously  answers  to  the  structure  so  named  in  the  Cope* 
poda. 

The  mandibles  fill  up  a  large  space  in  the  sternal  mem- 
brane, with  which  their  edges  are  continuous  on  each  side 
of  the  oral  aperture ;  externally,  the  sternal  membrane  bends 
suddenly  downwards  into  the  pleural  ridge,  continuous  with 
the  branchiostegite  of  the  carapace,  and  becomes  calcified ; 
while,  anteriorly,  it  is  very  difficult  to  say  where  the  mandi- 
bular sternum  terminates.  In  front  of  the  mouth  the 
sternal  membrane  becomes  developed  into  a  large  median 
lobe,  containing  three  small  calcified  plates  on  each  side 
of  the  middle  line.    This  is  the  labrum  (Fig.  72,  e). 

Hie  mandible  itself  (Fig.  71,  A)  is  thick  and  strong  at  its 
inner  end,  where  it  is  divided  by  a  deep  excavation  into  an 
upper  and  a  lower  portion,  (a,  h,)  the  edge  of  each  being 
toothed.  The  outer  division  of  the  mandible  extends  along 
the  whole  width  of  the  somite,  and  tapers  to  its  ex^mity, 
which  presents  an  articular  head,  the  outer  condyle. 
Attached  to  its  anterior  margin  is  the  palp(o),  which 
represents  the  terminal  joints  of  the  mandibular  endo- 
podite.  The  exopodite  and  the  epipodite  have  no  re- 
preaentatives  in  this  appendage.  Superiorly,  the  outer 
portion  of  the  mandible  is  concave,  and  its  posterior  ed%<^ 


314       THZ  AKATOn  OT  UTTE&TIBKUID   JUntAi^, 

gives  attadunent  to  the  calcified  tendon  of  the  miHaatot 
lu&ndibuls  {S). 

In  &ont  of  the  labrom  and  mandibles  ia  m  wide,  Bome- 
what  pentt^onal  area,  prolonged  into  a  point  in  tlie  »»iAlLi 
line  fornards,  and  presenting  a  small  spine  on  encli  n^; 
thia  IB  the  epittoma  (Fig.  72,  B,  Q,  and  it  is  chiefly,  if  not 
entirely,  formed  hy  the  sternnm  of  ibe  antennaiy  ■^m't^, 
On  each  side  of  ite  triangular  anterior  eitremitj  it  pre- 
Fig.  72. 


.  „.  .      -A.    AnMrior  eilreniity  of  tfae  o«p   _      . 

with  A  portion  of  the  cuvpace  lemoved.  B.  Vertical  Ketionorilta 
tnttriat  part  of  ths  cephftlu-tbom.  a,  rostrum;  A,  ophthalmle 
pedoDoln  ;  iT,Bnt<Dnulae;  d,  snteQiuB  ;  c,  Ubnim  ;  /,  mgtwtonk ; 
ff,  0 aI  ftpertnn ;  A,  procephalic  proc««es ;  f,  ophthunic  •tanun ; 
il,'auteDualu7  ucrDum ;  I,  aateiiDary  itenium  or  sfdatoma. 

■enta  a  wide  articular  cavity  for  the  articulation  of  tlie 
antenns.  Is  these  organs  (Fig.  72.  B,  d)  the  same  parts 
can  be  recognised  as  in  the  other  appendages,  viz.,  an 
imperfect  basal  joint,  produced  into  a  prominent  cone, 
perforated  behind  and  internal  to,  its  apex;  and  here 
called  eoxoceriU,  Next,  a  haticeriU,  to  the  outer  portion 
of  which  a  flattened  plat«,  the  representative  of  tlie 
exopodite,  and  here  called  the  icaphocmHe,  is  articnlated; 
while  to  its  inner  portion  an  itchioeeritt  is  connected, 
bearing  a  m^oeeriU  arid  earpoeerite,  while  the  last  segment, 
or  proceriie,  coneista  ot  a  long  multi-articnlato  filament. 

The  stoma  of  the  next  two  somites  are  narrow  and  elon- 
gated; that  of  the  antennary  somite  is  well  calcified,  but 
that  of  the  ophthalmic  somito  is  almost  entirely  mem- 


A8TACU8  FLUYIATIIJ8.  315 

The  anteimiiles  (Fig.  72,  B,  e)  present  an  enlarged  trigonal 
basal  joint,  succeeded  b  j  two  others.  These  represent  the 
protopodite,  and  carry  at  their  extremities  two  many-jointed 
filaments,  which  probably  represent  the  exo*  and  endopo- 
dites. 

Thepednnclesof  the  eyes  (Pig.  72,  h),  lastly,  are  composed 
of  two  joints,  a  small  proximal  b<uu)phOialmUe,  and  a  larger 
terminal  podopMhalmUe. 

Such  are  the  stmctore  and  arrangement  of  the  sternal 
portions  of  the  several  cephalo-thoracic  somites,  and  the 
nature  of  their  appendages.  On  regarding  the  sternal 
region  as  a  whole,  there  are  yet  some  very  important 
points  (the  morphological  value  of  which  has  been  fully 
pointed  out  by  Milne-Edwards)  to  be  noticed.  A  longi- 
tudinal median  section,  in  fact,  shows,  that  while  a  line 
drawn  through  the  sterna  of  the  somites  behind  the  mouth 
is  nearly  straight  and  parallel  with  the  axis  of  the  body,  a 
similar  line  drawn  through  the  sterna  of  the  somites,  in 
front  of  the  mouth,  ascends  as  it  passes  through  the 
antennary,  antennulary  and  ophthalmic  sterna,  and  thus 
takes  a  position  at  right  angles  to  the  former  line  (Fig.  72, 
B).  The  sterna  of  the  somites,  in  front  of  the  mouth,  are, 
therefore,  bent  up  so  as  to  look  forwards  instead  of  down- 
wards ;  and  it  is  of  essential  importance  to  bear  in  mind 
this  cephalie  flexure,  in  considering  the  structure  of  the 
head  in  these  and  other  ArthropocUi. 

Just  as  the  lateral  regions  of  the  abdominal  somites  are 
produced  into  the  plewra,  so  are  the  lateral  regions  of  the 
cephalo-thorax  similarly  prolonged.  Thus  the  membranous 
lateral  walls  of  the  posterior  cephalo-thoracic  somite  are 
reflected  superiorly,  and  bent  down  again  to  the  level  of 
the  bases  of  the  legs,  where  they  become  continuous  with 
a  calcified  layer  corresponding  with  the  tergal  half  of  the 
pleura,  and  forming  the  posterior  part  of  the  carapace.  In 
like  manner,  the  more  or  less  calcified  epimera  of  all  the  other 
Bomites  are  reflected  superiorly  into  a  membrane  which 
passes  downwards,  and  the  free  lower  edge  of  which  is  con- 
tinuona  with  the  edg^  of  the  carapace.     The  caxOk^^fi^^ 


316   THE  ANATOMY  09  ZVYSBTXBBATBD  ANIKAX8. 

therefore,  correspondB  in  poeitiosi  with  the  terga  and  tergtl 
halves  of  the  pleura  of  all  the  Bomitea  which  are  thm 
reflected  into  it,  and  these  somites  include  all,  without 
exception,  from  the  last  thoracic  to  the  ophthahnie.  Fot- 
tei-iorly,  the  edges  of  the  carapace  are  a  little  prolonged 
beyond  the  last  thoracic  somite,  and  take  the  form  of  a 
fold,  with  an  imder  layer  distinct  from  the  upper.  An* 
teriorly,  in  the  middle  Une,  the  carapace  is  prolonged  in  a 
similar  manner,  but  to  a  much  greaJter  extent;  it  thus 
gives  rise  to  the  long  rogtrumj  which  overhangs  the 
sterna  of  the  ophthalmic  and  antennulary  somites.  At 
the  sides  of  the  antennulary  and  antennary  somites  the 
rostral  prolongation  of  the  carapace  is  the  direct  con- 
tinuation outwards  of  the  epimera  of  those  somites,  and 
there  is  nothing  to  be  compared  to  an  apodeme ;  but  the 
sternum  of  the  ophthalmic  somite,  after  giving  off  the 
lamella  which  forms  the  inf eromedian  region  of  the  roetmnit 
is  prolonged  on  each  side  of  the  middle  line  backwards  and 
outwards  into  a  free,  expanded,  thin,  calcified  process,  which 
applies  itself  against  the  carapace  by  its  upper  surface,  and 
by  its  under  surface  gives  attachment  to  the  anterior  gastric 
muscles.  Corresponding  processes  are  developed  from  the 
carapace  itself,  in  some  Podophthalmia  (e.  g.  Oalatkea^  Car* 
cinus),  for  the  attachment  of  the  posterior  gastric  muscles. 
From  the  last  thoracic  to  the  maxillipedaiy  somites,  the 
pleural,  or  free  part  of  the  carapace,  termed,  from  its 
function,  the  branchiogtegUef  or  cover  of  the  gills,  encloses 
a  wide  space,  bounded  internally  by  the  epimera  of  the 
somites.  This  is  the  branchial  ohamher.  In  front  of  the 
maxiUipedes  and  cervical  fold,  however,  the  chamber  snd* 
denly  becomes  narrowed  by  the  rapid  widening  of  the 
sterna  of  the  maxillary  and  mandibular  somites,  and  by  the 
lowering  of  the  point  at  which  the  reflection  of  their 
epimera  into  their  pleura  takes  place.  Finally,  on  the 
antennary  somite,  and  in  front  of  it,  the  pleuron  becomes 
a  mere  fold  separated  by  a  shallow  groove,  the  repreeen> 
tative  of  the  branchial  chamber,  from  the  epimera. 
On  the  dorsal  surface,  there  is  no  indication  of  any  division 


ABTACxrs  WLjmATiua,  317 

of  the  carapace  into  terga  oorrespomding  with  the  sterna  of 
the  Bomit^  bnt  it  is  marked  by  a  well-defined,  curved 
groove,  the  posterior  convexity  of  which  extends  across  the 
carapace,  rather  behind  its  middle,  and  the  lateral  portion 
of  which  runs  downwards  and  forwards,  towards  the  anterior 
part  of  the  antennary  stemnm.  This  is  the  eerviaU  groove ; 
that  part  of  the  carapace  which  lies  in  front  of  it  is  the 
o^halotUgite,  while  that  which  is  behind  is  the  omoHegiie. 

The  omostegite,  again,  is  divided  into  three  portions  by 
a  groove  on  each  side  of  the  middle  line — the  brone^to- 
cardicus  grooves.  The  branohiocardiac  groove,  and  the 
lateral  portion  of  the  cervical  gpx>ove,  on  the  dorsmn  of  the 
carapace,  correspond  very  closely  with  the  line  at  which 
the  epimeral  is  reflected  into  the  pleural  membrane,  on  its 
ventral  surface.  The  transverse  portion  of  the  oervical 
groove,  on  the  other  hand,  corresponds  with  the  posterior 
boundary  of  the  stomach,  and  the  anterior  extremity  of 
the  heart,  and  continues  inwards  the  line  of  the  cervical 
fold;  so  that,  in  a  longitudinal  section  of  an  AMkusus,  the 
direction  of  the  cervical  fold,  if  followed  upwards  and 
backwards,  strikes  against  the  inner  surface  of  the  cara- 
pace, at  a  point  corresponding  with  the  summit  of  the 
cervical  groove,  on  its  outer  surface.  By  cutting  through 
the  cervical  fold,  therefore ;  through  the  membrane  joining 
the  second  maxillary  with  the  first  maxillipedaiy  sternum ; 
and  through  the  carapace  in  the  transverse  part  of  the 
cervical  groove,  it  is  possible  to  separate  an  anterior  portion 
of  the  cephalo-thorax,  containing  the  whole  of  the  cephslo- 
stegite,  and  the  first  six  somites,  with  their  appendages, 
from  a  posterior  portion,  consisting  of  the  omostegite,  and 
the  last  eight  cephalo-thoracic  somites.  And,  in  making 
this  artificial  separation,  we  should  be  merely  carrying  out 
a  distinction  between  these  two  sets  of  somites,  already 
very  clearly  indicated  by  the  cervical  fold  and  groove. 

It  is  for  this  reason  that  I  differ  from  Milne-Edwards  in 
regarding  the  somite  which  bears  the  first  maxillipedes  as 
the  first  of  the  thorax,  and  not  as  the  last  of  the  head. 
And  tlie  acceptance  of  this  natural  delimitatioa  ol  ^<^ 


31^        THE    ANATOMY    OF    INVERTEBRATED    ANIMALS. 

head  in  the  higher  Crustacea,  has  the  advantage  of  bringing 
its  structure  into  accordance  with  that  of  the  same  region 
in  the  Eniomagtraca,  in  which  it  is  the  role  that  the  hatd 
possesses  ejes,  antennnles,  antennfle,  mandibles,  and  two 
pairs  of  maxillse. 

Another  mark  upon  the  carapace  is  a  large  and  ronnded 
convexity,  occupying  nearly  a  third  of  the  whole  width  ol 
the  x>osterior  half  of  the  cephaloetegite.  This  impression 
is  bounded  internally  by  a  line  drawn  from  the  outer  angle 
of  the  base  of  the  rostrum,  directly  backwards ;  and,  exter- 
nally by  a  curved  depression,  deepening  into  a  pit  ante- 
riorly ;  it  corresponds  with  the  attachment  of  the  base  of 
the  adductor  muscle  of  the  mandible. 

The  mouth  of  the  Crayfish  is  a  wide  aperture,  situated 
between  the  labrum  in  front,  the  metastoma  behind,  and 
the  mandibles  on  each  side.  It  serves  as  the  entrance  to 
an  equally  wide  oesophagus,  a  short  tube  with  plaited 
walls,  which  takes  a  slightly  curved  direction  upwardJs  and 
a  little  backwards,  to  open  into  the  large  stomach,  which  is 
not  only  situated  directly  over,  but  extends  forwards  in 
front  of,  the  gullet.  The  stomach,  in  fact,  occupies  almost 
the  whole  cavity  of  the  body  in  front  of  the  cervical 
suture,  and  is  divided  by  a  constriction  into  a  large  anterior 
moiety,  the  cardiac  division,  and  a  small  posterior,  pyloric 
portion.  The  anterior  half  of  the  cardiac  division  has  the 
form  of  a  large  membranous  bag,  the  inner  surface  of 
which  is  closely  set  with  minute  hairs ;  but,  in  the  posterior 
half  of  this,  and  on  the  whole  of  the  pyloric  division,  the 
walls  of  the  stomach  are  strengthened  by  a  very  peculiar 
arrangement  of  uncalcified  and  calcified  plates  and  bars 
articulated  together,  which  are  thickenings  of  the  chitinoos 
cuticula  of  the  epithelium  of  the  alimentaiy  canal,  and 
constitute  the  gastric  skeleton.  The  most  important 
part  of  this  apparatus  is  that  which  is  developed  in  the 
posterior  cardiac  region. 

It  consists,  in  the  first  place,  of  a  transverse,  slightly 
arooated  emrdiao  plate  (Fig.  73,  ea\  calcified  posteriorly, 
which  extends  across  the  whole  width  of  the  stomach,  and 


▲BTACUS  VLUYIATILIS.  319 

articulates  at  each  extremity  by  an  oblique  suture  with  a 
small  curved  triangular*  an^o-2a(eraZ  or  pierocardi4ie  {pt) 
ossicle.  On  each  side,  a  large,  elongated  postero-laieral  or 
vygocardiac  ossicle  {se)  wider  posteriorly  than  anteriorly, 
is  connected  with  the  lower  end  of  theantero-lateral  ossicle, 
and,  passing  upwards  and  backwards,  becomes  continuous 
with  a  transYcrse  arcuated  plate,  calcified  in  its  anterior 
moiety,  and  situated  in  the  roof  of  the  anterior  dilatation 
of  the  pyloric  portion;  this  is  the  pyloric  ossicle  (Fig. 
73,  py). 

These  pieces,  it  will  be  observed,  form  a  sort  of  six-sided 
frame,  the  anterior  and  lateral  angles  of  which  are  formed 
by  moveable  joints,  while  the  posterior  angles  are  united  by 
the  elastic  pyloric  plate. 

From  the  middle  of  the  cardiac  piece  a  strong  calcified 
wroeardiae  process  {ca')  extends  backwards  and  downwards, 
and,  immediately  under  the  anterior  half  of  the  pyloric  ossicle, 
terminates  in  a  broad,  thickened  extremity,  which  presents 
inferiorly  two  strong  rounded  tuberosities,  or  cardiac  teeth. 
With  this  process  is  articulated,  posteriorly,  a  broad  pre- 
pyloric ossicle,  which  passes  obliquely  upwards  and  forwards, 
in  the  front  wall  of  the  anterior  dilatation  of  the  pyloric 
portion,  and  articulates  with  the  anterior  edge  of  the 
pyloric  ossicle,  thus  forming  a  kind  of  elastic  diagonal 
brace  between  the  urocardiac  process  {ca')t  and  the  pyloric 
ossicle.  The  inferior  end  of  this  pre-pyloric  ossicle  is  pro- 
duced downwards  into  a  strong  bifid  urocardiac  tooth  (oe). 
Finally,  the  inner  edges  of  the  postero-lateral  ossicles  are 
flanged  inwards  horizontally,  and,  becoming  greatly  thick- 
ened and  ridged,  form  the  large  lateral  cardiac  teeth  (cc). 
The  membrane  of  the  stomach  is  continued  from  the  edges 
of  the  pre-pyloric  to  those  of  the  postero-lateral  ossicle 
in  such  a  manner  as  to  form  a  kind  of  pouch  with 
elastic  sides,  which  act,  to  a  certain  extent,  as  a  spring, 
tending  to  approximate  the  inferior  face  of  the  pre-pyloric 
oande  to  the  superior  face  of  the  median  process  of  the 
cardiao  ossicle. 

The  result  is  that  there  is  a  certain  position  of  equilibriuxoi 


rVEKT&BRATED  AN  III  A  LS. 


of  the  whole  apparatus,  when  the  urocardiac  process  and 
the  pre-pfloric  oedcle  make  a  small  angle  wiUi  one  uu>thw. 


Flf .  73.— .^riacw.— Upper  FIgur« ;  LongltndliiKl  & 
A.  Aotnlornitrio  muMle.  B.  Poaterior  gutrlo  miwcle.  (B.  sa>- 
phuni.  P.PjloTiu.  en.  CtrdioctiHicla.  <  a'.  lu nioeudiao  proMM. 
a  e.  llrMtrdiM  tooth.  /))i.  PjlorieosglFle.  The  oblique  bar,  eztend- 
Inf  ttma  tbe  aid  ef  the  ourdlae  Ui  th«  pjlorie,  li  the  prepylotlfl  iiliil« 


B^ptarooardlao.    it.  PoMero-Uteral  cudUo,  vith  it«  grtat  tooth,  ac 

i  tbn*ll  Inftriot  tooth,     t.  C»rdlo-pjloric  vaWe.    6.  lufercMBedln 

vrlorlo  tidp.    a,  Lktanl  pyloric  lidn.    d.  Superior  pjlorla  ridge. 

^  Uio-pjlorio  odialc.    zy.  Line  of  Mctlon ;  tbe  eotertor  &>•  of 


the  poetorior  eegment  being  ihown  in  the  lovar  Sgiu«. 

and  the  antero-lateral  oisicleH  form  an  almost  nnbrokon 
tmursrse  curve  with  the  cardiac.  When  nudiBtarbed,  the 
l^puatna  totdi  to  UKune  this  poaition. 


▲8TACU8  rLUTIATILia.  821 

Two  pairs  of  powerful  muaoles  are  afctacHed  to  thia  gas* 
trie  skeleton.  The  anterior  pair  arise  from  the  prooephalio 
processes,  and  are  inserted  into  the  roof  of  the  stomach, 
somewhat  in  front  of  the  cardiac  ossicle ;  the  posterior  have 
their  origin  in  the  carapace  immediately  aboYS  and  behind 
the  pyloric  end  of  the  stomach,  and  their  insertion  into  the 
pyloric  ossicle  and  the  wide  posterior  part  of  the  postero- 
lateral pieces. 

From  the  attachment  of  these  muscles  it  is  dear  that 
their  action  mnst,  in  a  general  way,  resemble  that  produced 
by  pulling  ux>on  the  cardiac  and  pyloric  pieces  when  the 
stomach  is  removed  from  the  body.  Now  the  result  of  doing 
this  is  that,  the  cardiac  and  pyloric  pieces  being  diyaricated, 
the  pre-pyloric  ossicle  assumes  a  vertical  position,  and  the 
uro-cardiac  tooth  turns  downwards  and  forwards.  At  the 
same  time  the  antero-lateral  or  pterocardiac  pieces  are 
pulled  backwards,  and,  owing  to  their  oblique  articulation 
with  the  cardiac  piece,  their  inferior  ends  moye  down- 
wards, backwards,  and  inwards,  carrying  with  them  the 
anterior  ends  of  the  postero-lateral  pieces,,  the  teeth  of 
which  (lateral  cardiac)  come  into  contact  with  the  uro- 
cardiac  and  cardiaq  teeth,  with  a  force  proportional  to  that 
exerted  in  traction.  On  ceasing  to  pull,  the  apparatus 
returns  to  its  former  position,  its  backward  moyement 
being  facilitated  by  the  reaction  of  the  elastic  pouch  men- 
tioned above,  and  being  doubtless  also  assisted,  in  the 
living  state,  by  a  pair  of  small  cardio-pylorie  muscles, 
which  pass,  one  on  each  side,  between  the  cardiac  and 
pyloric  ossicles,  beneath  the  membrane  of  the  stomach,  the 
looseness  of  which,  in  this  region,  where  it  unites  the  various 
ossicles  of  the  gastric  mill,  greatly  assists  the  free  move- 
ment of  the  whole  apparatus. 

Nothing  can  be  more  easy  than  to  perform  the  ex- 
periment, and  to  convince  oneself  that  these  structures  do 
really  constitute  a  most  efficient  masticatory  apparatus; 
and  it  is  surprising  that  Oesterlen,  in  his  elaborate  essay 
on  the  stomach  of  AHacus,  should  have  questioned  the 
crushing  action  of  the  teeth. 


rtl'l        THE    ANATOMY    OF    INVERTEBKATED    ANIMALS. 

A  ^reat  bilulx'd  valvular  process  i.Fig.  73,  c)  rises  up  from 
the  sternal  region  of  the  stomach,  opposite  the  cardio-pyloric 
constriction,  and  apparently  prerente  the  food  from  piifwiTig 
inte  the  pyloric  division  until  it  is  properly  comminuted. 
And,  in  front  of  this  valve,  the  infero-lateral  parietes  of  the 
stemach  are  strengthened  by  a  number  of  other  plates  and 
bars;  one  of  which  on  each  side  bears  a  small  tooth 
{infero-lateral  cardiac,  I),  and  is  continued  into  a  brotd 
uncalcified  plate,  lying  in  the  hinder  and  lower  part  of 
the  side  walls  of  the  stomach,  and  covered  with  hain 
internally.  There  are,  therefore,  altogether  seven  gastric 
teeth,  three  median,  the  cardiac,  and  the  uro-cardiac ;  and 
two  lateral  on  each  side,  the  latend  cardiac,  and  the  infeio- 
lateral  cardiac. 

In  the  pyloric  diWsion  of  the  stomach  the  food  has  to 
undergo  a  further  series  of  comminutions  and  strainings. 
A  ridge  covered  with  long  hairs  projects  in  the  median 
line  above;  other  hairy  ridges  extend  inwards  from  the 
sides  to  meet  it,  and  nearly  close  the  passage  laterally. 
These  ridges  are  very  convex  inferiorly,  and  their  con- 
vexities abut  against  the  concavities  of  an  inferior  median 
ridge,  which  rises  up  to  meet  them,  and  is  prolonged 
posteriorly  into  a  sort  of  valvular  process,  covered  at  its 
termination  with  long  hairs,  which  bar  the  space  left 
between  the  upper  parts  of  the  lateral  ridges.  The 
concave  faces  of  this  median  process  are  covered  by 
close-set  parallel  ridges,  which  only  become  free  hair-like 
processes  at  the  posterior  margin  of  the  plate,  each  ridge 
giving  attachment  to  a  regular  series  of  minute  hairs. 
These  are  directed  inwards  nearly  parallel  with  the  surface, 
which  looks  at  first  as  if  it  were  merely  ruled  with  close-set 
transverse  lines,  connected  by  still  finer  and  closer  longi- 
tudinal ones. 

This  apparatus  constitutes  the  "  ampoule  cartilagineux" 
of  Milne-Edwards.  Behind  it  there  is  yet  another  laf  era* 
median,  and  two  lateral  setose,  valyular  prominences,  which 
form  the  last  barrier  between  the  food  and  the  intestine. 

Mr.  T.  J.  Parker,  who  has  recently  carefully  examined  the 


ASTACV8  FLUTIATILIS.  d2S 

Btmctnre  of  tbe  stomacli  of  tLe  Crajfisli,*  finds  that,  be- 
sides the  anteriorand  posterior  gastric  and  the  cardio-pjlorio 
muscles,  there  are  intrinsic  fibres  in  the  walls  of  the  stomach, 
some  encircling  the  posterior  pyloric  region,  others  passing 
between  the  hindermost  accessory  ossicle  and  the  postero- 
lateral and  pyloric  pieces;  these  must  tend  to  diminish 
the  cavity  of  the  stomach,  and  the  last-named  fibres  possibly 
assist  in  mastication  by  bringing  the  lateral  cardiac  into 
contact  with  the  infero-lateral  cardiac  tooth.  Moreover 
there  are  nine  pairs  of  minor  extrinsic  muscles,  of  which 
two  pairs  pass  from  the  anterior  wall  of  the  stomach  and 
gullet  to  the  antennary  sternum,  passing  between  the 
(esophageal  commissures  and  on  either  side  of  the  azygos 
nerve  of  the  visceral  system ;  three  pairs  pass  between  the 
side  walls  of  the  stomach  and  oesophagus  and  the  mandibular 
sterna ;  a  sixth  pair  arises  from  the  forward  processes  of  the 
intermaxillary  apodeme  and  is  inserted  into  the  oesophagus ; 
two  more  pairs  arise,  one  from  the  internal  thickened  edge  of 
the  mandible,  the  other  from  the  intermaxillary  apodeme,  and 
are  inserted  into  the  inferior  surface  of  the  pyloric  region ;  and 
a  ninth  pair  arises  from  the  carapace  just  behind  the  posterior 
gastric  muscles,  and  goes  to  be  inserted  into  the  posterior 
pyloric  dilatation.  There  are  also  a  few  more  inconspicuous 
fibres  passing  between  the  oesophagus  and  the  neighbouring 
hard  parts.  All  these,  at  least  when  acting  together,  must 
antagonise  the  intrinsic  muscles,  and  dilate  the  stomach. 

The  pyloric  portion  of  the  stomach  passes  into  the  an- 
tenor  portion  of  the  intestine,  which  is  smooth  internally,  and 
presents  superiorly  a  csecal  process,  the  remains,  according 
to  Bathke,  of  one  lobe  of  the  vitellaiy  sac  of  the  embryo. 

This  anterior  portion  of  the  intestine  is,  however,  very 
short,  and  almost  immediately  becomes  dilated  into  the 
wider  posterior  division,  which  extends  to  the  anus.  The 
inner  surface  of  the  dilatation  is  produced  into  six  ridges, 
jwhioh  are  continued  into  a  corresponcUng  number  of  series 
of  papillffi  along  the  rest  of  the  intestine. 

The  only  glandular  apparatus  of  any  kind  which  opens 
*  *  Journal  of  Anatomy  and  Phytiology,'  Oei.  l^l^. 


^4       THE  ANATOMY  OF  INYBRTSBBATED  ANHCAUB. 

into  the  alimentary  canal  is  the  liver,  and  the  apertures 
of  the  wide  hepatic  ducts  are  seen  on  each  side  of  the 
pylorus.  Each  duct  conveys  the  secretion  from  the  mul- 
titudinous csecal  tubes,  which  constitute  the  principal  mast 
of  the  corresponding  bilobed  half  of  the  liver.  The  two 
halves  lie  on  each  side  of  the  stomach,  and,  though  thej 
remain  perfectly  distinct  from  one  another,  come  into  dose 
contact  below. 

Asicicua  possesses  neither  salivary  glands  nor  any  csBcal 
appendages  to  the  intestine,  such  as  exist  in  the  Brach^ura 
and  some  Macrura,  unless  the  short  csBcum  just  now 
described  is  the  homologue  of  the  longer  caeca  of  Maia  and 
Hatnaru8, 

In  the  spring  and  summer,  two  very  curious  diacoidal 
calcareous  plates,  the  so-called  "  eyes  *'  of  the  Crayfish,  are 
found  imbedded  in  the  walls  of  the  dilated  anterior  portion 
of  the  cardiac  division  of  the  stomach,  the  middle  of  the 
lateral  surface  of  which  they  occupy.  These  bodies  com- 
mence as  calcareous  deposits  underneath  the  chitinous  gas- 
tric lining,  and  increase  in  size  until  the  period  arrives 
at  which  the  Crayfish  casts  its  skin.  They  are  then  cast, 
together  with  this  lining  membrane  and  the  gastric  arma- 
ture ;  and  it  would  appear  that,  like  the  latter,  they  become 
broken  up  and  destroyed  within  the  new  stomach.  The 
purpose  of  these  concretions  is  not  understood ;  the  ordi- 
nary theoiy,  that  they  are  stores  of  calcareous  matter,  ready 
to  be  distributed  through  the  young  integument  after 
ecdysis,  appearing  to  be  negatived  by  their  small  size. 
Oesterlen  states  that  they  rarely  weigh  more  than  two 
grains,  and  judiciously  suggests,  that  if  it  be  admitted  that 
the  Crayfish  can  derive  all  the  calcareous  matter  it  requires, 
except  two  grains,  from  other  sources,  it  is  hardly  necessary 
to  look  on  those  two  grains  as  a  special  supply. 

The  circulatory  apparatus  of  Askieua  is  well  developed. 
The  heart  (Fig.  74,  C)  has  the  shape  of  an  irregular  poly- 
gon, and  lies  immediately  behind  the  stomach  and  beneath 
4he  cardiac  region  of  the  carapace,  in  a  chamber  which  is 
oommonly  tenned  the  **  pericazdium,"  to  the  walls  of  which 


ASTAOHB  IXUTIATILIB. 

Fig.  :4. 


Fig.  14.—Aitaau,  Longiludiiial  SeaUon.— 1.  II.  III.  Slenw  of  fint, 
MOond,  and  third  Hmltei.     a.  (Etopbagu*.     A.  I^hruiD.     L  Mcla- 
■toiDS.   G.  M«mbnnouipartof  theilomwh.   e.CardlacoMiole.    pt. 
Urourdiae.    cL  LuanI  eardlaa.    p.  Cwdio- 
JnfBTior  Djiorle  tkItuIu  appantiu.    ■>.  Antariol 
I*.  iDimfaD  of  pa«t«ikiT  gaatrlo  moaclM.    pt. 
UpaniBg  of  bapaiia  dMot    •.  V^teiSK 


Planwardlao. 
Iijlorie  Tal*e.  p 
natrio  muacle. 
PiaocphaUo 


326   THE  ANATOMY  OF  INYBRTEBRATSP  ANIMALS. 

cecum.  I,  k.  Intestine,  p  n.  Testis,  p  n\g  n".  Vas  deferens.  C.  Heart. 
a  o.  Ophthalmic  artery,  a  a.  Anfennary.  a  A.  Hepatic.  a«.  Sternal. 
a  p.  Superior  abdominal  artery,  b.  Cerebral  ganglia.  9g,  Aiygot 
vigceral  nerve. 

it  is  attached  bj  six  ligaments,  corresponding  with  the 
alsB  of  the  heart  in  insects,  but  not,  like  them,  muscular. 
Except  by  these  ligaments,  and  by  the  arteries,  which  pass 
through  it,  the  walls  of  the  pericardial  cavity,  or  blood  ainua 
(for  such  it  really  is),  are  wholly  unconnected  with  the  heart» 
>diieh  thus  is,  in  a  manner,  suspended  freely  in  the  blood. 

Six  apertures,  two  of  which  are  superior,  two  inferior, 
and  two  lateral,  provided  with  yalyes,  which  open  inwards, 
allow  the  blood  to  enter  the  cavity  of  the  heart  during  the 
diastole,  and  preyent  its  egress,  except  by  the  arteries, 
during  the  systole.  The  arterial  trunks  are  six  in  number, 
fiye  being  given  off  anteriorly,  and  the  other  from  the 
posterior  portion  of  the  heart. 

Of  the  five  anterior  arteries  one,  the  ophthalmic,  is  single, 
and  situated  in  the  middle  line ;  it  passes  forwards  on  the 
stomach  to  the  head,  where  it  supplies  the  eyes  and  ant^n- 
nules.  The  other  arteries  are  in  pairs ;  two  pass  on  the 
stomach  forwards  and  outwards,  giving  off  branches  to  the 
carapace,  and  eventually  supplying  the  antennae ;  the  other 
two  pass  downwards,  between  the  anterior  lobes  of  the 
genitalia,  and  divide  into  a  multitude  of  branches  upon  the 
hepatic  caeca. 

The  posterior  trunk,  or  sternal  artery,  is  the  largest  of 
all,  and  presents  a  sort  of  bulbus  arteriosus  at  its  com- 
mencement. It  turns  almost  directly  downwards,  usually 
(m  the  right  side  of  the  intestine,  to  the  sternal  canal,  which 
it  enters,  passing  between  the  antepenultimate  and  pen- 
ultimate thoracic  ganglia  to  the  lower  surface  of  the 
ganglionic  cord ;  it  gives  off  two  abdominal  branches,  one 
superior,  close  to  its  origin  from  the  heart,  which  tra- 
verses the  middle  of  the  tergal  region  above  the  intestine, 
the  other  inferior,  which  takes  a  corresponding  course 
along  its  sternal  region  beneath  the  nervous  system.  The 
arterial  trunks  are  provided  with  valves  at  their  com- 
menoement,  so  arranged  as  to  prevent  the  regurgitation 


ASTACU8   PLUVIATILIS.  327 

of  the  blood.  Thej  ramify  minutelyi  but  How  far  a 
capillary  ajstem  can  be  said  to  exist,  is  a  question  requir- 
ing farther  investigation.  In  transparent  Zocb<b,  I  have 
plainly  observed  the  abrupt  termination  of  the  arterial 
trunks  by  open  mouths,  through  which  the  blood  was  poured 
into  wall-less  lacume,  and  into  the  general  cavity  of 
the  body ;  nor  can  there  be  the  least  doubt  that  a  similarly 
lacunar  condition  of  the  circulation  exists  in  those  lower 
adult  CruBtiicea,  the  transparency  of  which  allows  of  their 
examination  with  the  requisite  powers  of  the  microscope. 
The  probability  is  that  a  similar  state  of  things  obtains  in 
the  vascular  system  of  all  other  Crustacea,  and  that,  after 
undergoing  a  greater  or  less  amount  of  subdivision,  the 
arterial  vessels,  or  their  capillary  continuations,,  cease  to 
exist,  the  blood  then  making  its  way  into  lacunn  between 
the  organs,  and  into  the  general  perivisceral  cavity;  and, 
as  in  most  MoUttsca,  ceasing  to  be  contained  in  vessels  with 
distinct  walls. 

The  blood  thus  poured  out,  eventually  makes  its  way  into 
irregular  sinuses  or  reservoirs,  the  chief  of  which,  lodged  in 
the  sternal  canal,  communicates  by  lateral  channels  with 
others  which  lie  above  the  bases  of  the  thoracic  appen- 
dages, and  from  which  the  afferent  branchial  canals  pass 
into  the  stems  of  the  branchisB,  on  the  exterior  faces  of  which 
they  ascend,  giving  off  branches  to  the  lateral  filaments. 
Corresponding  canals  return  the  blood  from  these  filaments 
to  the  efferent  branchial  canals,  which  run  down  the  inner 
side  of  the  branchial  stems,  and  unite  above  the  bases  of 
the  limbs  into  six  trunks,  which  ascend  beneath  the  epimera 
and  open  into  the  sides  of  the  pericardial  sinus.  The  floor 
of  this  sinus  is  formed  by  a  continuous  membrane,  which 
appears  to  shut  it  off  completely  from  the  general  visceral 
cavity  (at  least  it  retains  air  or  fluid  thrown  into  it),  and,  if 
this  be  really  the  case,  it  may  be  said  to  be  functionally  a 
branchial  auricle,  containing  pure  unmixed  aerated  blood. 

The  branchise  are  eighteen  in  number  upon  each  side,  and 
are  attached  from  the  eighth  to  the  fourteenth  somites 
inclusively.    Six  of  these  branchise  are  attached  to  thft 


328       THE  ANATOMY  OF  imTEBTEBRATBD  AVIMALS. 

epipodites  of  the  eighth  to  the  thirteenth  somites,  and  difier 
very  considerablj  in  appearance  from  the  other  twelve. 
Each  epipodite  ia,  in  fact,  expanded  at  its  npper  extremitj 
into  a  broad,  bilobed  membrane,  which  is  folded  upon 
itself,  so  that  the  two  lobes  are  directed  posteriorly,  and 
receive  the  epipodite  of  the  next  limb  (Fig.  71,  K).  The 
membrane  of  the  lobes  is  obliquely  plaited,  so  that, 
doubtless,  they  subserve  respiration  to  a  certain  extent ;  but, 
in  addition,  the  anterior  edg^  of  the  epipodite  is  beset  with 
a  number  of  branchial  filaments,  similar  to  those  on  the 
other  branchis. 

The  latter  (Fig.  71,  M,/,  g)  are  simple  plumes,  consisting 
of  a  stem,  to  which  are  attached  many  delicate,  cylindrical 
filaments.  Two  of  these  plumes  are  attached  to  the  epimera 
and  coxo-epimeral  articular  membranes  of  the  ninth,  tenth, 
eleventh,  twelfth  and  thirteenth  somites.  They  increase  in 
size  posteriorly.  The  eighth  and  fourteenth  somites,  on 
the  contrary,  only  carry  one  plume.  A  tuft  of  long  byasus- 
like  filaments  is  attached  to  the  coxopodite  of  each  of  the 
last  six  thoracic  appendages  (Fig.  71,  F,  M). 

The  respiratory  organs  of  the  Crayfish,  not  being  pro- 
vided with  cilia,  require  some  special  arrangement  for  the 
renewal  of  the  water  with  which  they  are  in  contact. 
This  object  is  attained  principally  by  the  action  of  the 
scaphognathite,  which  lies  immediately  behind  the  anterior 
opening  of  the  branchial  chamber ;  and,  during  life,  is  inces- 
santly in  motion,  baling  out,  as  it  were,  the  water  which 
has  become  impure  through  the  anterior  opening,  and  thus 
compelling  the  flow  of  fresh  fluid  into  the  branchial  chamber 
through  its  posterior  and  inferior  opening,  constituted  by 
the  space  left  between  the  lower  edge  of  thebranchiostegite 
and  the  bases  of  the  limbs. 

The  nervous  system  of  Antaeus^  is  composed  of  thirteen 
principal  ganglionic  masses,  of  which  one,  cerebral,  lies  in 
the  head,  in  front  of  the  mouth  ,*  six,  thoracic,  are  situated 

*  For    the    histology   of  the      stnicrure  of  the  tissuee  of  the 
nervoiit  mtem,  tee  an  elaborate      Crayfish,  in  the  *  Arcliiv  fur  Ans- 
hj  Hacekel,  on  the  mlnate      tomie,'  1857. 


ASTACUS    FLUVIATILIS. 


329 


in  the  sternal  canal ;  and  six,  abdominal,  lie  in  the  median 
sternal  region  of  the  six  anterior  somites  of  the  abdomen. 

The  oerebral  ganglia  (Fig.  74,  b;  Fig.  75,  a)  give  o£f 
nerves  to  the  eyes  and  to  the  muscles  of  the  ophthalmic 
appendages;  to  the  antennnles  and  the  auditory  org^ans 
which  they  contain ;  to  the  antenn»  and  the  sae  of  the 
antennary  gland ;  to  the  carapace  in  front  of  the  cerrical 
suture;  and  finally  they  send  posteriorly  two  long  and 
stout  commissural  cords  to  the  anterior  thoracic  ganglionic 
mass.    These  commissures  are  connected  by  a  transrerse 

Fig.  75. 


Fig.  75. — Visceral  nerves  of  Attacu»,~-a,  Cerebral  ganglia,    b.  Com- 
missures, that  of  the  right  side  is  cut  and  turned  back.    c.  Trans- 
1^.^  verse  oord    uniting  them  behind  the  oesophagus,  (£.     «U  d,  d» 
^*r    Aj^gos  nerve.       h.  Ganglion.       t.  Lateral    branch    of  azygos, 
anmng   with    postero-lateral   nerve  g,     e.  Antero-lateral    nerve. 
/.  ICedio-lateraf  nerve,   k.  Hepatic  nerve.    P.  Pyloric.    C.  Cardiac 
portion  of  stomach. 

cord  immediately  behind  the  oesophagus  (Fig.  75,  c).  The 
size  and  form  of  the  anterior  thoracic  ganglion  would  lead 
to  a  suspicion  of  the  complex  nature  which  development 
shows  it  to  possess.  It  supplies  the  somites  and  their 
appendages  from  the  fourth  to  the  ninth  inclusively,  and 
sends  forwards  delicate  filaments  to  the  cesophagus. 

Posteriorly  it  is  connected  with  the  ganglionic  mass  of 
the  tenth  somite  by  two  commissures,  and  the  other  tho- 
racic ganglia  are  similarly  brought  into  communication,  the 
commissures  of  the  ultimate  and  penultimate  on^.^  >^vci'^ 


330       THE  ANATOMY  OF  INYBRTXBBATSD  ANIMALS. 

remarkable  for  their  brevity.  The  abdominal,  which  are 
much  smaller  than  the  thoracic  ganglia,  are,  with  the 
exception  of  the  last  two,  united  hj  single  cords,  which 
represent  coalesced  double  commissures.  Each  of  these 
ganglia  supplies  the  muscles  and  the  appendages  of  the 
somite  to  which  it  belongs,  and  the  posterior  abdominal 
ganglion  sends  brunches  into  the  telson. 

The  Crayfish  possesses  a  remarkably  well-developed 
system  of  visceral  or  stanuitogastric  nerves,  which  has  been 
the  subject  of  special  study  by  Brandt,  Milne-Edwards, 
Krohn  and  Schlemm,  each  of  whom  has  described  a  larger 
or  smaller  portion  of  the  system  with  accuracy,  but  has 
omitted  to  mention,  or  has  denied,  the  existence  of  some 
other  part.  Each  of  the  great  commissures  (Fig.  75.  b), 
as  it  passes  over  the  sides  of  the  oesophagus,  becomes 
slightly  swollen,  and  from  the  enlargement  four  nerves 
arise ;  one,  external,  passes  towards  the  mandibular  muscles ; 
a  second  postero-lateral  branch  (Fig.  75,  g)  runs  upwards 
and  backwards  to  the  inforo-lateral  regions  of  the  stomach, 
and  eventually  enters  into  the  composition  of  the  hepatic 
nerve  [k);  a  third  branch  (/)  turns  directly  inwards  and 
upwards,  and  unites  upon  the  oesophagus  with  its  feUow 
and  with  an  azygos  nerve  (d)  which  passes  up  in  the 
middle  line  of  the  anterior  face  of  the  oesophagus  and 
stomach,  and  enters  a  ganglion  placed  between  the  anterior 
gastric  muscles  (i^),  from  whence  a  lateral  branch  is  given 
off  on  each  side,  while  a  posterior  median  branch  (d) 
continues  the  direction  of  the  azygos  nerve.  Having 
reached  the  cardiac  ossicle,  this  nen-e  divides  into  two 
branches  ({),  each  of  which  passes  downwards  and  out- 
wards, unites  with  the  postero-lateral  nerve  of  its  side,  and 
thus  forms  the  hepatic  nerve  (k).  The  fourth  and  last,  or 
an tero- lateral  branch  (e)  descends  at  first  to  near  the  mouth, 
and  then  cui*ving  forwards,  ascends  to  unite  on  the 
anterior  face  of  the  oesophagus  with  the  anterior  con- 
tinuation of  the  azygos  nerve,  which  passes  forwards  and 
upwards  and  enters  the  cerebral  mass.  I  am  inclined  to 
think  that  this  part  of  the  azygos  nerve  forms  a  portion  of  a 


ASTACirS  PLirVIATILIg,  331 

of  neiTOus  filaments  which  pass  from  the  cerebral 
ckwards  to  the  lining  membrane  of  the  carapace, 
flection  of  these  fine  filaments  and  the  demonstra- 
ir  continuity  is  a  matter  of  no  ordinary  difficulty, 
estine  is  supplied  by  two  nerres  which  arise 
last  abdominal  ganglion,  and  unite  into  a  single 
•m  which  small  branches  are  given  off  back- 
[  two  principal  ones  forwards,  which  supply  the 
rt  of  the  intestine.  According  to  Brandt,  the 
■eceiye  branches  of  the  fourth,  fifth,  and  sixth 
mglia. 

J  certainly  known  organs  of  sense  in  AeAacnis 
«  and  the  auditory  organs.  The  eyes  are  seated 
emities  of  the  ophthahnic  peduncles,  the  integu- 
e  outer  extremity  of  which  becomes  translucent 
'orm  space,  and  constitutes  the  corneal  membrane. 
>rane  is  divided  into  a  great  number  of  minute 
•al  facets,  each  of  which  corresponds  with  the 
rystalline  cone.* 

»er  face  of  the  trihedral,  proximal,  and  largest 
e  antennule  presents  an  oval  space,  covered  by 
rush  of  complex  hairs  having  their  points  all 
iwards.  On  cutting  these  hairs  away  close 
>ases,  however,  it  is  seen  that  they  cover  an 
rider  above  than  .below,  and  about  one-sixteenth 
long.  The  hairs  are  attached  to  the  outer  lip  of 
ire,  and  some  are  directed  so  as  to  lie  within 
lip,  but  the  majority  cover  it.  A  good-sized 
ses  with  great  ease  into  this  aperture,  and  if 
and  outer  walls  of  the  basal  joint  of  the 
be  now  removed,  and  the  soft  parts  carefully 
way,  the  end  of  the  bristle  will  be  seen  to  have 
>  a  wide  delicate  sac  about  one-twelfth  of  an 
which  is  attached  by  a  narrower  neck  round  the 

r.  Newton's  careful  1875,  to  which  I  have  referred 

of  the  eye   of  the  above,  may  be  taken  as  a  guide 

The  Quarterly  Jour-  to  the  study  of  the  minute  struo- 

icopical  Science '  for  ture  of  the  eye  in  the  Cnb')6sA^«  > 


332       THE  ANATOMY  OV  IirTXRTXBBATSD  ASTDCALS. 

aperture,  the  lipe  of  which  are  continuooB  with  its  walli. 
The  sac  is  filled  with  minute  sandy  particleB,  sospeiided 
in  a  mucous,  dirtj-looking  fluid,  and  when  emptied  of  then 
contents  a  band,  consisting  of  several  lines  of  Yerj  fine 
hairs,  like  those  which  guard  the  mouth  of  the  sao,  but 
more  delicate,  is  seen  to  skirt  its  inner  contour.  The 
hairs,  projecting  inwards,  come  into  dose  contact  with  the 
solid  particles  suspended  in  the  mucous  fluid. 

A  nerve  may  be  traced  accompanying  the  antennnlarj 
nerve  to  the  sac,  and  appears  to  be  distributed  principally 
along  the  setigerous  band,  so  that  the  extremities  of  the 
nerve  fibrils  come  into  close  relation  with  the  bases  of  the 
hairs.  Some,  if  not  all,  of  the  sandy  particles  are  insoluble 
in  strong  acetic  acid,  and  would  appear  to  be  silicious.* 

Two  glandular  sacs  commonly  known  as  the  green  ^lancEf, 
which  were  formerly  regarded  as  the  auditory  organs, 
lie  in  the  cavity  of  ^the  head.  An  aperture  is  visible  on 
the  inner  or  oral  side  of  a  conical  prominence,  upon 
the  inferior  portion  of  the  coxal  joint  of  the  antenna.  A 
bristle  passed  into  this  aperture  enters  a  larg^  but  very 
delicate  and  transparent  sac,  filled  with  a  clear  fluid, 
which  is  usually  conspicuous  on  each  side  of  the  anterior 
end  of  the  stomach,  when  the  carapace  is  carefully 
removed.  A  nerve  which  comes  off  from  the  cerebral 
mass  close  to  the  antennary  nerve,  passes  to  the  neck  of 
this  vesicle,  and  is  distributed  over  its  surface  between  the 
outer  and  inner  membranes,  of  which  it  is  composed. 
Inferiorly  the  vesicle  rests  upon  a  large  greenish  ap- 
parently glandular  mass,  but  is  directly  connected  with 
the  latter  only  at  two  points,  firstly  by  a  vascular  cord, 
which  passes  to  the  central,  and  usually  more  yellow 
portion  of  the  gland,  and  secondly  by  a  short  neck-like 
continuation  of  the  sac  itself,  which  is  attached  over  a 
small  circular  space,  midway  between  the  centre  and  the 
periphery  of    the    gland,  and    opens    into  the    circular 

*  See  for  a  fall  account  of  the  Hcnsen's  '  Studien  uber  dai 
Bniaate  structure  of  the  auditory  Gehororgan  der  Decapoden,* 
oigaiif  in  ,the  higher  Cruiiacea,       1863. 


A8TAOI78  rLITYIATILIS.  S33 

principal  duot  of  the  gland.  There  is,  therefore,  a  free 
commnnication  between  the  cayitj  of  the  gland  and  the 
exterior  by  means  of  the  sao,  which  is,  in  this  respect, 
simply  a  dilated  duct.  A  section  of  the  gland  shows  it  to 
be  composed  of  two  substances,  a  central  and  a  cortical. 
The  latter  is  composed  of  minute  csca,  fiUed  with  a 
homogeneous  gelatinous  matter,  containing  many  large 
nadei ;  the  former  is  trayersed  in  all  directions  by  large 
canals,  so  as  to  have  a  spongy  appearance.  The  ccBca 
open  into  the  ultimate  ramifications  of  the  canals,  and  the 
spongy,  lung-like  texture  of  the  central  mass  seems  to  arise 
merely  from  the  very  free  anastomosis  of  their  larger 
brandies,  which  eyentually  enter  the  circular  canal  which 
communicates  with  the  yesicle. 

There  is  little  in  these  structural  features  to  suggest  an 
organ  of  special  sensation,  but  much  to  show  that  the 
green  mass  is  a  secreting  organ,  and  that  the  vesicle  acts 
(whatever  other  purposes  it  nmy  subserve)  as  its  duct. 
In  all  probability  the  green  gland  is  an  organ  of  the  same 
nature  as  the  shell  gland  of  the  Entomodraoa. 

Leydig  has  attributed  an  olfactory  function  to  certain 
groups  of  delicate  eetsB  which  occur  on  the  joints  of  the 
outer  division  of  the  antennule  of  the  Crayfish. 

The  most  remarkable  part  of  the  muscular  system  of  the 
Crayfish  is  the  great  extensor  muscle  of  the  abdomen, 
a  complex  mass  of  fibres  which  is  attached  in  part  to  the 
endophragms  of  the  thorax  in  front,  and,  behind,  to  the 
sterna  of  the  abdominal  somites,  a  large  part  of  the  cavity 
of  which  it  occupies.* 

The  essential  parts  of  the  reproductive  organs  in  the  male 
and  female  Astaeus  are  very  similar  to  one  another  in  f orm^ 
both  ovarium  and  testis  having  the  figure  of  a  trilobed 
gland,  situated  immediately  behind  the  stomach,  and  below 
the  heart.    Two  of  the  lobes  are  applied  together,  and  pass 

*  For    details,    see    Suckow,  Lobster  at  length  In  the  *Hif- 

« AnatomlBch-Pl^siologische  Un-  toire    natuielle   des   Cnulaces,' 

tersacbongen.'     Milne-£dwards  torn.  i. 
hat  deseribed  the  mnsclet  of  the 


334       THE  ANATOMY  OF  IKYSBTEBIIATSD  ANIMALS. 

forwards;  the  other  lobe  is  directed  in  the  middle  line 
backwards.  The  ducts  take  their  origin,  one  on  each  side,  at 
the  junction  of  each  antero-lateral  with  the  posterior  lobe. 

In  minute  structure,  however,  the  two  organs  differ  widely. 
Each  lobe  of  the  testis  is  composed  of  a  number  of  small 
cteca,  in  which  the  spermatozoa  are  developed,  and  which 
open  into  a  central  duct.  The  ovarium,  on  the  other  hand, 
is  essentially  a  wide  sac,  produced  into  three  large  OBca, 
each  of  which  corresponds  with  a  lobe;  and  the  ova  are 
developed  in  the  epithelial  lining  of  the  sac.  The  efferent 
ducts,  again,  have  little  resemblance,  the  oviducts  being 
short,  wide  tubes  which  open  on  the  coxopodites  of  the 
antepenultimate  thoracic  appendages,  while  the  vasa  defe- 
rentia  are  canals  as  long  as  the  body,  at  first  veiy  narrow, 
but  afterwards  widening,  which  lie  coiled  up  on  either  side 
of  the  posterior  part  of  the  thoracic  cavity,  where  their 
white  contents  make  them  very  conspicuous  (Fig.  74, 4^'). 
Eventually,  they  open  on  the  coxopodites  of  the  posterior 
thoracic  appendages. 

The  spermatozoa,  like  those  of  many  other  Cru&Uteea, 
are  motionless,  and  have  the  form  of  cells,  provided  with  a 
nucleus  and  produced  into  several  delicate  radiating  pro- 
cesses. They  are  united  in  their  course  down  the  vas 
deferens  into  cylindrical  masses,  which  becoming  invested 
by  a  fine  membranous  coat,  probably  secreted  by  the  walls 
of  that  duct,  constitute  the  spermatophoree,  which  maj  not 
unfrequently  be  found  adhering  to  different  parts  of  the 
body,  not  only  of  female  but  of  male  Crayfish. 

The  ova  are  fecundated  while  still  within  the  parent; 
they  become  surrounded  in  their  passage  down  the  oviduct, 
by  a  coat,  corresponding  with  that  of  the  spermatophore, 
which  is  produced  into  a  pedicle,  the  extremity  of  which 
becomes  attached  to  one  or  other  of  the  abdominal  appen- 
dages. Great  numbers  of  ova,  attached  in  this  way,  may 
be  observed  during  the  breeding-season,  within  the  incuba- 
tory chamber  formed  by  the  flexure  of  the  abdomen  upon 
itBdf;  and  it  is  in  this  cavity  that  the  •embryos  pan 
through  the  whole  of  ih&x  f  ostal  existence. 


THB  DEYELOPMBNT  OF  A8TACUS.  835 

The  deyelopment  of  the  Orayfish  has  been  the  subject  of 
one  of  the  most  beautiful  of  tiie  many  admirable  memoirs 
on  development,  for  which  we  are  indebted  to  the  genius 
and  patience  of  Bathke.*  After  fecundation  a  blastoderm 
arises  upon  the  surface  of  the  yelk,  and  gradually  extending 
over  the  whole  yelk,  becomes  thickened  at  one  part,  so 
as  to  form  an  oval  germinal  disk,  with  a  central  depres- 
sion. 

This  disk  next  becomes  widened  and  bilobed  at  its  anterior 
extremity,  the  lobes  being  identical  with  the  prooephalic 
lobes,  to  be  hereafter  described  in  the  embryo  of  Mysis, 
The  edges  of  the  disk  are  raised  into  a  fold,  and  within 
the  fold  a  papilla,  the  rudiment  of  the  abdomen,  and  of 
the  greater  part,  if  not  of  the  whole  of  the  thorax,  makes 
its  appearance,  while,  anteriorly,  three  pairs  of  transverse 
elevations  constitute  the  rudiments  of  the  antennules, 
the  antennae,  and  the  mandibles.  The  labrum  arises  as 
a  median  papilla,  situated  at  first  between  the  antennules. 
The  ocular  peduncles  are  next  developed  in  front  of  the 
antennules  as  ridges,  which  only  subsequently  become  free 
processes. 

The  thoracico-abdominal  process  lengthens,  and  the  anal 
aperture  makes  its  appearance.  It  is  to  be  remarked,  that 
the  anus  is  at  first  situated  on  the  dorsal  side  of  the  ex- 
tremity of  the  abdomen,  and  that  there  is  no  telson.  This 
is  developed  only  at  a  much  later  period  from  the  dorsum 
of  the  end  of  the  abdomen ;  and,  by  its  outgrowth,  forces 
the  anus  to  the  ventral  side  of  the  body. 

In  the  meanwhile,  the  oral  aperture  is  developed  behind 
the  labrum,  which  moves  backwards;  while  the  maxiUsB, 
maxiUipedes  and  ambulatory  feet  appear  in  succession  as 
elevations  or  ridges  of  the  substance  of  the  embryo,  which 
are,  at  first,  all  alike,  and  gradually  become  speciidised  into 
their  ultimate  forms. 

*  *Ueber    die    Bildang     and  Brochet   de   la    Perche   et    de 

Entwiokelimg  des  Flosskrebses,'  I'EcrevieM,*  1862 ;   and  the   ao- 

Bd.    29.     See  also  LerebouUet,  countof  Bobretaky'sretearchesin 

*  Beeherehei  d'enibr>ologie  com-  Hofmann  and  Sohwalbe, '  Jahret- 

pai^  for  le  d^veloppement  da  bericht' for  1873  0^7&)* 


336       THB  AHATOMT  OF  INYEBTBBBATBD  AHIICALS. 

When  these  appendages  first  appear,  the  maTillm  and 
first  pair  of  maxillipedes  are  attached  to  the  embiyo  in 
front   of   the   thoracico-abdominal   process,    the    seoond 
maxillipedes   lie  in  the   angle   between   them,  and   the 
third  maxillipedes  and  following  appendages  are  attached 
to  the  sternal  surface  of  the  thoracico-abdominal  proceBi 
itself ;   and,  as  this  process  is  at  first  bent  forwards  upon 
the  rest  of   the  germ,  it  follows    that  the   appendages 
attached  to  it  look  upwards,  while  those  attached  to  the 
anterior  part  of  the  embryo  look  downwards.    As  develop- 
ment proceeds,  however,  the  embryo  gradually  straightens 
itself;  more  and  more  of  the  anterior  part  of  tiie  thoracico- 
abdominal  process  becoming  continuous  in  direction  with 
the  anterior  part  of  the  embryo ;  until,  at  length,  the  whole 
of  the  cephalo-thoracic  portion  forms  a  convex  surface, 
parallel  with  the  vitellary  membrane,  only  the  abdomen 
remaining  bent  upon   the  ccphalo-thorax.     The   middle 
portion  of  the  carapace  is  formed  by  the  continuous  calci- 
fication of  the  dorsal  walls  of  the  cephalo-thorax  of  the 
embryo.    Its  pleura  are  developed  as  two  distinct  folds,  one 
of  which,  the  rudiment  of  the  branchiostegite,  encircles  the 
embryo  posterioriy,  and  extends  forwards  on  each  side  as  far 
as  the  mandibles;  while  the  other,  the  rudiment  of  the 
rostrum,  and  anterior  cephalic    pleura,  is   developed   in 
front  of  the  eyes,  and  extends  on  each  side  to  meet  the 
former.    Rathke^s  clear  account  of  this  matter  is  in  perfect 
accordance  with  what  I  have  observed  in  Mysis,  and  shows 
conclusively  that  the  carapace  is  not  developed  from  any 
one  or  two  somites   in  particular^  but  that   its    teif^ 
portion  corresponds  with,  and  is  formed  by,  the  terga  of 
all  the  cephalo-thoracic  somites,  while  the  branchiostegites 
and   rostrum  are    developments  of  the  lateral    portions 
of   all  these   somites;    in    fact,    represent   their    pleura, 
which,    like   the   terga,    are    connate   and   continuously 
calcified. 

The  appendages  are  thus,  at  first,  similar  to  one  another, 
and  each  consists  of  a  ridge  which  eventually  takes  the  form 
of  a  plate^  free  at  the  outer  end.   This  plate,  in  ^all  the 


THB  DBTBLOPMBHT  OV  A8TA0U8.  337 

members,  except  the  ophthalmic  peduncles  and  the  man* 
dibles,  then  becomes  bilobed  externally,  the  inner  lobe  re< 
presenting  the  endopodite,  while  the  outer  is  the  represent 
tative  of  the  exopodite  and  epipodite.  The  two  latter, 
when  they  are  independently  developed,  become  separated 
by  the  division  of  the  outer  lobe.  The  gills  arise  partly  as 
ontg^wths  from  the  epipodites,  partly  as  distinct  processes 
from  the  parts  to  which  they  are  eyentually  attached.  The 
division  of  the  limbs  into  articulations  takes  place  from 
their  distal  towards  their  proximal  ends.  The  heart  appears 
late,  at  the  posterior  extremity  of  the  cephalo-thorax,  and 
therefore  behind  the  yelk  sac. 

The  nervous  system  of  the  post-oral  portion  of  the  ce- 
phalo-thorax consists  at  first  of  eleven  pairs  of  ganglia, 
corresponding  with  the  mandibles,  maxilla,  maxillipedes, 
and  ambulatory  legs.  The  six  anterior  post-oral  ganglia 
of  each  side  soon  coalesce  in  pairs,  so  as  to  form  as  many 
single  ganglia ;  and  of  these  the  four  anterior,  namely,  the 
mandibular,  the  two  maxillary,  and  the  first  maxillipedary 
ganglia,  unite  into  a  single  mass ;  the  two  hinder  ganglia, 
that  is  to  say,  those  of  the  second  maxillipedary  somite, 
next  coalesce  in  the  same  way,  and  it  is  only  subsequently 
that  the  two  masses  thus  formed  become  fused  into  the 
single  anterior  post-oral  ganglion  of  the  adult.  The  other 
ganglia  not  only  remain  separate,  but  become  wider  apart 
with  advancing  age.  A  ridge  on  each  side  of  the  cesophagus 
at  first  represents  the  cerebral  ganglion  and  the  com- 
missural cords,  the  latter  being  developed  out  of  the  pos- 
terior part  of  the  ridge,  and  the  former  from  its  anterior 
portion.  The  cerebral  g^anglia  are  at  first  two  on  each  side, 
but  the  posterior,  whence  the  nerves  to  the  antennary 
organs  proceed,  is  much  larger  than  the  other,  and  would 
appear  to  represent  two  ganglia.  The  endostemites  arise 
as  processes  from  each  of  the  eight  posterior  cephalo- 
thoracic  sterna,  which  eventually  arch  over  the  ganglionic 
cord,  and  unite  with  one  another. 

The  alimentary  canal  is  produced  by  the  gpradual  dif- 
ferentiation and  demarcation  of  the  sternal  part  of  the 


338       THE  ANATOMY  OT  nTTSBTBBItATKD  AVDCALS. 

hypoblast,  which  invests  the  whole  yelk,  from  the  tergal 
part,  which  becomes  the  yelk  sac.* 

After  the  liyer,  genitalia,  and  antennary  glands  axe 
deyeloped,  the  yelk  sac  eventnally  becomes  rednced  to 
a  small  c»cal  diverticalum,  situated  at  the  pyloric  end 
of  the  stomach.  The  genital  dncts  in  both  males  and 
females  are  originally  diyerticnla  from  the  corresponding 
regions  of  the  genital  glands;  their  external  apertures 
and  the  copnlatory  appendages  of  the  first  abdominal 
somites  in  the  male  are  not  deYel<^>ed  nntil  some  time 
after  birth. 

The  modifications  of  stmcture  observable  within  the 
limits  of  the  PodopMhalmia  are  exceedingly  interesting. 

Excluding,  for  the  present,  the  SquiUidcR,  the  gronp  ii 
divisible  on  clear  morphological  gronnds  into  the  following 
subdivisions: — 1.  The Bfuchyvra ;  2.  The Anomwra;  3.  The 
Mctcrura ;  4.  The  Schizopoda. 

The  morphological  relations  of  the  Macrwra  are  nearly 
such  as  are  indicated  by  their  position  in  this  series ;  and 
Astaeus,  as  a  central  genus  of  the  central  group,  thus  becomes 
a  sort  of  natural  centre  for  the  whole  of  the  Podophihalmiia, 
whence  we  may  trace  a  gradual  series  of  modifications,  lead- 
ing on  the  one  hand  to  the  SchiMopoda,  with  their  large 
abdomen  and  small  cephalo-thorax ;  and  on  the  other  to  the 
Brctchyura,  with  their  rudimentary  abdomen  and  comjMura- 
tively  enormous  cephalo-thorax. 

In  all  the  Mticrura,  the  branchiae  are  numerous,  and  are 
covered  by  the  branchiostegites.  The  abdomen  is  large, 
and  is  used  as  a  locomotive  organ,  the  appendages  of  its 
sixth  somite  being  well  developed.  The  thoracic  ganglia 
usually  form  an  elongated  chain,  and  the  external  maxilli- 
pedes  never  form  broad  opennilar  plates  over  the  other  jaws. 

*  A ccording  to  Bobretsky  (/.c.)  encrottches  upon  the  vitellos,  nntH 

there  \s  no  proper  velk-sac,  the  the  latter  is  all  absorbed.    The 

Btmctnre  lo  termed  by  Bathke  hypoblattic  sao  is  converted  into 

beins    the   saccular    hypoblast,  the  liver  and  the  intestine.    The 

whion  Is  formed  by  invagination  stomach  arises  independently  by 

of  tbs  primitive  bkttodenn  and  invagination  of  the  epiblast. 


■■4 


THB  PODOPHTHALMIA.  339 

In  some  of  the  lower  Macrura  {Peneus,  PctatpJuBo),  the  exo- 
I>odite  persists  as  an  appendage  at  the  base  of  the  thoracic 
limbs ;  and  in  two  genera,  Sergeties  and  Acetes,  the  posterior 
thoracic  members  become  rudimentary  or  even  entirely 
abortiye,  though  the  abdominal  appendages  remain. 

In  the  higher  Maerura,  snch  as  Palinurus,  the  nervous 
system  exhibits  a  greater  degree  of  concentration,  the 
thoracic  ganglia  constituting  an  elongated  oral  mass ;  and 
it  is  in  this  genus  and  its  allies  that  the  head  and  its  appen* 
dages  exhibit  modifications,  which  prepare  ua  for  those 
which  are  presented  by  the  BraehyiMra.    In  this  respect  the 
PaUnwnu  vulgaris  (Bock  Lobster,  Sea  Crayfish,  or  Spiny 
Lobster)  is  particularly  worthy  of  attention.    The  rostrum 
is  rudimentary  and  represented  by  a  mere  spine,  leaving 
the  anterior  cephalic  somites  uncoyered.     The  cephalic 
flexure  is  so  strong  as  to  throw  the  ophthalmic  sternum, 
which  is  yery  wide,  completely  to  the  top  of  the  head. 
The  basal  joints   of   the    antennsB,    or    coxocerites,    are 
enormous,  fixed  to  the  surrounding  parts,  and  united  by 
their  anterior  extremities  in  the  middle  line  below.    Supe- 
riorly, they  seemed  to  have  coalesced  with  the  antennulary 
sternum,  so  as  to  form  a  projecting  wedge-shaped  mass, 
which  separates  the  antennules  from  the  ophthalmic  ster- 
num, and  causes  them  to  appear,  at  first,  as  if.  they  were 
inferior  to  the  antennsB.      In  this  genus,  the  basicerite, 
ischiocerite,  and  merocerite  are  much  thicker  and  stronger 
than  the  corresponding  joints  of  any  of  the  other  appen- 
dages ;  and  in  the  closely  allied  ScyUarus,  the  facial  iiegion 
of  which  is,  on  the  whole,  similarly  constructed,  these  joints 
become  extremely  expanded  and  flattened,  and  are  succeeded 
by  no  procerite.  In  these  genera  the  scaphocerite,  or  squame, 
usually  attached  to  the  base  of  the  antenna,  is  absent; 
and,  in  ScyUaruSf  there  is  another  approximation  to  Brachy- 
uran  structure  in  the  existence  of  distinct  orbits,  formed 
by  a  lobe  of  the  carapace,  which  descends  on  the  inner 
Bide  of  the   ocular   peduncle,   to  meet  t^e  base  of  the 
antenna.    No  median  septum  is  formed  by  the  rostrum, 
however,  nor  are  the  antennules  capable  of  beinf^  lc&dkfidL 

Li 


340       THE  ANATOMY  OV  INYBBTBBItATBD  AKIMkLS. 

back  into  distinct  chambers  in  any  Macmran  at  present 
known. 

The  Anomura  are  so  completely  intermediate  in  stractare 
between  the  Macrura  and  the  Brciehywra,  that  they  need 
not  be  specially  noticed,  except  to  draw  attention  to  the 
singular  deviation  from  the  ordinary  habits  and  form  of 
the  higher  Crustaceans,  presented  by  the  Pciguridct,  or 
Hermit  Crabs,  so  common  on  all  coasts.  Essentially  Ma- 
cmran in  their  organisation,  these  Crtutacea  are  distin- 
guished from  all  true  Mcierura  by  the  uncalcified  and  soft 
condition  of  the  integ^ument  of  their  unsymmetrical  abdo- 
men, the  appendages  of  which  are  for  the  most  part 
abortiye,  those  of  the  sixth  somite  being  modified  so  as  to 
serve  as  claspers.  It  is  by  means  of  these  that  the  Hermit 
Crab  retains  firm  hold  of  the  columella  of  the  empty 
gasteropod  shell  into  which  it  is  his  habit  to  thrust  his 
unprotected  abdomen,  and  covering  over  his  retracted  body 
with  the  enlarged  chela,  which  takes  the  place  of  an 
operculum,  resists  all  attempts  at  forcible  extraction. 

The  internal  structure  of  the  Brcuihywa  is,  on  the  whole, 
similar  to  that  of  the  McLcrwra ;  but  the  thoracic  ganglia 
have  coalesced  to  a  much  greater  extent  than  in  Aataeug, 
forming  a  single  rounded  mass.  The  branchis  are  few, 
never  exceeding  nine  on  each  side,  and  sometimes  not 
more  than  seven.  The  branchiostegite  fits  closely  down 
upon  the  bases  of  the  four  posterior  pairs  of  thoracic 
limbs,  and  sometimes  encloses  a  space  which  is  very  large 
in  proportion  to  the  branchiae.  This  is  particularly  the  case 
in  the  Land  Crabs  (Oecareintut),  where  the  spacious  branchial 
chamber  is  lined  by  a  thick  and  vascular  membrane,  which, 
in  these  almost  wholly  terrestrial  CrugUicea,  either  takes  on 
to  some  extent  the  respiratory  function,  or  serves  to  keep 
the  air  within  the  branchial  chamber  saturated  with  mois- 
ture. 

The  abdomen  in  the  Braehyura  is  comparatively  small ; 
its  sixth  somite  possesses  no  appendages ;  and  the  othefs, 
if  they  exist  at  all,  subserve  only  a  sexual  purpose,  the  two 
Miterior  pairs   commonly  forming  accessory  copnlatovy 


k> : 


THB  BSACHYUIU..  841 

organs  in  the  male ;  while,  in  the  female,  so  many  of  these 
appendages  as  remain  giye  attachment  to  the  ova,  which  are 
carried  about  nntil  hatched,  between  the  thorax  and  the 
abdomen,  which  is  bent  up  against  it.  The  female  Bra4:hyura 
also  possess  a  spermatheca  attached  to  each  oviduct,  which 
is  absent  in  the  Macrura ;  and,  in  this  sex,  the  abdomen  is 
larger  and  broader  than  in  the  males.  In  accordance  with 
the  rudimentary  condition  of  this  part  of  the  body,  the 
abdominal  ganglia  are  represented  only  by  a  cord,  which 
proceeds  from  the  posterior  part  of  the  great  thoracic  mass. 
It  is  in  the  construction  of  their  skeleton,  however,  that 
the  BfuchyiMra  present  the  most  interesting  deviations  from 
the  Macrura,  Thus,  if  we  select  the  common  Shore-crab, 
Carcintts  moetuu  (Fig.  76),  as  a  typical  example  of  a  Brachy- 
uran,  we  find  that  the  carapace  is  a  wide  shield,  broader 
than  long,  having  a  somewhat  pentagonal  shape,  and  bent 
sharply  inwards  at  the  sides,  instead  of  taking  an  even  sweep 
down  to  the  base  of  the  l^s.  It  is  in  such  close  contact 
with  the  four  posterior  pairs  of  thoracic  limbs,  as  to 
leave  no  passage  or  aperture  such  as  exists  in  Astacua,  the 
only  inlet  for  the  water  required  for  respiration  being 
placed  above  the  basal  joints  of  the  chelate  anterior  ambu- 
latory limbs.  The  edges  of  the  carapace  pass  completely 
in  front  of  the  bases  of  the  limbs,  and  then  turn  suddenly 
forwards,  parallel  with  one  another  and  with  the  axis  of 
the  body,  as  the  pterygostomial  plates  of  Milne-Edwards, 
to  join  the  antennary  sternum,  which  is  very  wide,  but 
short  from  before  backwards.  The  space  included  be- 
tween the  edges  of  the  pterygostomial  plates  and  the 
antennaiy  sternum  is  the  "  cadre  buccal,"  or  peristome ;  the 
antennary  sternum  itself  receives,  as  in  the  Astacus,  the 
specific  appellation  of  epistoma ;  and  the  plate  which  stretches 
backwards  and  supports  the  labrum,  within  its  posterior 
forked  boundary,  is  the  endostoma. 

The  middle  of  the  dorsal  surface  of  the  carapace  is  marked 
somewhat  nearer  its  posterior  than  its  anterior  boundary  by 
a  short  transverse  depression,  which  is  continued  on  each 
side  forwards  and  outwards,  and  then  curves  directly  ouV 


342       THE  ANATOMY  OT  IirTSBTBBItATBD  AHIXAIiS. 

irards  to  the  edge  of  the  carapace  (Fig.  76,  e  t).    Further 
than  this  I  cannot  ti'ace  this  homologae  of  the  cervical 

Fig.  76. 


^ 


Fig.  76.— Of  the  two  upper  figures  the  left  represents  the  doml  lurliMe 
of  the  cftrapAoeof  ComniMniflnia*.  /.  Rostmm.  o.  OrUt.  c.  «.  Ger- 
Tical  groove.  ^.  Epigastric  lobe.  g\  Protogastric.  ^.  MesogM- 
tric  g*,  Hypogmstric.  g^,  Urogastric.  c  c^  Anterior  and  posterior 
cardiac,  h.  hepatic,  ft*,  6*,  6*.  Epibranchial,  mesobranchial,  md 
metabranchiftl  iobes.  The  lower  figure  represents  a  Tentrai  Tiew  of 
the  anterior  half  of  the  same  carapace,  a.  Rostral  septom. 
h.  Antennary  sternum,  c.  Suture  between  these,  d,  SunrmcaUaiy 
lobe.  €.  Internal  suborbitar  lobe.  /.  Antenna,  g.  Articular  cavi^ 
for  the  ophthalmic  peduncle,  h.  The  same  for  the  antennule.  o.  Or- 
bit. jA.  Subhepatic  region,  ep.  Anterior  pleural  region.  The  rigfat- 
haad  upper  ^gure  gives  a  tide  view  of  the  carapace  of  fifaao- 
rAyadka*  />4atoiyt»w,  the  common  **  spider-crab.*'  o.  Orbit. /.>| 
/^Boatrom.    aJU  Antennule.    of.  Antenna.    9.  Epistoma. 

groove  of  Adacm:    Elevations  and  depreanons  upon  the 
of  the  oara>paoe  in  front  of  the  oorvioel  groove, 


THB  BBAOHTCnUL  343 

which,  as  in  Agtaeui,  is  oomposed  of  the  ooxmate  terga  of 
the  six  cephalic  somites,  mark  it  out  into  certain  definite 
regions  of  considerable  systematic  importance.  An  irregu- 
lar transrerse  depression,  crossing  the  carapace  near  the 
anterior  margin,  bounds  an  anterior  or  facial  region, 
divided  into  a  middle  fironkd  lobe  (/),  and  lateral  erbiUU 
lobes  (o),  from  a  posterior,  much  larger,  gastro-hepatic  area, 
diyided  into  small  lateral  hepatic  lobes  (h),  and  a  large 
complex  gadrie  lobe  {g\  g*,  etc.)*  The  latter  is  again 
subdiyided  into  two  ^pigcutne  lobes  (g^),  two  pratoguuirie 
lobes  (9*),  a  median  meeogasbrio  lobe  (^),  two  meUigatstrio 
lobes  (^),  and  two  wrogagtrie  lobes  (^),  making  altogether 
nine  subordinate  diviaions.  The  gastric  lobes  correspond 
in  a  general  way  to  the  stomach;  the  hepatic  lobes,  to  a 
portion  of  the  Urer.  The  region  behind  the  cervical  suture 
consists  of  the  connate  terga  of  the  eight  thoracic  somites ; 
it  is  divided  by  two  strong  longitudinal  grooves,  the  branchio' 
cardiac  grooves,  into  a  middle  region,  corresponding  with 
the  heart,  and  two  lateral  regions,  forming  the  roof  of 
the  branchial  chamber.  A  transverse  depression  divides 
the  middle  region  into  an  anterior  and  a  posterior  cardiac 
lobe,  while  the  branchial  region  is  subdivided  into  epu 
branchial  (b^),  meiobranchicU  (6"),  and  metdbranchial  (l^) 
lobes. 

On  turning  to  the  inflected  inferior  portion  of  the  carapace, 
a  sutural  line  or  groove  is  seen  running  from  the  epistoma, 
outwards  and  backwards,  very  nearly  reaching  the  outer 
edge  of  the  carapace,  opposite  its  external  angle,  and  then 
sweeping  backwards  parallel  with,  and  but  little  distant 
from,  its  postero-lateral  boundary,  until  it  cuts  its  posterior 
edge.  The  portion  of  the  carapace  internal  to  this  sutural 
line,  is  called  by  Milne-Edwards  the  inferior  branchio- 
gtegiU,  and  is  considered  by  him  to  be  composed  of  an 
anterior  {e  p)  and  posterior  ^pimeral  piece,  corresponding 
with  the  tub-hepatic  (« h)  and  sub-branchial  regions  of  the 
surface  of  the  carapace  between  the  suture  and  the  line  of 
inflection.  I  cannot  regard  these  paxts,  however,  as  having 
any  relation  with  the  true  epimera.    The  sutnxe,  or  t^^Jbeit 


Mi     thj:  anatomy  of  invertebrated  animals. 

groove,  seems  rather  to  correspond  with  that  which  markB 
off  the  pleuron  from  the  rest  of  the  somite  in  AtiaeuB, 

The  anterior  cephalic  somitee  in  Careinus  have  undergone 
some  singular  modifications,  whereby  their  true  relations 
are  g^reatly  obscured.  The  broad  trilobed  plate  (Fig.  76,/) 
correq)onds  with  the  elongated  rostrom  of  AttaoiM;  is< 
f eriorly  it  is  produced  in  the  median  line  into  a  strong 
ridge  or  septum,  the  lower  and  posterior  edge  of  which 
is  convex,  and  fits  closely  into  the  concavity  formed 
by  the  antennulary  and  ophthalmic  stema»  as  they  bend 
back  from  the  sternal  flexure.  This  rostral  aeptnm, 
therefore,  abuts  below  and  behind  on  the  epistoma,  and 
constitutes  a  sort  of  partition  (Fig.  76,  a),  by  which 
the  cavities  in  which  the  antennules  and  eyes  of  the 
two  sides  are  lodged,  are  completely  separated  from  one 
another.  The  lateral  portions  of  the  rostrum  form  a 
flattened  roof  over  the  inner  portions  of  these  cavitieB, 
which  contain  the  bases  of  the  ophthalmic  peduncles  and 
the  antennules ;  but  the  outer  angles  of  the  rostrum  are 
produced  downwards  (d),  to  form  the  w/pracUiary  lobe* 
The  outer  half  of  the  lateral  cavities  or  chambers  is  more 
excavated,  and  is  bounded  by  a  strong  pointed  process,  the 
external  orbitar  lobe,  which  is  divisible  into  a  eupra-orbiial 
and  avh-orbUal  portion.  The  latter  passes  gpradually  into 
a  strong  process  of  the  sub-hepatic  region,  called  the 
ifUemal  eub-orbiiar  lobe  (Fig.  76,  e);  this  turns  forwards 
and  upwards  towards  the  supraciliary  lobe,  which  it  ap- 
proaches, but  does  not  meet,  the  base  of  the  antenna 
being,  as  it  were,  wedged  between  the  two. 

The-  supraciliary,  external  orbitar,  and  internal  sab-oir- 
bitar  lobes,  and  the  ant^insB,  thus  together  circumscribe  a 
cavity  widely  open  in  front,  which  is  called  the  orbit, 
inasmuch  as  it  lodges  the  terminal  portion  of  the  opbthal- 
mic  peduncles,  with  the  eyes  which  they  support.  The 
proximal  portions  of  the  peduncles  pass  through  the 
oomparatively  narrow  opening  by  which  the  inner  and 
outer  chambers  communicate,  between  the  antenna  and 
Hie  sapmciliary  process,  jand  are  inserted  as  usual  into  th^ 


THB  BRLOHYJJRk.  345 

articular  oayities  on  each  side  of  the  opbihahnic  stemuin, 
which  is  narrow,  and  hardly  wider  than  the  septam.  It 
thus  comes  to  pass  that  the  eyes,  lodged  in  their  orbits, 
appear  to  be  altogether  external  to  the  antennules,  the 
enlarged  bases  of  which  hide  the  ophthahnic  pedoncles,  and 
appear  to  be  the  sole  contents  of  the  inner  division  of  the 
sub-frontal  chamber;  but  the  trae  position  of  the  eyes 
is  precisely  the  same  as  in  Astaeua,  that  is  to  say,  anterior 
and  superior  to  the  antennules.  Another  interesting 
peculiarity  about  the  facial  region  of  the  carapace  is 
that  the  basal  joints  of  the  antenna  have  coalesced  with 
the  sternum  of  the  antennary  somite,  and,  consequently, 
that  the  bases  of  the  antennse  are  immoTcable.  There  is 
no  yestige  of  a  scaphocerite,  and  the  aperture  of  the 
organ  which  answers  to  the  green  gland  of  AMtaeua, 
is  proTided  with  a  peculiar  moreable  plate,  provided  with 
a  projecting  internal  stem,  to  which  delicate  muscles  are 
attached  in  Carciwus,  It  is  this  structure  which  has  been 
compared  to  an  auditory  ossicle;  but,  as  in  Astaeua,  the 
auditory  sacs  are,  in  fact,  lodged  in  the  dilated  basal  joint 
of  the  antennule. 

A  cervical  fold,  lodging  the  scaphognathite,  occupies  the 
same  relative  position  as  in  Astticus,  and  marks  off  the 
cephalic  from  the  thoracic  region,  on  the  sides  of  the 
body.  The  thoi*acic  sterna  gradually  increase  in  breadth, 
and  the  posterior  ones  are  marked  externally  by  a  strong 
median,  longitudinal  depression,  answering  to  a  corre- 
sponding fold  on  the  inner  surface.  The  apodemal  cells  are 
well  formed,  but  the  sternal  canal,  so  largely  developed  in 
the  Macrura,  is  absent  in  this,  as  in  all  other  BrcLchi/wra. 

The  structure  of  the  appendages  is  essentially  the  same 
as  in  AHcums,  but  the  third  thoracic  appendage,  or  external 
maxillipede,  has  its  ischiopodite  and  meropodite  greatly  en- 
larged, 80  as  to  form  a  broad  plate,  which,  with  its  f^ow, 
covers  over  the  other  organs,  and  hence  receives  the  name 
of  the  ffntUhostegi^.  The  three  terminal  joints  of  the  limb 
remain  small,  and  constitute  a  palpiform  appendage — ^the 
endognaikal  piUp. 


346      THB  ANATOMY  OS*  DfTS&TBBItATSD  AHIKALS. 

In  some  of  the  lower  Maerura,  the  thoracic  limbs  are  pro- 
vided with  a  short  exopodite,  and  the  posterior  maxillipedeB 
become  indistinguishable  from  the  ordinary  thoracic  limbs. 
Such  forms  lead  us  naturally  to  the  SchiMpadOy  a  group 
the  name  of  which  is  deriyed  from  the  apparent  splitting  at 
the  limbs  produced  by  the  great  deyelopment  of  the 
exopodite,  which,  in  these  Crustacea,  is  as  large  as  the 
endopodite.  In  this  group,  again,  a  line  can  hardly  be 
drawn,  in  many  cases,  between  any  of  the  maxiUipedes 
and  the  thoracic  limbs,  the  anterior  pair  only  being 
somewhat  smaller  than  the  rest.  Hence  Thysawjpoda  is 
admitted,  by  Milne-Edwards,  to  have  eight  pairs  of  thoracic 
limbs  ('  Crustac^,'  ii.  464).  The  branchiae  in  the  SehiMopoda 
are  frequently  absent;  when  well  developed,  as  in  2%- 
aanopoda,  they  are  not  included  under  the  branchiostegite, 
but  hang  down  freely  from  the  bases  of  the  thoracic  limbs. 
In  Mysis,  the  only  representative  of  a  branchia  (if  it  be 
one  in  reality)  is  a  process  attached  to  the  first  thoracic  ap- 
pendage. CfffUhia  has  its  branchial  appendages  attached 
to  the  abdominal  members. 

In  Thyganopoda,  Mysia,  and  Cynthia,  the  general  struc- 
ture of  the  body  is  similar  to  that  of  the  Maerwra,  except 
that,  in  Mysis,  the  greater  number  of  the  abdominal  appen- 
dages are  rudimentary. 

In  Leueifer,  the  antennary  somite  is  produced  into  a  very 
long  and  narrow  peduncle,  which  supports  the  eyes,  on 
their  great  stalks,  the  antennules,  and  the  antennse,  at  its 
extremity,  separating  them  from  the  rest  of  the  cephalo- 
thorax,  which  is  covered  by  a  delicate  carapace,  bent  down 
at  the  sides.  The  anterior  thoracic  members  are  rudi- 
mentary, and  the  posterior  pair  is  absent.  The  heart 
is  short  and  rounded,  and  situated,  as  usual,  in  the  thorax. 

It  has  been  seen  that  in  Asta4>iut  fluviaHUs^  as  in 
Limulus  and  Daphnia,  the  embryo  slowly  and  gradually 
passes  into  the  form  of  the  adult  ,*  to  which  it  is  so  iniwilM* 
when  it  leaves  the  egg,  that  the  changes  of  the  young 
present  nothing  comparable  to  the  well-known  metamor- 
phoses of  Butterflies  and  Beetles. 


THB  BBACHTimA. 


S47 


But  most  Podophthahnia  rather  resemble  the  Copepoda 
and  the  majority  of  the  Eniomo$iraca,  in  the  fact  that  the 
joung,  when  they  leave  the  egg,  have  a  totally  diBHimilar 
form  to  that  of  the  parent,  and  only  acquire  the  adnlt 
condition  after  a  seriee  of  eodyses. 

The  obserrationB  of  Fritz  Miiller  *  have  shown  that  the 
yonng  of  a  species  of  Prawn  (Peneua)  undergo  a  metamor- 
phosis which  mns  parallel  with  that  of   the  Copepoda, 

Fig.  77. 


Fig.   77. — Peneus.^Ay   Nauplivs-atAge,    B,  Zocta  or  Copepod  stage. 
C,  Sehizopod-BtBifiB.    (After  Muller.) 

When  it  leaves  the  egg  (Fig.  77,  A),  the  young  Penetu  has  an 
oval,  unsegmented  body  with  a  single  frontal  eye,  a  large 
labrum  and  three  pairs  of  natatorial  appendages — ^it  is 
in  fact,  to  all  intents  and  purposes,  a  Navpliua.  The 
NiaupUuS'torm  next  developes  a  rounded  tergal  shield,  or 
carapace ;  the  first  and  second  pairs  of  appendages  remain- 
ing long,  become  the  antennules  and  the  antennse ;  while 
those  of  the  third  pair,  their  bases  enlarging  at  the  expense 

*  •Fiir  Darwin/ 1864. 


348      THE  AHATOMT  OF  INYXBTBB1U.TBD  ▲VOCALS. 

of  the  rest  of  the  appendage,  become  the  mandiUeB.  Four 
pairs  of  appendages  subsequently  appear  behind  the  man- 
dibles. The  hinder  three  pairs  are  bifurcated  and  beoome 
the  two  pairs  of  maxilltB  and  the  first  and  second  mazilli- 
pedes.  Behind  these  again  are  five  pairs  of  short  lamellar 
processes,  which  eyentoaUy  are  conyerted  into  the  rest  of  the 
thoracic  appendages.  The  six  somites  of  the  abdomen  an 
long  and  distinct,  and  the  last  ends  in  two  setose  prooesaei. 
Thej  are  at  first  without  appendages.  In  this  stage  (Fig. 
77,  B),  which  answers  to  the  so-called  ZocBO-torm  of  other 
Podophthalmia,  the  principal  locomotiye  organs  are  the 
antennsB  and  antennules,  and  the  resemblance  to  an  adult 
Copepod  is  so  striking  that  it  may  be  termed  the  Copepod 
stage.  Next,  the  antennsB,  diminishing  in  relation  to 
the  rest  of  the  body,  cease  to  be  the  principal  organs  of 
locomotion,  and  the  rapidly  elongating  abdomen  assumes 
that  function.  The  stalked  double  eyes  which  made  their 
appearance  in  the  Copepod  stage,  become  more  fully  dere- 
loped.  The  jointed  exopodite  of  the  antenna  is  replaced 
by  a  single  plate.  The  greatly  enlarged  thoracic  limbs  are 
provided  with  an  endopodite  and  an  exopodite,  as  in  the 
Sehizopoda,  the  branchisB  are  deyeloped  from  them,  and 
the  abdominal  appendages  make  their  appearance.  This 
may  be  termed  the  Schizopod  stage  (Fig.  77,  C).  Lastly, 
the  median  eye  yanishes,  the  exopodite  of  the  locomotiye 
thoracic  limbs  disappears,  and  the  larva  assumes  all  the 
characters  of  the  adult  Feneus. 

In  the  great  majority  of  the  Podophihalmia  the  embrjo 
undergoes  as  remarkable  a  metamorphosis  after  it  leaves 
the  egg.  This  fact  was  first  indicated  by  Siebold,  after- 
wards demonstrated  by  Yaughan  Thompson,  whose  obser* 
vations  have  been  confirmed  and  extended  by  many  more 
recent  observers,  notably  by  Spence  Bate*  and  Glau8.t 
But  the  stages  of  this  metamorphosis  differ  from  thoae 

*  <*On  the    Development    of  stracenlarven.**  (W&rzbiirg  *  |fs> 

Decapod  Crustacea."     (Philoao-  tumisHenBchafUiohe   Zeittohrifli' 

phical  Transactions,  1857.)  1861.) 

t  **  Zur  Kenntniss  der  Malako- 


TRI  DXTSLOPMBm  OT  TBI  PODOPHTHAUfU.     34d 

obaerred  in  Peneiu  in  the  apparent  absence  c^  the  first  or 
JVawpIitu  ooodition.  Fosoibly,  however,  this  is  represented 
1^  a  delicate  cnticulor  iavestmeiit  which  the  larva  throws 
off  soon  after  leaving  the  e^.  It  then  corresponds  with  the 
later  form  of  the  Copepod  stage  of  P«n«Ht,  and  is  termed  a 
Zomi.  The  Zoom  has  a  short  carapace,  of  t^i  provided  in 
the  median  frontal  and  dorsal  regions  with  long  spine-like 
prolongations.  There  is  a  median  simple  ej'e  between  the 
lateral  sessile  faceted  eyes,  a  pair  -of  antennnles,  a  pair 


Fig.  78. 


of  ant«iuiB9,  a  pair  of  mandibles,  and  two  pairs  of  masilln ; 
in  short,  all  the  appendages  of  the  head.  Of  the  append^es 
of  the  thorax,  the  first  two  pairs  are  well  developed,  and 
terminate  in  an  eiopodite  and  an  endopodite.  But  behind 
those,  which  become  the  first  and  the  second  pair  of  maiil- 
Upedea,  onlj  short  radimente  of  the  six  remaining  pairs 
at  thoracic  appendages  are  to  be  foond,  and  the  somite* 
of  the  long  abdomen  have  no  appendages  at  all.  Subse- 
qocstl;  these  make  their  appearance,  the  posterior  thorsciu 


S^ix'      ZSM  AJAXomr  K'j 


■jsemixn  :^-:r«r;iae  in  hzc.  t'-e  ejes  becose  raiaed  npon 
j42^r:  p*i:22--*le5.  ±r  I  :"-■*  Lin-A  r«-eiiible«  one  of  the  lower 
Jf-j«rvi.  Tz-i  canr^iir  =.er:  c^x-mea  broader,  and  its 
iffL^e*  si'.r^cr.  -^-lilr  :"i.r  A:r:b-ili:orT  thoracic  limbs  take 
.'S  tj-e  .:I:-irA.r:crs  -.f  :h:5^  ■:■£  the  a:i:ili,  the  bifurcated  first 
i2.i  i*^.vai  pairs  r^:'.min^  metamorphc^ed  into  the  fint 
Aa«i  w-.x^ni  ziAxillir^i-r*.  The  ac-iomen  becomes  relatively 
jj^. r:  ani  slenier.  a.ni  the  Lirva  takes  on  the  characters 
:t  .'ce  of  the  -lF.:"i'ir.i.  In  :"..:s  sta^  it  has  been  named 
.V  V'l*  y*!-  Bv  fv.r:b.er  ■.  haa^r^T?  in  the  same  direction,  the 
AaoE'^ran  c».nli::.n  passes  in:-:*  that  of  the  young  Bra- 
/jTuraa.  Ail  ihes-?  m-.-iinoations  of  form  are  accompanied 
?T  exuviations  of  the  ohitinou?  oiitioula. 

The  «uoi.'os*iive  sta^e.*  are  well  exemplified  bj  the  jonng 
of  the  Shure-orab.  Oir:-'t  u^  }y\'iu'vt  .Fig.  78,  A,  B,  C). 
The  larva,  on  leavinj  the  ej;^.  has  sessile  eyes,  a  long 
ix'inred  rostrum,  an- 1  a  sT-ine  projecting  from  the  middle 
of  the  oarapavo :  ruilimentary  antenna?,  and  two  pairs  of 
kvomotive  appondaires  —  the  ruiliments  of  the  anterior 
aiixillipedfs.  The  ali<li>minal  somites  are  without  appen* 
Jftare^.  and  the  telson  is  l-roa*!  and  Inlobed  iFig.  78,  A). 

This,  the  Ztxea  stairo.  after  repeated  ecdyses,  assumes  the 
yi^ilopa  form  represented  in  Fig.  7s.  B.  Finally,  the 
oarui^ioe  l^eoomes  broailer.  the  abdomen  loses  its  appendages, 
And  is  bent  up  under  the  thorax :  the  peculiarities  of  the 
ta^'ial  region,  charaoteristio  of  the  Brachyura,  are  developed ; 
the  antennules  and  ambulatory  mem]>er8  acquire  their  cha- 
•^neristic  proportions ;  and  the  little  Brachyuran  by  degrees 
jitumes  the  special  peculiarities  of  Carcinus  [Tig.  78,  C). 

The  development  of  the  Opossum  Shrimp  (My»is)*  is  par- 
f^iilarly  interesting,  as  it  appears  to  indicate  the  rela- 
li,90B  between  the  two  modes  of  development,  that  with  and 
j|yt  without  metamorphosis,  which  obtain  in  the  Crustacea 

ri«.79). 

Ifce  ova  consist  of  a  vitelline  mass,  enclosed  within  t 
jilieate  chorion.    The  blastoderm  apx>ears  as  an  oval  patch 

Beneden,  "  IXcveloppcmcnt  des  Mysif.**  (*  Bolletln 
Bnizellei,'  1869.) 


THS  DITBLOPMXHT  07  MT8I8.  S51 

Rirfaoe  of  tHe  yelk  (Fig.  79,  A,  e),  thickeflt  in  the 
nd  here  presentiiig  a  more  or  leas  marked  de- 
Fig.  79,  A,  B,  e).  It  is  sharply  defined  from  the 
yelk  (h),  and  consistB  of  a  finely  granular  mass, 
moltitades  of  nuclei,  about  yg^  to  j^^  of  an 
■meter,  are  imbedded. 

Btoderm  next  becomes  larger  at  one  end  than  at 

and  a  median  sinuation  gradually  diyides  this 

into  two  lobes,  which  will  eventually  form  the 

Moietes  of  the  head,  and  may  be  called  the  pro- 

lian  depression  becomes  more  decided,  and,  at  the 
ite  theprocepbalic  lobes,  theblastoderm  is  produced 
b  of  papilla,  directed  forwards.  This  is  the  rudi- 
le  caudal  extremity.  From  the  anterior  part  of  the 
Q  there  arise,  on  each  side,  two  papiUsB,  the  points 
ore  directed  backwards,  and  which  will  become  the 
IS  and  antennae.  The  whole  of  these  parts  are 
>y  a  delicate  cnticular  membnvne,  which  gradually 
rer  and  invests  the  whole  yelk  beneath  the  vitellary 
3.  At  the  end  of  the  caudal  papilla  it  forms  a 
cess,  produced  into  eeta),  which  sometimes  appear 
sometimes  so  deeply  bifid  as  to  resemble  two 

bryo  has  now  reached  what  we  may  term  its  larval 
;  in  this  condition,  it  leaves  the  vitellary  membrane 
lich  it  was  enclosed,  and  lies  free  in  the  ovigerous 
iie  parent.  At  the  same  time,  the  caudal  extremity 
and  straightens  itself  out,  so  that  no  indication 
rious  inflexion  against  the  thoracic  portion  of  the 
n  remains.    The  larva  thus  much  resembles  a  pear 

ceeediDgly  interesting  the  vertebrate  embryo;  and  the 

the   correspondence  cephalic   flexure  of  the  Cmsta- 

e  embryonic  structure  cean  or  Insect  has  its  analogue, 

I  of  Myitis  (and  I  may  if  not  its  homologue,  in  the  angle 

other  Arthropoda)^  And  which  the  trabecular  region  of 

head  of  a  vertebrate  the  base  of  the  skull  at  first  makes 

The  procephalic  pro-  with   the  parachordal  region  in 

mble  in  a  remarkable  almost  all  Vertebrata, 
e  trabecule  cranii    of 


352       THI  AVATOMT  OT  UITIBTXBBATU>  *»Tif*iJi, 

(Fig.  79,  D,  !E),  with  four  processes  (2, 3).  the  anteuiinki  and 
aiit«jitue,  which  have  now  become  much  elongated,  on  i 
surface. 

The  joung  Xygit  next  growi  lapidl;  and  Trndergoes  great 
changes  in  form :  but  it  is  a  Terj  remarkable  fact,  Uiat  tbe 
primitive  integnment  remains  tmaltered;  gradnaUj  ea- 
larging,  to  accommodate  itaelf  to  the  increased  aiae  of  the 
ftetua,  indeed,  bat  otherwiae  taking  no  share  whaterer  in 
its  changes.  The  young  Myrit  might,  therefore,  in  t 
condition  be  joetlj  termed  a  papa,  for  Hie  relation  of  tiw 
primitive  integnment  to  tbe  animal  which  it  encloses  ia 
preciselj  that  of  the  pupa  skin  to  the  imago  of  an  insect 

Fig.  79. 


THE  DXTBLOPHBHT  OF  1 
Fig.  73-, 


Pig.  79.— Th«  development  of  AJyiii.— A.  Side  

which  the  blutodenn  bM  jrut  appeued.  B.  Side  view  further  *d- 
Ttneed.  C.  Front  view  of  embrro  at  the  nme  age,  thowlng  the 
proccphalle  lobe*,  here  marked  b.  D.  Larre,  TOotral  Tiew.  " 
Side  Tiew.  (Theie  two  %urea  have  heen  Inverted  b;  the 
graver.)  F.  Toung  pupa.  G.  Further  advanced,  U.  Young 
^'  «,iihicb  hag  lettltapupaakin.  I.  Aatvrloi  portion  of  the  ume, 
'  h  the  carapaoe  ttuown  hacic.  a.  Vitelline  meni- 
I.  Tellt.  c.  Central  depresaloQ  of  the  blaelodenn.  <f .  Pro- 
cephalic  lobe*.   /.  Larval  integument     j.  Iti  caudal  eol ' — ' 


3fViu,  which 
enlarged,  and 


The  anteniMilea  and  antemue  renuun  intact  within  the 
■heaths  afforded  bj  the  primidre  integnment,  bat,  becoming 
immenBel;  elongated  and  divided  at  their  extremitiee, 
aamune  more  and  more  their  proper  adult  confonnataon. 

In  front  of  the  antennulei.  a  large  rounded  protsbeisncc 
mokea  ite  appearanoe  upon  each  procepbalic  lobe,  and 
tnentaaHy  beoomea  the  ophthalmic  peduncle.  At  flivt,  the 
sternal  portione  of  the  eomitee,  coireepondii^  witti  Otmt 
three  pairs  of  appendage*,  occupy  the  nme  plane  with  tmt 
%  k 


354       THE  ANATOMY  OF  nrVEBTEBRATBD  ANIMALS. 

another  and  the  posterior  sterna  (Fig.  79,  F,  G) ;  but,  by  de- 
grees, they  become  bent  up  (Fig.  79,  H),  and  at  length  the 
ophthalmic  sternum  occupies  the  upper  and  front  part  of 
the  head  (Fig.  79, 1).  In  this  way  the  "  cephalic  flexure  "  is 
produced.  The  mouth  is  indicated  behind  the  anten- 
nary  sternum,  which  projects  backwards  in  the  middle 
line  to  form  the  labrom.  On  each  side  of  it  the  radiments 
of  the  mandibles  appear,  and  behind  these  are  the  papil- 
lary commencements  of  the  two  pairs  of  maxillsB.  Behind 
the  second  pair  of  maxillse,  a  distinct  constriction  in- 
dicates the  commencement  of  the  thorax,  the  appen- 
dages of  which  appear,  at  first,  as  tubercular  elevations, 
all  of  precisely  the  same  character,  and  all  directed  back- 
wards parallel  with  one  another.  The  abdomen  is  at  first 
very  small,  and  the  appendages  of  its  sixth  somite  early 
acquire  a  far  larger  size  than  the  others.  The  telson  is 
developed  from  the  middle  line  above  the  anus.  While  all 
these  changes  are  going  on,  the  blastoderm  gradually 
extends  over  the  tergal  surface  of  the  embryo  and  closes 
it  in.  When  the  carapace  is  first  distinguishable  it  appears 
as  a  ridge  arising  from  the  sides  of  the  posterior  thoracic 
Idomites,  beginning  at  the  last  but  one,  and  gradually 
extending  forwards  as  far  as  the  antennary  somites.  The 
ridge  increases  and  becomes  a  fold,  which  overhangs  the 
bases  of  the  thoracic  appendages  (Fig.  79,  G) ;  and  if  this 
fold  be  turned  back  (Fig.  79,  I),  its  actual  attachments 
may  be  readily  demonstrated. 

Having  advanced  thus  far  in  its  development,  the  foetal 
Mysis,  with  all  its  organs  fully  formed,  though  somewhat 
different  in  appearance  from  those  of  the  adult,  casts  its 
pupa-skin  and  straightens  its  body,  which  from  having  its 
posterior  portion  bent  on  the  anterior,  as  in  the  embryo 
(Fig.  79,  B)  had  gradually  in  the  pupa  (Fig.  79,  F,  G) 
assumed  the  opposite  curvature.  Its  dimensions  are  three- 
fold those  of  the  embryo,  and  it  exhibits  yivacious  moye- 
inents  when  extracted  from  the  pouch  of  the  parent.  It  is 
not  improbable  it  may  yet  undergo  another  change  of  in* 
.tegamfint  before  acquiring  the  full  form  of  the  adult. 


THX  OLl^S-CBABS  OB  PEYLLOSOIUTA. 


355 


Thna  it  appears  that  in  Myei»,  tlie  Naupliw-atage  (Fig. 
79,  D,  E)  ia  passed  over  eo  rapidly  that  the  embrjo  has 
gone  through  it  at  a  verj  earlj  period,  and  nothing  but  the 
cnticnlar  eheath  of  the  bodj  appertaining  to  this  stage 
remains  to  prove  its  existence.  A  step  further,  in  the  ab- 
breviation of  the  ^aupJttM-stage,  and  there  would  be  nothing 


le  body;    C, 


oXIQ'n, 

le  nenodi  ajBtem;  I>,'thc 


to  distingoiah  the  general  coarse  of  the  development  of 
Mynt  from  that  of  Aitactu.  On  the  other  hand,  anothei- 
Schizopod,  Euphangia,  has  been  shown  by  Uetscbnikoff  *  to 
leave  the  egg  as  a  true  NaupUus. 

•  '  ZdUchrift  fur  WiM.  Zool.,'  1371. 

1  Kl 


356      THB  iLHATOMT  OF  IVYEBTIIBRATBD  AVDCALS. 

The  Glass-crabs,  or  PhyUosomaia  (Fig.  80),  are  mngnlar 
marine  pelagic  cmstacea,  in  which  the  body  connsti 
almost  wholly  of  two  large,  extremely  flat  and  transparent 
disks,  devoid  of  any  segmentation.  The  anterior  of  these 
bears  the  pedunculated  eyes,  the  antennnles  and  the  antenna 
on  its  anterior  margin ;  while  the  labrom,  with  the  mandibles 
and  anterior  pair  of  mazillsB,  form  a  small  projection 
posteriorly  on  its  yentral  surface.  The  second  pair  of 
mazillae  is  situated  a  little  more  backwards  and  outwards, 
and  bears  a  scaphognathite ;  and  just  behind  these  appen- 
dages is  the  fold  of  a  cervical  groove  which  separates  the 
anterior  disk  from  the  posterior.  The  anterior  disk  con- 
tains the  stomach  and  the  liver,  and  in  this  respect,  as  in 
its  appendages,  corresponds  exactly  with  the  cephaloetegite 
of  the  carapace  of  an  ordinary  Crustacean,  and  its  six 
cephalic  sterna.  The  posterior  disk,  on  the  other  hand, 
contains  the  short  and  almost  roimd  heart,  with  the 
intestine,  and  bears  the  eight  pairs  of  thoracic  appendages, 
the  anterior  and  posterior  of  which  are  not  uncommonly 
rudimentary.  The  abdomen  is  usually  very  small,  and 
situated  in  a  notch  at  the  posterior  edge  of  the  thoracic 
disk.  It  is  provided  with  six  pairs  of  appendages.  No 
generative  organs  have  been  found  in  the  PhyUosomatat 
and  there  is  reason  to  believe  that  they  are  merely  larv» 
of  the  Mocruran  genera  PalinuruSf  Scyllarus,  Thenua,  and 
their  allies. 

The  CirMA.CE A.. — These  are  very  remarkable  forms,  allied 
to  the  Schizopoda  and  Nehaliaf  on  the  one  hand,  and  on 
the  other  to  the  Edriophthalmia  and  d^pepoda ;  while  th^ 
appear,  in  many  respects,  to  represent  persistent  larvs  of 
the  higher  Crustacea, 

Ownia  Bathkii  might,  at  first,  be  readily  mistaken  for  a 
Copepod.  It  possesses  a  comparatively  small  thick  cara- 
pace, apparently  produced  into  a  rostrum  anteriorly,  and 
succeeded  by  a  series  of  twelve  gradually  narrowing  free 
segments,  the  appendages  of  which  are  in  great  part  ob- 
jBolete.  The  last  of  these  segments  is  a  pointed  telson ;   the 


k*  . 


THB  CUMACBA.  357 

anterior  five,  belonging  to  the  thorax,  bear  thoracic  limbe, 
while  the  eleventh,  the  last  tme  somite  of  the  body,  carries 
its  characteristic  stjliform  appendages.  The  appendages 
of  the  preceding  abdominal  somites  may  be  either  absent 
or  very  small  and  rudimentary.  Dohm  has  proved  that 
this  is  tme  only  of  the  females  among  the  Cwmaeea,  The 
males,  which  were  formerly  referred  to  the  genera  Bodatria 
and  Alauna,  often  have  well-developed  abdominal  limbs, 
though  they  appear  late.  It  is  interesting  to  find  that  the 
females,  in  this  respect,  retain  more  of  the  larval  character 
than  the  males. 

On  examining  the  apparent  rostrom  with  care,  it  is 
f onnd  to  be  divided  along  the  middle  line  by  a  fissure 
which  runs  in  front  of  the  eye  (which  is  here  single  and 
sessile)  divides  into  two  branches,  which  run  backwards 
and  outwards,  and  terminate,  before  traversing  half  the 
length  of  the  carapace ;  they  thus  cut  off  a  median  lobe, 
bearing  the  eye  at  its  apex,  from  two  lateral  processes. 
The  lateral  processes  are  simply  prolongations  of  the 
antero-lateral  regions  of  the  posterior  division  of  the  cara- 
pace (as  it  were  the  antero-lateral  angles  of  the  carapace  of 
Mysie,  excessively  produced  and  meeting  in  the  middle 
line) ;  while  the  middle  lobe  corresponds,  I  believe,  with  the 
cephalostegite  of  the  carapace  in  ordinary  PodophthaJmia, 
the  insertions  of  the  mandibular  muscles  occupying  their 
normal  position,  towards  its  posterior  boundary.  The 
hinder  part  of  the  carapace  will  therefore  correspond  with 
the  terga  of  the  three  anterior  thoracic  somites,  the  five 
posterior  ones  being,  as  has  been  seen,  free  and  moveable. 

The  five  anterior  pairs  of  thoracic  appendages  are  con- 
structed much  on  the  same  plan  as  those  of  the  Schuopoda ; 
the  three  posterior  have  no  exopodite.  In  the  female,  the 
sixth  abdominal  somite  alone  has  appendages,  but  in  the 
male  the  two  anterior  abdominal  somites  are  provided  with 
styles.  O vigorous  plates  are  attached  to  the  fourth,  fifth, 
and  sixth  thoracic  appendages  in  the  female.  The  structure 
of  the  head  is  peculiar.  No  ophthalmic  sternum  nor  oph- 
thalmic peduncles  are  discernible,  the  single,  or  closely 


358       THE  ANATOMY  OF  INYBBTEBBATED  AITIMALS, 

approximated  two,  eyes  being  sessile  on  the  median  line  on 
the  superior  surface  of  the  head.  The  coxopodites  and 
basipodites  of  the  antennules  and  antenns  are  bent  down 
almost  at  right  angles  with  the  axis  of  the  body,  and 
appear  to  be  connate,  or  confluent,  with  their  sterna.  The 
succeeding  joints  are  free  and  pass  forwards,  the  anten- 
nules being  much  longer  and  stronger  than  the  antennai 
in  the  females,  while,  in  the  males,  the  antennso  are  yerj 
long;  the  labrum  is  large;  the  mandibles  strong  and 
unprovided  with  a  palp.  There  is  a  distinct  metastoma, 
and  the  maxillffi  are  delicate  and  foliaceous.  A  papillose 
branchial  plate  is  attached  to  the  base  of  the  first  thoracic 
appendage.  The  surface  of  many  parts  of  the  body  in 
some  species  exhibits  a  very  peculiar  sculpturing,  singu- 
larly like  that  exhibited  by  the  Eurypterida, 

As  in  the  FodopMhalmiay  the  heart  is  short  or  moderately 
elongated,  and  situated  in  the  posterior  part  of  the  thorax. 

Dohm*  has  shown  that  the  development  of  the  Cumtuea 
takes  place  without  metamorphosis.  In  most  respects  the 
embryo  resembles  that  of  Mysis ;  but,  instead  of  the  cuti- 
cular  investment  of  the  transitory  Nauplius-staige  with 
its  two  pairs  of  appendages,  there  is  only  a  sort  of  cuti- 
cular  sac  with  a  thickening  in  the  middle  line  of  the  tergal 
aspect,  which  the  embryo  bursts  as  it  acquires  a  larger 
size.  In  this  respect,  the  resemblance  of  the  embryonic 
development  of  the  Onmacea  to  that  of  the  EdHophihalmia 
is,  as  Dohrn  points  out,  very  striking,  and  no  doubt  they 
form  a  connecting  link  between  the  Podophthalmia  and  the 
Edriophthalmia.  Having  regard  to  their  whole  organisa- 
tion, on  the  other  hand,  they  stand  at  the  bottom  of  the 
Malacostracan  group,  and  are  comparable  to  a  PeneMB- 
larva  in  the  Copepod  stage,  the  limbs  and  body  of  which 
are  modified  in  the  direction  of  the  Schizopoda,  while  the 
fore  part  of  the  head  has  remained  Copepodous. 

Fossil  Brachyura  are  abundant  in  tertiary  deposits,  but 
are  rare  in  formations  of  earlier  date.    J&focrura  of  a  pecii« 

*  «  Ueber  den  Bau  imd  die  Entwickelung  der  Camaoeen."  ('  Unter- 
saohangen  uber  Bau  und  Entwickelong  der  Arthropodeo,'  1870.) 


THB  EDBIOPHTHALMTA.  359 

liar  type  {Bryon)  occur  in  the  mesozoic  rocks,  and  perhaps 
the  carboniferous  Chimpaonyx  should  be  referred  to  the 
Podophthahnia. 

The  Edbiophthalmia. — ^These  resemble  the  Podophthal- 
mia  in  never  possessing  a  greater  than  the  typical  number 
(20)  of  somites,  though,  in  some  members  of  the  group,  the 
body  is  composed  of  fewer  somites,  in  consequence  of  the 
abortiTC  or  rudimentary  condition  of  the  abdomen.  Eyes 
may  be  absent ;  when  present,  they  are  usually  simple,  and 
are  either  sessile  or  seated  upon  immoveable  peduncles 
(Mtmna),  The  antennules  almost  disappear  in  the  terres- 
trial Isopoda,  while  the  antennss  become  rudimentary  or 
vanish  in  some  Amphipoda.  The  mandibles  lose  their  palps 
in  the  WoodHce ;  which  thus,  as  in  the  presence  of  only  one 
pair  of  well-developed  antennary  organs,  approach  Insects. 
Ordinarily,  the  posterior  seven,  and,  at  fewest,  the  poste- 
rior four,  thoracic  somites  are  perfectly  distinct  from, 
and  freely  moveable  upon,  one  another.  The  ophthalmic 
and  antennary  somites  have  coalesced  with  the  rest  of  the 
head;  the  branchise  depend  from  the  thoracic  limbs,  or 
are  modifications  of  the  abdominal  appendages;  and  the 
heart  is  elongated  and  iminy-chambered.  But  the  salient 
characters  of  the  group  will  be  best  understood  by  the 
study  of  such  a  genus  as  Amphiihoe,  the  principal  details 
of  the  organisation  of  which  are  reptesented  in  Fig.  81. 

The  body  of  this  animal  is  compressed,  bent  upon  itself, 
and  divided  into  fifteen  very  distinct  segments,  reckoning 
the  head  as  the  first  and  the  telson  as  the  last. 

The  head  presents  a  rounded  tergal  surface ;  the  anterior 
face  is  disposed  perpendicularly  to  the  axis  of  the  body,  and 
is  produced  anteriorly  into  a  strong,  curved,  and  pointed 
rostrum ;  on  each  side,  it  bears  an  aggregation  of  simple 
eyes,  and,  in  front,  immediately  beneath  the  rostrum,  this 
face  gives  attachment  to  two  long,  many-jointed  anten- 
nules. Below  these,  two  antenns,  shorter,  and  fewer-jointed 
than  the  antennules,  are  inserted,  and  the  inferior  part  of 
the  face  is  completed  by  a  large  moveable  labrum.    Behind 


B  come  the  ationg.  toothed  palpigaoiiB  .n^nJiMM  (ITO. 
Fig  »I. 


Fig.  81— ^n/iAitAoF.— Ths  1ett«n  Mil  flguras  have  the  Mnt  algnUo^ 
lion  ■■  Id  other  Sguret  of  Cru>t>c»  except  «,  ooategite.  A'. 
bnuchin.  C.  LatenI  Tiaw  of  itonwcb  (D)  opeaed  (rwa  abot*. 
a,i,e.  DifTerent  pwUof  thearnuturc. 

and  two  pain  of  more  or  less  foUaceoiu  mftrillff,     Insa- 


TRB  BDBIOPHTHAUOA.  861 

le  ejea  are  sessile,  these  five  pairs  of  appendages 
.t  belong  to  tlie  head  proper ;  but,  just  as  in  the 
^/mia,  certain  of  the  anterior  thoracic  appendages 
ted  into  accessory  gnathites,  so,  in  AmphUhoe, 
»air  of  these  members  are  applied  against  the 
1  form  a  large  lower  lip  (VII'). 
)ad "  of  Amphithoe,  therefore,  is  formed  by  the 
3  of  the  seven  anterior  somites  of  the  body ;  but 
lat  the  tergum  of  the  seyenth  (or  first  thoracic) 
bsolete,  as  in  a  Stomatopod,  and  hence  that  the 
face  of  the  head  of  the  Edriophthahma  corre- 
ictly  with  the  cephalostegite  (or  that  part  of  the 
yhich  lies  in  front  of  the  oerrical  grooTe)  in 
InUa.  Mr.  Spence  Bate  has  shown,  in  his  valu- 
»rt  on  the  EdriophihcUmict,*  that,  in  the  Cnutaoea 
nnder  discussion,  a  strong  apodeme  arises  on 
Erom  the  posterior  part  of  the  sternal  region  of 
ind  passing  inwards  and  forwards  meets  with  its 
orm  an  endophragmal  arch,  which  supports  the 
I  and  stomach,  and  protects  the  nervous  com- 
etween  the  first  and  second  sub-oesophageal 
hich  runs  under  it. 

overer  of  this  structure  conceives  that  it  repre- 
erga  of  the  three  somites  immediately  succeeding 
I ;  but  I  cannot  see  that  it  is  other  than  the  re- 
re  of  the  precisely  similar  mesophragm  formed 
berior  apodemes  in  Asiaeus,  In  fact,  the  corre- 
in  structure  between  the  head  of  an  AmphUhoe 
)phalic  portion  of  the  cephalo-thorax  of  Astcunis 
tie  striking.  There  is  the  same  sternal  flexure, 
elative  position  of  the  stomach,  and  of  the  inser- 
he  mandibular  muscles.  The  great  difference 
3  abortive  condition  of  the  ophthalmic  appen- 


;  endophragmal  arch  ent  connexions  (Fig.  83).    A  very 

sub-cesophageal  gan-  similar  endophragmal  arch  is  found 

mmiBBures  m>m  the  in  the  Insect  nead.  Seethedescrip- 

uUia^  but  has  differ-  tion  of  the  head  of  BhUa  {hrfru). 


362       THE  ANATOMY  OF  INYEBTSBRATBD  AHOCALB. 

The  Beven  free  somites  of  the  thorax  each  give 
attachment  to  a  pair  of  limbs.  It  is  characteristic  of 
Amphiihoe,  as  of  the  Amphipoda  in  general,  to  haye  the 
five  anterior  pairs  of  thoracic  members  directed  for- 
wards. Each  limb  consists  of  an  expanded  coxopodite, 
succeeded  by  the  other  six  joints  of  the  typical  cmstaoeaii 
limb. 

In  the  male,  a  single  vesicular  lamella,  the  branchia,  is 
attached  to  the  inner  side  of  the  coxopodite  of  the  appen- 
dages of  the  ninth  to  the  fourteenth  somites  inclusiTelj ; 
but,  in  the  female,  an  additional  plate,  convex  extemallj 
and  concave  intemallj,  is  attached  above  and  internal  to, 
the  branchia  of  the  9th  to  the  I2th  somite.  These  oods^ 
gUeSf  as  they  may  be  called,  enclose  a  cavity  in  which  the 
incubation  of  the  eggs  takes  place. 

The  abdomen  consists  of  six  somites  and  a  veiy  small 
terminal  telson.  The  appendages  of  the  three  anterior 
somites  are  terminated  by  two  multiarticulate  setose  fila- 
ments (Fig.  81,  XV)  while  in  the  three  posterior,  the  corre- 
sponding parts  are  siylif orm,  and  serve  as  a  fulcrum  for  the 
abdomen  when  the  animal  leaps,  by  the  sudden  extension 
of  that  region  of  the  body. 

The  Edriophthalmia  are  ordinarily  divided  into  three 
groups.  The  Amphipoda,  which  resemble  AmphWioet  are 
characterised  by  their  compressed  form  and  their  ordinarily 
saltatory  habits ;  by  having  thoracic  branchise ;  by  the  for- 
ward direction  of  their  four  anterior  locomotive  limbs  (2nd 
to  5th  pairs  of  thoracic  appendages),  and  by  the  contrast 
between  the  three  anterior  and  the  three  posterior  pairs  of 
abdominal  appendages.  The  common  Sand-hopper  is  the 
most  familiar  example  of  this  division.  The  second  group 
is  that  of  the  Lcemodipodaf  distinguished  by  the  rudimen- 
tary state  of  the  abdomen,  which  is  reduced  to  a  mere 
papilla,  and  by  the  coalescence  of  the  second,  as  well  as  the 
first,  thoracic  somite  with  the  head,  so  that  the  anterior 
limbs  appear  to  be  as  it  were  suspended  under  the  necL 
The  strangely  formed  genera  Cyamus,  the  parasite  of 
whales,  and  CapreUa,  which  is  very  common  upon  our  own 


THX  KDSIOPHTHAUfU.  363 

eoMt,  adhering  to  coralliaeH,  sea-weeds  aud  etarfisli,  beioi^ 
to  this  group. 

The  Iiopoda,  which  couHtitute  the  third  group  of  the 
Edricphthalmia,  are  UHaally  depressed  instead  of  com- 
preMed,  and  rtm  or  crawl  instead  of  leaping.    Hanj,  like 

Fig.  ea. 


1  Woodlonse  (OnUci 
rolling  themselvea  into  a  ball  i 
the  last-named  genns,  are  terrMtrial;  others,  like  the 
A»eUv»,  inhabit  fresh  waters,  bnt  the  great  majority  are 
marine;  and  among  them  are  many  pecoliarlj  modified 


364      THB  AITATOMT  07  IHTBBTSBRATXD  AHDCALS. 

parasitio  forms  (Fig.  82,  Cymoihoa ;  Bopyrus).  The  ooiii* 
position  of  the  head  and  mouth  in  the  laopoda  is  essentiAllj 
the  same  as  in  the  Amphipoda,  though  differing  oonaider- 
ablj  in  details.  The  branchiie  of  the  thoracic  members 
are  absent,  their  functions  being  performed  bj  the  endo- 
podites  of  some  of  the  abdominal  members,  which  are  soft 
and  yascular.  The  three  anterior  pairs  of  thoracic  members 
are  usually  directed  forwards — the  four  posterior  pairs  back- 
wards. In  some  Jgopoda  the  abdominal  somites,  partly  or 
wholly,  coalesce  with  one  another. 

In  all  the  EdriopMkdImia  the  alimentary  canal  is  straight 
and  simple,  and  its  anterior  gastric  dilatation,  frequently 
strongly  armed,  is  situated  in  the  head.  The  liver  is  repre- 
sented by  a  variable  number  of  straight  csBca. 

Occasionally  there  are  on6  or  two  cseca  which  open  into 
the  posterior  part  of  the  intestine,  and  appear  to  be  mrinaiy 
organs  analogous  to  the  Malpighian  caeca  of  insects. 

The  respiratory  organs  vary  greatly  in  structure.  In  most 
Edriophikalmia,  they  are  simple  plates  or  sacs,  the  delicacy 
of  the  integument  of  which  permits  of  the  free  exposure 
of  the  blood  circulating  in  them  to  the  air.  In  the  amphi- 
pod  genus  Phrosina,  however,  the  branchiae  are  composed 
of  rudimentary  lamellae,  attached  to  an  expanded  stem,  and 
resemble  not  a  little  the  epipoditic  branchiae  of  Astacut. 
In  some  SplueromidcB,  Duvemoy  and  LerebouUet  found  the 
branchial  endopodites  transversely  folded,  so  as  to  approach 
those  of  the  Xiphosura, 

The  exopodites  of  the  abdominal  members  of  the  Inpoia 
frequently  cover  the  modified  endopodites,  forming  opercu]a» 
and  the  first  pair  of  abdominal  limbs  is,  in  many  genera* 
altered  in  such  a  manner  as  to  form  one  such  large  oper- 
culum for  the  four  pairs  which  succeed  it.  In  the  IdatMa 
it  is,  on  the  other  hand,  the  sixth  pair  of  abdominal  limbs 
which  are  so  modified  as  to  form  the  curious  door-like  oper- 
cula  which  cover  the  gills. 

In  certain  of  the  terrestrial  Isopoda,  (PoreelUo^  Arm^ 
diUidifimj)  some  of  the  opercular  plates  of  the  branchiiB, 
usually  the  two  anterior  pairs,  contain  curiously  ramified 


THB  KPBIOPHTH  ALlf  I A .  365 

cavities,  wldoh  open  extemallj,  and  contain  air.  The  genus 
Tyhs  possesses  respiratory  organs,  which  present  a  still 
more  interesting  approximation  to  those  of  the  pnrely  air- 
breathing  Articulata.  Thej  are  thus  described  by  Milne- 
Edwards: — 

"The  abdomen  presents  inferiorly  a  deep  cavity,  very 
similar  to  that  of  the  SphceromcB,  in  which  the  five  anterior 
pairs  of  appendages  are  lodged;  but  this  cavity,  instead  of 
being  completely  open  below,  is  imperfectly  closed,  in  its 
posterior  half,  by  two  series  of  lamellar  prolongations,  which 
arise  from  the  sides  of  the  inferior  faces  of  the  third,  fourth, 
and  fifth  abdominal  segments,  and  pass  horizontally  in- 
wards ;  the  first  pair  of  these  plates  is  small,  those  of  the 
third  pair  are,  on  the  other  hand,  very  wide,  and  almost 
meet  in  the  median  line.  The  four  anterior  pairs  of  abdo- 
minal appendages,  lodged  in  this  cavity,  each  carry  a  wide 
and  short  quadrilateral  appendage,  the  surface  of  which 
is  raised  into  a  transverse  series  of  large  longitudinal  eleva- 
tions, and  each  of  these  elevations  presents  inferiorly  a  linear 
aperture  leading  to  a  respiratory  vesicle,  the  parietes  of 
which  are  covered  with  a  multitude  of  little  arborescent 
csBca.  These  vesicles  when  extracted  from  the  interior  of 
the  limb  closely  resemble  a  brush-like  branchia,  having  its 
longitudinal  canal  in  communication  with  the  atmosphere 
by  a  longitudinal  stigma.  The  fifth  pair  of  abdominal 
members  are  rudimentary,  while  the  sixth  constitute  the 
door-like  triangular  valves  covering  the  anus,  and  all  the 
inferior  face  of  the  last  abdominal  segment."  * 

The  nervous  system  in  the  Amphipoda  consists  of  supra- 
oBSophageal  or  cerebral  ganglia,  united  by  commissures  with 
an  infra-OBSophageal  mass,  whence  commissural  cords  pass 
under  the  endophragm  to  the  anterior  of  the  thoracic 
ganglia,  of  which  there  are  commonly  seven  pairs,  succeeded 
by  five  or  six  pairs  of  abdominal  ganglia.  In  some  laopoda 
{Cymothoa,  Idotea)  the  abdominal  ganglia  are  also  distinct ; 
bat  in  others,  such  as  JEga  hicarinata  (according  to  Bathke), 
thej  are  fused  into  a  single  mass  placed  in  the  anterior 

*  'Histoire  Naturelle  des  Crnitacet,'  vol.  iU.  p.  187. 


366       THE  ANATOMY  OF  INYBBTXBSATBD  AVDfAIA 

part  of  the  abdomen,  presenting  onlj  traces  of  a  divisioit 
into  five  portions.  In  the  CymathoadoB  and  terrestrial 
laopoda,  again,  the  abdominal  ganglia  appear  to  have  oom- 
pletelj  coalesced  with  the  last  thoracic  ganglia  and  form 
a  mass,  whence  the  abdominal  nerves  radiate.  Finally,  in 
the  short-bodied  Lcemodipodat  snch  as  Oyomtw,  there  are 
not  more  than  eight  pairs  of  post-(Bsophageal  ganglia* 
the  posterior  commissures  of  which  are  so  ahortcoied 
that  the  nervous  system  ends  in  the  antepennltiinate 
somite. 

Brandt  describes  splanchnic  ganglia  like  the  lateral  pair 
of  Insects  in  the  Oniscidce,  It  is  one  of  the  manj  respects 
in  which  the  Isopoda  simulate  Insecta. 

No  other  organs  of  sense  than  eyes  have,  as  jet,  been  cer- 
tainly demonstrated  to  exist  in  the  Edriophihodmia^  though 
the  fine  setse  which  beset  the  antennary  appendages,  haTe 
been  supposed  to  be  organs  of  the  olfactory  sense.  The 
eyes  vary  in  their  structure,  from  the  simple,  more  or 
less  closely  aggregated  ocelli  of  Lcsmodipoda,  and  of  many 
Isopoda  and  Amphipoda,  to  the  strictly  compound  eyes,  as 
complex  as  those  of  the  highest  Articulata,  which  exist  in 
.^a  and  in  Fhrosina, 

The  female  genitalia  of  the  EdriophlhcUmia  consist  of  two 
simple  sacs,  the  ducts  of  which  usually  open  on  the  ventral 
surface  of  the  antepenultimate  thoracic  somite,  or  on  the 
bases  of  the  limbs  of  this  somite.  In  the  male,  one  or  moxe 
cseca  on  each  side  constitute  the  testis,  which  ordinarily 
opens  on  the  last  thoracic  or  first  abdominal  somitei,  in 
connexion  with  one  or  two  pairs  of  copulatory  organs  de- 
veloped from  the  anterior  abdominal  somites. 

The  eggs  of  the  ordinary  Edriophthalmia  usually  undergo 
their  development  in  the  chamber  beneath  the  tiiorax  en- 
closed by  the  oostegites  of  the  thoracic  appendages.  In 
most  cases,  the  young  differ  so  little  from  the  adults  that  no 
metamorphosis  can  be  said  to  take  place.  They  frequently* 
however,  want  the  last  thoracic  somite.  The  young  of  the 
parasitic  Ed/riophthalmia,  such  as  Bopyrus,  Phryxus,  Cfwuh 
thoa,  Cyamus  and  the  Hyperinae,  on  the  other  liand,  are 


THB  8TOMATOPODA.  367 

widely  different  from  the  adults;  and  not  onlj  in  their 
metamorphosis,  but  in  the  small  proportional  size  and  less 
aberrant  form  of  the  male,  Bopyrua  and  Phrymu  recall  the 
parasitic  Cop^oda. 

In  certain  Amphipods  {(xammarus  loetista  and  Deamo- 
phUus)  the  yiteUus  undergoes  complete  division ;  while,  in 
closelj  allied  forms  {Chmmarus  fitmatUis  and  ptUex),  and 
still  more  completely  in  those  Isopoda  which  have  been 
studied,  the  part  of  the  yitellus  which  divides  into  blasto- 
meres,  becomes  more  or  less  completely  separated  from 
the  rest  immediately  after  fecundation,  and  the  so-called 
partial  yelk  division,  take  place.* 

In  all  Edriophthalmia,  the  development  of  which  has  been 
examined,  before  any  other  organs  appear,  a  cuticular  invest- 
ment or  sac  is  formed,  which  is  eventually  burst  and  thrown 
off.  This  appears  to  represent  the  Nauplius  cuticle  of 
MysUf  and,  in  close  relation  with  it,  are  peculiar  tergal 
structures,  such  as  the  bifid  lamellm  of  AseUus  and  the 
unfortunately  named  "  micropjle  apparatus  "  of  other  Edri- 
ophthalmia. 

The  Edriophthalmia  are  not  abundant  in  the  fossil  state ; 
but  they  may  be  traced  back  as  far  as  the  later  Palaeozoic 
strata  {Prosoponiscua,  AmphipeUis), 

The  Stomatopoda. — Of  the  Stomaiopoda  of  Milne- 
Edwards,  two  of  the  three  divisions,  the  Carid&ides  and  the 
Bieuirasses  have  since  found  a  place  among  the  Schizo- 
podous  Podophthahnia,  or  among  the  larvsB  of  certain 
Macrura;  but  the  third,  the  Stomaiopodea  unicuiraasea, 
comprising  Squilla,  Oonodactylus,  and  Coronis,  appear  to 
me  to  differ  so  widely  and  in  such  important  structural 
peculiarities,  not  only  from  the  Podophthalmia  proper,  but 
from  all  other  Crustacea,  as  to  require  arrangement  in  a 
separate  group,  for  which  the  title  of  Stomatopoda  may  well 
be  retained. 

*  E.  van  Beneden,*  Recherches  sur  la  Composition  et  la  Signification 
de  rCEnf/  1870. 


THE  AJrA.TOHT  OF  IHYBSTZBSATED  AirilUI.8. 

The   genera  named,  in  feet,  stand  alone   among   the 
~  '  n  that  the  opbtlialinio  and  antennnlu;  tomitei 
[X>mplct«  rings,  moveable  apou  one  another  and  the 


TRB  8TO1IAT0PDDA.  369 

that  of  the  bodj,  so  that  there  is  no  sternal  flexure.  Nnmerons 
pairs  of  hepatic  cseca  open  into  the  elongated  alimentary 
canaL  The  heart,  again  is  not  short  and  broad,  with  at 
most  three  pairs  of  apertures  and  confined  to  the  thoracic 
region,  as  in  the  proper  PodophUudmia ;  but  it  is  gpreatly 
elongated,  mnltilocolar,  and  extends  into  the  abdomen.  The 
branchisB  are  plumes  attached  to  the  abdominal  members 
(Fig.  88,  A,  br)y  and,  iso  far  as  I  have  been  able  to  ascertain, 
the  carapace  is,  in  all,  connected  exdnsively  with  the 
cephalic  somites.  This  is  particnlarlj  well  seen  to  be  the 
case  in  SquUla  seahricauda  (Fig.  83),  where  five  completely 
developed  posterior  thoracic  terga  can  be  counted,  un- 
covered by  the  short  carapace,  beneath  which  the  terga 
of  the  three  anterior  thoracic  somites  are  represented  by 
a  membrane  which  passes  forwards  to  be  reflected  into  the 
carapace. 

The  free  somites  of  the  thorax,  and  those  of  the  abdomen, 
in  this  species  and  in  the  Stomatopoda  generally,  are  so 
large  relatively  to  the  carapace,  that  the  latter  is  not  larger 
in  proportion  to  the  body  than  the  tergal  covering  of  the 
head  in  many  EdriopMhalmia,  with  which  order  the  Stoma- 
topoda present  many  marked  affinities.  Indeed,  if  we  leave 
the  eyes  out  of  consideration,  the  organisation  of  the  Sto- 
maiopoda  is  more  Edriophthalmian  (and  especially  Amphi- 
podan)  than  Podophthalmian.  The  five  anterior  pairs  of 
thoracic  members  are  turned  forwards,  and  are  subchelate. 
The  first  pair  are  small  and  slender.  The  second  pair  are 
the  largest  of  all,  and  have  the  characters  of  powerful 
prehensile  limbs,  the  terminal  curved  and  spinose  joint  of 
which  shuts  down  mto  a  groove  in  the  penultimate  joint, 
as  the  blade  of  a  x>ocket  knife  does  into  its  handle.  The 
three  posterior  thoracic  limbs,  on  the  other  hand,  are  turned 
outwards,  and  terminated  by  an  endopodite  and  an  exopo- 
dite. 

SquiUa  lays  its  eggs  in  burrows  in  the  bottom  of  the  sea, 
which  the  w.Tiim«.la  inhabit.  The  earliest  condition  of  the 
free  larva  is  not  fully  known,  but  the  young  larva  have 
a  single  eye,  'and  the  hinder  thoracic  and  the  abdominal 


370       THE  AKATOMY  OF  IVYBSTBBRATBD  AITIKALS. 

appendages  are  not  developed.*  The  larvn  paas  into  f onus 
whicli  under  the  names  of  Alima,  EriehikyM,  and  SqmUler- 
iehihys,  were  formerly  considered  to  be  independent  geneim. 
Claos's  investigations,  however,  have  rendered  it  probable 
that  the  two  latter  genera  are  simplj  larval  stages  of 
Chnodactylus,  and  that  Alima  is  a  larval  stage  of  SqtUUa. 

•  Frits  MuUer,  <  FUr  Dtrwin.'  See  also  Claus,  «Die  Metamorphose 
der  Squillideis*  1872. 


THB  ▲SA.OHmDA.  871 


CHAPTEB  Vn. 

THE  AIS-BBBATHINO  ABTHBOPODA. 

Among  these  Arihropoda,  no  forms  absolutely  devoid  of 
limbs  are  at  present  known,  though  the  appendages  are 
reduced  to  two  pairs  of  minute  hooks  in  theTermiform 
parasite  LinffucUula, 

The  Abachkida  have  pediform  gnathites,  and  the  least 
modified  forms  of  this  group  (the  Arthrogadra  or  Scorpions 
and  Pseudo-scorpions)  exhibit,  in  manj  respects,  extra- 
ordinarily close  resemblances  to  the  Merostomaia  among 
the  Crustacea, 

The  Abthbooastba. — ^The  anterior  port  of  the  body  of 
a  Scorpion  (Fig.  84)  presents  a  broad  shield-like  tergal  plate, 
resembling  that  of  Ewrypterua  in  form.  Two  large  eyes  are 
situated  one  on  each  side  of  the  middle  line  of  the  shield, 
while  smaller  eyes,  which  vary  in  number  according  to  the 
species,  are  ranged  along  its  antero-lateral  margins. 

Six  wide  plates,  representing  the  terga  of  as  many  somites, 
follow  the  anterior  shield,  and  are  connected  only  by  the 
soft  integument  of  the  sides  of  the  body  with  their  sterna. 
The  seventh  is  united  with  its  sternum  (XY)  posteriorly, 
while  the  five  following  terga  and  sterna  form  continuous 
rings,  which  constitute  the  joints  of  the  so-called  "tail." 
The  anus  is  situated  behind  the  last  sternum.  A 
moveable  terminal  piece,  answering  to  the  telson  of  a 
Crustacean,  which  is  swollen  at  its  base,  and  then  rapidly 
narrows  to  a  curved  and  pointed  free  end,  overhangs  the 
anuB,  and  constitutes  the  characteristic  weapon  of  offence 


872     THx  i.KjL,Toinr  or  nmsTiBKATiD  utisAxs. 

of  the  Scorpion.  This  sting,  in  fact,  contaiiiB  two  glimda 
which  secrete  a  poisonotiB  fluid,  and  their  dacts  convej  it 
to  the  minute  apertore  sitoated  at  the  sharp  point  of  the 
organ.    On  the  sternal  enrface  of  the  body,  there  are  fonr 

Fig.  8*. 


Fig>  B4.— AamTwa/ir.^A,  teitnland  BiSteraalTiewof  thabodf ;  At, 
oiialiosra  ;  iv',  pedi|iBlpi ;  v',  vi',  puUrior  pair  of  ocphKllo  ^^en- 
<Um;  Tii',  vu^iftuurior  thoneie^mb*;  /■(,. peetinM ;  St,sWMi; 
CM,  oepbalD-Uwnx.    (After  UilnB-EdmrdiAsdDagii.*) 

wide  and  long  sternal  plat«B  (xi-w),  which  correspond  with 
the  third,  fourth,  fifth  and  sixth  of  the  free  terga.  £acb  of 
th«ee  bean  a  pair  of  oblique  sUta,  which  are  Ute  op^iingB 

*  'Bignt  Animd,'  Ifiwtn(«d  Edition. 


TBI  ASTHSOOABTKL  373 

of  tlie  reepiratorj  organs  [Fig.  85,  e).    The  atema  of  Uie 
Fig.  8J. 


Fig.  85 — A  diagnm  of 


VII-XX,  the  Kventh  to  the  t-enlieth  Kimite.    fv,  V  VI,  tha  UhI 
Joiato  of  tha  pedlpalpl,  and  two  tbllowing  pain  of  litnba. 

fint  and  second  free  eomitea  (ix,  x)  an  ver;  noalli  thaJu  (A 


374       THE  AKATOMT  OF  IHTBBTSBILLTSD  AVI1CAIJ3. 

the  first  carries  the  valyes  which  cover  the  genital  apertore ; 
that  of  the  second  bears  a  pair  of  verj  curious  appendageSt 
somewhat  like  combs,  which  are  termed  the  peeHnet,  The 
nerrous  trunks  which  enter  the  pectines,  are  distributed  to 
the  numerous  papillse  which  cover  them,  and  are  probably 
tactile  in  function.  Thus  there  are  twelve  somites  behind 
the  eye-bearing  shield,  and  none  of  these  are  provided  with 
appendages,  unless  the  pectines  be  such. 

The  truncated  anterior  extremity  of  the  body,  beneath 
the  shield,  is  formed  by  a  very  large  setose  labrum,  behind 
and  below  which,  in  the  middle  line,  is  the  extraordinarily 
minute  aperture  of  the  mouth  (Fig.  86,  M).  On  each  side 
of  it  is  attached  a  three-jointed,  pincer-ended,  appendage, 
the  ehelieera.  Behind  these  follow  the  pedipalpi,  large  che- 
late limbs,  the  stout  basal  joints  (iy')  of  which  lie  on  each 
side  of  the  mouth. 

The  following  four  pairs  of  appendages  are  seven-jointed 
ambulatory  limbs,  each  terminated  by  three  claws.  The 
basal  joints  of  the  first  two  [y*,  yi')  lie  behind  the  mouth,  the 
posterior  and  inferior  boundary  of  which  they  form,  and 
are  directed  forwards.  The  basal  joints  of  the  last  two 
(yii',  yiii'),  on  the  other  hand,  directed  inwards,  are  firmly 
united  together,  and  are  altogether  excluded  from  the  mouth. 

Thus  the  mouth  is  situated  between  the  labrum  in  front, 
the  bases  of  the  pedipalpi  and  those  of  the  first  two  pairs 
of  ambulatory  limbs,  at  the  sides  and  behind;  just  as  in 
Limulus,  the  mouth  lies  between  the  labrum  and  the  basal 
joints  of  the  third,  fourth,  and  fifth  limbs,  which  answer  to 
the  mandibles  and  first  and  second  maxillffi  of  the  higher 
Crustacea,  If  this  comparison  is  just,  there  is  one  pair  of 
pr»-oral  appendages,  which  exist  in  Limulus,  wanting  in 
the  Scorpion ;  and  the  difference  between  the  two  may  be 
represented  thus : 

Lmndnt,  Antennule.  Antenna.    Mandible.    Maxilla  1.  MazillaS. 
Scorpio,  Chebcera.  Pedipalpus.     Leg  1.         Leg  S. 

Again,  if  the  eye-bearing  part  of  the  head  may  be  r»* 


TBI  ABTHBOOABniA.      '    '   '  '  375 

^rded  as  a  Bomito,  then  the  body  of  the  Scorpion,  like 
that  of  a  nuJaeofltfaooQS  crastocean,  will  ooneist  of  twAity 
Bomitea  and  a  teleon.  We  may  regard  the  six  posterior 
Bomites  (ZT-xx)  as  the  homolo^ea  of  those  which,  con< 
Btitate  the  abdotDOD  in  the  cmetoceent  whOe  the  eight 
middle  aoiniteB  (vii-xit)  will  answer  to  thoie  which  enter  into 
the  thorax  of  the,latter ;  and  the  head  will  rwamble  tliatof  an 
Edriophthalmian  with  one  pair  of  autennary  o^ans  com- 
pletely sapprewed.  Upon  this  view,  the  eye-bearing  shield 
is  a  campace  oorering  a  oephalo-thorax,  into  whioh  Hm  two 
Pig.  M. 


Fig.  86.  — ScnrfUD.— Vcrtioal  lectioD  of  the  oepbalo.thorki ;  .if,  cheli- 
oon ;  lb,  libmni ;  M,  mouth ;  a,  pbujageal  Bae ;  N,  N ',  inpra.  uid 
laftvHzMphage&l  ganglia ;  b,  mophagiu ;  d,  opeoing  of  the  i^Tary 
duett;  e,m(««tiDe;  U,  heart. 

anterior  thoracic  somites  only  enter.  These  are  followed 
by  six  free  thoisoio  somites,  the  four  posterior  of  which 
are  pulmoniferoos.  Bnt  no  trace  of  the  sapposed  misginff 
antennary  appendage  has  been  met  with  in  the  embryonic 
conditioii,  so  that  the  alternative  poedbilitj  that  the  month 
is  situated  one  lomitfi  further  forward  in  the  Scorpion 
than  in  the  Omstacean  most  be  borne  in  mind.  It  is  a  very 
interesting  fact  that  Meldchuikoff  *  has  fotind  mdiments  of 
•  "  Etnbiyologle  dcs  SooiploDi."  ('  Zcitwihiift  fSr  Wiu.  Zoologle,' 
1871.) 


376       THB  ANATOKT  OF  INYBBTSBR^TSD  AKOfAIiS. 

limbs  on  those  somites  of  the  embryo  Scorpion  on 
the  stigmata  are  situated,  a  ciroumstanoe  which  soggeste 
the  suspicion  that  the  Scorpion  is  deriyed  from  some  foam 
possessing  more  numerous  limbs. 

The  minute  oral  aperture  leads  into  a  small  pTrifoim 
lateraUj-eompressed  sac  (Fig.  86,  a)  with  ohitinous  eUuitio 
walls.  Muscles  pass  from  these  to  apodemes  of  the  sternal 
wall  of  the  head,  and  doubtless  act  as  divaiicators  of  the 
wall  of  the  sac.  As  the  Scorpion  sucks  out  the  juices  of  its 
prey,  it  is  probable  that  the  elastic  sac  acts  aa  a  kind  of 
buccal  pump  — the  nutritious  fluid  rushing  in  when  the 
sides  of  the  pump  are  separated,  and  being  squeezed  into 
the  (Bsophagus  when  the  elasticity  of  the  walls  brings  them 
back  to  their  first  position.* 

The  oesophagus  (Fig.  86,  h)  is  an  exceedingly  narrow  tube, 
'  which  springs  from  the  tergal  and  posterior  aspect  of  the 
sac  just  mentioned,  traverses  the  nervous  ring,  and  then, 
passing  obliquely  upwards  and  backwards,  enlarges  into  a 
dilatation  which  receives  the  secretion  of  two  large  salivazy 
glands,  by  a  wide  duct  on  each  side.  The  alimentary 
canal  narrows  again,  and  becoming  a  delicate  cylindrical 
tube  which  widens  posteriorly,  passes  straight  through  the 
body  to  the  anus.  The  numerous  ducts  of  the  liver  open 
into  the  anterior  part  of  this  region  of  the  alimentary 
canal,  and  it  receives  two  delicate'  Malpighian  tubuli. 

The  liver  is  a  vast  follicular  gland,  which  occupies  all  the 
intervals  left  between  the  other  organs  in  the  enlarged  part 
of  the  body,  and  even  extends  for  some  distance  into  the 
narrow  posterior  somites. 

The  eight-chambered  heart  (Fig.  86,  H)  is  a  lai^ger  and  more 
conspicuous  structure  than  the  alimentary  canal,  above 
which  it  lies,  in  a  pericardial  sinus  situated  in  the  middle 
line  of  the  tergal  aspect,  between  the  eye-bearing  shield  and 
the  tail ;  each  chamber  is  wider  behind  and  narrower  in  front, 
and  has  two  valvular  apertures,  by  which  blood  is  admitted 
from  the  pericardial  sinus  at  its  postero-lateral  angles.    It 

•  Hoxley,  <*Oii  the  Mouth  of  the  Scorpion."  (<  Quart.  Jouni.  of 
Microscopical  Science,'  1660.) 


377 

giy«s  off  small  lateral  arteries,  and  ends  in  fnmt  aad  beliind 
in  a  wide  aortic  tnmk.  Of  theae  the  anterior  is  larger  than 
tlie  ceaophagns,  and  both  aort«e  give  oif  biaacdiea  which  are 
diatribnt«d  widely  through  tiie  body.  A  large  tnmk  liea 
on  the  tergal  aspect  oi  the  gangliimic  chain,  and  is  niut«d 
with  the  anterior  doisol  aorta,  by  a  lateral  aortic  arch,  on 
each  side  of  the  bodj.  The  veins,  on  the  other  hand,  are 
irregnlar  passages,  the  blood  of  whic^  is  oarriod  to  two 
afferent  pwItmnMry  rimtsw,  one  for  each  act  of  respiratory 

These  respiiatorj  orgsiu  are  fonr  pairs  of  flattened  sacs, 
which  open  externally  by  as  many  stigmata,  on  the  et^na 
of  the  four  posterior  free  thoracic  somites  (Fig.  85,  xi-xit) 

Fig.  87. 


Fig.e 


(After] 


d.) 


;  reiplnlory  lMfl«t*  of  Scorpb  a 


in  front  of  the  tail.  Each  lies  with  one  flat  aide  eternal 
and  the  other  tergal,  in  front  of  its  stigma,  and  its  walls 
are  bo  folded  as  to  divide  ite  cavity  into  a  multitude  of  sub- 
divisions, each  of  which  opens  into  the  oommoa  obamber 
which  commnBicates  with  the  exterior  by  the  stigma(f%.  87). 
The  organ,  in  fact,  somewhat  reeemblea  a  porte-motmaie 
irith  many  pockets.  The  blood  circulates  in  the  folds  and, 
after  being  thus  exposed  to  the  inflnence  of  the  air,  is 
carried  by  efferent  puimonary  nniiae*  to  the  pericardial  sinuB. 
Expiration  ia  effected  by  muHclca  which  pass  vertically  be- 
tween the  sterna  and  terga  of  the  free  eomites. 

The  bilobed  cerebral  ganglion  supplies  nerves  to  the  eyes 
and  chelicerw,  and  is  connected  by  thick  conunitsurea  with. 


378       THB  AKATOMT  OF  nTYSBTSBlLLTSI)  AVIILLLB. 

the  pofit-ceeophageal  ganglion,  a  large  oral  mass,  whence 
branches  are  given  to  the  Tnaxillm  and  following  aomitee. 
A  long  cord  formed  by  two  closely-applied  oomzniasnies 
passes  to  the  three  ganglia  placed  in  the  twelfth  to  the 
fourteenth  somites.  There  are  four  ganglia  in  the  ab- 
domen, two  distinct  cords  passing  from  the  last  to  its 
extremity.  The  visceral  nervous  system  is  represented  by 
an  oesophageal  ganglion  receiving  roots  from  the  cerebnd 
ganglion,  and  giving  branches  to  the  alimentaxy  canaL* 

Two  lateral  ovarian  tubes,  connected  by  transrerse  ana* 
stomoses  with  a  median  tube,  end  in  two  oviducts,  which 
open  by  a  fusiform  vagina  on  the  first  free  sternum  (ix). 
The  tubular  testes  end  in  a  pair  of  deferent  ducts,  on 
which,  before  their  union  at  the  common  orifice,  two  long 
and  two  short  cseca  are  found,  the  former  playing  the 
part  of  vesiculffi  seminales.  Both  male  and  female  organs 
lie  imbedded  in  the  hepatic  mass  in  the  posterior  thoracic 
region,  their  ducts  passing  forwards.  Partial  yelk-division 
takes  place,  and  the  ova  undergo  development  within  the 
ovarian  canals,  in  a  manner  which  is  very  fiimilar  to  that  of 
AsUteus.  Thus  there  is  no  metamorphosis,  and  the  young 
differ  but  little  from  the  adult  in  any  respect  but  size. 

The  Pseudo-scorpions  (Chelifer,  Ohigium)  resemble  the 
Scorpions  in  form  and  in  the  nature  of  their  appendages, 
but  they  have  no  aculeate  telson  nor  poison  gland.  They 
possess  silk-glands  which  open  close  to  the  genital  aperture, 
and  their  two  pairs  of  stigmata  are  connected,  not  with 
pulmonary  sacs,  but  with  tracheal  tubes.  According  to 
Metschnikoff,  the  eggs  undergo  complete  yelk-division,  and 
the  young  leave  the  egg  provided  only  with  that  pair  of 
appendages  which  become  the  pedipaJpi. 

In  the  number  of  the  appendages,  and  in  the  segmentation 
of  the  abdomen,  Oaleodei  (or  Solpuga)  agrees  with  the 
Scorpions  and  Pseudo- scorpions.  But  the  three  somites 
which  bear  the  three  hinder  pairs  of  ambulatory  limbs 

*  Newport,  ''On  the  stnic-  and  Maemrons  Araehnidm." 
tore  &o.,  of  the  nervous  and  cSr-  (*  Philosophical  Tianaaetion^' 
cuiatory  tyitemB  in  Myriapoda      1843.) 


l"'* 


THX  ABAinsnrA^ 


379 


(ti,  yii,  yiii  in  the  Scoipion)  retain  their  distinctnesB,  and 

there  is  no  cephalo-thorax,  in  the  proper  sense  of  the  word. 

In  form  and  function  the  pedipalps  resemble  the  first  pair 

of  ambulatory  limbs,  while  the  chelicene  are  subchelate. 

The  organs  of  respiration  are  tracheal 

The  PhalcmgidcB  {Phalangiv/m,  Chnylepius)  have  chelate 

chelicersB,  but  the  pedipalps  are  filiform  or  limb-like,  and 

the  articulated  abdomen   is  relatively  short  and  broad. 

They  have  no  silk-glands,  and  their  respiratory  organs  are 

tracheal. 

Fig.  88. 


^Stffk 


Fig.  88. — Mygale  c(ementana,—A,  female  of  the  nataral  rise:  At,  eheli- 
ceraB ;  iv',  pedi palpi ;  v*,  vi',  maxillary  feet ;  vii',  viii',  thoracic  feet ; 
Cthj  cephalo-thorax ;  B,  the  last  joint  of  the  pedipalpus  of  the  male 
much  magnified;  C.  terminal  Joint  of  the  chelicera  At^  with  the 
poiaon  gland ;  D,  the  left  pulmonary  sac  viewed  from  its  dorsal 
aspect ;  Stp,  stigma :  Pm,  pulmonary  lamellae ;  £,  the  two  arachni- 
dial  mammillae  of  the  left  side,  the  smaller  &>1  is  situated  on  the 
base  of  the  huge  one  S^2.    (After  Duges,  *  Regne  Animal.') 

While  the  last-mentioned  forms  lead  from  the  ArthrO' 
gastra  to  the  Acarina^  the  pulmonate  Phrynidoe,  or  Scorpion- 
spiders  {Thelyphonus,  Phrynvs),  are  in  many  respects  inter- 
mediate between  the  Arihrogastra  and  the  Araneina, 

The  Abaneina. —  The  Spidei-s  stand  in  somewhat  the 
same  relation  to  the  Scorpions,  as  the  brachynrons  to  the 
macmroas  Cnuiacea,    That  part  of  the  body  which  Ilea 


t 


330       THE  ANATOMY  OF  IKYXBTIBSATBD  ANIMALS. 

behind  the  ceplialo-thorax  and  answers  to  the  free  somites 
of  the  body  of  Scorpio  is  swollen,  and  presents  no  distinct 
division  into  somites. 

The  chelicersB  are  snbchelate,  that  is  to  say,  the  distal 
joint  is  folded  down  upon  the  next,  like  the  blade  of  a 
pocket  knife  upon  the  handle.  The  duct  of  a  poison  gland, 
lodged  in  the  cephalo-thoraz,  opens  at  the  summit  of  the 
terminal  joint.  The  pedipaJpi  are  filiform,  and,  in  the 
males,  their  extremities  are  converted  into  singular  spring 
boxes,  in  which  the  spermatophores  are  received  from  the 
genital  apertures  and  conveyed  to  the  female  (Fig.  88,  B). 

The  pulmonary  sacs,  two  or  four  in  number,  are  similar 
to  those  organs  in  Scorpio,  and  are  placed  in  the  anterior 
part  of  the  abdomen ;  a  tracheal  system  is  also  present,  a 
pair  of  sternal  stigmata,  situated  either  behind  the  pulmonary 
saes,  or  at  the  end  of  the  abdomen,  leading  into  two  more 
or  less  branched  tubes.  There  is  a  complex  pharyngeal 
apparatus,  probably  having  the  same  function  as  in  Scorpio* 
The  stomach  gives  off  csecal  prolongations  which  may 
extend  far  into  the  limbs.  There  is  usually  a  dilated  short 
rectum,  into  which  the  branched  Malpighian  ducts  open. 
The  nervous  system,  more  concentrated  than  that  of  the 
Arthrogastra,  is  reduced  to  a  supra-OBsophageal  ganglion  and 
a  single  post-<Bsophageal  mass,  with  four  indentations  on 
either  side.  There  are  six  or  eight  simple  eyea  in  the 
anterior  part  of  the  carapace.  Auditory  organs  have  not 
been  discovered  in  these  or  any  other  Arachnida, 

One  of  the  most  characteristic  organs  of  the  Araneina  is 
the  arachnidivm,  or  apparatus  by  which  the  fine  silky  threads 
which  constitute  the  web,  are  produced.  H.  Meckel,t  who  has 
fully  described  this  apparatus  as  it  occurs  in  Epeira  diadema, 
states  that,  in  the  adult,  more  than  a  thousand  glands, 
with  separate  excretory  ducts,  secrete  the  viscid  material, 

*  Lyonet*s  ^  Anatomie  de  diff^  piklps  of  the  male  spiders, 

nnteiesp^eef  d'lnsectet"  C  Mtfm.  t  *'  Mikrographie  einiger  DrG- 

daMiii^iim  d'Hiitoire  NatureUe,'  ten  -  apparate      der      nlederen 

1889)  ooatsins  an  elaborate  ao-  Thiere.*^  (Mailer's  Arohiv,  1846.) 

floapl  of  this  apparatoB,  as  well  See  abo  Buchbola  and  Landols. 

is  of  tlis  stmoture  of  the  pedi-  (Ibid.,  1868.) 


TBB  JJUBimi..  381 

whicb  when  ezpooed  to  the  air,  hardens  into  eilk.  These 
glands  are  diviaibU  into  five  different  kinds  (ociniform, 
ampnllate,  aggregate,  tubnlifonn,  and  tnberona),  and  their 
dncta  ultimately  enter  the  aix  prominent  arachnidial  mam- 
m^la,  which,  in  thi«  species,  project  from  the  hinder  end  of 
the  abdomen.  The  superior  and  inferior  Tnummillio  are 
three-jointed,  the  middle  one  ia  two-jointed.  Their  terminal 
r\g.  89,  A.  Fig.  W,  B. 


Fig.  8 


—The  heart  sod  ktMtIsI  tcucIi  of  the  u 


faces  are  tmncated,  forming  on  area  beeet  with  the  minnte 
anitfhMdtal  pa^Ue  b;  which  the  secretion  of  the  glanda  ia 
ponred  out. 

The  males  are  smaller  than  the  females,  and  their  ap- 
pioaohes  to  the  latter  are  made  with  extreme  oantion,  as 
ibej  mn  the  risk  of  being  devoured ;  extending  their  pedi* 
palps,  they  deposit  the  apermatophorea  in  tihe  female  genital 
ap«rtni«,  and  betake  themselTea  to  flight 


382     THK  ASATom  or  nrmBTiBKA.TiD  axjxai^ 

The  Anmeina  are  onparoiu,  bnt  the  development  of  Uie 
embiyo  takes  place  as  in  the  Artkrogeutra,  and  then  is  no 
metamorpliOBiB.* 

The  ACABIHA.— In  the  Hit«8  and  Ticks,  the  hinder 
eoniit«s  are,  as  in  the  Spiders,  distinctly  separated  from  obc 


Fig.  90.~Iioda  cicmm,  r>ii»le  (uter  PagciiitFCher).|  — a,  nundibabr 
booklets;  A,  i/,c^  fourth,  third,  &ndi«eondjoiDti  of  the  palp;  c,  book- 
lets of  eternal  larfece  of  proboaeii ;  /,  tax  of  tlie  praboeoU ;  t,  ttig- 
ma ;  h,  genital  aperture  ;  i,  anal  vafvee. 

another,  bnt  the;  am  not  separated  by  anj  constriotioii 
from  tbe  anterior  somites. 


•  CIspsiWe,  "Becherebes  em 
riwlafa  flM  AlSlBDrin,"  ISSS. 


t  '  Anatoraie  dcr  lUIben,'  IBCD. 


«    Tt 


THB  AOABIHA.  383 

The  bases  of  tlie  cbelicerse,  and  of  the  pedipalpi,  coalesce 
with  the  labram,  and  give  rise  to  a  suctorial  rostrum  (Fig. 
90). 

There  are  turaallj  several  gastric  cansa,  but  no  distinct 
liver.  Salivary  glands  occur  in  some,  and  Malpighian  caeca 
are  occasionally  found.  No  heart  has  yet  been  discovered. 
Special  respiratory  organs  are  sometimes  wanting  (e.  g, 
Sareopies) ;  when  present,  they  are  tracheal  tubes,  springing 
brush-wise  from  a  common  trunk  which  opens  by  a 
stigma.  The  stigmata  are  usually  two,  sometimes  anterior 
and  sometimes  posterior  in  position.  The  ganglia  of  the 
nervous  system  are  concentrated  round  the  guUet,  as  in  the 
Spiders;  and  the  reproductive  aperture  is  situated  far 
forwards,  sometimes  close  to  the  rostrum. 

The  greater  number  of  the  Acarina  are  parasites  upon 
other  animals  or  upon  plants. 

Most  are  oviparous,  but  the  OribatidtB  are  viviparous. 
The  course  o(  the  development  of  the  embryo  is  the  same  as 
in  the  Spiders.  The  young,  when  bom,  are  frequently  pro- 
vided with  only  three  pairs  of  ambulatory  limbs,  the  fourth 
pair  making  its  appearance  only  after  ecdysis  has  occurred. 

In  some  Acarina,  a  singular  kind  of  metamorphosis  occurs. 

Thus,  in  Aiax  Bonzif  Claparede  *  observed  that,  before  the 
limbs  appear  on  the  blastoderm,  a  chitinous  cuticula  is  sepa- 
rated and  forms  an  envelope,  which  he  terms  the  "  sac  of 
the  deutovum."  The  proper  vitelline  membrane  bursts 
into  two  halves,  much  as  in  Limulue,  and  the  deutovum 
emerges.  In  the  meanwhile,  the  anterior  end  of  the  blasto- 
derm becomes  fashioned  into  two  procephalic  lobes;  while  five 
pairs  of  tubercles,  answering  to  the  rudiments  of  the  cheli- 
cer»,pedipalpi,  the  two  posterior  gnathites,  and  one  pair  of 
thoracic  limbs  of  the  Spiders,  make  their  appearance  beneath 
the  sac  of  the  deutovum.  The  rudiments  of  the  chelicerse 
and  pedipalpi  apply  themselves  together,  and  coalesce  into 
a  proboscis.  Thus  the  first  larval  form  is  completed.  It 
tears  the  pseudoval  sac,  emerges,  and  buries  itself  in  the 

*  *<S(Ddien  an  Acariden."  (<  Zeitschrift  fBr  Win.  Zoologie. 
1868.)  * 


884       XBB  ANATOMT  OV  IIlVSBTIBBATmD  AXDUIB. 

bnnchue  of  th«  freebwatermnMel  (ITmo),  upon  vhieh  it 
iB  parasitic.  The  cnticnlar  inTestment  of  Hm  fiist  lam 
now  becomes  diBteoded  bj  absorption  of  Tater,  and  fanna 
K  globular  case,  the  limbs  bein^  drawn  oat  of  tiieir  rtf  the 
The  second  larval  stage  completes  itself  within  tlie  aao 
formed  b;  this  dngnlar  ecAjmi.    The  two  palpi  are  dere- 


Flg.  91,—Ammolhra  pfomgnoidti,  femtle  (ktter  QnktrefkgM).^ — ■, 
iEiaph4giu ;  d,  anteiiDa  ;  b,  iloDuoh  with  Iti  prolongatloa  Into  tta 
uitaniue  uid  limbi  « ,-  c,  reatum. 

loped  from  tbe  pedipalpal  portion  of  the  proboeoia;   two 
homj   books   from  the  oheliceral  portion;    and,   finallf, 
tite  binder  pair  of  thoracic  tirobs  is  added.     This  seotmd 
larva  gmdnaUf  passes  into  the  adult  Aiax. 
Is  the  Aoama  (Xyobia  eoarekUa)  of  tbe  Mouse,  ClaparUe 


THB  PYCNOOOKIDA.  385 

observed  tbat  the  deutoYum  stage  is  followed  by  a  tritoYum ; 
the  chitinous  sac,  which  invests  the  embryo  within  the 
deutovum,  apparently  representing  the  cuticle  of  the  first 
larva  of  Atax.  In  this  case,  it  presents  a  parallel  to  the 
Naupliue  cuticle  of  MysU. 

The  Arthrogastra,  the  Araneina  and  the  Acarina  (with 
some  doubtful  exceptions  among  the  latter)  possess  the 
same  number  of  appendages,  and  do  not  differ  from  one 
another  so  much  as  do  the  different  forms  of  the  Copepoda, 
among  the  Crustacea.  But  the  remaining  groups  which 
are  usually  included  among  the  Arachnida;  namely,  the 
Pycnogonida,  the  Arctisca,  and  the  Pentastomida,  diverge 
widely  from  the  Arthrogastra  and  the  Araneina,  though 
each  exhibits  certain  approximations  to  the  Acarina. 

The  Pycnooonida. — These  are  marine  animals  with 
short  bodies  terminated  in  front  by  a  rostrum  like  that  of 
the  Mites,  but  with  a  mere  tubercle  in  place  of  the  pos- 
terior thoracic  and  abdominal  somites.  The  adult  has  four 
pairs  of  enormously  elongated,  many-jointed  ambulatory 
limbs,  in  front  of  which  are  three  pairs  of  short  appen- 
dages, the  anterior  of  which  may  be  chelate,  while  the 
posterior  are  more  or  less  rudimentary  (Fig.  91). 

The  alimentary  canal  sends  off  very  long  csBca  into 
the  legs.  There  is  a  short  heart,  but  no  distinct  respi- 
ratory organs  exist.  A  cerebral  nervous  mass  is  con- 
nected with  a  ventral  chain  of  four  or  five  pairs  of  ganglia. 
Four  eyes  are  seated  upon  a  dorsal  tubercle  above  the 
brain.  The  sexes  are  distinct,  and  the  testes  and  ovaria 
are  lodged  in  the  legs  and  open  upon  their  basal  joints. 

The  embryo  emerges  from  the  egg  as  a  larva  provided 
with  a  rostrum,  and  with  three  pairs  of  appendages,  which 
represent  the  short  anterior  three  pairs  in  the  adult.*  The 
four  pairs  of  gieat  limbs  of  the  adult  are  produced  by  out- 
growths from  a  subsequent  posterior  elongation  of  the 
body. 

*  \,   Dohm,  *  Untersuchungen  uber  Baa  and  Entwickelang  der 
Arthropodeo.*    Enter  Hett.    1870. 


386       THK  ABATOMY  OP  IKV8BTXB&ATKD  AKIItLLB. 

The  comparison  of  the  embryos  of  the  Pyenogomda  with 

tiiose  of  the  ABarina,  ea^eciallj  sach  as  leave  the  egg  with 

three  paire  of  appeuda^a,  appear*  to  me  to  leave  little 

Fig.  M. 


I  itylela^ 


xino).— a.m  alb  with rfatrcl 
uUvar7El*D(k;  d,  MMmWt 
ii;  ff,  teitis;  1,^,8,4,  "-"^ 


llnpillw- 


(.ovary;  f 
Greaft*) 

donbt  that  the  rostrum  of  the  larval  Pyanagonmm  it  formed, 
u  in  the  Mitee,  by  the  coalesced  repreaentRtJTM  of  tbe 


THB  PXmrASTOMIDA.  887 

chelicene  and  pedipalpi.  If  so,  the  ■even  other  pairs  of 
limbs  are,  bj  three  pairs,  in  excess  of  the  nnmber  found  in 
any  Arachnidan.  On  the  other  hand,  the  hezapod  larva  of 
the  Pyenoganida  differs  from  the  hezapod  Naupliiu  of  the 
Cnuiaeea,  inasmuch  as  the  three  pairs  of  appendages  of  a 
Ndupliua  always  represent  antennary  and  mandibular  ap- 
pendages, and  these,  by  the  hypothesis,  are  to  be  sought  in 
the  rostrum  of  the  Pycnogonida. 

The  fact  to  which  reference  has  already  been  made,  that 
the  embryo  Scorpion  has  siz  pairs  of  rudimentary  appen- 
dages, attached  to  as  many  of  the  anterior  free  somites, 
of  which  one  pair  only  remain  (as  the  pectines)  in  the  adult, 
leads  me  to  suspect  that  the  Pycnogonida  may  represent  a 
much  modified  early  Arachnidan  form,  from  which  the 
Arthrogastra,  Araneidea,  and  Acaridea  have  branched  off. 

The  Abctisca,  orTABDiOBADA,  are  microscopic  animals, 
found  in  association  with  Botifera,  in  moss  and  in  sand, 
rarely  in  water,  which  present  many  points  of  resemblance 
to  the  Acarina,    The  body  (Fig.  92)  is  vermiform,  with  four 
pairs  of  tubercles  representing  limbs,  terminated  by  two 
or  more  claws.    The  fourth  pair  is  directed  backwards  at 
the  hinder  end  of  the  body,  so  that  if  these  appendages 
answer  to  the  hinder  pair  of  limbs  in  the  typical  Arachnida, 
the  hinder  thoracic,  and  all  the  abdominal,  somites  are  un- 
developed.   The  mouth  is  situated  at  the  extremity  of  a 
rostrum  provided  with  two  stylets,  which  is  so  like  that 
of  the  Acarina,  that  it  may  probably  be  regarded  as  formed 
by  the  coalescence  of  cheliceral  and  pedipalpal  tubercles. 
There  is  a  muscular  pharynz,  leading  into  a  wide  alimentary 
canal,  which  gradually  narrows  to  the  anus.    No  organs  of 
circulation  or  of  respiration  exist.      The  paired  ventral 
ganglia,  which  correspond    in  number  with  the    appen- 
dages, are  large.      They  are  connected    by  longitudinal 
commissures  with  one  another,  and  with  a  prsB-oesopha- 
geal    cerebral    mass  which    sometimes    bears    two    eyes. 
The  Aretieca  are  hermaphrodite,  the  ovarian  sac  and  the 
two  testes  opening  together  into  a  doacal  dilatation  in 


388       THE  ANATOm  OT  IHVSBTKBKATXD  liltr-^JJi 

wliich  the  intestine  terminEiteB.  The  ova  are  reiaiJveljreTy 
lar^e.  and  the  cuticle  of  the  parent  is  cast  off  and  enclosea 
them  when  thej  ore  laid,  ua  a  sort  of  ephippinm.  Com- 
plete jelk  division  takes  place.  The  jouug  have  one-third 
the  size  of  the  adnlt  when  they  are  hatched,  and  they 
undergo  no  netamorphoeia,  beyond  the  addition,  in  some 
cases,  of  one  pair  of  limba  after  birth.* 
The  Pentastomida. — A  still  more  abemuit  foi-m  is  the 


Fig.  91- 

.  eod  iif  Iha  body ;  a,  ■■■ .  ,     . 

c,  rudimenlu'y  p*1pifann  organi.    (Arii 

parautic  Idngwttula,  or  Penlattmn'um,  which  is  found  in 
ft  sexless  condition  in  the  lungs  and  liver  of  herbivorous 
mammals  and  of  reptiles,  and  in  the  sexual  state  in  the 
nasal  cavities  and  maxillary  antra  of  Carnivores.  Thus, 
1^    Lenckart*s   investigations   have  proved,  Penlaatornvm 


THE  PBNTASTOMIDA. 


389 


toBnioides,  which  inhabits  the  latter  Cavities  in  the  Dog  and 
the  Wolf,  is  the  sexual  state  of  the  P.  dentictUcUunif  which 
occurs  in  the  liver  of  Hares  and  Babbits.* 

The  Pentastomida  are  elongated  vermiform  animals,  the 
bodies  of  which  are  divided  by  close-set  transverse  con- 
strictions into  numerous  short  segments.  At  first  sight,  they 
appear  to  be  entirely  devoid  of  appendages,  but,  on  careful 
inspection,  four  curved  hooks  are  foimd,  two  on  each  side 
of  the  mouth,  which  is  situated  rather  behind  the  anterior 
extremity  of  the  body.  Each  hook  is  solid,  and  its  base 
projects  into  the  cavity  of  the  body  and  gives  attachment 
to  the  muscular  bands  by  which  it  is  moved. 

The  mouth  is  surrounded  by  a  chitinous  ring ;  a  narrow 
CBSophagus  leads  from  it  into  a  nearly  cylindrical,  straight, 

,  Fig.  94. 


Fig.  94. — Embryo  of  Pentastomum  tcdnioides, 

alimentary  canal,  which  terminates  in  the  anus,  in  the 
middle  line  of  the  posterior  extremity  of  the  body.  A 
mesentery  is  attached  to  the  whole  length  of  the  alimentary 
canal  and  holds  it  in  place.  A  nervous  rin^  surrounds  the 
oesophagus,  and  posteriorly  presents  a  ganglionic  enlarge- 
ment whence  nerves  ai*e  given  off  to  the  body.  The  muscles 
are  striated.  The  sexes  are  distinct,  and  the  males  are 
usually  much  smaller  than  the  females. 

The  testicle  is  an  elongated  sao  which  lies  on  the  ventral 
aspect  of  the  intestine,  and  is  connected  anteriorly  with 
two  vasa  deferentia.  These  terminate  on  the  fore  part 
of  the  ventral  aspect  of  the  body,  each  having  a  saccular 

*  *  Baa  and  Entwiokelungsgesehiehte  der  FentMtom^ix^  Y^^. 


390       THE  ANATOMY  OF  IKYEBTBBBATED  ANIMALS. 

dilatation  wliich  contains  a  very  long,  coiled,  chitinoos  penis. 
In  the  female,  the  ovary  is  also  a  large  sac  and  the  ovi- 
ducts come  off  from  its  anterior  end,  but  the  genital 
aperture  is  close  to  the  anus. 

The  ova  undergo  their  development  in  the  ovary.  The 
embryos  are  oval,  but  taper  to  the  posterior  end.  In 
the  middle  line,  in  front,  are  three  sharp  protractile 
,  styles,  of  which  the  middle  is  the  longest.  Two  pairs 
of  articulated  limbs  are  attached  to  the  middle  of  the 
ventral  aspect;  each  is  terminated  by  a  double  hooked 
claw.  The  embryo  of  Lingtuitula  thus  resembles  those 
of  the  Acarina,  on  the  one  hajid,  and  those  of  such  parasitic 
Crustacea  as  Anchorella^  on  the  other. 

In  the  case  of  Pentatiomum  Uenioides,  the  embryos,  enclosed 
in  their  vitelline  membranes,  pass  out  of  the  bodies  of  the 
dog  or  wolf,  along  with  the  nasal  mucus.  Taken  into  the 
body  along  with  the  food  of  the  hare  or  rabbit,  they  emerge 
from  the  egg,  penetrate  the  walls  of  the  intestine,  and 
lodge  themselves  in  the  liver.  Here  they  become  encysted, 
grow,  and  go  throiigh  a  seiies  of  changes  of  form,  accom- 
panied by  repeated  ecdyses,  until  they  pass  into  the  state 
known  as  Pentastomum  denticulatum.  If  the  flesh  of  the 
rodent  containing  P.  denticulatum  is  devoured  by  a  dog,  the 
parasite  passes  into  the  frontal  sinuses,  or  maxillary  antra 
of  the  latter,  gradually  takes  on  the  form  of  P.  tcenioides^ 
and  acquires  sexual  organs.  The  parasitism  of  the  Pen^ 
tastomida,  therefore,  is  very  similar  to  that  of  the  Cestoidea, 

Spiders  and  Mites  abounded  in  the  tertiary  epoch,  as  their 
remains  preserved  in  amber,  show.  Various  Arthrogastra 
occur  in  themesozoic  formations,  while  Spiders  and  Scorpions 
of  large  size  have  been  found  in  the  carboniferous  rocks. 

The  Mykiapoda.  —  In  these  Arthropods,  the  body  is 

divided  into  many  segments,  the  most  anterior  of  which 

takes  on  the  characters  of  a  distinct  head ;  and  almost  all 

tiiese  segments  bear  articulated  limbs  terminated  by  claws. 

la  tlie  Centipedes  (Chilopoda),  the  segments  of  the  body 

Iwre  broad  stema,  and  the  bases  of  the  limbs  are  far  apart; 
Ik 


THE  KTBUPODX.  391 

but,  in  the  Millipedes  [Chiiognatlia),  the  stenul  region  it 
mdimentaiy,  and  the  bases  of  the  limbs  are  close  together. 
Uoreover,  in  the  latter  group,  the  miyjoritj  of  the  segments 
of  the  bodj  bear  two  pairs  of  limbs,  sai  probably  represent 
two  somites. 

Pig.  95. 


n  (CA%»4i)- 


The  bead  ia  either  flatt«ned  front  above  downwards 
[Chilopoda),  or  from  before  backwards  {ChiUi^naiha).  Some 
species  are  blind,  but  the  majority  bare  ejee,  which  are 
generallj  aniall  and  not  very  numerous  ocelli,  though,  in 

*  '  Bigne  AnimaL'    lllnttnUd  edition. 


392       THE  ANATOXT  OF  II[TEBTKBBA.TKD 

BOm«  caaea,  they  are  lai^  compound  «jei.    Tliere  ia  almje 
»  pair  of  jointed  uiteiuuB. 

The  miyoritj  liave  the  mouth  conaliiict«d  for  biting,  and 
are  prorided  with  a  pair  of  mandibles,  the  most  important 
pecnliaritj  of  which  is  that  they  are  jointed,  and  tliaB 
depart  le«a  from  the  type  of  the  ordinary  limb  than  do 


Fig.  98— SmfcpBHfro  Hop>:l  (sfler  Newport). 

A,  duFMl  view  of  the  uilerior   part  of  the  bodj.    a.  antcniiM.     A, 
ccphallo  wgnient;  B,  builar  segmrnt. 

B,  imtnl  Yiew  of  theheftil ;  n,  B,  M  bsforc. 

C,  under  view  of  the  eephnlio  wgineiit,  ■howing  the  uitennK,  a  ;  the 
e}e>*;  tbe  l&bmin  and  the  mandibles,  iv'.   - 

D,  the  lecond  pair  of  gnathitet  v',  and  the  finC  pair  uf  appeniJaBCi  of 
the  baallai  Hginent  vi'. 

those  of  insects,  while,  to  the  same  eitent,  they  approach 
the  gnathites  of  the  Peripaiidea.  The  mandibles  are  more 
modified  in  the  Chiiopoda  (Fig.  96)  than  in  the  ChilogiuMa. 
In  the  latter,  the  second  pair  of  gDatbit«B  form  a  broad 
lonr-lobed  plate  which  plays  the  part  of  on  underlip,  while, 


THB  MYBIAPODJL.  893 

in  the  ChUapoda,  thej  are  soft  and  jointed,  and  nnited  at 
their  bases  bj  a  bilobed  median  process  (Fig.  96,  y').  In 
the  Chilogncdha  the  four  segments  which  follow  the  head  are 
free,  and  their  appendages .  resemble  ordinary  limbs.  The 
anterior  pair  is  tamed  forwards  and  comes  into  relation 
with  the  month,  and  the  tergam  of  the  first  somite  is  often 
enlarged ;  of  the  other  three  somites,  the  appendages  of  one 
appear  to  be  always  abortive.  Thus  there  are  three  seg- 
ments with  single  pairs  of  legs.  The  rest  eackbear  two  pairs. 

In  the  Chilapoda,  on  the  contrary,  the  head  is  followed 
by  a  basilar  segmeni  (Fig.  96,  B),  formed,  according  to 
Newport,  by  the  union  of  four  embryonic  somites,  and 
carrying  three  pairs  of  appendages.  Of  these  the  first  are 
limb-like,  but  are  turned  forwards  beneath  the  mouth  (Fig. 
96,  D  Yi') ;  the  second  pair  are  the  strong  recurved  poison- 
claws,  and  the  hindermost  pair  may  become  functional  legs, 
resembling  those  which  are  attached  to  the  succeeding 
somites,  but  are  always  smaller  than  the  others,  and  may  be 
altogether  aborted  in  the  adult  The  somites  of  the  body 
never  bear  more  than  one  pair  of  limbs. 

The  alimentary  canal  is  usually  straight  and  simple,  like 
that  of  an  insect  larva.  There  are  large  salivary  glands, 
and  the  intestine  is  provided  with  Malpighian  tubules. 

The  heart  extends  through  the  greater  part  of  the  length 
of  the  body,  and  is  many-chambered,  there  being  one 
chamber  for  each  of  the  somites  in  which  it  lies.  Each 
chamber  is  somewhat  conical  in  shape,  being  broader  behind 
than  in  front,  and  admits  the  blood  by  a  pair  of  lateral 
clefts,  while  the  blood  leaves  it,  in  part,  by  the  communica- 
tion with  the  adjacent  chamber,  in  part,  by  lateral  arterial 
branches.  A  median  aortic  trunk  continues  the  heart  for- 
wards, and  the  lateral  trunks  encircle  the  OBsophagus  and 
unite  into  an  artery  which  lies  upon  the  ganglionic  chain. 
The  arterial  system  in  the  ChUopoda  is,  in  fact,  as  complete 
as  that  of  the  Scorpions.* 

*  Newport,  *'  On  the  structure,      in  the  Mvriapoda  and  macrurous 
relations  and  development  of  the      Arachnida."  (*  Philosophical 

nervous  and  circulatory  systems      Transactions,'  1863.) 


394        THE    ANATOMY    OF    INVERTEBRATED   ANIMALS. 

The  respiratory  organs  are  trachese,  which  open  by  stig- 
mata on  the  lateral  or  ventral  surface  of  more  or  fewer  of 
the  somites.  In  Scutigera  the  stigmata  are  situated  in  the 
median  dorsal  line  of  the  body. 

The  nervous  system  presents  a  ventral  chain,  with  a  pair 
of  ganglionic  enlargements  for  each  segment  of  the  body, 
the  most  anterior  of  which  are  connected  by  commiasures, 
which  embrace  the  oesophagus,  with  the  cerebral  ganglia. 

The  ovary  in  both  ChUognaiha  and  Chilopoda  is  long, 
single,  and  tubular  in  form.  It  lies  above  the  alimentary 
canal  in  the  latter,  between  the  alimentary  canal  and  the 
nervous  system  in  the  former.  The  double  vaginsB  open  on, 
or  close  behind,  the  bases  of  the  second  pair  of  legs  in  the 
ChUognaiha ;  at  the  posterior  end  of  the  body,  beneath  the 
anus,  in  the  ChUopoda,  Two  spermathecss  and  eoUeterial 
glands  are  very  generally  present. 

The  testes  in  the  ChUognaiha  are  tubular  glands,  which 
occupy  the  same  position  as  the  ovary  and  open  in  the  same 
region.  They  have  lateral  cseca,  and  are  connected  by 
transverse  ducts.  Two  copulatory  organs,  or  penes,  are 
developed  on  the  sternal  face  of  the  sixth  segment  which 
follows  the  bead,  or  are  connected  with  the  bases  of  the 
seventh  pair  of  legs. 

In  the  Chilopoda  there  is  a  good  deal  of  variation  in  th4 
structure  of  the  testis.  Thus  in  LUhobius,*  the  testis  is  a 
single  filiform  tube,  connected  at  the  hinder  end  with  two 
deferent  ducts  which  embrace  the  rectum.  A  large  caBcum, 
apparently  a  vesicula  seminalis,  opens  into  each  deferent 
duct.  But,  in  most  Chilopods,  the  testes  are  fusiform  acini, 
imited  by  delicate  ducts  with  a  median  vas  deferena 
Two,  or  four,  pairs  of  accessory  glands  are  connected  with 
the  opening  of  the  male  apparatus. 

The  spermatozoa  are  enclosed  in  spermatophores  in  Seohh 
pwdra,  Crypiops,  and  ChophUus, 

The  ChUognaiha  copulate.  In  Olomeris  and  Pol]fxenus  the 
genital  apertures  of  the  two  sexes  are  brought  together 

:   *  Favre,  **  Anatomie  dee  organes  reprodacteurs  des  Myriapodes.** 
•f^Aanalca  des  Sciences  Matiirelles,*  18D5.) 


THB  MTBIAPODA.  895 

during  copulation ;  but,  in  Itdua,  the  penes  of  the  male  are 
charged  with  the  spermatic  fluid  before  copulation  takes 
place,  and  it  is  by  their  agency  that  the  female  is  impreg* 
nated. 

The  Chilopoda  have  not  been  observed  to  copulate,  indeed 
the  female  shows  a  tendency  to  destroy  the  males,  as  among 
Spiders.  The  male  €hophilus  spins  webs  like  those  of 
spiders  across  the  x>assages  which  he  frequents,  and  deposits 
a  spermatophore  in  the  centre  of  each, 

Metechniko£f  *  has  recently  shown  that,  in  the  ChUogfuUha, 
the  process  of  yelk-division  is  complete,  and  confirms  the 
observation  of  Newport  (Phil.  Trans.  1841)  that  the  sternal 
face  of  the  blastoderm  becomes  sharply  infolded  down  its 
centre,  in  such  a  manner  that  the  anterior  and  the  posterior 
halves  of  that  face  of  the  embryo  become  closely  applied 
together.  MetschnikofF  further  points  out  that  only  two 
pairs  of  appendages  are  converted  into  gnathites;  and 
that  a  chitinous  cuticula,  apparently  identical  with  what 
Newport  describes  as  the  "amnion"  in  lulus,  is  early 
thrown  off  from  the  embryo.  In  some  species,  it  developes 
a  median  tooth-like  process  which  serves  to  burst  the 
vitelline  membrane.  Newport  describes  a  short  cord,  or 
funiculus,  which  connects  the  anal  extremity  of  the  embryo 
with  the  so-called  "amnion."  It  is  not  improbable  that 
this  is  simply  the  continuation  of  the  first  larval  skin  into 
the  rectum. 

The  embryo  lultu  at  first  bursts  the  vitelline  mem* 
brane,  and  is  enclosed  only  in  the  embryonic  integument. 
At  this  period,  its  body  is  divided  into  eight  segments,  of 
which  the  first  represents  the  head.  Traces  of  the  antennse 
are  visible  on  the  sides  of  the  head,  and  the  four  following 
segments  exhibit  papillsB;  those  of  the  second,  third  and 
fifth  segments  develope  into  the  three  pairs  of  functional 
limbs,  with  which  the  young  myriapod  is  at  first  provided. 

Between  the  terminal  segment  and  the  seventh,  the  body 
grows    and  becomes  divided    into    six  rudimentary  new 

*  **  Embryologie   der   doppelftUsigen   Myriapoden  {Chiloynatha)." 
(« Zeitsohrift  fur  Wiss.  Zoologie,'  1874.) 


There  is  this  difference,  however,  bet' 
tlio  larval  inyriapiMl.  that  since,  iu  tl 
ouly  twu  pairs  of  <^iiathites,  which  r 
mandibles  and  first  maxillae  of  iusecl 
appendages  of  the  second  segment 
second  maxillsQ  of  insects;  and  hen< 
apparently  the  oame  number  of  somit 
there  must  in  reality  be  one  fewer  in 
myriapod  larva  therefore,  notwithsta 
character,  is  essentially  different  from 

The  sixth  and  the  seventh  segment 
of  legs,  as  do  all  the  newly-formed  i 
worthy  of  notice  that  the  male  copula 
much  as  it  is  situated  in  the  seventh 
segment  in  the  adult,  is  developed  froi 
segments  of  the  embryo,  and  not  in 
added  segments.  New  segments,  each 
pairs  of  limbs,  are  developed  by  su 
region  between  the  penultimate  segmei 
of  the  newly -formed  segments,  until 
the  adult  is  complete. 

In  all  other  Chilognaiha  of  which  1 
been  traced,  the  young,  at  first,  posses 
#nT»/»firtTift.l  Ifiopfl :  and  one  of  the  four  oi 


THB   IN8BCTA.  397 

early  stages  of  development  of  Oeophiltts  have  been  de- 
scribed by  Metsclmikoff.*  Complete  yelk-division  takes 
place,  and  when  the  young  leaves  the  egg  it  has  a  cylindri- 
cal body,  like  that  of  one  of  the  Chilognatha,  and  possesses 
many  pairs  of  limbs.  Newport  f  has  pointed  out  that,  in 
Geophilus  longicomis,  the  basilar  segment  is  formed  by  the 
confluence  of  four  somites,  of  the  appendages  of  which  only 
two  are  ultimately  developed.  Thus  the  basilar  segment 
of  the  head  of  the  ChUopoda  appears  to  correspond  very 
closely  with  the  four  somites  which  follow  the  head  in  the 
Chilognatha.  Under  these  circumstances,  the  difference  in 
the  position  of  the  reproductive  apertures  in  the  two  groups 
is  exceedingly  remarkable. 

Fossil  Myriapoda  occur  both  in  the  tertiary  and  secon- 
dary formations,  and  there  seems  no  reason  to  doubt  that 
the  Xylohius  sigillarioR  discovered  in  the  coal  of  Nova  Scotia 
by  Lyell  and  Dawson  is  to  be  referred  to  this  group. 

The  Insecta. — Notwithstanding  the  vast  number,  and 
the  singular  diversity  of  form  of  Insects,  the  fundamental 
unity  of  their  structure  is  remarkable,  and,  in  this  respect, 
the  group  exhibits  a  striking  conti*ast  to  the  Crustacea. 

The  division  of  the  body  into  three  regions,  head,  thorax 
and  abdomen,  is  usually  well  marked,  not  only  by  the 
peculiar  modifications  which  the  cephalic  and  thoracic 
somites  undergo,  but  by  the  attachment  of  the  three  pairs 
of  ambulatory  limbs  exclusively  to  the  latter.  The  head 
possesses  four  pairs  of  appendages,  that  is  to  say,  one  pair 
of  antennsB  and  three  pairs  of  gnathites ;  and,  as  a  general 
rule,  there  is  a  pair  of  compound  eyes,  sessile  upon  the  sides 
of  the  head;  sometimes  simple  eyes  are  added  to  them. 
The  first  pair  of  gnathites  are  the  mandihlesj  which  are 
always  devoid  of  a  palp.  The  second  pair  are  the  maxillcsy 
which,  in  those  insects  in  which  the  mouth  is  least  modified, 
are  distinct  from  one  another  and  laterally  moveable ;  while 

*  *  Zcitschrift  fur  Wiss.  Zoolo-       riapoda,  order  Chilopoda.  (Trans- 
gie,'  1875.  actions  of  the  Linnean  Society, 

t  Monograph  of  the  class  My-      zix.) 


398       THE   ANATOMY   OF   INVEBTEBRATED  ANIMALS. 

the  third  pair  of  gnathites  are  united  together  in  the 
median  line,  and  constitate  the  ItMum  of  entomologistL 
In  front  of  the  oral  aperture  is  a  median  plate,  the  lahntm; 
while  from  the  floor  of  the  mouth  formed  bj  the  lahinm 
another  median  process,  the  lingua,  is  osnally  developed. 

It  is  hardly  open  to  doubt  that  the  mandibles,  the  tna^yil^m^ 
and  the  labium,  answer  to  the  mandibles  and  the  two  pain 
of  maTJllffi  of  the  crustacean  mouth.  In  this  case,  one  pair 
of  antennaiy  organs  found  in  the  latter  is  wanting  in  in- 
sects, as  in  other  air-breathing  Arthropods,  and  the  existeiiee 
of  the  corresponding  somite  cannot  be  proved.  But  if  it 
be  supposed  to  be  present,  though  without  any  appendage, 
and  if  the  eyes  be  taken  to  represent  the  appendages  of 
another  somite,  the  insect  head  wiU  contain  six  somites, 
the  prsBoral  sterna  being  bent  up  towards  the  tergal  aspect* 
as  in  the  higher  Crustacea. 

The  three  somites  which  succeed  the  head  are  termed 
respectively  prothoraXf  mesothorax,  and  metaihorax.  A  pair  of 
legs  is  normally  attached  to  each ;  and,  when  wings  exist, 
they  are  lateral  expansions  of  the  tergal  region  (corre- 
sponding with  the  pleura  of  Cnuiacea)  of  the  mesothoraz 
or  the  metathorax,  or  of  both. 

In  the  abdomen  there  are,  at  most,  eleven  somites,  none 
of  which,  in  the  adult,  bear  ambulatory  limbs.  Thus, 
^^iMmTnlng  the  existence  of  six  somites  in  the  head,  the 
normal  number  of  somites  in  the  body  of  insects  will  be 
twenty,  as  in  the  higher  Crustacea  and  Amchnida,* 

One  of  the  commonest  of  insects,  the  Cockroach  {Blatta 
{Periplaneta)  orientdlia)  is  fortunately  one  of  the  oldest,  least 
modified,  and  in  many  ways  most  instructive  forms ;  at  the 
same  time,  it  is  not  too  small  for  convenient  dissection.t 

In  this  insect,  the  head  is  vertically  elongated,  flattened 

*  It  It  open  to  quef  don  whether  four  lor  the  heed,  three  for  tht 

Hm  podienl   plates   repraeent  a  thorax,  and  ten  for  the  abdomen. 

■OMite;  and  toerelbre  it  mutt  be  t  8^  f^r  an  excellent  fignn 

weoliaflted  that  the  total  number  anddeecription,  Rolleston,*  Forms 

af  somites,  the  existence  of  which  of  Animal   Life,'  p.  IW,  plate 

be  aetoaUy  demonstrated  In  vi. 


JasfifltSi  Is  only  seventeen,  vis., 


THE  COOKBOACH.  399 

from  before  backwards,  and  connected  by  a  distinct  neck 
with  the  prothorax.  The  antennsB  are  slender,  as  long  as,  or 
rather  longer  than,  the  body.  Large  reniform  compound 
eyes  are  situated  at  the  sides  of  the  head.  The  tergal  por- 
tion of  the  prothorax  {pronotwrn)  is  a  wide  shield,  which 
overlaps  the  head,  in  front,  and  the  tergal  portion  of  the 
mesothorax,  or  mesonotum,  behind.  The  legs  are  strong, 
and  increase  in  length  from  the  first  pair  to  the  last.  The 
abdomen  is  flattened  from  above  downwards,  and  bears  a 
pair  of  elongated,  many-jointed,  setose  styles  {cerci)  at  its 
hinder  extremity. 

The  males  differ  very  considerably  from  the  females. 
They  have  two  pairs  of  wings,  of  which  the  anterior  are 
brown,  and  are  of  a  stiff  and  homy  texture.  As  they  serve 
to  cover  the  posterior  wings,  they  are  termed  teffmina. 
When  closed,  the  left  overlaps  the  right,  and  they  extend 
back  as  far  as  the  posterior  edge  of  the  tergum  of  the  fifth 
abdominal  somite. 

The  posterior  wings,  on  the  contrary,  are  thin  and  mem- 
branous;  and,  in  a  state  of  rest,  are  folded  longitudinally 
upon  themselves,  the  folded  edge  being  internal.  In  this 
condition  they  are  triangular,  the  base  of  the  triangle  lying 
close  to  the  posterior  edge  of  the  fourth  abdominal  somite, 
and  the  right  a  little  overlapping  the  left.  When  forcibly 
unfolded  and  made  to  stand  out  at  right  angles  to  the  body, 
each  of  these  wings  is  seen  to  have  a  nearly  straight, 
thickened,  anterior  edge,  while  its  rounded  outer  and  pos- 
terior edges  are  very  thin.  The  wing  is  strengthened  by 
radiating  thickenings,  or  nervures,  united  by  delicate  trans- 
verse ridges ;  and,  when  left  to  itself,  it  springs  back  into 
its  folded  state  with  some  force. 

The  abdomen  of  the  male  is  not  very  broad.  The  sterna 
of  the  abdominal  somites  are  all  flattened;  and,  to  the 
hindermost,  two  minute  u^jointed  styles  are  attached, 
while  some  singular  hooked  processes  are  seen,  on  close 
inspection,  to  protrude  between  the  hindermost  tergum  and 
the  hindermost  sternum.  The  abdomen  of  the  female  is 
yery  much  broader,  especially  towards  the  middle  of  ita 


1*'»'">    TKK  ANATOMY  OF  IN VEKTEDKATKD  ANIMALS. 

length.  Tlio  hin<lermust  sternum  is  convex  and  lx>at -shaped, 
and  its  posterior  half  is  separated  along  the  middle  line  into 
two  halves,  united  only  by  a  thin  and  flexible  membrane. 
Sometimes,  the  great  egg-case,  which  the  female  carries 
abont  for  some  time  before  it  is  laid,  is  seen  protrading 
between  the  posterior  terga  and  sterna.  The  female  has 
moveable  tegmina,  but  they  are  very  small,  inasmuch  as 
they  do  not  extend  beyond  the  middle  of  the  metathoraic, 
and  are  wi<Iely  separated  in  the  middle  line ;  they  are,  in 
fact,  mere  rudiments  of  the  anterior  wings.  The  posterior 
wings  appear,  at  first,  to  be  altogether  wanting.  But  the 
outer  extremities  of  the  metanotum,  or  tergal  portion  of 
the  metathorax.  present  triangular  areas,  in  which  the  in- 
tegument is  very  thin  and  exhibits  markings  which  simu- 
late the  nervures  of  the  wings.  There  can  be  no  doubt, 
in  fact,  that  these  are  undeveloped  wings,  and  they  show,  in 
a  very  instructive  manner,  that  the  wings  are  modiflcations 
of  that  part  of  the  insect  skeleton  which  answers  to  the 
pleura,  and  therefore  to  the  lateral  parts  of  the  carapace, 
of  a  crustacean. 

The  convex  dorsal  wall  of  the  head  of  the  Cockroach 
(Fig.  97),  is  termed  the  epicranium,  A  median  suture,  the 
epicranial  ntture,  may  be  seen,  especially  in  young  Cock- 
roaches, traversing  it  from  before  backwards,  and  dividing 
between  the  eyes  into  two  branches,  one  of  which  passes 
towards  the  articulation  of  each  antenna.  The  basal  joint 
of  the  antenna  is  attached  to  a  transparent  flexible  mem- 
brane, which  occupies  an  oval  space,  the  antennaiy  fossa, 
and  allows  of  the  free  play  of  the  antenna.  A  little  pro- 
jection of  the  hard  chitinous  skeleton  when  it  bounds  the 
inferior  margin  of  the  fossa,  helps  to  support  the  joint. 
On  the  inner  side  of  and  above  the  antennary  fossa,  there  is 
an  oval  fenestra,  covered  only  by  a  thin  and  transparent 
portion  of  the  integument,  which  allows  a  subjacent  tissue 
d  glistening  white  appearance  to  be  seen  (Fig.  97, 1.  II.  h). 
These  have  been  regarded  as  rudimentary  ocelli  by  some 
entomologists ;  but  their  structure  needs  careful  examina- 
tkm  before  this  view  can  be  adopted. 


THX  COCKBO^CR,  4ftl 

The  tnuuparent  cornea,  of  the  eje.  aitnated  external  to 
and  behind  the  antennaij  foaaa,  is  elongated,  wider  abOYe 


Fig.  V3.—  Btatla  otienlaliM.—l.  II.  lid*  and  fhint  vlem  of  the  head; 
a.  the  epicnnld  lurure,  kt  the  endi  of  the  lateral  bnuidie*  of  which 
■re  h.  the  feneelm-,  /,  tba  anteniuc  ;  g,  the  efca',  &,  the  labrnai; 

-      -'--  -naiKliblei  «i,Uib  aardii;  •(  tb«»tipo»;  ja,  the  g"- 


the  palpal  of  the  maxilla ;  p,  the  pUpDi,  a,  the  mentom  and  lub- 
mentum  of  (he  labium  ;  i,  Che  margins  of  the  occipital  forameD  ;  i, 
t,  inferior  ceriieal  ■clerilei ;   le,    lateral  cerrical   lolerltaij   p  a, 

KT    "■" 


in.  the   labium  'aad'  the  right  maiilla,  TiVw«l'  f^ 
,    letter!  ai   before  except  b,  lacinia  of  the  maxilla ; /ip, 
paraglouee  ;  U,  llgnla  -,  %  mentum  ;  na,  labmeDtum  of  the  lahlnm. 

than  below,  and  has  aconcare  uit«Tior,  and  alightlf  convts 


402       THE   ANATOMY   OF    IXVERTEBRATED   ANIMALS. 

posterior  margin.  The  numerous  facets  into  which  the 
oomea  is  divided,  are  hexagonal  in  8hax>e,  and  very  small. 

The  broad  flattened  region  of  the  fore  part  of  the  head, 
on  the  oral  side  of  the  epicranial  sntore,  is  the  elypeu9.  It 
is  prolonged  in  front  of  the  month,  and  with  the  truncated 
edge  of  this  prolongation,  the  flap-like  labnun  is  freely 
articulated.  Behind  the  labmm  are  two,  very  stout,  corred 
mandibles,  strongly  toothed  at  their  extremities  (Fig.  97, 
II.  m  n).  Each  mandible  is  articulated  with  the  truncated 
edge  of  the  lateral  part  of  the  skeleton  of  the  head,  beneath 
the  eyes,  which  is  termed  the  gena,  in  such  a  manner  as  to 
be  freely  moveable  towards  and  from  the  median  line,  but 
in  no  other  direction.  The  proximal  end  of  the  TnnTilla 
(Fig.  97,  m.)  is  formed  by  an  elongated  basal  articulation, 
the  cardo,  which  is  directed  transversely  to  the  axis  of  the 
head,  and  is  connected  with  the  inferior  margin  of  the  epi- 
cranium,  or  rather  with  a  thin  skeletal  band  which  runs 
round  the  posterior  margin  of  the  epicranium,  and  is  firmly 
united  with  it  only  on  its  dorsal  side.  This  band  forms  the 
boundary  of  the  so-called  oecipUal  foramen,  by  which  the 
cavity  of  the  head  communicates  with  that  of  the  neck,  the 
chitinous  wall  of  the  latter  region  being  continuous  with 
it.  Articulated  at  right  angles  with  the  cardo  is  the  Hipes, 
or  second  joint  of  the  maxilla.  This  is  freely  moveable  in 
the  lateral  direction,  and  its  outer  distal  angle  bears  the 
continuation  of  the  limb,  or  palpus^  formed  by  two  short 
and  three  long  joints.  Two  processes  terminate  the  stipes ; 
of  these  the  anterior  and  outer,  the  galea,  is  soft,  rounded 
and  possibly  sensoiy  in  function,  while  the  posterior  and 
inner — the  ladnia—  is  a  curved  cutting  blade  with  a  toothed 
and  spinose  inner  edge. 

The  labium  (Fig.  97,  III.)  consists  of  two  incompletely 
separated  median  plates,  the  wbmerUwn  behind,  and  the 
mewhim  in  front;  upon  the  latter  follows  a  bilobed  terminal 
piece,  the  Ugula,  each  lobe  of  which  is  again  divided  lon- 
gitadinally  into  two  portions,  which  have  considerable 
nxnUarity  to  the  galea  and  lacinia  of  the  maxilla.  The  outer 
ii  usually  termed  the  parciglosM, 


THB  COOXBOACH.  403 

Between  the  mentmn  and  the  ligala,  on  each  outer  edge 
of  the  labium,  a  small  piece,  the  pcUpiger,  is  articulated ;  it 
bears  the  three-jointed  labial  palpus,  which  is  to  be  regarded 
as  the  proper  free  termination  of  the  second  maxilla.  The 
resemblance  between  the  labium  and  a  pair  of  wiftTillya 
which  have  coalesced,  is  obyious. 

The  submentum  is  not  directly  articulated  with  the 
cranial  skeleton,  but  its  posterior  edge  is  close  to  one  of 
the  eerviedl  telerUea,*  or  skeletal  elements  observable  in  the 
chitinous  integument  of  the  neck,  of  which  there  are  alto- 
g^her  seven.  One  is  dorsal,  median,  and  marked  bj  a  deep 
longitudinal  depression.  It  articulates  with  the  dorsal 
margin  of  the  occipital  foramen.  Four  are  lateral,  two  on 
each  side  (Fig.  97, 1,  le) ;  these  take  an  oblique  course  from 
the  dorsal  part  of  the  boundary  of  the  occipital  foramen, 
with  a  tubercle  of  which  the  anterior  piece  is  articulated,  to 
the  anterior  edge  of  the  epistemimi  of  the  prothorax.  The 
inferior  cervical  sclerites  (Fig.  97,  I.  ic)  are  two  narrow 
transverse  plates,  one  behind  the  other  in  the  middle  line. 
Thej  appear  to  represent  the  part  called  ffula,  which  in  many 
insects  is  a  large  plate,  confluent  with  the  epicranium  above 
and  supporting  the  submentum  anteriorly.  I  think  it  is 
probable  that  these  cervical  sclerites  represent  the  hinder- 
most  of  the  cephalic  somites,  while  the  band  with  which  the 
Tnn-TiUm  are  united,  and  the  gense,  are  all  that  is  left  of  the 
sides  and  roof  of  the  first  maxillary  and  the  mandibular 
somites ;  the  epicranial  expansions  being  mainly  formed  by 
the  upward  and  backward  extension  of  the  ophthalmic  and 
antennary  sterna,  which  arise  out  of  the  procephalic  lobes  of 
the  embryo.  In  addition  to  these  externally  visible  sclerites, 
there  is  a  sort  of  internal  skeleton  (endocraniwn  or  ten- 
torium), which  extends  as  a  cruciform  partition  from  the 
inner  face  of  the  lateral  walls  of  the  cranium,  close  to  the 
articulation  of  the  mandible,  to  the  sides  of  the  occipital 

*  I  me  this  term,  in  the  senie  nous  skeleton.    It  Is  to  the  latter 

in  which  it  has  been  employed  by  what  a  distinct  ossification  is  to 

Milne-Edwards,  to  denote  any  de-  the  skeleton  of  a  venebrated  ani- 

finite  hardened  part  of  the  ebiti-  mal. 


404       THE  ANATOMY  OF  INYEBTEBSATED  ANIMALS. 

foramen.  The  centre  of  the  cross  is  perforated  bj  a  rounded 
ax>ertiire,  through  which  the  oesophageal  nerye-commissores 
pass.  The  commencement  of  the  oesophagus  traversee  the 
interspace  between  the  anterior  processes  of  the  cross ;  the 
tendons  of  the  great  adductors  of  the  mandible  pass  through 
the  lateral  apertures ;  and  the  backward  continuation  of  the 
gullet  enters  the  thorax  through  the  posterior  aperture,  in- 
cluded between  the  tentorium  and  the  margins  of  the 
occipital  foramen. 

In  each  somite  of  the  thorax,  a  distinct  median  sclerite, 
the  stemumt  may  be  observed ;  and  a  much  larger  tergal 
piece,  the  noium.  At  the  sides  of  the  somite  are  other 
definitely  arranged  sclerites,  the  anterior  of  which  appear 
to  answer  to  the  epistemum  and  epimera  in  the  OrusUtcea, 
while  the  posterior,  perhaps,  properly  belong  to  the  attached 
limb. 

Forked  or  double  apodemes,  the  a/ntefurea,  medifurca,  and 
postfwrca,  project  from  the  sternal  wall  of  each  somite  of 
the  thorax  into  its  cavity.  They  support  the  nervous  cord 
and  give  attachment  to  muscles. 

The  legs  present  a  large  basal  joint,  the  coxa,  between 
which  and  the  third,  termed /entur,  a  small  articulation,  the 
trochanter,  is  interposed.  Upon  the  femur  follows  an 
elongated  tibia;  and  this  is  succeeded  by  the  tarsus,  which 
consists  of  six  joints.  Of  these,  the  proximal  joint  is  long 
and  stout,  the  three  next  are  short,  the  fifth  is  elongated 
and  slender;  the  sixth,  very  short,  is  terminated  by  two 
curved  and  pointed  claws  (ungties),* 

The  broad  differences  in  the  structure  of  the  abdomen 
of  the  male  and  female  have  been  already  pointed  out. 
Of  the  eight  terga  externally  visible  in  the  female  (Pig. 
98),  the  first  is  shorter  than  those  which  succeed  it;  and 
the  hindermost  (Fig.  98,  lo)  is  escutcheon -shaped,  deflexed 

*   Mr.    Westwood     (*  Modern  Mr.  Westwood  tervaB puhUIwt,  but 

Classification  of  Insects,'  vol.  i.  p.  it  is  a  true  joint  provided  with  a 

416)  says  that  the  tarsi  are  five*  special  flexor,  the  slender  tendon 

jointed,  and  that  there  is  a  pul-  of    which,     however,    traverses 

villus  between  the  ungues.  The  several  of  the  joints  of  the  tanus. 
lixth  joint  appears  to  be  what 


THB  COOKBOAOH.  405 

at  the  sides,  thin  in  the  middle,  and  notched  at  the  end. 
When  this  tergum  is  gently  pulled  backwards,  two  other 
very  narrow  terga  (Fig.  98,  8,  9),  of  which  the  anterior 
overlaps  the  posterior,  and  which  were  hidden  between  it 
and  the  antepenultimate  or  seventh  tergum  become  visible. 
The  apparent  eighth  tergum  is  therefore  really  the  tenth. 
Beneath  the  tenth  tergum  are  two  triangular  J90(2ica2  plates 
(Fig.  98,  11),  one  on  each  side  of  the  anus.  Provisionally, 
I  take  them  to  be  the  sclerites  of  the  eleventh  abdominal 
somite. 

The  first  sternum  is  confluent  with  the  second,  and  largely 
hidden  by  the  cozsb  of  the  metathoracio  limbs.  The  seventh 
is  g^reatly  enlarged,  and  its  posterior  edge  is  produced  into 
a  boat-shaped  process,  nearly  divided  into  two  portions  by 
an  inward  fold  of  the  integument  along  the  median  line. 

Completely  hidden  by  the  seventh  sternum  is  a  thin  plate, 
narrower  in  front  than  behind,  where  it  is  produced  on  each 
side.  Anteriorly,  it  is  articulated  with  the  stemimi  of  the 
following  somite,  so  as  to  form  a  sort  of  spring-joint,  which 
ordinarily  keeps  it  applied  against  the  latter,  and  therefore 
directed  obliquely  upwards  and  a  little  forwards.  The  large 
aperture  of  the  vulva  (Fig.  98,  v)  lies  in  the  middle  of  this 
plate.  On  the  sternal  region  behind  the  vulva,  between  it 
and  the  anus,  arises  a  pair  of  elongated  processes,  divided 
into  two  portions,  of  which  the  outer  is  thick  and  soft, 
the  inner  slender,  pointed,  and  hard.  They  embrace  and 
partly  ensheath  two  other  processes  having  somewhat  the 
shape  of  knife  blades,  the  anterior  fixed  ends  of  which  are 
curved,  and,  being  attached  to  the  sides  of  the  somite  to 
which  they  belong,  are  distant,  while  the  blades  meet,  and 
are  applied  together  in  the  middle  line.  Of  these,  which 
may  be  termed  gonapophysea,  the  study  of  their  develop- 
ment shows  that  the  posterior  bifid  pair  belong  to  the 
ninth  somite,  while  the  anterior  pair  belong  to  the  eighth. 

The  cerci  (x)  are  attached  to  the  dorso-lateral  part  of  the 
tenth  somite. 

In  the  abdomen  of  the  male  Blatta  (Fig.  99).  the  ten 
terga  are  readily  discemible;  but  the  eighth  and  ninth  are 


4*)\j        THE  ANATOMY  OF  INVERTEBRATED  ANIMALS. 

very  short,  and  the  fcjrmer  overlaps  the  latter.  The  tenth 
tergnm  is  flat,  and  has  a  freely  projecting,  truncated,  pos- 
terior margin.  Articulated  beneath  ita  lateral  edge  are 
two  multiarticulate  cerci  (as),  similar  to  those  of  the  female. 

Beneath  the  tenth  tergum,  and  hidden  bj  it,  are  the  two 
podical  plates  (11)  between  which  the  anus  opens.  The  first 
sternum  is  small,  and  may  easily  escape  notice.  The  second 
to  the  bixth  sterna  are  of  nearly  equal  width  and  length. 
The  seventh  and  eighth  are  narrower;  the  ninth  still 
narrower  and  longer,  about  half  of  its  length  being  covered 
by  the  eighth.  The  covered  half  is  dififei'ent  in  texture 
from  the  uncovered,  being  thinner  and  more  transparent* 
and  its  anterior  margin  is  deeply  notched.  The  uncovered 
half  is  strong,  homy  and  dark-coloured,  convex  below  and 
concave  above;  its  free  posterior  margin  is  obscurely  tri- 
lobed  by  two  lateral  shallow  notches.  On  each  side,  a 
slender,  unjoioted,  setose  style,  which  projects  backwards 
and  outwards,  is  attached  to  this  sternum. 

Thus  the  tergal  surface  of  the  abdomen  of  the  male 
essentially  resembles  that  of  the  female,  while  the  sternal 
surface  differs  in  exhibiting  two  sterna  more  (namely,  the 
eighth  and  ninth)  without  dissection.  Hence,  while,  in 
the  female,  the  opening  of  the  recto-genital  chamber  lies 
between  the  tenth  tergum  and  the  seventh  sternum,  in 
the  male  it  lies  between  the  tenth  tergum  and  the  ninth 
sternum. 

When  the  tenth  tergum  and  the  podical  plates  are  re- 
moved, a  very  singular  apparatus,  the  male  genital  ar- 
mature, comes  into  view.  It  consists  of  a  number  of 
chitinous  processes  having  the  form  of  plates  and  hooks, 
the  exact  form  and  disposition  of  which  could  be  made 
intelligible  only  by  numerous  figures.  It  may  be  stated 
generally,  however,  that  these  plates  and  hooks  tenninate 
processes  of  the  sternal  region  of  the  tenth  somite,  on  each 
side  of  the  aperture  of  the  vas  deferens,  and  therefore, 
though  they  are  of  the  same  nature  as  the  gonapophyaee  of 
the  female,  they  are  not  their  exact  homologues. 

The  most  conspicuous  division  of  the  right  gonapophysif 


Pig.  9S.— Longltudlaftl  uid  ver- 
ti»l  aection  of  ft  feirole  Cock- 
ruach  (Blatta).  —  i  to  ii, 
■omltet  of  ths  body;  1  to  11, 
KimiMi  of  the  ■bdomen ;  A, 
uitauiik ;  lb,  iBbnim ;  a,  mouth  ; 
i,  <eioptugua ;  t,  crop ;  d,  pro- 
ventricului;  c,  pylario  ckc*; 
/,  objLifia  TCDlriclej  g,  iuMT- 
tionoriiieHalpiglilmacteu;  A, 
inteitliie;  i,reotum;  e,  tuIts; 
I,  Mlivftry  glud;  »,  Mlliuy 
reorptrcle.  B;  aa  error  the 
duct  li  nude  to  terminftte  above 
inWnii  of  beneeUi  the  lingiu; 
a,  poritlon  of  heaiti  m,  emrt- 
bnl  puigU>j  N,thDiacic  gut- 


oru  giwguBi  1' 


403       THE  AKATOITT  OV  UTVIBTIBSATBD  AHtKALB. 

is  a  broad  pUt«  divided  a.t  the  eitremitj  into  two  portdtma, 
th«  inner  of  which  carvea  inwrnrds  and  ends  in  two  or  Uiree 
sharp  apinea,  while  the  outer  is  coiled  npon  itself  ao  aa  to 
resemble  a  short  corkscrew.    The  left  gonapopbTsiB  is  pro* 

Fig.  99. 


-LongiliidinAl  and  vertical  Mctlon  of  tlwBbdonea  of  ■  mala 
Moh  (BJoda).— 1,  S.  a.  4,  fco.,  terga  and  ilena  of  tin  abdo- 
I,  muihiDom-iluped  giaiid ;  e,  ■pertore  of  the  Taa  daferaM ; 


Tided  with  a  long  proceaa  like  a  tonacnlnm,  the  incDrred 
extremitr  of  which  is  denticolatod. 

The  alimentary  canal  of  the  Oockroach  commences  br  tl>e 
oral  canty,  aitnated   between  the  labmm  in  front,   tlw 


THX  COOKBOACH. 


409 


mandibles  and  maxilliB  at  the  sides,  and  tlie  labium,  with 
the  large  lingua,  or  hypopharynx,  behind.  The  (Bsophagns, 
beginning  as  a  narrow  tube,  passes  between  the  anterior 
crura  of  the  tentoriimi,  and  then  leaving  the  head  bj  the 
occipital  foramen  and  traversing  the  neck  and  thorax, 
g^radnally  widens  into  the  large  crop  or  infflumed  (Fig.  98, 
c),  which  lies  in  the  abdomen.  TMs  is  followed  bj  the  small 
thick- walled  proventriculus  (Fig.  98,  d),  shaped  like  a  pear, 
with  its  broad  end  applied  against  the  crop.  The  narrow 
end  of  the  proventricnlus  opens  into  a  wide  canal,  the  so- 
called  chylifie  venkricle,  or  ventrietUue  (Fig.  98,  /),  an  elon- 
gated tube,  the  junction  of  which  with  the  intestine,  is 
marked  by  the  insertion  of  the  nimieroTia  Malpighian  tabes. 
The  anterior  end  ot  the  ventriculas  is  provided  with  seven 
or  eight  csBcal  diverticula  of  unequal  lengths  (Fig.  98,  e), 
the  pyloric  cceca.  The  first  portion  of  the  intestine  {iieum) 
is  narrow.  The  next,  termed  the  colon,  is  very  wide,  and 
somewhat  sacculated.  A  constriction  marks  off  the  region 
of  the  colon  from  the  straight  short  rectwn  (Fig.  98,  i), 
which  terminates  in  the  anus,  situated  at  the  hinder  ex- 
tremity of  the  body  between  the  podical  plates.* 

The  aperture  by  which  the  mouth  communicates  with 
the  gullet  is  small,  and  situated  at  the  superior  and  anterior 
part  of  the  buccal  cavity.     A  broad  projection  of  the 


*  M.  F.  Piateaa  CRecherches 
Bar  les  ph^aomtees  de  la  digestion 
ches  les  InsectM,'  1874; '  Mote  Bar 
les  phenom^nes  de  U  digestion 
chex  la  filatta  americaine  IPeri* 
planeta  americanci],*  1876;  and 
^Rechercbes  sor  les  pbenomines 
de  la  digestion  chez  les  Myria- 
podes,'  1876),  dividea  the  alimeiv- 
taiT  canal  of  insects  and  myria- 
pods  into  a  buccal,  a  median,  and 
a  terminal  portion.  The  baccai 
portion  consists  of  the  oesophagus, 
crop,  and  proventriculus— wluch 
last  he  considers  to  be  a  mere 
strainer  and  to  hare  no  mastica- 
tory ftinction.  The  middle  divi- 
sion lies  between  the  proventri- 
colns  and  the  insertion  of  the 


Malpighian  tubes.  The  terminal 
division  extends  from  the  latter 
point  to  the  anus.  With  the 
solitary  exception  of  /k/m,  the 
secretions  of  the  alimentary  canal 
are  always  alkaline,  and  that 
which  effects  the  transformation 
of  the  albuminoid  elements  of  the 
feod  into  peptones  appeara  to  be 
iiimished  by  the  middle  division, 
which  is  lined  by  epithelium,  de- 
void of  any  cuticie.  In  carnivor- 
ous insects  digestion  may  take 
place  in  the  crop  by  the  flow  of 
the  secretion  of  the  middle  in- 
testine into  it.  The  salivary' 
fluid  of  BlaUm  rapidly  eflfects  the 
transformation  of  Btaroh  into 
sugar. 


410       THB  ANATOMY  OF  INYBSTEBBATBD  ANIMAIiS. 

posterior  and  inferior  wall  of  the  buccal  cavity  occupies  all 
thfe  space  between  the  cesophageal  opening  of  that  cavity 
and  the  labium,  and  ends  in  a  free  subcylindrical  procefls. 
This  is  termed  hypopharynx  or  lingua,  but  it  might  be  well 
to  reserve  the  term  lingua  for  the  free  end,  and  hypopharynx 
for  the  attached  posterior  portion.  The  anterior  surface 
of  the  hypopharynx  slopes  downwards  and  forwards;  its 
sides  are  supported  by  two  sclerites,  which  are  narrow  and 
rod-like  above  and  broad  below,  where  they  unite  in  an  arch 
on  the  dorsal  face,  just  where  the  free  part,  or  lingua, 
begins.  On  the  under  side  of  the  lingua  are  two  broader 
sclerites,  which  also  unite  and  form  an  arch,  which  lies 
over  the  opening  of  the  salivary  duct.  The  anterior  surface 
of  the  lingua  and  hypopharynx  is  beset  with  fine  hairs. 

The  two  salivary  glands,  with  their  receptacles,  are 
greatly  developed  in  the  Cockroach.*  The  glands  (Fig.  d8, 
I)  lie  on  each  side  of  the  CBsophagus  and  crop,  extending 
through  the  thorax,  as  far  as  the  commencement  of  the 
abdomen.  Each  gland  is  a  white  mass,  as  much  as  a  quarter 
of  an  inch  long  and  composed  of  numerous  acini.  The 
ducts  which  arise  from  these  acini  unite  first  into  a  single 
trunk  on  each  side,  and  then,  beneath  the  sub><£8ophageal 
ganglion,  the  two  trunks  join  to  form  the  single  short 
salivary  duct  which  opens  beneath  the  lingua.  The  ducts 
of  the  salivary  glands  are  lined  by  a  transversely  ribbed 
chitinous  membrane,  so  that  they  greatly  resemble  tracheae. 

The  salivary  receptacles  (Fig.  98,  k)  are  elongated  oval 
sacs,  three-eighths  of  an  inch  long,  each  of  which  is  situated 
at  the  extremity  of  a  long  duct.  The  ducts  unite  in  front 
with  one  another,  and  with  the  duct  of  the  gland,  to  form 
the  short  terminal  common  duct.  The  receptacle  and  its 
ducts  have  a  chitinous  lining  similar  to  that  of  the  duct  of 
the  glands,  but  the  spiral  marking  does  not  extend  over  the 
walls  of  the  receptacle. 

The  pioventriculus  has  a  thick  muscular  coat,  and  the 

*  The  salivary  glands  are  well  tische  und  uropoietisohe  System 
described  by  Basoh,  **  Unter-  der  BlatU  orientalis."  ('SiUli. 
sttcbuDgen  uber   die  chylopoie-      Wiener  Akad./  1858.)  , 


THE  COCKBOACH.  411 

chitmous  lining  which  is  oontinaed  into  it  from  the  ingluvies 
is  greatlj  thickened  and  produced  into  six  hard,  brown 
ridge-like  principal  teeth.  Posterior  to  these  is  a  circle  of 
six  prominent  cushions  covered  with  setaB,  and  similar  sets 
beset  the  lining  membrane  of  the  funnel-shaped  cavitj  into 
which  thej  project.  Between  each  pair  of  principal  teeth 
are  five  smaller  tooth-like  ridges,  of  which  the  median  is 
the  largest,  and  a  variable  number  of  still  finer  longitudinal 
elevations  lie  between  them. 

The  proventidculus  leads  posteriorly  into  a  narrow,  thick- 
coated  canal,  the  tubular  extremity  of  which  projects  freelj 
into  the  much  wider  anterior  end  of  the  chylific  ventricle, 
and  constitutes  a  very  efficient  valve. 

The  short  and  narrow  anterior  division  of  the  intestine 
i^ilewn)  is  separated  from  the  colon  by  a  circular  valve,  the 
surface  of  which  is  Leset  with  small  spines. 

The  Malpighian  glands  are  very  numerous  (20-30), 
delicate,  csecal  tubules,  of  even  diameter  throughout,  and 
lined  by  a  small-celled  epithelium  enclosing  a  central 
cavity. 

The  communication  between  the  colon  and  the  rectum 
is  very  narrow,  but  is  not  valvular.  The  walls  of  the  rectum 
itself  are  raised  into  six  ridges,  which  project  into  its 
interior  and  are  abundantly  supplied  with  tracheas ;  these 
are  the  so-called  rectal  glands.  Anal  glands  appear  to  be 
absent. 

The  histology  of  the  alimentary  canal  has  been  particu- 
larly studied  by  Basch.*  From  the  oral  cavity  to  the 
funnel-shaped  extremity  of  the  proventriculus,  it  is  lined  by 
a  chitinous  coat  continuous  with  the  chitinous  layer  of  the 
integument,  and  beset  for  the  greater  part  of  its  extent 
with  fine  setiform  processes.  Beneath  this  is  the  proper 
endoderm,  consisting  of  a  layer  of  cells.  Next  follows  a 
structureless  membrana  propria  or  basement  membrane; 
and  this  is  succeeded  by  two  layers  of  striped  muscular 
fibres,  the  internal  disposed  longitudinally,  and  the  ex- 
ternal circularly.  In  the  proventriculus,  the  muscular 
*  *  Si.zungtberichte  der  Wiener  Aksdemie/  xxxili.,  1658,  ^ 


412   THE  ANATOMY  OF  INYBSTEBBATED  ANIMALS. 

lajers  become  mucli  thicker,  and  some  of  those  of  the  outer 
layer  acquire  a  radial  arrangement,  while  the  longitudinal 
muscles  are  disposed  in  bundles  t^hich  correspond  with  the 
six  principal  ridges.  In  the  chjlific  ventricle,  the  muscular 
layers  and  the  basement  membrane  are  disposed  much  as 
before.  The  basement  membrane  presents  pits  on  its  free 
surface  in  which  rounded  cells  are  lodged,  and  is  beset  be- 
tween these  by  the  elongated  cells  of  a  cylinder  epithelium. 
The  free  ends  of  these  present  a  thick  wall,  marked  by 
vertical  striations.  ^1  here  is  no  chitinous  layer.  The  csBca 
are  merely  diverticula  of  the  wall  of  the  chylific  ventricle. 

The  intestine,  finally,  repeats^ the  structure  found  in  that 
part  of  the  alimentary  canal  which  lies  in  front  of  the 
chylific  ventricle  and  is  provided  with  a  setose  chitinous 
lining. 

Basch  found  the  secretion  of  the  salivary  glands  and  the 
contents  of  the  crop  acid,*  and  that  an  infusion  of  the 
salivary  glands,  acidulated  with  hydrochloric  acid,  digested 
fibrin.  The  contents  ot  the  chylific  ventricle  were  neutral 
or  alkaline;  and  an  infusion  of  the  chylific  ventricle  at 
once  turned  starch  into  sugar.  The  same  effect  was  pro- 
duced by  an  infusion  of  the  salivary  glands. 

The  heart  (Fig.  98,  h)  ia  a,  slender  inconspicuous  tube, 
which  occupies  the  middle  line  of  the  dorsal  wall  of  the 
abdomen  and  presents,  at  intervals,  pairs  of  lateral  apertures. 
The  wall  of  the  abdomen  internal  to  the  chitinous  integu- 
ment is  lined  by  a  soft  cellular  substance  (hypodermis),  the 
outer  layer  of  which  represents  the  ectoderm  or  epidermis, 
while  the  deeper  part  is  the  parietal  layer  of  the  mesoderm. 
This  last  contains  a  stratum  of  longitudinal  muscular  fibres, 
divided  into  segments  or  myotomea^  in  correspondence  with 
the  somites,  and  numeroua  tracheee.  The  heart  is  enclosed 
in  the  abdominal  wall  which  surrounds  it  on  all  sides,  leaving 
(mly  a  small  pericardial  space.f    Beyond  the  slender  aortic 

*  Plateau  denies  that  the  sali-  t  Cornelius     (*  Beitrage      snr 

vary  secretion  of  Blatta  is  ever  naheren  Kenntniss  von  Peripla' 

acid,  and  ascribes  the  occasional  neia   {Blatta^   oriemtaHt^    18^X 

aoldityof  the  contents  of  the  crop  found  that  tne  pulsations  of  the 

to  the  food.  heart  could  readily  be  obaened 


THB  COCKROACH.  413 

canal  in  which  the  heart  terminates  anteriorly,  and  which 
passes  into  the  thorax  and  the  head,  no  yessels  appear  to 
be  given  off  from  the  heart. 

Delicate  triangular  sheets  of  mnscnlar  fibre,  the  alary 
muscles,  are  attached  in  pairs  by  their  bases  to  the  wall  of 
the  pericardial  chamber,  while  their  apices  are  inserted  into 
the  hjpodermis.  They  occupy  the  interspaces  left  by  the 
principal  dorsal  branches  of  the  trachesB,  which  form  arches 
on  each  side  of  the  heart. 

From  the  inner  face  of  the  abdominal  wall,  processes  are 
given  off,  some  of  which  appear  to  hang  freely  into  the 
abdominal  cavity,  while  others  accompany  the  nnmerons 
trachesB  which  pass  to  the  alimentary  cajial.  When  the 
abdominal  cavity  is  laid  open,  its  inner  lining  has  a  villous 
appearance  and  often  seems  to  be  full  of  free  granular 
matter,  as  the  processes  very  readily  break  up  into 
fragments.  The  substance  which  thus  fills  up  the  interspace 
between  the  parietes  of  the  abdomen  and  the  contained 
organs  is  the  corpus  adipogwm.  It  is  made  up  of  cells  often 
so  arranged  as  to  form  a  network,  and  it  usually  has  a  milk- 
white  colour,  which  arises  partly  from  the  air  contained 
in  the  tracheee,  and  partly  from  innumerable,  strongly  re- 
fracting granules  contained  in  its  component  cells. 

There  are  ten  stigmata  on  each  side  of  the  body  of  Blatta, 
eight  in  the  abdomen,  and  two  in  the  thorax.  The  latter 
are  situated  between  the  prothorax  and  the  mesothorax, 
the  mesothorax  and  the  metathorax,  respectively ;  above  the 
attachment  of  the  coxse  and  beneath  the  terga.  The  ab- 
dominal stigmata  lie  in  the  soft  integument  which  connects 
the  sterna  and  terga  of  the  somites.  All  the  stigmata  are 
situated  in  conical  thickened  elevations  of  the  integument. 
The  thoracic  stigmata  are  the  largest,  and  the  anterior 
pair  have  a  distinctly  two-lipped  aperture,  the  anterior  lip 
being  notched  in  the  centre.   The  openings  of  the  abdominal 


in  BlatttB  which  had  recently  minate;  but  allowance  most  be 
undergone  eodysit.  They  were  made  for  the  diaturbed  condition 
aa   frequent   aa  eighty   in    the      of  the  inaeota  under  obaenration. 


414       THE  ANATOMY  OF  imTEBTEBSATBD  AKDCALS. 

jtigmata  are  more  oval  and  are  inclined  baclnrards.  Im- 
mediately within  each  stigma  the  tracheal  tronk  into  which 
it  opens  is  provided  with  a  yalvnlar  arrangement,  by  which 
the  passage  can  be  closed  or  opened. 

4 

Fig.  100. 


Fig.  100.— Bfa/teorwnte/a.— A,  the  brain  with  the  antennary  (a)  and 
optic  (6)  nerves;  c,  e,/,^,  A,itomato-ga»tric  nerves;  B,  the  anie 
rfor  end  of  the  gullet ;  C,  the  crop ;  D,  the  gizsard. 


The  large  trache»  which  take  their  origin  from  these 
stigmata  immediately  divide  and  give  off  dorsal  and  ventral 
hranoheB;  the  former  unite  in  a  series  of  arches  on  each 
«de  of  the  heart,  while,  on  the  ventral  side,  the  branches 


\ 


THE  COCKBOACH.  415 

are  connected  by  trunks  which  run  parallel  with  the  ab- 
dominal ganglia.  Large  tracheae  pass  from  the  anterior 
thoracic  stigma  through  the  neck  into  the  head  and,  in  the 
abdomen,  the  yiscera  receive  an  abundant  supply  of  air- 
tubes. 

The  lobes  of  the  corpus  adiposum  are  also  plentifully 
supplied  with  tracheae,  while  fine  trunks  enter  the  substance 
of  the  ganglia  and  nerves  and  there  ramify.  Trachese 
accompany  the  nervures  of  the  wings  and  are  abundantly 
distributed  to  the  muscles. 

The  nervous  system  consists  of  the  snpra-oesophageal 
ganglia  (Fig.  100,  A),  commonly  termed  the  brain,  united  by 
thick  and  short  commissures  with  an  infra-cesophageal 
ganglionic  mass,  situated  in  the  head;  of  three  pairs  of 
large  coalesced  ganglia  in  the  thorax,  one  for  the  prothoraz, 
one  for  the  mesothoraz,  and  one  for  the  metathorax;  of 
six  pairs  of  closely  united  smaller  ganglia  in  the  abdomen  ; 
and  of  a  set  of  visceral  or  atomato-gadric  nerves.  The 
several  pairs  of  thoracic  and  abdominal  ganglia  are  united 
by  double  commissural  cords.  In  the  males  the  commis- 
sures which  unite  the  abdominal  ganglia  are  not  straight, 
but  are  bent,  as  if  it  were  needful  to  make  allowance  for 
the  possible  elongation  of  the  abdomen.  The  supra-oeso- 
phageal  ganglia  give  off  the  nerves  to  the  antenns  from 
their  antero-lateral  angles;  while  their  postero-lateral 
angles  are  produced  into  the  great  optic  nerves.  Above 
the  margin  of  each  antennary  nerve  there  is  a  small 
rounded  tubercle  which  is  in  immediate  relation  with  the 
silvery  patch  which  shines  through  the  fenestra  on  the 
inner  side  of  the  antennary  fossa.  Beneath  this  tubercle, 
and  on  the  inner  side  of  the  antennary  nerve,  arises  the 
root  of  the  stomato-gastric  system  of  nerves.  Each  root 
passes  forwards  for  a  short  distance,  then  turns  inwards, 
and  in  the  middle  line,  enters  a  heart-shaped  ganglion 
situated  on  the  gullet  (Fig.  100,  e).  From  this  a  median 
cord  passes  backwards  beneath  the  brain  and  enters  a 
ganglion,  which  is  connected  on  each  side  with  two  others 
(e,  e).     The  continuation  of  the  median  cord  passes  back 


416       THE  ANATOMY  OF  INYEBTBBBATBI)  AKIMALS. 

along  the  tergal  wall  of  the  oesophagns,  and  where  this 
begins  to  dilate  into  the  crop  ends  in  a  small  triangolar 
ganglion  (g),  whence  lateral  branches  are  given  off,  which 
can  be  traced  as  far  as  the  gizzard. 

The  exact  form  and  arrangement  of  the  male  organ  of 
generation  has  only  recently  been  made  oat.  The  most 
conspicuous  of  these  organs  is  a  mushroom-shaped  gland 
(Fig.  99,  t)  composed  of  a  great  nnmber  of  short  cseca 
attached  to  the  extremity  of  the  also  very  short  vas  deferens. 
It  is  lodged  in  the  hinder  end  of  the  abdomen,  and  covers 
the  posterior  abdominal  ganglion.  The  contents  of  the  caeca 
are  viscid,  granular,  and  usually  brilliantly  white.  The 
anterior  end  of  the  vas  deferens  is  dilated,  and  the  cseca  are 
arranged  in  two  groups  which  open  into  each  side  of  the 
dilatation.  The  contents  of  the  vas  deferens  are  also  white 
and  viscid,  and  evidently  consist  in  great  measure  of  the 
secretion  of  the  cflBca.  In  the  adult  male,  however,  in- 
numerable spermatozoa  with  straight  rod-like  heads,  and 
long  flagella  are  to  be  found  intermingled  with  the  contents 
of  the  vas  deferens  and  its  dilatation.  On  the  sternal  side 
of  the  mushroom-shaped  gland,  between  it  and  the  last 
abdominal  ganglion,  there  is  an  accessory  gland  composed 
of  dichotomous  monilated  tubes,  lined  by  a  columnar 
epithelium,  all  bound  together  by  a  common  investment 
into  a  flattened  elongated  mass. 

As  the  duct  of  the  mushroom-shaped  gland  in  the  adult 
male  always  contains  spermatozoa,  and  no  other  organ  con- 
taining spermatozoa  is  to  be  found,  this  gland  has  naturally 
been  taken  for  the  testis.  Btg'ewsky,*  however,  has  re- 
cently pointed  out  that  the  true  testes  are  situated  in  the 
tergal  region  of  the  abdomen,  and  that  they  may  be  found 
in  this  region  in  the  young  and  yet  wingless  males,  though 
they  are  much  obscured  by  the  corpus  adiposum  which  in- 
vests them.  He  traces  the  efferent  duct  of  the  testis  to  the 
glands  just  mentioned.  In  the  adult  male  the  testes 
atrophy,  and  are  hardly  to  be  discovered  among  the  masses 

*  Hoftnann  and  Sehwalbe,  *  Jahresbericht,*  187.5.   The  original  paper 
ii  in  Rnsslui,  and  I  have  not  seen  it 


THX  COOKSOAOR.  417 

of  Qie  corptu  adipoBnm.  I  have  foimd  the  teatee  in  the 
young  males  in  the  poeition  aeeigned  to  them  b;  Bt^eirskj. 
Thej  comd^  ot  nnmerona  oval  or  pjriform  sace  attached  bj 
short  pedicles  to  a  common  duct. 

The  ovaries  (Fig.  101)  are  two  groups  o(  eight  tnbra,  aitn- 
ated  on  each  side  of  the  hinder  hall  of  the  abdomen.  The 
OTBrian  tubes,  or  omrtolet,  of  each  gronp  commniiicate  with 
a  short  OTiduct,  which  soon  unites  with  its  fellow  in  the 

Fig.  101. 


Fig.  lO\.—BrMa  orintlfll*  — Feaikle  genital  orgaoi :  a,  the  |)0*t«rlor 
■ibdoniiiul  gaoglion  j  b,  tha  oTiducts ;  c.ii,  e,  the  oviriui  tnbca  { /, 
Dte  fflunent  by  vrhich  their  eilremitiei  va  oolted  ;  g,  tb«  ipeniM- 
theca;  h,  tbe  colleterial  glands. 

middle  line  and  opens  extenutllj  by  the  Tery  short  and 
wide  Tagiua.  Tbe  finely  tapering  anterior  ends  of  the  ova- 
rioles  of  each  side  are  continued  forwards  by  delicate  cellu- 
lar prolongations.  These  finally  unite  together  into  one 
long  filament,  which  can  be  traced  for  some  distance  for- 
wards among  the  lobes  of  the  corpus  adipoeom.  Itis  a 
cellular  cord,  which  appears  to  be  nothing  bat  a  process 
2  B 


418       THE  ANATOMY  OV  UfYBBTKBBATBD  AKIMAI.8. 

of  the  mesoderm.  Numerous  nucleated  cells,  from  some  of 
which  the  ova  take  their  origin,  while  others  remain  as  in- 
terstitial ceUs,  which  are  eyentually  conyerted  into  an  epi- 
thelium, make  up  the  substance  of  the  slender  anterior 
terminations  of  the  ovarioles.  The  ova  situated  behind 
these  enlarge,  and  become  disposed  in  a  single  series. 
Further  on,  the  epithelial  cells  form  a  thick  stratum  ronnd 
each  egg,  and  possibly  assist  in  the  formation  of  the  large 
▼itellus  with  which  it  is  ultimately  provided.  As  the  egg 
adyances  towards  maturity,  the  vitellus  acquires  first  a 
finely,  and  then  a  coarsely  granular  structure,  and  the  ger- 
minal vesicle  and  spot,  previously  conspicuous,  are  no 
longer  to  be  seen.  Behind  the  junction  of  the  oviducts 
with  the  vagina,  and  the  last  abdominal  ganglion  which 
lies  upon  the  latter,  there  is  a  small  sac  with  a  long  neck 
from  which  a  short  csdcal  process  is  given  off.  It  has  a 
thick  chitinous  lining  and  a  muscular  investment,  and  is 
the  spermcUheca.  Behind  it  are  two,  large,  ramified,  tubular 
colleterial  glands,  which  probably  give  rise  to  the  substance 
of  which  the  egg  case  is  formed.  Their  conjoined  ducts 
open  behind  the  spermatheca. 

The  eggs  are  enclosed,  sixteen  together,  in  strong  capsules 
of  a  homy  consistency,  shaped  somewhat  like  a  cigar  case, 
and  presenting  a  longitudinal  slit,  the  raised  and  serrated 
edges  of  which  are  closely  applied  to  one  another.  It  is 
through  this  slit  that  the  fully  developed  young  make  their 
exit.  The  eggs  attain  J  of  an  inch  in  length.  Each  has  its 
own  thin  but  tough  brownish  shell,  the  surface  of  which  is 
beautifully  ornamented  with  hexagonal  patches  of  minute 
tubercles.  They  are  arranged  parallel  with  one  another 
in  two  opposite  series,  one  series  occupying  each  half  of  the 
ease.  The  eggs,  adapting  themselves  to  the  form  of  the  case, 
are  oonvez  outwards  and  concave  inwards,  and  thus,  though 
their  ends  touch,  a  median  space  is  left  between  the  two 
sets.  The  inner  concave  face  of  the  egg  is  that  on  which 
the  sternal  face  of  the  embryo  is  situated.  The  female 
eanies  the  egg-case  about  for  a  week  or  more,  before 
4epoeitiiig  it.    The  young  leave  the  eggs  as  minute  active 


THB  COCntOJLCH.  41^ 

insects,  oolonrless,  except  for  the  large  dark  eyes.  Before 
they  are  hatched  they  acqtdre  eyes,  antemuB,  gnatliiteB, 
legs,  and  short  oerci,  which  differ  only  in  detail  from  those 
of  the  perfect  BlaUa,  into  which  the  larva  passes  by  snc- 
cessive  ecdyses.  According  to  Comelins  (I.  e.  p.  29),  the 
Cockroach  undergoes  seven  ecdyses ;  the  first  immediately 
on  leaving  the  egg,  the  second,  a  month  later.  After  the 
second  ecdysis,  the  insect  sheds  its  skin  only  once  a  year ; 
so  that  it  attains  its  adult  condition  only  in  its  fifth  summer. 
The  chitinous  cuticula  splits  along  the  median  line  of  the  ter- 
gal aspect  of  the  head,  thorax  and  abdomen,before  it  is  cast. 
Thus  the  Cockroach  is  said  to  be  an  insect  without  meta- 
morphosis. For  although  the  male,  in  the  later  stages  of 
its  growth,  acquires  wings,  and  thus  does  become  very 
sensibly  metamorphosed  from  a  merely  cursorial  animal  to 
one  which  has,  at  any  rate,  the  capacity  for  flight,  there  is 
no  period  in  the  life  of  this  insect  in  which  the  larva  paases 
into  a  resting  condition,  during  which  it  takes  no  food,  aud 
in  the  course  of  which  it  developes  its  wings.  In  other 
words,  the  Cockroach  passes  through  no  pupa  state,  which 
the  insect  enters  as  a  larva,  and  leaves  as  an  imago,  such 
as  is  so  well  known  to  occur  in  the  course  of  the  develop- 
ment of  Moths  and  Butterflies.  The  term  meiamorphoM, 
in  its  technical  entomological  sense,  is  applied  only  to  that 
succession  of  changes  of  which  such  a  definite  pupal  con- 
dition forms  the  middle  term. 

It  is  obvious  that  a  metamorphosis,  in  this  sense,  is  a 
secondary  complication  superinduced  upon  the  direct  and 
gradual  process  of  development  exhibited  by  such  insects 
as  the  Cockroach  ;*  and  that  the  Metaibola,  as  insects  having 
a  metamorphosis  are  termed,  are,  so  far,  more  differentiated 
than  the  Ametabola,  or  those  which  have  no  metamoiphosis. 
Again,  in  each  of  these  divisions,  it  is  clear  that  the  insects 
which  never  possess  wings  are  less  differentiated,  or  more 

*  Sir  John  Lubbock  has  shown  panied  by  a  slight  change  of  form 

that  the  ^oong   Chioecm  {Ephe-  m  its  passage  to  the  aduH  state. 

wktra)  dimtdiatum  undergoes  more  (Trans.  Linn.  Soc.  1863.) 
than  twimty  eodyteai  each  aecom* 


420      THB  AKATOMT  OF  nTYBKTBBBATKD  AKIKALS. 

embiyoiiio,  than  those  which  are  winged.  And  finally, 
insecta  with  the  parta  of  the  month  in  the  condition  of 
ordinary  gnathitea  are  less  differentiated  than  those  in 
which  such  gnathites  are  changed  in  form  and  function,  or 
become  confluent. 
The  insects  which,  in  this  view  of  their  morphological 

Fig.  102. 


Fig.102. —  CampodeattaphyUnui,  one  of  the  Tf^$aHura  (after  Labboek).* 

idations,  occupy  the  lowest  position  in  the  group,  are  the 
CdUembola  and  Thysanura,  the  MaUophaga,  and  the  Pedi- 
euUna,  inasmuch  as  they  possess  no  trace  of  wings  and 
undergo  no  metamorphosis. 

The  CoUembola  and  Thyscmwra  undergo  no  metamor- 
*  *Monognph  on  the  OoUemboh  and  V^mmmra^'  pL  liiL 


THTaAinXBA. — PSDICULINA.  421 

pliosiB,  and  are  always  wingless.  The  abdomen  contains 
six  segments  only  in  the  CoUembola  (Podwra,  Smynihiwrus, 
ToTtioeeros),  in  which  group  the  mouth  is  usually  provided 
with  mandibles  and  mazillsB,  though  these,  instead  of  being 
articulated  with  the  sides  of  the  head,  are  capable  of  being 
retracted  into  its  interior.*  In  the  genus  Anoma  the  mouth 
is  suctoriaL 

The  Thyaanwra  (Lepiama,  Campodea,  Japym)  resemble  the 
young  Blattce.  They  have  ten  well-marked  abdominal^  so- 
mites (CampodeOj  Fig.  102),  and  the  gnathites  conform 
to  the  mandibulate  type.  The  abdomen  in  McuJietea  has  a 
pair  of  elongated  cylindrical  appendages  attached  to  every 
segment  except  the  first ;  while  Campodea  and  Japym  have 
seven  pairs  of  such  abdominal  appendages-f 

The  CoUembola  are  provided  with  a  curious  tube  or  sucker, 
which  is  attached  to  the  sternum  of  the  first  abdominal 
somite,  and  gives  exit  to  a  glandular  process,  which  secretes 
a  viscid  matter.  Most  of  the  insects  belonging  to  this 
group  possess  a  curiously  contrived  "spring  and  catch'* 
attached  to  the  sternal  region  of  the  penultimate  or  ante- 
penultimate somites  of  the  abdomen,  by  the  help  of  which 
they  execute  their  vigorous  leaps. 

Sir  John  Lubbock  could  find  no  trace  of  trachese  in 
any  of  the  Collembola  except  SmtfrUhwrvs,  though  they  are 
easily  seen  in  many  of  the  Tkyaanura,  According  to  the 
same  authority  Lepisma  has  four  Malpighian  tubes,  while 
Campodea,  Japyx,  and  many  Collembola  have  none. 

The  MaUophaga  are  parasites  upon  mammals  and  birds, 
on  the  hairs  and  feathers  of  which  they  feed.  The  head 
and  body  are  depressed,  the  eyes  simple,  the  gnathites  of 
the  masticatory  type.  The  abdomen  has  nine  or  ten  visible 
segments. 

The  Pedieulina,  or  Lice,  subsist  upon  the  blood  of  the 
mammals  on  which  they  are  parasites.    The  gnathites  are 

*  Lubbock  *  Monograph  on  the       has  similar  appendages  attached 
CoUembola  and  Thytanura,*  p.  37.        to  each  segment  along  with  legs, 
t  The  myriapod  SeolopendriUa       (Lubbock,  /.c.) 


422      THB  ANATOMY  OF  IKyBBTKBRATX]>  AKIMALS. 

conyerted  into  a  piercing  and  sacking  apparatoB.  The 
under  aide  of  the  head  presents  a  soft  protrosible  pro- 
boscis, provided  externally  with  minute  homj  ho<^u,  and 
trayersed  bj  a  canal  which  leads  into  the  CBsophagns. 
The  proboscis  incloses  two  grooved  chitinons  sidles  which 
are  applied  together  hj  their  concave  sides;  and,  within 
the  sheath  thns  formed,  lie  two  finely-pointed  chitinons 
aet»  which  can  be  moved  up  and  down  in  the  sheath.*  . 
The  proboscis  is,  in  all  probability,  formed  by  the  union 

Fig.  103. 


Fig.  lOS.— ^ctIei  iitTra.— a,  the  aqoatie  apterom  larra.  B,  one  of  the 
transitional  stages  between  this  and  the  perfect  insect  C.  (*  ^^^P® 
Animal/) 

of  the  labrum  with  the  second  pair  of  maxiUss,  while  the  two 
halves  of  the  homy  sheath  are  the  mandibles,  and  the  setsB, 
the  first  maxillae.  The  prothorax,  mesothorax,  and  meta- 
thorax  are  hardly  distinguishable,  and  the  abdomen  has 
nine  visible  segments. 

The  Orihoptera  (Pig.  103)  and  the  Hemiptera  (Fig.  104)  are 
ametabolous.  The  majority  have  two  pairs  of  similar 
or  more  or  less  dissimilar  wings  in  the  adult  state,  and 

*  Qeisifeldt,  *  Ueber  die  Mondtheile  dcr  Sangenden  Inseetan,'  1853. 


OBTHOITKBA. — HBHIFTEK^  428 

in  the  apterona  fotms  it  ia  probable  that  tlie  wings  on 
aborted,  not  tTpicalljr  absent.  In  the  Orthofi&n*  (the' 
Termites,  Cockroaches,  Orasahoppers,  Cricketa,  Day-fliea, 
Dragon-fliea  and  Earwiga),  the  month  ia  constracted  npon 
the  same  plan  aa  that  of  Blatta;  but  the  Phytopoda  or 
TkifaanTptera  (Thript  and  ite  allies),  small  winged  inaecta 
which  live  chieflj  in  fiowen,  present  a  modification  whioh 
ia  tranaitional  to  the  Hemipt«ran  month  (Gerstieldt,  I.  e.)- 
There  ia  a  proboscis  directed  backwards  and  formed  bj  the 
anion  of  the  labnun  with  the  labium,  which  last  ia  provided 
with  palps,  though  thej  are  sometimes  tstt  smalL  Tha 
Fig.  10*. 


Fig.  \0\.—Aphii ptiargoitii.     ApteroiU  ■gsmogenelio  form. 

maxilli'!  are  palpigerons  and  are  united  at  their  bases  with 
the  labium.  The  mandibles  are  atjliform  setce  enctoeed  in 
the  proboscifl. 

In  the  Semtpfem.t  all  of  which  sack  the  blood  of  n.i>imnl» 
or  the  juices  of  plants  (Bags,  FUnt-lice,  Cieiida),  wings 
may  be  present  or  abaent,  and  the  eyes  are  usually  com- 
pound. The  visible  abdominal  somites  may  be  rediuwd  to 
six.  The  gnathites  are  modified  to  form  a  piercing  and 
suctorial  apparatus,  which  ia  similar,  in  many  respects. 

•  The  Tl^iaaura  and  the  PAy-       with  the  Nruroptta. 
Kpoda  arc  ot'len  ualted  with  the  t  The    MalUfkaga     and     the 

OHhoptcra  in  modem  eluaiflca^       Ptdiculiiia   are   onlwd  wlih  llie 
~ K^tors  by  lome  aulhon- 


424       THE  1.ITAT01IT  OF  IHTEBTKBEATXD  AimULS. 

to  that  of  the  Pediealina.  There  ia  &  Twiadly  aharp  arad 
pcmt«d  labmiii,  while  the  mandiblea  and  maxilhe  are  mere 
tubercles,  ennnoant«d  by  long  chitinoiM  pointed  styles,  of 
which  therefore  there  are  four.  The  lahiom  ia  OBtuJly 
represented  by  a  median,  jointed,  fleshy,  elongated  body, 
the  snt«rior  face  of  which  presenta  a  longitudinal  groove 
in  which  the  m&ndibles  and  ntinT'lli''  are  enclosed.  Neither  . 
the  maiillie  nor  the  labium  are  provided  with  palps. 

Thns,  in  the  series  of  ametabolons  insects  there  are  some 

with  Biasticatory,  others  with  suctorial  months.    It  is  I7 

no  means  clear  that  the  gnathitee  of  the  aoctorial  montii  of 

the  Hem^iera    are  to   be  r^arded    as  modificatiotis  of 

tie.  10^- 


H-  lOS. — Hydrtmkilia  puma. 
(■  Ri^ne  Animal.') 


B,    pup.-*. 


masticatory  gnathites  of  the  type  exhibited  by  the  Oriho- 
ptera.  The  absence  of  palps  is  a  very  significant  fact,  ang- 
geating  that  the  Hemipteron  mouth  is  the  extreme  term  of 
a  series  of  modifications  for  the  commencement  of  which 
we  must  go  back  to  the  Myriajmda. 

The  metabolons  CoUopfera,  or  Beetles  (Pig.  105),  hare 
masticatory  mouths  of  the  same  general  type  as  those  of  the 
OrthopUra ;  with  which  they  are  closely  connected  through 
the  Earwigs.  The  two  constituents  of  tJie  labium  are  how- 
ever much  more  completely  confluent  than  in  the  Ortkoplera, 


NBUBOPTEBA. — I>IPTB&A«  425 

There  are  nBuallj  two  pairs  of  wings,  the  anterior  pair  being 
conyerted  into  stiff  homj  elytra ;  these  take  no  part  in  the 
act  of  flight,  but  serve  as  covers  to  the  metathoracic  wings, 
which,  in  the  state  of  rest,  are  folded  np  beneath  them.  The 
number  of  apparent  somites  of  the  abdomen  is  often  much 
reduced.  In  the  metabolous  Neuroptera  (Ant-lions,  Caddis- 
flies,  Scorpion-flies),  in  some  of  which  the  insect  is  more  or 
less  active  during  the  pupa  state,  the  parts  of  the  mouth 
are,  for  the  most  part,  very  similar  to  those  of  the  Ortho- 
ptera.  In  two  groups  of  Neuroptera,  however,  the  mouth 
becomes  suctorial.  Thus  in  the  Trichoptera,  or  Caddis-flies, 
the  labrum  is  elongated  and  grooved  posteriorly;  the 
mandibles  are  aborted,  the  bases  of  all  the  gnathites  are 
united,  and  the  labrum  is  a  spoon-shaped  body.  In  the 
Scorpion-flies  (Panorpina),  there  is,  according  to  Gerstfeldt, 
a  proboscis  formed  in  front  by  the  elongated  clypeus  and 
labrum,  and  behind  by  the  coalesced  maxillsB.  The  man- 
dibles are  small,  and  the  first  marillm  much  elongated. 
The  ordinary  four  palps  are  present. 

The  Neuroptera  have  two  pairs  of  wings  of  a  delicate 
reticulated  structure.  The  metathoracic  wings  may  or  may 
not  be  folded. 

What  appears  to  be  a  further  development  of  this  type 
of  mouth  is  found  in  the  Lepidoptera  (Butterflies  and 
Moths).  The  labrum  and  the  mandibles  abortf  and  the 
labium  is  represented  only  by  a  triangular  plate  which 
bears  two  large  palps.  On  the  other  hand,  the  maxillse,  the 
palps  of  which  are  always  very  small,  are  often  immensely 
elongated  and  applied  together  by  their  channelled  inner 
faces,  thus  constituting  a  sucking  proboscis  (Fig.  106, 107). 
The  wings,  similar  in  character,  and  covered  with  minute 
scales,  are  rarely  absent.    Both  pairs  are  used  in  flight. 

In  the  metabolous  Diptera  (Flies  and  Fleas,  Fig.  108),  the 
mouth  is  constructed  upon  the  same  plan  as  that  of  the  Hemi- 
ptera,  so  far  as  the  conversion  of  the  labium  into  an  organ  of 
suction  is  concerned ;  but  usually  the  metamorphosis  of  the 
gnathites  is  carried  still  further,  and  the  maTillte  have  palps. 
Thus  in  the  Fleas,  which  are  parasitic  on  mammals  and 


42S       THE  AHATOMT  OF  IHTUtnBKATID  AKIMALS. 

birda,  what  appears  to  be  the  labmm  is  an  elongfttod,  alcnder 
st^le,  which  lies  between  the  two  elongated  nutadiUM. 
The  first  maiilla  are  broad  triangular  plates,  each  with  a 
four-jointed  palp.  The  second  marilhe  (labinm)  are  re- 
presented  bj  a  short  median  lamella,  which  boands  the 
Fig.  106.  Fig.  107. 


Fig.  106.— The  biad,  A,  md  p«msnf  the  month,  B 
C,  of  ^Ajjtf  iifftattri-^ii,  antenna;    b^  epicn 

/,  nund'ible;  p'mixMt;  A/niuilkVy'  pilpiu 
t,  labial  palpiu.      B,  bue  of  the  HKillla  witi 


tbBH 


(.Uter  Newport.) 


m;  C,  lateral  view  of 


t,    papilUe;  4, 
hooVs       wUch 


month  behind  and  is  provided  with  two.  long  palps,  wfaicb 
resemble  knife  blades  and  are  imperfectly  divided  into  tooT 
joints.  The  three  somites  of  the  thorax  are  distinct,  and 
the  two  hinder  ones  have  lamellar  appendages,  whieh 
posnblf  represent  wings.  The  abdomen  has  ten  somites.* 
*  8aa  L.  Lutdols, '  Anstomla  dee  HnDdeflobet,'  1S66, 


&- 


427 


In  those  dipterouB  inaects  wliioli  are  tenned  Ftipipara^ 
which  are  apterouB,  or  nearly  so,  and  parasitic  npon 
mammabs,  birds  and  bees,  a  circular  wall,  or  short  pro- 
boscis, inrests  the  other  parts  of  the  month.  There  are, 
first,  two  lateral,  protrasible,  homj  plates;  secondly, 
an  anterior  and  a  posterior  seta;  the  latter  stronger  and 
grooved  longitudinally  in  front.  Between  these  is  a  single 
fine  seta.  Gerstfeldt  considers  that  the  last  answers  to 
the  hypopharynx ;  the  second  pair,  to  the  labrom  and  the 
second  Tni^Tillm ;  the  first  pair,  to  the  first  maxillm ;  and  that 
there  are  no  mandibles. 

The  ordinary  Dipiera,  which  possess  one  j^air  of  functional 
wings  attached  to  the  mesothorax,  resemble  the  Hemipiera 
in  possessing  a  usually  fieshy  proboscis,  often  tumid  at  its 

Fig.  108. 


Fig.lOS.^Syrphusribesu.—A^lamL,    B,  papt.    C,  imago.    (*  Regne 
Animal.') 

extremity,  which  is  formed  by  the  confluent  second  maxillse. 
As  in  Hemiptera  also,  the  labrum  is  a  more  or  less  elongated 
pointed  plate,  and  the  mandibles  and  maxillae  are  usually  ter- 
minated by  chitinous  cutting  setsB  (Fig.  109).  But  the  bases  of 
these  parts  are  constantly  united  together;  there  is  a  pair  of 
maxillary  palpi,  and  often  a  median,  more  or  less  styliform 
structure,  usually  considered  to  be  the  hypopharynx.  It 
seems  doubtful,  howeyer,  whether  this  may  not  be  formed  by 
the  coalesced  terminations  of  the  maxillsB.  In  the  common 
House-fly,  the  labrum,  mandibles,  and  maxiUse  coalesce  at 
their  origins  to  constitute  the  base  of  the  proboscis,  which 
is  mainly  formed  by  the  confluent  second  maxillm.  Its 
longitudinal   grooved   anterior  face  is  overhung  by  the 


428   THE  ANATOMY  OF  INTSBTSBSATSD  ANIMALS. 

elongated  stjliform  labmm.  The  gnathitee  here  exhibit 
almost  the  extreme  modification  of  the  piercing  and  sucking 
type  of  mouth. 

FinaUj,  the  metabolous  HymenopUra  with,  usually,  two 
pairs  of  reticulated  scaleless  wings  present  a  series 
of  modifications  from  the  essentiallj  masticatory  mouth 
of  the  Ants  to  the  partly  masticatory  and  partly  suctorialt 

Fig.  109. 


Fig.  109. — ErhtatU  floreiu.—d^  front  of  the  head  ;  e,  labrum  ;  /,  man- 
dible ;  g^  maxilla  and  palpus ;  t,  labium ;  t*  extremity  of  the  labium 
semrately  and  more  magnified ;  t"**,  inner  surface  of  the  paragtoMV ; 
i*^,  the  rows  of  hairs  on  the  inner  surface ;  ly  the  ligiila ;  «,  the 
cardo  and  submentum.    (After  Newport.) 

or  rather,  lapping  mouth,  such  as  is  met  with  in  the 
Bees.  In  the  latter  (Fig.  110)  the  labrum  is  small;  be- 
neath it,  a  median  fleshy  lobe — the  epipharynm — OTcr- 
hangs  the  minute  apertiure  of  the  mouth.  The  mandibles 
are  strong  with  wide,  almost  spoon-shaped,  extremities. 
The  part  of  the  maxilla  which  appears  to  answer  to 
the  lacinia  in  BlaUa,  is  shaped  like  a  knife-blade  and 
lolds  upon  the  stout  sHpea,  Like  a  clasp-knife  in  its  handle. 


THI  HmXOFTBK^ 


The  ahort  and  almost  mdimentai;  palp  is  attached  to 
the  eztremitj  of  the  atipee.      The  cardinei  are  t(aig  and 


Tig.  no.— (DpFCTftgnre.)  FectioDof  thchcwlot  Jlamhu.  t.oeella*; 
Ct  kntemu ;  d^  cl jpnu ;  tf,  labrum  ;  y,  muidiblA  ;  ff^  cjriphUTiu ;  hy 
rnulUa ;  t,  urdo ;  j,  4,  /,  submentum  4iid  menlum ;  n,  in',  laUal  pal- 
pal; n,  paraglMsa;  o,  lingua  or  mediin  proceai  of  tha  Ugala; 
■,  DodpltBl  fomnen  ;  1,  3,  sclariln  of  the  hjpopharjnx. 

(LcftlowcrBgure.)    Tenninil  porlion  of  amasilia. 

(Middle  lower  figure.)  Epipharjrax  and  hjpopbaryni  nuRnifled  ;  1,S, 
■dertlai  of  the  hypopharyni ;  3,  cat  and  of  the  niopliagni ;  4,  5, 
•elerltea  tn  Ihe  wall  of  the  CHophigni  and  ildea  of  the  mouth  ;  fi,  Kp- 
likfl  pnqeetlon  of  the  hypopbaryni ;  f,  epipharyni. 

(Right  lower  figure.)  a.  Quadrate  iclerita  coDneoted  by  a  MaDgnlar 
pteoe  with  c,  one  of  the  lancet  of  Ihe  sting ;  b,  doct  of  the  pobon 
gland ;/,  gnwTed  median  piece  In  which  the  laucea  play;  h,  ODa  of 
die  latenfietoae  palplform  sheath-piecei ;  g,  genllal  aperttm. 

■lender  and  give  rise  to    a   hinge    joint,  wlierebj   the 
maxillia  and  labiom  can  be  folded  back,  like  a  carriage 


430       THE  ANATOMY  OF  HrYSBTSBSATBD  ANIMALS. 

step,  under  the  head.  The  mentum  is  lar^,  the  labial 
I>alp8  long  and  slender ;  there  are  two  large  paraglosssB  and, 
between  them,  a  median,  annulated,  setose,  cylindrical 
organ  proceeds,  which  either  represents  the  lingaa,  or  is  an 
independent  prolongation  of  the  ligula.  Fnnctionallj,  this 
organ  is  a  tongue,  and  enables  the  bee  to  lap  up  the  honey 
on  which  it  feeds.  The  mandibles  and  maxillfB  are  em- 
ployed Hs  cutting  and  modelling  implements,  but  appear  to 
have  little  or  nothing  to  do  with  mastication,  properly  so 
called. 

The  gnathites  and  the  mouth  are  abortive  in  some 
insects,  as  the  Day-flies,  which  take  no  food  in  the  adult 
condition.  The  development  of  the  different  divisions  of 
the  alimentary  canal  varies  greatly.  Salivary  glands  are 
very  generally  present.  In  many  suctorial  insects,  the 
ingluvies  is  a  sac  opening  by  a  long  duct  into  the  gullet ; 
a  distinct  proventriculus,  provided  with  chitinous  ridges, 
may  be  present  or  absent.  The  ventriculus  appears  to  be 
always  devoid  of  an  inner  cuticula.  It  may  be  devoid 
of  csBca  or  beset  with  short  cseca  throughout  its  whole 
extent.  The  number  of  the  Malpighian  tubes,  which  are 
sometimes  branched,  varies  from  two  to  a  multitude.  In 
many  cases  they  have  been  found  to  contain  uric  acid ;  bat 
no  biliary  matter  has  yet  been  proved  to  exist  in  them. 
Anal  glands  are  frequentiy  appended  to  the  termination  of 
the  rectum,  and  may  secrete  an  acrid  or  stinking  fluid. 

In  some  larvsa  {Myrmecoleo,  Dytiscus)  there  is  no  proper 
median  oral  aperture,  but  canals  which  open  on  the  ex- 
tremities of  the  mandibles  lead  into  the  oesophagus,  ^e 
alimentazy  canal  has  no  posterior  opening  in  the  lar^s 
of  many  Hymenopiera,  of  Myrmeeoleo  and  of  the  Pttpipara, 
The  salivary  glands  secrete  the  silken  material  in  which 
the  larvse  of  the  Lepidopiera  invest  themselves ;  while,  in 
Myrmeeoleo  and  the  HemerchidcB,  it  is  the  rectum  which 
fnzniahes  the  silk. 

The  poison  of  the  Hymenoptera  is  a  fluid  strongly  im* 
pregnated  with  formic  add,  which  is  secreted  bj  a  special 


«  « 


OYIP08ITOB8  AXm  STIKOS.  431 

gland  and  poured  into  a  reservoir  connected  with  the 
sting. 

In  many  winged  insects  both  pairs  of  wings  are  de- 
Teloped  and  take  equal  shares  in  flight  {Hymenoptera, 
Lepidoptera,  Newropiera),  In  the  Coleoptera,  the  anterior 
pair  are  converted  into  homj  wing-covers  {ehftra),  and 
the  posterior  pair,  much  larger  than  the  anterior  and 
folded  up  under  them  when  the  insect  is  at  rest,  subserve 
flight.  In  the  Diptera  the  posterior  wings  are  represented 
only  bj  short  processes,  the  hctUeres,  In  ike  Strepgipiera,  on 
the  other  hand,  it  is  the  anterior  pair  of  wings  which  abort. 
In  all  orders  of  winged  insects,  individual  cases  of  complete 
abortion  of  the  wings  occur  either  in  the  female  alone,  or 
in  both  sexes. 

The  posterior  abdominal  somites  often  undergo  extensive 
modifications ;  thej  may  be  small  and  retracted  within  the 
anterior  somites,  or  they  may  even  become  more  or  less 
completely  abortive.  In  many  insects,  processes  of  the 
somites  in  the  genital  region  of  the  female,  which  answer 
to  the  gonapophyses  of  BlaUa,  are  converted  into  organs 
which  assist  in  the  deposition  of  the  eggs  and  are  termed 
ovipaniora.  The  saws  of  the  Saw-flies  and  the  stings  of 
other  Hymenoptera  are  to  be  regarded  as  specially  modified 
ovipositors.  The  laborious  and  thoughtful  investigations 
of  Lacaze-Duthiers  *  led  him  to  the  conclusion  that  all 
these  organs  are  constructed  upon  the  same  plan;  that 
they  are  developed  from  that  somite  of  the  abdomen  which 
lies  immediately  behind  the  opening  of  the  vulva;  that 
this  opening  is  always  situated  between  the  eighth  and  the 
ninth  somite ;  and  is  therefore  separated  by  ihiee  somites 
(the  ninth,  tenth,  and  eleventh),  from  the  anus. 

According  to  Lacaze-Duthiers,  in  those  insects  which  are 
provided  with  an  ovipositor,  saw  or  sting,  the  ninth  somite 
always  consists  of  a  single  median  tergal  sclerite,  to  the 
inferior  angles  of  which  are  connected  two  small  more  or 
lees  triangular  pieces,  each  of  which  carries  a  long  styli- 

*  **  Recherches  ear  Tarmure  g^nitale  femelle  des  InaectM.*'  ('  AnsAleB 
det  Sdencet  NatureUes/  1S4»-1853.3 


432       THS  ANATOMY  OF  INTSBTBB&ATBB  AWTMAT^. 

form  appendage.  There  is  a  smgle  median  sderite,  wbich 
is  the  most  important  part  of  the  boring  apparatus;  two 
small  sclerites  are  united  with  the  lateral  angles  of  this 
piece,  and  there  are  two  other  elongated  sclerites  which 
constitute  a  valvular  sheath.  Thus,  according  to  Lacaxe* 
Duthiers'  view,  in  the  sting  of  Bombtu  (Fig.  94)  k  is  one 
of  the  elongated  lateral  sternal  sclerites,  which  with  its 
fellow  forms  a  sheath  for  the  rest  of  the  apparatus ;  /  is  the 
median  sternal  sclerite;  it  is  pointed  and  grooved  on  its 
sternal  surface;  while  c,  one  of  the  lances,  is  a  prooesB 
of  the  tergal  half  of  the  somite.  Each  lance  is  sharp  and 
slender,  and  its  tergal  edge  fits  upon  the  margin  of  the 
groove  of  the  median  style,  in  such  a  manner  as  to  be  able 
to  slide  backwards  and  forwards  upon  it.  The  sternal  edges 
of  the  two  lances  meet  in  the  middle  line,  and,  together  with 
the  median  sternal  piece,  enclose  a  canal  which  serves  to 
convey  the  secretion  of  the  poison  gland  into  the  wound 
made  by  the  sting.  In  the  operation  of  stinging,  the  median 
piece  serves  as  a  sort  of  "  director  "  for  the  two  lances. 

However,  recent  investigations  into  the  development  of 
stings  and  ovipositors,*  e.g.  the  sting  of  the  Hive-bee,  and 
of  the  Wasp  and  the  ovipositor  of  an  Ichneumon-fly  (Cryphu 
migrator),  show  that  while  the  median  grooved  piece  and  the 
two  sheath-pieces  arise  from  papillsB  developed  upon  the 
sternal  surface  of  the  ninth  abdominal  somite  of  the  larva, 
the  lances  are  the  result  of  the  metamorphosis  of  papills 
seated  on  the  sternal  surface  of  the  eighth  somite;  and 
these  papillae  are  so  similar  to  those  from  which  the  limbs 
are  developed,  that  it  becomes  (to  say  the  least)  probable, 
that  they  represent  true  appendages  of  the  somites  to 
which  they  are  attached,  rather  than  mere  modificati<Mi8  of 
the  sclerites  of  the  body- wall,  as  Lacaze-Duthiers  supposed 

*  Kraepelin,  **  Untersuchungen  des    SUchels    und    der    L^e- 

Ciber  den  iBaa,  Mechimismuif  und  scheide."  (*  Zeitschrift  fur  Vfin, 

Entwickelangsgeschichte        des  Zoologie,'1875.)    See  also  the  ob- 

Stachels      der       Bienenarti^en  servations  of  Packard,  *On  the 

Thipre**    C  Zeitsehrift  fiir  Wist.  develupinent  aud  poaiUon  of  the 

Zoolofrie,'    1873);   and    Dewitz,  iJymenoptera,'  1866. 
^Ueber  Bau  und  Entwickeinng 


THB  COPULA.TOBY  ORGANS  OF  IK8ECT8.  433 

them  to  be.  In  like  maziner,  the  examination  of  the  develop- 
ment of  the  ovipositor  of  Locusta  viridiasima  has  proved 
that,  of  the  three  pieces  of  which  each  half  of  it  is  com- 
posed, two  are  developed  from  the  sternum  of  the  ninth 
and  one  from  that  of  the  eighth  somite.  But  the  two 
median  pieces  of  the  ninth  somite  do  not  unite  together  to 
form  a  single  piece  grooved  below,  as  in  the  hymenopterous 
sting  or  ovipositor.  And  observations  which  I  have  made 
on  the  development  of  the  gonapophjses  of  BlaUa,  lead  me 
to  the  conclusion  that  the  posterior  bifid  pair  are  developed 
from  the  ninth,  and  the  anterior  curved  pair  from  the 
eighth  somite.  In  this  case  the  latter  will  be  the  homo- 
logue  of  the  lances  of  the  Bee  sting. 

Thus  it  would  appear  that,  while  there  can  be  no  doubt 
as  to  the  general  unity  of  plan  of  ovipositors  and  stings, 
the  view  of  Lacaze-Duthiers  must  be  modified.  It  must 
be  admitted  that  these  apparatuses  appertain  to  the  eighth 
and  ninth  somites,  and  not  to  the  ninth  alone;  and  that 
there  is  much  reason  to  suspect  that  their  chief  constituent 
parts  are  modified  limbs. 

The  male  copulatory  organs  *  are  often  very  complicated, 
and  their  homologies  have  not  yet  been  fully  determined. 
Kraepelin  (I,  c.)  who  has  examined  the  development  of  these 
parts  in  the  Drone,  and  the  modifications  found  in  herma- 
phrodite Bees,  is  led  to  the  conclusion  that  they  are  developed 
from  the  eighth  and  ninth  somites  of  the  abdomen,  and 
therefore  are  the  homologues  of  the  parts  of  the  sting  in 
the  female.  In  the  male  Blatta,  however,  it  is  obvious  that 
the  male  copulatory  apparatus  belongs  to  a  more  posterior 
somite  than  that  upon  which  the  female  gonapophyses  are 
developed. 

The  heart  usually  has  the  form  of  a  flattened  tube,  closed 
at  its  posterior  end,  but,  in  front,  continued  into  the  aorta, 

*  The  male  LibelMida  possess  ordmtry  position^  and  hence,  be- 

a  peculiar  copulatory  apparatus  fore  copulation,  the  male  has  to 

developed  upon  the  sternum  of  bend  the  extremity  of  his  abdo- 

the    second   abdominal    somite.  men*  upwards  in  order  to  load 

The   genital   apertore    has   the  this  apparatus  with  spermatosoa. 

2  V 


42i       THE  ANATOMY  OF  INYEBTBBBATBD  AKIK ALS. 

which  may  be  traced  as  far  as  the  cerebral  ganglia^  and 
appears  to  give  off  no  branches.  The  sides  of  the  tube 
present  slit-like  openings  {ogHa),  which  ybtj  in  number 
from  two  to  nine  pairs ;  and,  when  there  are  several  pairs, 
each  pair  answers  to  a  somite  of  the  abdomen.  The  mai^ins 
of  the  ostia  may  be  simple,  or  may  be  produced  inwards 
into  folds  which  play  the  part  of  yalves.  Moscnlar  or 
UgamentouB  fibres  may  extend  from  the  hypodermis  to 
the  dorsal  aspect  of  the  heart,  and  serve  to  suspend  it  in 
place. 

The  alary  muscles,  which  in  most  insects  are  fan-shaped, 
and  lie  in  pairs,  opposite  one  another,  on  each  side  of  the 
heart,  either  unite  in  the  middle  line,  or  are  inserted  into 
a  sort  of  fascia,  on  the  sternal  aspect  of  the  heart,  to  which 
organ  they  are  not  directly  attached. 

The  septum  between  the  pericardial  cavity  and  the 
general  cavity  of  the  abdomen  thus  formed,  is  termed  by 
Graber*  the  pericardial  septum.  From  their  anatomical 
relations,  therefore,  the  alary  muscles  can  have  nothing 
to  do  with  the  diastole  of  the  heart,  the  pulsations  of  which 
indeed,  go  on  just  as  well  when  the  alary  muscles  are  cut 
through.  Graber  throws  out  the  very  probable  suggestion 
that  the  contraction  of  the  alary  muscles  causes  the  peri- 
cai'dial  septum  to  move  towards  the  axis  of  the  body,  and 
by  thus  enlarging  the  cavity  of  the  i)ericardium,  facilitates 
the  flow  of  blood  to  the  ostia  of  the  heart.  The  same 
investigator  asciibes  a  special  i-espiratory  function  to  the 
abundant  trachea)  which  are  distributed  to  the  walls  of  the 
pericardium,  and  which,  undoubtedly,  must  tend  to  facili- 
tate the  aeration  of  the  returning  blood. 

In  many  insects,  a  septum,  provided  with  transverse 
muscles,  overlies  the  abdominal  nerve-cord  and  separates 
a  ventral  blood  sinus,  in  which  the  cord  lies,  from  the 
abdominal  cavity.  The  sinus  is  open  in  front  and,  as  the 
muscles  of  the  septum  contract  rhjrthmically  from  before 

♦  "Ueber  den  v''op"^wi^oni-  187.^),  and  **Ueber  den  pulti- 
sehen  Apparat  der  Insecten  **  renden  BauchsinuB  der  Inftecten." 
(<  Zeltschrift  fur  Wise.  Zoologie/       (Ibid.,  1876.) 


THB  BBSPnULTOBT  OBOANS  OF  INSBCT8.  435 

backwards,  they  tend  to  drive  the  blood  which  enters  it 
to  the  posterior  end  of  the  body. 

In  the  respiratory  system  of  insects  the  number  of 
stigmata  is  observed  to  vary  from  one  to  ten  pairs.  As  a 
rule,  none  are  found  in  the  head,*  or  between  the  head  and 
the  first  thoracic  somite,  and  they  are  usually  absent  from 
the  terminal  somites  of  the  abdomen.  A  very  common 
number  is  nine  pairs ;  the  first  being  situated  between  the 
mesothorax  and  the  metathorax,  and  the  rest  between  the 
following  somites.  Only  two  pairs  of  stigmata  are  found  in 
the  lAhelluUdoR  and  Ephemendos,  and  they  are  seated  upon 
the  thorax.  In  Nepa  and  Banaira,  there  is  only  one  pair  of 
abdominal  stigmata,  in  addition  to  those  in  the  thorax,  and 
in  the  larvsB  of  Tipulidce  and  of  HydrophiluSt  the  stigmata 
are  reduced  to  one  terminal  abdominal  pair.  The  stigmatic 
openings  are  usually  situated  upon  the  sides  of  the  abdomen, 
but  in  some  Coleoptera  (e.  g.  Dytiscus)  they  are  dorsal,  and 
in  many  Hemiptera  they  are  situated  on  the  ventral  aspect  of 
that  region  of  the  body.  Either  the  lips  of  the  stigmatic 
aperture  itself,  or  the  walls  of  the  tracheal  trunk  which  arises 
from  it,  are  so  disposed  as  to  constitute  an  occlusor  apparatus, 
provided  with  a  muscle,  by  the  contraction  of  which  com- 
munication with  the  external  air  can  be  cut  off.  This  occlusor 
apparatus,  long  ago  described  in  certain  insects  by  Strauss- 
Durckheim,  Newport,  Burmeister,  Siebold  and  others,  has 
recently  been  specially  investigated  by  Landois  and  Thelen,t 
who  describe  it  as  usually  consisting  of  four  essential  parts  : 
the  how  (Verschluss-biigel),  the  lip  (Verschluss-band),  the 
lever  (Verschluss-hebel),  and  the  muscle.  The  bow  is  a 
thickening  of  one-half  of  the  circumference  of  the  chitinous 
lining.  The  lip  is  formed  by  the  other  half  of  the  circum- 
ference, and  the  lever  is  a  chitinous  process  connected  with 
one  end  of  the  bow,  or  with  the  lip.  When  the  lever  is 
single,  the  muscle  which  is  attached  to  it  passes  over  the  lip 

♦  Sir  John  Lubbock  found  the  t  "  Der  Stigmenverschlu's  bei 

two  spiracles  pf  Smynthurus,  to  be  d  en  Insecten.       (*  Zeitschrift  iiir 

situated  on  the  under  side  of  the  Wisscnschattliche          Zoolngie/ 

head,  immediately  below  the  an-  lb67.) 

teniue.  2  F  2 


486       THB  ANATOMY  OF  IKYERTBBSATSB  AKOCAL8. 

and  is  inserted  into  the  opposite  end  of  the  bow.  When  it 
contracts,  it  therefore  presses  the  lip  against  the  bow.  When 
two  levers  are  present,  they  are  attached  to  opposite  ends 
of  the  lip  and  bow,  and  the  muscle  extends  between  their 
extremities.  The  effect  of  its  contraction  is  to  throst  the 
free  edge  of  the  lip  against  the  bow. 

The  tracheal  trunk  which  arises  from  a  stigma  may 
ramify  without  communicating  with  the  rest ;  but,  usually, 
the  trachese  which  proceed  from  each  stigma  enter  into 
more  or  less  extensive  anastomoses.  Yery  commonly  the 
main  trunks  of  each  side  give  off  wide  anastomotic  branches, 
which  unite  and  form  a  longitudinal  trunk  on  each  side  of 
the  body,  while  transverse  trunks  often  connect  the  main 
trachese  of  opposite  sides. 

In  many  insects,  especially  those  which  possess  great 
powers  of  flight,  more  or  fewer  of  the  trachese  become 
dilated  into  sacs,  in  which  the  spiral  marking  of  the 
chitinous  lining  is  interrupted  or  disappears.  In  Bees 
and  Flies,  a  vast  air-sac  is  thus  develop^,  on  each  side  of 
the  abdomen,  from  the  longitudinal  anastomotic  trunk. 

The  aquatic  larvae  of  many  Orthoptera  (EphemeridcB, 
Agrion,  Calopteryx)  and  Neuroptera,  and  of  some  Dipiera, 
Lepidopteray  and  Coleopiera,  though  provided  with  a  fully- 
developed  tracheal  system,  possess  no  stigmata.  The 
somites  of  the  abdomen  or  of  the  thorax  are,  however, 
provided  with  delicate  foliaceous  or  filamentous  processes, 
into  which  branches  of  the  trachese  enter  and  ramify.  The 
air  contained  in  these  trachese  is  therefore  separated  from 
that  dissolved  in  the  water  only  by  a  very  thin  layer  of 
integumentary  tissue,  and  an  exchange  of  gaseous  con- 
stituents  between  the  two  readily  takes  place.  These  are 
often  called  hranchioe,  but  they  are  obviously  of  a  totaUy 
different  nature  from  true  branchise.  The  larvse  of  some 
Dragon-flies  {Libellula  and  ^schna)  present  yet  another 
form  of  respiratory  organ.  Although  they  possess  a  pair 
of  thoracic  stigmata,  these  appear  to  have  little  or  no 
functional  importance,  but  respiration  is  effected  by  pump- 
ing water  into  and  out  of  the  rectum.    The  walls  of  the 


THE  SOUNDS  PBODUCED  BT  INSECTS.  437 

j«  produced  into  six  double  series  of  lamellae,  in  the 
r  of  which  trachese  are  abundantly  distributed,  and 
play  the  same  part  as  the  tracheal  branchise  just 
ned.  These  rectal  respiratory  organs,  in  fact,  appear 
b  complicated  form  of  the  so-called  "  rectal  glands  " 
ure  so  generally  met  with  in  insects, 
chief  agent  of  the  movements  of  expiration  and 
tion  in  insects  is  the  abdomen,  the  capacity  of  which 
)  diminished  by  the  approximation  of  its  terga  and 
and  the  shortening  of  its  length  by  the  retraction 
posterior  into  its  anterior  somites;  while  it  may 
irged  by  movements  in  the  opposite  directions, 
bhe  cavity  is  enlarged,  air  rushes  in  at  the  stigmata, 
en  it  is  diminished,  if  the  stigmata  are  open,  expira- 
3ur8 ;  but,  if  the  stigmata  are  shut,  the  effect  of  the 
Dry  act  must  be  to  drive  the  air  into  the  ultimate 
itions  of  the  trachese.  The  movements  of  inspira- 
d  expiration  vary  in  rapidity  with  the  condition  of 
K;t.  In  the  Bee,  Newport  observed  that  in  the  state 
they  were  as  few  as  forty,  but  that  they  rose  to  one 
i  and  twenty  with  muscular  exertion. 
Eur-sacs  doubtless  assist  flight  by  the  diminution  of 
tcific  gravity  of  the  insect,  which  follows  upon  their, 
on. 

sounds  produced  by  insects*  are,  in  a  great  propor- 
cases,  effected  by  the  friction  of  hard  parts  of  the 
lent  one  against  the  oth^.  Thus  the  Grasshopper 
3  femur  of  the  hind  leg  against  a  ridge  on  the  anterior 
ad  the  chirp  of  the  Crickets  and  Locusts  is  produced 
friction  of  the  elytra.  The  parts  which  thus  rub 
r  are  provided  with  serrations  and  ridges,  which 
M>n8tant  and  characteristic  disposition.  The  longi- 
»etles  produce  a  sound  by  the  friction  of  the  tergum 
)rothorax  upon  a  process  of  that  of  the  mesothorax. 
Dung-beetles  by  rubbing  the  coxae  of  the  hind  legs 
the  hinder  edge  of  the  third  abdominal  sternum. 

lAndois,   **Die    Ton-  and   Stimm-Appante  der   Insecten." 
rift  fiir  Wiss.  Zoologie,*  1867.) 


438       THB  ANATOMY  OF  INYERTEBBATEB  ANIMALS. 

Further,  sounds  ai*e  necessarily  produced  by  the  extremely 
rapid  vibration  of  the  wings,  which  characterises  the  flight 
of  many  insects.  Landois,  however,  found  that  the  thorax 
of  a  Bluebottle  fly  continued  to  buzz  after  the  separation 
of  the  head,  the  wings,  the  legs,  and  the  abdomen.  The 
separation  of  the  halteres  weakened  the  sound  but  slightly. 
The  acoustic  apparatus,  in  fact,  lies  in  the  immediate 
neighbourhood  of  the  thoracic  stigmata.  The  main  trunk 
of  the  trachesB  dilates  into  a  hemispherical  sac,  which  opens 
externally  by  the  stigmatic  orifice.  The  sac  presents  a 
hooplike  thickening,  to  which  are  attached  free  chitinous 
folds  or  processes,  and  it  is  to  the  vibration  of  these  that 
Landois  ascribes  the  sound.  The  vocal  organ  of  the  Fly 
would  thus  appear  to  be  a  modification  of  the  occlusor 
apparatus  of  the  stigmata,  just  as  the  organ  of  voice  of 
mammals  is  a  modification  of  the  occlusor  apparatus  of 
their  i^espiratory  opening. 

In  the  Cicad<2  the  vocal  organs  are,  according  to  Landois, 
the  posterior  thoracic  stigmata.  These  open  into  chambers, 
in  the  walls  of  which  tense  membranes  are  so  disposed  as 
to  intensify  the  sound  by  their  resonance. 

As  in  the  Crustacea^  so  in  insects,  the  central  nervous 
system  varies  very  much  in  the  extent  to  which  its  com- 
ponent ganglia  are  united  together.  In  most  Orthoptera  and 
Neuroptera  and  in  many  Coleopteraf  the  thoracic  and  ab- 
dominal ganglia  remain  distinct  and  are  united  by  double 
commissures  as  in  Blatta.  In  the  Lepidoptera,  the  thoracic 
ganglia  have  coalesced  into  two  masses  united  by  double 
commissures ;  while  in  the  abdomen  there  are  five  ganglia, 
with  single  or  partially  separated  commissural  cords.  The 
concentration  goes  furthest  in  some  Diptera  and  in  the 
Strepsiptera,  in  which  the  thoracic  and  abdominal  ganglia 
are  fused  into  a  common  mass. 

A  system  of  stomato-gastric  nerves  similar  in  its  general 
arrangement  to  that  of  Blatta^  is  very  generally  present. 

A  special  system  of  nerves,  termed  respiratory  or  trantvene, 
is  found  in  very  many  insects,  both  in  the  larval  and  in  the 
perfect  condition.    The  principal  nerves  of  this  system  are 


THB  AUDITOBY  ORGANS  OF  IK8BCT8.  4S9 

arranged  in  pairs  on  the  sternal  aspect  of  the  body,  and  their 
outer  extremities  anastomose  with  branches  of  the  ordinary 
peripheral  nerres  and  are  distributed  to  the  muscles  of  the 
stigmata.  Their  inner  ends  unite  into  a  plexus,  which  lies 
OTer  the  interval  between  two  of  the  ganglia  of  the  central 
nervous  cord,  and  they  are  connected  by  longitudinal  cord^ 
with  one  another,  and  with  th^se  ganglia. 

In  insects,  as  in  other  arthropods,  the  branches  of  the 
nerves  which  are  distributed  to  the  integpunent,  and  espe* 
cially  those  which  pass  to  the  bases  of  the  larger  or  smaller 
setcD  with  which  the  integument  is  provided,  frequently  end 
in  minute  ganglia.  Hensen  has  shown  that  in  the  Orustcieec^ 
s^TTiWar'  setsB  in  all  probability  have  an  auditory  function ; 
and  Leydig,  Hicks,  Lespes,  Landois,  and  others,  have  as- 
cribed functions  of  special  sensation  to  these  structures 
in  insects.  But  whether  these  setse,  on  the  antennse  or 
elsewhere,  'subserve  eith^  hearing  or  smell,  is  still  very 
doubtful ;  and  the  only  organs  which  can  safely  be  regarded 
as  auditory  in  insects,  are  those  which  occur  in  Grasshoppers 
(AerididoB),  Crickets  (Achetidoe),  and  Locusts  (LocugHdce),  and 
which  were  first  accurately  described  by  Von  Siebold.* 
Recently,  they  have  been  studied  by  Leydig,  Hensen,  Ilanke,t 
and  Oscar  Schmidt,^  but  it  must  be  confessed  that  much 
obscurity  still  hangs  over  their  minute  structure. 

In  the  AcrididcB,  the  chitinous  cuticula  of  the  metathorax 
presents  on  each  side,  above  the  articulation  of  the  last 
pair  of  legs,  a  thin  tympaniform  membranous  space  sur- 
rounded by  a  raised  rim.  On  its  inner  face,  the  cuticular 
layer  of  the  tympaniform  membrane  is  produced  into  two 
processes,  one  of  which  is  a  slender  stem  ending  in  a  hollow 
triangular  dilatation.  A  large  tracheal  vesicle  lies  over  the 
tympanic  membrane,  and  between  its  wall  and  the  latter, 
a  nerve  derived  from  the  metathoracic  ganglion,  passes  to 
the  region  occupied  by  the  processes,  and  there  enlarges  into 

♦  »Archiv     fttr    Naturgeschi-       1875.) 
chte,'  1864.  X  Schmidt,   "Die   Oehrorgane 


t  ^  Beitriige  zu  der  Lehre  von       der     Ueuschrecken."     Q  Archiv 
den  UebergaDgs-Sinnesorganen."       fiir  Mikr.  Anatomie/  1875.) 
('  Zeitachrift  fur  Wiss.  Zoologie,' 


440   THE  ANATOMY  OF  INYEBTEBBATED  ANIMALS. 


a  ganglion,  tlie  outer  face  of  which,  beset  with  nninercms 
glassy  rods  arranged  side  bj  side,  is  in  contact  with  the 
tjmpaniform  membrane.  A  nerve  arising  from  this  gan- 
glion passes  along  a  groove  to  the  '  stem '  and  ends  in  a 
ganglion  in  its  dilatation.  From  this  ganglion  certain 
fine  filaments  proceed. 

In  the  AcheHdce  and  LocustidcBy  the  tibisB  of  the  fore  legs 
present  similar  tympaniform  membranes  which  are  easily 
seen  in  the  common  Cricket,  but,  in  other  forms,  become 
hidden  by  the  development  over  them  of  folds  of  the  cuticle 
of  the  adjacent  region  of  the  limb.  Two  spacious  tracheal 
sacs  occupy  the  greater  part  of  the  cavity  of  the  tibia,  and 
a  large  nerve  ends  in  a  ganglion  in  the  remaining  space. 
Upon  this  ganglion  a  series  of  peculiar  short  rod-like  bodies 
are  set. 

The  compound  eyes  of  insects  differ  only  in  detail  from 
those  of  the  Crustacea. 

In  the  ocelli,  or  so-called  simple  eyes,  a  sclerotic,  a  cornea, 
a  lens,  a  vitreous  humour,  and  a  choroid  coat,  have  been 
distinguished,  and  the  whole  organ  has  been  compared  to 
the  vertebrate  eye.  But  the  *  lens '  appears  to  be  always  a 
mei*e  thickening  of  the  cuticle  which  constitutes  the  cornea, 
and  the  so-called  *  vitreous  humour '  is  partially  or  wholly 
made  up  of  crystalline  cones  analogous  to  those  which  are 
found  in  the  compound  eye.  In  this  respect  the  ocellus 
of  the  insect  resembles  the  simple  eye  in  Arachnida  and 
Crustacea.* 

Many  insects,  as  the  Glow-worm  and  Lantern-flies,  are 
remarkable  for  their  power  of  emitting  light. 

According  to  Schulze  f  the  males  of  Lampyris  splendidula 
possess  two  photogenic  organs,  which  lie  on  the  sternal 
aspects  of  the  penultimate  and  antepenultimate  abdominal 


♦  Leydig,  *  Das  Auge  der 
Gliedcrthiere,'  U64.  Landois, 
*«  Die  Raupcnaugo  "  (« Zeitsdirift 
fur  Wiss.  Zoologie,'  18t6),  and 
''Zur  Entwickelungsgeschichte 
der  faeetdrten  Augen  von  Tene- 
bris  moiitor"  (Ibid.,  1^67). 


t  **  Zor  Kenntniss  der  Leucht- 
organe  von  Lampyris  splendi- 
duiar  r*Archiv  fur  Mikr. 
Anatomie,  1855.)  See  also  Kdl- 
liker,  *  Wurzburg  Phys.  Med.  Ge- 
sellschaft,'  1857. 


THB  PHOTOOBNIO  OSOAKS  OF  Iir8BCT8.  441 

Bomitee.  Each  is  a  thin,  whiidah  plate,  one  face  of  which 
is  in  contact  with  the  transparent  chitinons  cnticnla,  while 
the  other  is  in  relation  with  the  ahdominal  nerre-cord  and 
the  viscera.  The  sternal  gives  ont  mnch  more  light  than 
the  tergal  face.  The  photogenic  plate  is  distinguishable 
into  two  layers,  one  occupying  its  sternal  and  the  other  its 
tergal  half.  The  former  is  yellowish  and  transparent,  the 
latter  white  and  opaque,  in  consequence  of  the  multitude  of 
strongly  refracting  granules  which  it  contains.  TiachesB 
and  nerves  enter  the  tergal  layer,,  and  for  the  most  part  tra- 
verse it  to  terminate  in  the  sternal  layer,  which  alone  is 
luminous.  Each  layer  is  composed  of  polygonal  nucleated 
cells.  The  granules  are  doubly  refractive,  contain  uric  acid, 
and  probably  consist  of  urate  of  ammonia  (Kolliker).  Hence 
the  cells  of  the  layer  which  contain  them  are  termed  by 
Schulze  the  "urate  cells,"  while  he  calls  the  others  the 
"  parenchyma  cells."  The  branches  of  the  tracheee  which 
ramify  among  the  parenchyma  cells  end,  like  those  of  other 
parts  of  the  body,  in  stellate  nucleated  corpuscles,  one  pro- 
cess of  the  corpuscle  passing  into  a  ramification  of  the 
trachea.  Schulze  is  inclined  to  think  that  the  other  pro- 
cesses end  in  parenchyma  cells. 

The  nerves  of  the  photogenic  plates  are  derived  from 
the  last  abdominal  ganglion ;  they  branch  out  between  the 
parenchyma  cells  into  finer  and  finer  branches,  which  even- 
tually escape  observation. 

The  female  reproductive  (M*gan8  of  insects  consist  of  the 
ovarian  tubes,  or  ovarioles^  with  their  so-called  peritoneal 
investments,  and  of  the  oviducts,  which  unite  into  a  vagina ; 
while  a  spermatheca,  and,  g^ierally,  accessory  glands  open 
into,  or  close  to,  the  vagina. 

The  ovarioles  may  be  few  or  very  numerous.  Each 
consists  of  an  external  structureless  membrana  propria, 
within  which  lies  a  solid  columnar  mass  composed  of  cells. 
The  anterior,  usually  tapering,  end  of  this  ovarian  mass  is 
composed  of  protoplasmic  substance  in  which  nuclei  are 
imbedded,  but  in  which  the  contours  of  the  cells  which  they 
indicate  are  not  distinguishable.    Further  back,  some  of 


442       THE  AKATOMY  OF  INYEBTEBBATSD  AKOCAUS. 

these  nuclei  enlarge,  become  surrounded  by  an  acciunu- 
lation  of  protoplasm,  and  constitute  the  primitive  OTa. 
Each  primitive  ovum  is  separated  from  its  fellow  by  a 
layer  of  nucleated  protoplasm  which  thus  forms  a  capsule 
around  it.  In  some  insects,  such  as  Blaikiy,  the  capsule 
is  hardly  distinguishable  in  those  ova  which  lie  between  the 
smallest  and  those  of  middling  size,  which  follow  the  former 
in  order  from  before  backwards.  But,  in  the  larger  ova  which 
succeed  these,  the  cells  of  the  ovicapsule  rapidly  enlarge 
in  a  direction  perpendicular  to  the  surface  of  the  ovum, 
and  constitute  a  very  well-marked  epithelial  layer.  I  am 
inclined  to  believe  that,  for  some  time,  an  addition  is  made 
to  the  vitellus  of  the  egg  by  these  epithelial  cells,  and  that 
they,  in  fact,  play  the  part  of  vitelligenous  cells.  But  however 
this  may  be,  before  long,  a  delicate  structureless  lamella 
appears  on  the  surface  of  the  vitellus  and  encloses  the  egg 
as  a  vitelline  membrane.  The  epithelial  cells  of  the  ovi- 
capsule next  secrete  from  their  surface  a  thicker,  often 
ornamented,  layer  of  chitinous  substance,  which  constitutes 
the  chorion,  and  the  egg  is  complete. 

The  ovarian  mass,  therefore,  as  Waldeyer  has  justly 
pointed  out,  corresponds  with  one  of  the  epithelial  tub^ 
of  the  ovary  of  a  vertebrated  animal,  and  the  ovicapsules 
answer  to  Graafian  follicles. 

In  some  insects,  as  Aphis,  the  indifferent  tissue  of  the 
anterior  end  of  the  ovarioles  gives  rise  not  only  to  ova 
and  ovicapsular  epithelium,  but  to  large  mtelligenous  cells. 
These  stay  in  the  dilated  anterior  chamber  of  the  ovarian 
tube.  But  each  ovum  is  originally  connected  by  continuity 
of  substance  with  one  of  these  cells,  and  the  pedicle  of 
connection  may  be  traced  even  to  the  second  and  third 
ovum.  It  seems  probable,  therefore,  that  these  "  vitelligenous 
cells,"  for  some  time,  supply  material  to  the  growing  ova. 

In  most  insects,  similar  vitelligenous  cells  are  found ;  but 
they  are  situated  at  the  anterior  end  of  each  ovicapsule,  so 
tfaat^  as  the  column  of  ovicapsules  lengthens  by  the  addition 
of  new  ovicapsules  to  its  anterior  end,  the  vitelligenous  oeUs 
axe  interposed  between  every  two  ova.    The  vitelline  mem- 


THB  OYABIA  OF  IKSBOTS.  443  ' 

brane  and  tlie  chorion  first  invest  the  posterior  extremity  ' 
and  the  sides  of  the  ovmn ;  and,  for  some  time,  leave  an 
opening  at  the  end  of  the  oynm  adjacent  to  the  vitelligenons 
cells.  This  opening  is  usually  only  partially  closed,  and 
what  remains  of  it  constitutes  the  aperture  or  apertures, 
termed  the  micropyle,  through  which  the  spermatozoa 
enter  when  the  egg  is  fecundated.  The  vitelligenous  cells 
usually  remain  outside  the  ovum,  and  eventually  undergo 
degeneration ;  but,  in  many  Diptera,  they  become  enclosed 
within  the  coats  of  the  ovum  and  their  substance  is  merged 
in  that  of  the  vitellus. 

Dr.  A.  Brandt  has  proposed  the  term  panoistic  for  ovaries 
of  the  first  mode,  and  meroisHc  for  those  of  the  second 
and  third  modes  of  development  of  the  ova  here  described. 
So  far  as  is  at  present  known,  only  the  Orthoptera  and  the 
Puliddce  possess  panoistic  ovaria. 

The  peritoneal  coat  of  the  ovarioles  is  a  cellular  structure, 
containing  many  trachese  and,  frequently,  muscular  fibres. 
It  is  usually  extended  beyond  the  anterior  end  of  each 
ovariole  into  a  filamentous  process,  which  after  uniting  with 
those  of  the  other  ovarioles  of  the  same  side,  is  continued 
into  the  pericardial  tissue.  At  its  opposite  extremity  it 
passes  into  the  walls  of  the  oviduct,  which  are  muscular  and 
are  lined  by  an  epithelium. 

The  development  of  the  ovaria  has  been  traced  in  Diptera 
and  Lepidoptera.  Each  ovary  is,  at  first,  a  rounded  mass  of 
indifferent  tissue,  from  which  a  filiform  prolongation  is 
given  off  backwards;  this  has  not  been  traced  into  con- 
nection with  any  other  organ,  and  appears  to  terminate  by 
a  free  end.  The  mode  of  origin  of  this  rudimentaiy,  or 
primary,  ovarium  is  unknown,  but  the  first  step  towards  the 
formation  of  the  genital  organs  is  the  separation  of  the 
peripheral  indifferent  tissue  from  the  central  portion,  and 
the  division  of  the  latter  into  as  many  elongated  solid 
cellular  bodies  as  ovarioles  are  to  be  formed.  The  peri, 
pheral  cells  become  the  peritoneal  layer.  Each  cellular 
rudiment  surrounds  itself  with  a  structureless  membrane, 
and  then  elongates  into  an  ovariole,  some  of  the  cells  filling 


444       THE  ANATOMY  OF  INYEBTBBBATBD  AKIMALS. 

the  posterior  end  of  which  then  become  differentiated 
into  the  first  primary  oTom  and  its  capsule,  with  or  with- 
out yitelligenous  cells.  The  contents  of  each  ovariole 
must  therefore  be  regarded  as  a  column  of  generatiye 
cells,  which  instead  of  burrowing  in  the  stroma  of  an  ovaiy, 
and  becoming  divided  into  ovisacs,  as  in  a  vertebrated 
animal,  grows  straight  backwards,  and,  as  it  grows,  becomes 
divided  into  ovisacs,  of  which  the  oldest  and  most  advanced 
is  the  hindermost. 

Nothing  is  certainly  known  respecting  the  origin  of  the 
vagina  or  the  oviducts,  though  it  may  be  suspected  that 
the  posterior  prolongations  of  the  primary  ovaries  give  rise 
to  the  latter. 

The  development  of  the  testes  takes  place  in  the  same 
manner  as  that  of  the  ovaries,  but  the  contents  of  the  testi- 
cular tubes  become  converted  into  spermatozoa.  The  origin 
of  the  vasa  deferentia  is  unknown.* 

In  most  insects,  the  vitellus  undergoes  partial  yelk- 
division.  In  some  Podwridoe,  however,  complete  division 
has  been  observed.  The  development  of  the  blastoderm 
takes  place  in  the  same  way  as  in  other  Arthropods,  and 
the  cephalic  end  of  the  embryo  terminates  in  two  procephalic 
lobes.  In  many  insects,  the  periphery  of  the  blastoderm, 
external  to  the  longitudinal  thickening  which  gives  rise  to 
the  sternal  region  of  the  body,  and  which  may  be  termed  the 


*  The  account  given  above  of 
the  structure  of  the  ovarian  tubes 
in  Blatta  and  AphU^  is  based  on 
my  own  observations,  which  are 
in  pretty  cloee  accordance  with 
those  of  A.  Brandt,  <'  Ueber  die 
EIrShren  der  Blatta  {Penplaneta) 
ormUalit**  («Mem.  de  TAcad.  St. 
Petersbourg,'  tome  xxi.,  1874). 
The  literature  of  the  subject  is 
•omewhat  extensive.  See  espe- 
cially Leydig,  '<Die  Eierstock 
QDd  die  Samentasche  der  Insec- 
ton  "  (<  Nova  Acta,'  xxziU.,  1867) ; 
Lobboek,  '*  The  ova  and  psendova 
oflnaeets"  (Phil.  Trans.,  1858); 
I,  **  Die  nachembryonale 


Entwickelung  der  Museiden  ** 
('Zeitschrift  fur  Wise.  Zoologie,' 
xiv.);  Bessels,  *' Entwickelung 
der  Sexualdriisen  bei  den  Lepi- 
dopteren  "  (*  Zeitschrift  fur  XViss. 
Zoologie,'  1857);  and  Von  Sie- 
bold,  *  Beitrage  xur  Partheno- 
genesis der  Arthropoden,*  1871. 
The  various  forms  uf  the  micro- 
pvle  and  the  structure  of  the 
chorion  are  dealt  with  by  Leuc- 
Icart,  in  his  elaborate  memoir, 
*'  Heber  die  Micropyle  und  den 
feineren  Bau  der  Schalenhaut  bei 
den  Inselcteneiem "  (*Muller*8 
Archiv/  1855.) 


AOAMOOENBSIS  IN  IN8B0TS.  445 

Hemdl  hand  (' Keimstreif '  of  the  Gterman  embryologists), 
gives  off  a  lamina  which  grows  inwards  over  the  sternal  face 
of  the  embryo,  and  eventaally  forms  a  complete  investment 
thereto.  The  lamina  may  be  formed  by  a  single  layer  of  cells, 
or  it  may,  from  the  first,  be  a  fold  of  the  blastoderm  and  thus 
consist  of  two  layers,  the  inner  of  which  is  continnons  with 
the  sternal  band,  and  the  outer  with  the  blastoderm  which 
invests  the  tergal  surface  of  the  vitellus.  In  the  latter 
case,  it  becomes  strictly  comparable  to  the  amnion  of  a 
vertebrated  animal;  and,  when  the  folds  have  united  in 
the  middle  line,  the  investment  in  question  is  distinguishable 
into  an  outer  membrane,  which  answers  to  the  lamina 
serosa,  and  an  inner,  which  corresponds  with  the  amnion 
proper  of  the  vertebrate  embryo.  In  some  cases,  the  vitel- 
line substance  fills  up  the  interval  between  the  la/mina 
serosa  and  the  amnion,  so  that  the  sternal  band  and 
the  latter  form  a  sac  plunged  into  the  interior  of  the 
yelk. 

The  development  of  a  more  or  less  complete  amniotic 
investment  has  been  observed  in  Orthoptera  (Libellula), 
Coleopiera,  Hemiptera,  Hymenoptera,  Lepidoptera,  and  Dip' 
tera,  but  it  does  not  appear  to  be  universal. 

Agamogenesis  is  of  frequent  occurrence  among  insects, 
and  occurs  under  two  extreme  forms ;  in  the  one,  the  parent 
is  a  perfect  female,  while  the  germs  have  all  the  morpho- 
logical characters  of  eggs,  and  to  this  the  term  parihe7U>' 
genesis  ought  to  be  restricted.*  In  the  other  the  parent 
has  incomplete  female  genitalia,  and  the  germs  have  not 
the  ordinary  characters  of  insect  eggs. 

In  Coccus  (Lecanium)  hesperidvm,  in  Chermes  ahieiis  and 
pint,  no  males  have  yet  been  observed;  but  the  perfect 
females  produce  ova,  out  of  which  only  females  proceed.  It 
is  probable  that  many  species  of  gall  insects  (Cynips)  are  in 
the  same  predicament. 

*■  The  excellent  *  Beitrage  zur      the  statements  in  the  text  respect- 
Parthenogenesis  '  (1871)  of  Yon      ing  Agamogenesb  in  Insects.  , 
Siebold  is  my  chief  authority  for 


446       THE  ANATOMY  OF  INYEBTEBBATED  ANIMALS. 

The  TmimpFegnated,  apterous,  caterpillar-like  females  of 
the  Lepidopterons  genera  Psyche  and  Solenobia,  lay  eggs 
out  of  which  only  females  issue.  The  males  occur  bnt 
rarely  and  locally,  and,  fix)m  the  impregnated  eggs,  males 
and  females  issue  in  about  equal  numbers. 

Leuckart  discovered  that  the  ovaries  of  so-called  nenters 
among  wasps,  hornets,  humble-bees,  and  ants,  often  contain 
more  or  less  well-developed  eggs,  and  that  in  the  wa^pB  and 
humble-bees,  such  eggs  are  laid  and  develope  young,  the 
sex  of  which  was  not  ascertained.  Yon  Siebold  has  ob- 
served that  the  neuters  of  Polistes  gallica  are  distinguished 
from  the  perfect  fertilisable  female,  by  little  more  than 
their  smaller  size,  and  that  they  possess  completely  deve- 
loped female  organs.  These  neuters,  or  rather,  small  females, 
laid  eggs  which  developed,  and  gave  rise  only  to  male 
Polistes.  The  unimpregnated  females  of  a  Saw-fly,  Nematus 
ventricosus  (the  larvsB  of  which  are  known  as  gooseberry 
caterpillars)  regularly  lay  eggs,  which  develope  and  produce 
male  offspring. 

The  terms  arrenotohous  and  thelytokous,  have  been  pro- 
posed by  Leuckart  and  Yon  Siebold  to  denote  those  par- 
thenogenetic  females  which  produce  male  and  female  young 
respectively. 

In  the  case  of  the  Hive-bee,  it  has  been  ascertained  that 
the  queen  either  impi'egnates,  or  does  not  impregnate,  the 
eggs  when  they  are  laid.  The  spermatheca,  in  which  the 
spermatic  fluid,  introduced  by  the  single  act  of  copulation 
which  takes  place,  is  contained,  contracts  as  the  eggs  pass 
along  the  vagina,  in  the  former  case,  and  remains  passive 
in  the  latter.  The  unimpregnated  eggs  give  rise  to  mal^ 
or  drones ;  the  impregnated  eggs  to  females,  which  become 
neutera  with  imperfect  reproductive  organs,  or  queens, 
with  perfect  organs,  according  to  the  nutriment  which  they 
receive. 

In  the  Aphides,  ova  deposited  by  the  impregnated  females 
in  the  autumn  are  hatched  in  the  spring,  and  give  rise  to 
forms  which  are  veiy  generally  wingless,  and  bring  forth 
living  young.    These  may  be  either  winged  or  wingless,  and 


AaAMOGENBSIS  IV  APHIDB8. 


447 


are  also  yiviparous.  The  number  of  Bnccessive  yiyiparous 
broods  thus  produced,  has  no  certain  limit,  but,  so  far  as 
our  present  knowledge  goes,  is  controlled  only  by  tempera- 
ture, and  by  the  supply  of  food.  Aphides  kept  in  a  warm 
room  and  well  supplied  with  nourishment,  have  continued 
to  propagate  viviparously  for  four  years. 

On  the  setting  in  of  cold  weather,  or,  apparently,  on  the 
failure  of  nourishment  alone,  in  some  cases,  males  and 
females  are  produced  by  the  yiyiparous  forms.  The  males 
may  possess  wings,  or  may  be  deyoid  of  them.  The  females 
appear  inyariably  to  be  apterous.  Copulation  takes  place 
and  the  eggs  are  laid. 

Sometimes  yiviparous  forms  co-exist  with  the  male  or 
female  forms,  and  some  viviparous  Aphides  are  known  to 
hybemate.* 

The  viviparous  forms  differ  essentially  from  the  ovi- 
parous forms  in  the  structure  of  their  reproductive  organs. 
They  possess  neither  spermathecse  nor  colleterial  glands, 
both  of  which,  as  Von  Siebold  first  demonstrated,  are 
present  in  the  females.  The  young  are  developed  within 
organs  which  resemble  the  ovarioles  of  the  true  females  in 
their  disposition  and  may  be  termed  psetidovaries.  The 
terminal  or  anterior  chamber  of  each  pseudovarian  tube  is 
lined  by  an  epithelium,  which  encloses  a  number  of  nu- 
cleated cells.  One  of  the  hindermost  of  these  cells  enlarges 
and  becomes  detached  from  the  rest  as  a  psevdovwm.  It 
then  divides  and  gives  rise  to  a  cellular  mass,  distinguish- 
able into  a  peripheral  layer  of  clear  cells  and  a  central  more 
granular  substance,  which  becomes  surrounded  by  a  struc- 
tureless cuticula.  It  is  this  cellular  mass  which  gradually 
becomes  fashioned  into  the  body  of  a  larval  Aphis.  A 
portion  of  the  cells  of  which  it  is  composed  becomes  con- 


♦  Huxley,  "On  the  Agamic 
Reproduction  and  Morphology  of 
Apnis.'*  P  Linnean  Transac- 
tionfl,'  1857.) 

The  papers  of  M.  Balhiani 
(*Ann.  des  Sciences  Naturelles' 
1869,  1870,  and  1872)  should  be 


consulted,  not  only  on  account  of 
their  richness  in  details,  but  for 
the  peculiar  views  tvhich  the 
author  entertains  respecting  the 
nature  of  the  reproductive  pro- 
cess in  the  Aphiaes, 


448       THE  AKATOMY  OF  INYBBTBBBATBD  AKIMAL8. 


verted  into  a  psendoyarimn,  and  the  development  of  new 
psendova  commences  before  the  young  leaves  the  body  of  its 
parent.  It  is  obvious  that  this  operation  is  comparable  to 
a  kind  of  budding.  If  the  pseudovum  remained  adherent 
to  the  parental  body,  the  analogy  would  be  complete.* 

The  agamogenetic  multiplication  of  CecidamyiaABrvm  is 
an  essentially  similar  process.  Professor  Nicolas  Wagner, 
of  Kasan,  f  discovered  that  the  larv»  of  a  Dipterous  insect 
belonging  to  the  genus  Cecidomyia,  or  to  a  closely-allied  f  orm, 
(Miagtor)  multiply  agamogenetically  in  the  autumn,  winter, 
and  spring.  In  summer,  the  final  terms  of  the  successive 
broods  of  grubs  thus  produced  are  metamorphosed  into 
males  and  females,  which  copulate  and  lay  eggs.  From 
these,  larvae  which  exhibit  the  same  phenomena,  emerge. 
In  this  case,  the  young  are  all  developed  from  germs  which 
are  found  lying  loose  in  the  perivisceral  cavity  of  the 
parent,  the  body  of  which  they  destroy  and  burst  in  order 
to  become  free.  Leuckart,  Metschnikoff,  and  Gkuiin,^  have 
sho^ini  that  these  germs  are  detached  from  the  pseud- 
ovarium,  which  occupies  the  place  of  the  rudimentary 
ovarium  ordinarily  found  in  larvsB ;  and  that  each  represents 
the  egg-chamber  of  an  ordinary  insect  ovariole  with  its 
epithelial  capsule,  ovum  and  vitelligenous  cells. 

In  the  ordinary  process  of  growth  of  an  insect,  from 
the  time  it  leaves  the  egg  until  it  attains  the  adult  con- 
dition, every  marked  .change  in  the  outward  form  of  the 


*  Leydig  C*  Die  Eierstock  und 
die  Samentasehe  der  Inseoten," 
*  Nova  AcU,'  1867)  affirms  that  in 
November  he  htut  met  with 
Aphidea  in  which,  in  the  same 
animal,  some  of  the  ovarian  tubes 
contain  fully  formed  ova,  and 
others  pseud  -  ova,  undergoing 
their  ordinary  method  of  develop- 
ment. Unfortunately  no  infor- 
mation is  afforded  as  to  whether 
these  aphides  possessed  a  sperma- 
theoa,  and  snowed  evidence  of 
impregnation  or  not  The  oo- 
corrence  pf  agamogenetis  along* 


side  of  sexual  propagation  is  in 
itaelf  nothing  unprecedented, 
e.ff.  Pyrosoma. 

t  K.  E.  von  Baer,  "Berichf 
('Bulletin  Acad.  St.  P^ten- 
bourg,'  1863.) 

t  Tieuckart,  **  Die  ungeschlecht- 
11  one  Vermehrung  der  Ceoidomy- 
ienlarven "  (*  G5ttinger  Nach- 
richtcn/  1865);  K.  von  Baer, 
"  Ueber  Prof.  Nic  Wagoer^s  Ent- 
deckung,'*  &c.  (*  Melanges  biolo- 
ffiques  tirtfs  du  Bulletin  de  I'Aead. 
Imp.  des  Sciences  de  St.  Peten- 
bourg/  1865). 


THB  MBTAMOBPHOSB8  OF  IN8BCT8.  449 

body,  or  of  its  appendages,  is  accompanied  bj  a  diedding 
of  the  cnticula.  In  some  cases  the  modification  effected 
at  each  ecdjsis  is  very  slight,  and  the  monltings  of  the 
cntide  are  nmnerons,  amounting  in  a  species  of  Day-fly 
{Chloeon)y  described  by  Sir  John  Lubbock,  to  as  many  as 
twenty.  In  such  a  case  as  this,  the  structure  of  the  adult 
is  gradually  substituted  for  that  of  the  lanra,  and  the 
organs  of  the  larva,  for  the  most  part,  pass  into  those  of 
the  adult. 

The  like  holds  good  of  some  insects  which  undergo 
metamorphosis,  that  is  to  say,  in  which  a  quiescent  pupal 
condition  is  interposed  between  the  active  larval  and  the 
active  imaginal  states.  Herold  and  Newport  have  de- 
scribed at  length  the  series  of  changes  by  which  the  elongated 
ganglionic  chain  of  the  Lepidopterous  caterpillar  is  con- 
verted into  the  much  more  highly  concentrated  nervous 
system  of  the  Butterfly;  and  Weismann  has  shown  by 
what  gradual  steps  the  apodal  Core^^ra-larva  acquires  the 
character  of  the  Dipterous  imago.  But,  in  the  Flesh-flies 
(Musca),  and  probably  in  many  other  members  of  the 
division  of  the  Diptera  to  which  they  belong,  the  apodal 
maggot,  when  it  leaves  the  egg^  carries  in  the  interior  of  its 
body  certain  regularly  arranged  discoidal  masses  of  in- 
different tissue,  which  are  termed  imaginal  disks.*  Of 
these,  twelve  are  situated  in  the  thoracic  region,  two  on 
each  side  of  each  thoracic  segment,  while  two  others  lie  in 
front  of  the  pro-thoracic  disks.  These  imaginal  disks 
undergo  little  or  no  change  until  the  larva  encloses  itself 
in  its  hardened  last-shed  cuticle,  and  becomes  a  pupa.  But 
they  then  rapidly  enlarge ;  each  of  the  sternal  thoracic  disks 
g^ves  rise  to  a  leg  and  to  its  half  of  the  sternal  region  of 
the  thorax,  while  the  tergal  disks  develope  into  the  tergal 
halves  of  the  corresponding  somites,  with  their  appen- 
dages, the  wings  and  the  halteres.  The  anterior  pair  of 
disks  originate  the  head  and  proboscis  of  the  fly.  As  the 
imaginal  disks  develope,  the  pre-existing  organs  contained 

*  See  the  remarkable  memoir  of  Weismann,  *  Die  naohembryonale 
Entwickelung  der  Mosciden.' 

2  a 


450       THK  AirATOKI  OT  UmBTBBBATKD  AHIIUX8. 

in  tbe  ha&d  and  thoisx  of  the  lura,  mtdergo  complete  or 
partial  reeolntioiL  On  the  other  hand,  tihe  abdomcm  erf 
the  flj  ia  produced  hj  the  contdnnooB  modifioatioit  of  tlie 
coiutitneata  of  the  larval  abdomen. 
As  in  the  Onutaeta,  bo  in  Jiuedo,  the  paisaitic  haint  is 
Fig. 111. 


Fig.  t  ll.-Tbe  lert-bBod  fi{ 
altrrimia  coacaiuiog  tiro  dcsiIt  hfti 
flgnrv,  a  newly  borti  Urrt  of  Stfb^ 

mmma.  A,  vcolrml  nuftec  of  ihc  tbonx;  B,  tha  ■bdomen; 
mandiblM ;  t,  labial  plata  and  moatti;  t,  tuItbj  1,2,3,  the  thr 
thoraeic  Mgnianta  onitsd.    (Afler  NawporU) 


rwmto  an  adult  famali  of  Stwhpt 
batcbed  em,  and  the  Hgbt-baod 
ib^  on  a  Dalr  of  Andnma  TVm- 


aooompanied  hj  extreme  modification  of  form.  In  ttiis 
respect  the  Strapa^itera,  which  are  pansitio  opon  Bmb, 
present  A  remu^aUa  hiatory.  Thef«mAle(Fig.  llljhsa  the 
fonn  of  a  hw  wiUi  ■  ihort  neck,  and  nerer  leaTes  the  bodj 
o/C&a^menoptemainKUcbaheiapanntic,    The  mala*. 


1 1 


THB  PUtASITISM  OF  INSBCT8. 


451 


on  the  contrary,  are  exceedingly  active  insects  provided 
with  a  single  pair  of  wings,  which  are  attached  to  the 
metathorax,  while  the  mesothoraz  has  a  pair  of  twisted 
appendages  in  the  place  of  wings. 

The  larvffi  of  both  males  and  females  when  they  leave 
the  egg,  are  minute  active  hexapod  insects  (Fig.  Ill),  with 
mdimentary  mandncatoiy  organs,  and  are  found  creeping 
about  between  and  on  the  hairs  with  which  the  abdomen  of 
their  host  is  provided.  In  this  condition  they  are  carried 
into  the  nests  of  the  bees,  and  they  attack  the  larvsB  of  the 
latter,  boring  their  way  through  the  integument  into  the  ab- 
dominal cavity  of  the  grub.  Here  they  cast  their  cuticle  and 
become  changed  into  sluggish  apodal  grubs,  provided  with 
a  mouth,  with  rudimentary  jaws,  and  with  an  alimentary 
sac,  but  devoid  of  an  anus.  About  the  time  that  the  Hymen- 
opterous  larva  x>asses  into  its  imago  state,  the  Strepeipteral 
larva  thrusts  the  anterior  end  of  its  body  (the  so-called 
cephalo-thorax)  between  two  of  the  abdominal  segments  of 
the  bee,  so  that  it  projects  externally.  The  male  becomes  a 
pupa,  and  eventually  makes  its  way  out  as  a  winged  insect 
The  female  on  the  other  hand  undergoes  little  change  of 
outward  form,  but  presents  an  opening,  which  plays  the  part 
of  a  vulva,  and  enables  the  male  to  effect  the  fecundation 
of  the  eggs.  These  are  developed  within  the  body  of  the 
female,  and  make  their  way  out  by  the  cleft  in  question.* 

The  Ichneumon-flies  deposit  their  eggs  within  the  bodies 
of  the  larvffi  of  other  insects,  and  the  grubs  thence  hatched 
devour  the  corpus  adiposum  of  their  host.  The  larvsB  of 
some  of  these  parasites  {PlaiygcuteTf  Teleas),  described  by 
Qanin  f  are  extraordinarily  unlike  other  insect  larvsB,  and 
have  a  certain  resemblance  to  Copepoda. 


*  See  Yon  Siebold.  <*Ueber 
Strepsipteren"  (*  Arehiv  fur  M»- 
torgetohiehte,'  1843),  and  New- 
port,  **  Katural  History  kc.  of  the 


Oil-beetle,  MelSe  '*  (Linn.  Trans. 
1847). 
t  *  Zeitsohr.  for  Zoologie,'  1869. 


^  ^^ 


452       THB  AKATOMT  OF  nfYXBTXBSATXD  AHIMALS. 


CHAPTER  Vm. 

THE   POLYZOA,  THE  BSACHIOPODA,  AND  THE  MOLLUSCA. 

HowsvEB  diverse  in  outward  appearance  and  in  complexity 
of  organisation  the  multitudinous  forms  of  a-nimftli^  which 
have  been  described  in  the  preceding  four  chapters  (Chap. 
lY.  to  YII.)  may  be,  the  student  passes  from  one  to  the 
other,  by  easy  and  natural  gradations,  from  the  simple 
Turbellarian  at  the  bottom,  to  the  most  highly  differen- 
tiated Arthropod  at  the  summit  of  the  series.  But  with 
the  higher  Crustacea,  Arachnida  and  Inaecta  the  scale  ends ; 
from  none  of  these  are  we  led  to  any  higher  form  of  f^niinal 
life. 

The  Cuttle-fish,  the  Whelk,  the  Snail,  and  the  other 
innumerable  forms  of  animals  with  univalye,  bivalye, 
and  multivalve  shells,  which  are  commonly  known  as 
MoUusca,  are  so  widely  different,  not  only  from  the  AtihrO' 
poda,  but  from  all  the  higher  members  of  the  group  of 
Worms  (Chap.  Y.)  that  any  connection  with  these  seems,  at 
first,  to  be  wanting.  The  segmentation  of  the  body,  which 
is  so  conspicuous  a  feature  of  the  greater  number  of  the 
members  of  the  series  which  ends  with  the  Arthropods,  is 
absent ;  limbs  are  wanting ;  instead  of  the  equality  of  the 
neural  and  haemal  faces  of  the  bilaterally  symmetrical  body, 
and  the  consequent  remoteness  of  the  oral  and  anal  aper- 
tures, which  is  usual  among  the  Arthropods  and  Worms, 
these  two  faces  are  usually  unequal.  The  haemal  face  is 
often  produced  into  a  longer  or  shorter  cone ;  the  anus  is, 
as  a  rule,  approximated  to  the  mouth ;  and,  very  often,  the 
hffimal  face  of  the  body  is  asymmetrical. 

The  higher  MoUuBkB,  in  Iaa^  ioxm.  the  final  term  of  a 


Aj^ 


THB  POLTZOA. 


453 


series  of  their  own,  which  commences  in  the  Polyzoa,  with 
animals  which  have  many  resemblances  to  the  Boti/era, 

The  PoLYzoA  or  Bbyoz.oa. — In  outward  form  these 
animals  bear  a  general  likeness  to  the  Sertnlarian  Hydrosoa, 
with  which  they  were  formerly  confounded  under  the  name 
of  "  Oorallinee."  Like  the  Sertularians,  they  almost  always 
form  compound  aggregations,  produced  by  repeated  acts 
of  gemmation  from  the  primitively  single  embryo,  and  have 
a  hard  cuticular  exoskeleton,  which  remains  when  the  soft 
parts  decay.     The   compound  organism  thus  formed  is 

¥i^,  112. 


Fig.  112.— A  portion  of  the  polyzoariom  of  FlunuOeUa  npent  (after 
Albnan).* 

termed  a  Polyzoarivm  (Fig.  112),  and  each  zooid  which  buds 
from  the  common  stock  is  a  Polypide,  The  outer,  chitinous 
or  calcified,  cuticular  exoskeleton,  is  termed  the  edocyst, 
and,  as  the  rest  of  the  body  of  the  polypide  is  contained  in, 
or  can  be  retracted  into,  the  hard  case  thus  formed,  it  is 
commonly  termed  a  "  cell." 

The  proper  ectoderm,  with  the  parietal  layer  of  the 
mesoderm  which  lines  and  secretes  this  cell,  is  termed  the 
endoeyst.     The  mouth  is  situated  on  a  disk,  termed  the 

"»  *  Monograph  of  the  Freth-waiec  PoVfiovs  ^^^^* 


lophopkore,  at  the  tree  end  of  the  poljpide;  anfl  the 
margina  of  the  lophopkon  are  produced  into  a  nomber 
of  ricblj  ciliated  tentaevJa.  At  the  oisl  aperture,  the 
ectodemi  paasea  into  the  endodermal  liniiig  of  the  a]i- 

Flg.  113. 


tli«didioi ,   , 

tioe;   i,  inuii  n,  miuelnj    v, 
ftmlcalui.     (After  AIIomd.) 


ft  borne  b; 
Itomaeh ;  K,  iotm- 
;   z,itatoblMU;  *, 


mentary  canal,  which  is  aJmoet  alwajB  divided  into  three 
jwrtionB,  a  long  and  wide  pharjm,  a  Bpacioos  stomach,  and 
a  iuun>w  inteotiite.    Tb«  \bM«t  ia  a^-n.-^^  N^bnli.  ti.^  aearlf 


THB  POLTZOA.  455 

parallel  with  the  pharynx,  and  terminatee  in  an  anus 
situated  beside  the  mouth.  As  the  nervous  ganglion  is 
placed  between  the  mouth  and  the  anus,  the  flexure  of  the 
intestine  is  newral,*  and  the  hsemal  face  of  the  body  is 
developed  greatly  in  excess  of  the  neural  face.  A  wide 
perivisceral  cavity  occupies  the  interval  between  the  ali- 
mentary canal  and  the  parietes  of  the  body,  and  sometimes 
the  walls  of  this  cavity  are  ciliated.  Very  generally,  the 
gastric  division  of  the  aHmentaiy  canal  is  connected  with 
the  parietes  of  the  body  by  a  sort  of  ligament,  theyunicu/tM, 
or  gckstrO'parietal  hand.  Circular  and  longitudinal  muscular 
fibres,  which  frequently  exhibit  distinct  transverse  stria- 
tions,  may  be  developed  in  the  body- wall;  and  there  are 
usually  special  muscles  for  the  retraction  of  the  lophophore 
within  the  cell,  and  others  for  the  closing  and  opening  of 
the  opercular  apparatus,  with  which  many  species  are 
provided. 

The  single  nervous  ganglion  is  situated,  as  has  been 
stated,  between  the  oral  and  the  anal  apertures.  In 
Serialaria,  Scrupocellaria  and  some  other  genera,  nervous 
cords  and  plexuses  connecting  the  ganglia  of  the  several 
polypides  and  constituting  what  F.  Miillerf  terms  a 
"  colonial  nervous  system,"  have  been  described.  But  it  is 
not  yet  certain  that  these  cords  and  plexuses  are  really 
nerves.  It  is  doubtful  if  there  are  any  special  organs  of 
sense,  unless  a  lobed  process — the  epistoma, — ^which  over- 
hangs the  mouth  in  many  fresh-water  Polyzoa,  be  of  this 
nature.  The  ectoderm  of  that  region  of  the  body  which  lies 
immediately  beneath  the  tentacula  is  always  soft  and  flexi- 
ble ;  and  when  the  lophophore  is  retracted,  becomes  invagi- 
nated,  so  as  to  form  a  sheath,  by  which  the  tentacles  are 
protected.  Sometimes,  as  in  the  Ctenostomata^X  ^^^  sheath 

*  In  dealing  with  the  morpho-  tres,  or  the  pedal  ganglia  (when 

logical  relations  of  the  parts  of  such  are  separately  distinguish- 

MoUusks,  it  is  very  necessary  to  able)  are  placed,  neural^  and  the 

employ  a  terminology  which  shall  opposite  hetmaL 
be  independent  of  the  ordinary  j  *Archiv      fur     Anatomic,' 

position  of  the  animals.     I  there-  1 860. 

fore  term  that  face  of  the  body  \  Pane,  ^*  0\>ii«r««.>aoTA  «vw  ^^ 

.  on  which  the  chief  nervous  cen-  nunute  «\"nic\»i^  ol  wasi&A  ^"^  ^^^ 


458      THK  AXATOmr  or  HmSTXBBATSD  AJnilAlB. 

in  aornxukded  b^  a  circle  of  chitinoim  filaments,  wliicl),  wboB 
the  teotacl«B  are  retracted.  fnmiBh  a  protectiTe  outer  oover- 
iug  to  them.  And,  aometimes,  aa  in  the  Cheilotlomala,*  part 
of  the  ectocjst  of  the  poljpe  cell  ia  diapoeed  in  anch  a 
mannar  as  to  coiiBtitut«  a  moTeable  lid,  which  shntB  domi 
on  dke  retiacted  poljpide.  This  opereuittin  is  placed  on  the 
opposite  side  of  the  poljpide  to  that  on  which  the  nerrona 
ganglion  ia  aitooted- 
In  manj  K<enef»,  the  cells  are  prorided  with  flagellifonn 
Fig.  lu. 


appenda{(es— the  vibraci^a  (Fig.  114).     These  are  nsnallj 
srticalated  with  short  dilated  processes  of  the  ectocjet,  and 


UKherfomuofFolTpi"  ("Pbll.  See  for  thil  gnap  Nitacfae'*  m- 
Ttsiw.' 1837).  Beicbert,  "  Veber  cent  ImporUnt  "Beitrigc  tat 
Zoobiibyo*  pdhcidM"  ('Abh.  d.  Kennmias  der  Bryoioei) "  (' Zdt- 
Kflnlgl.  Akul.  dar  WiaMMchafl-  >cbrlfl  fCr  Win.  Zoologie,  1869- 
«B,'B«lin,18«.).  711. 

Biuk,    'C*f*logiie    of    the 

JHaitot  FolTiM  in  the  Brittih 

Mwmam:  Chtlastanua,'  IKA-M, 


JITICUI.4XU  AKD  TIBEIOUI.^  457 

eseente  coxuitaut  laahing  muvementa.  In  oihen,  bodies 
shaped  like  birds'  beads,  witb  a  movable  mandiUe,-  and 
either  Mated  upon  slender  and  flexible  pednncles  or  sessile, 
snap  incessantl;.  Sometimes  these  last,  which  are  termed 
aoiadaTia  (Fig.  115),  are  present  along  with  vibnicula. 
Fig.  lis. 


Fig.  Ji^i.—Buj/tik 


idt,  BhDK 

iUcell(ji);  tbe  intestine  (i)  and  tiie  itonuh  udgnllct  (/>;  f,  n- 
(rictar  mutcles  ;  if.  cf,  svicul»rla.  One  of  thrae  U  boldlng  >  iunijt« 
wonn  whicb  it  his  aeiied.     In  front  ot  tlii>  ie  tetn  an  orioall. 

iculuiom  (rf),  viewed  Tram  the 


poljpide  » 

The  dilated  bases  of  the  vibracnla  contain  mnscles  bj 
the  contraction  of  which  the  flagelliform  appendage  is 
moved.  In  the  avictdaria,  a  huge  addnctoi  mnndft,'«\a.<^ 
takes  its  origin  troia  the  greater  p^rt  ol  ^!ki«  Vimet  bo:A.«rk> 


458       THE  AHATOMT  OF  IN7EBTBBBATSD  ANIMALS. 

of  the  "head,"  is  attached  bj  a  slender  tendon  to  the 
"mandible"  on  the  one  side  of  the  binge  line,  while  a 
smaller  diyaricator  mnscle  is  fixed  to  the  other  side.  The 
mechanism  of  adduction  and  divarication  of  the  mandible 
is  quite  similar  to  that  bj  which  the  dorsal  Talve  of  the 
shell  of  an  articulated  Brachiopod  is  moved  upon  the 
ventral  valve. 

Male  and  female  reproductive  organs  are  usuallj  com- 
bined in  the  same  poljpide.  Thej  are  cellular  masses, 
developed  in  the  funiculus,  or  in  the  parietes  of  the  body, 
whence  the  ova  or  spermatozoa  are  detached  into  the 
perivisceral  cavity.  They  sometimes  pass  thence,  and 
undergo  the  first  stages  of  their  development  in  dilatations 
of  the  wall  of  the  body,  termed  otnceUs. 

Multiplication  bj  gemmation  occurs  throughout  the 
group,  but  the  buds  usuallj  remain  adherent  to  the  stock. 
In  Loxosoma  and  Pedicellina,  however,  the  buds  become 
detached. 

Some  Polyzoa  multiply  agamogenetically  by  a  kind  of 
gemmule  developed  in  the  funiculvs,  provided  with  a  peculiar 
shell,  and  termed  a  statohlaat. 

With  these  general  characters,  the  Polyzoa  present  an 
interesting  series  of  modifications.  They  have  been  divided 
by  Nitsche  into  two  groups — the  Entoprocia,  in  which  the 
anus  lies  within  the  circle  of  tentacles ;  and  the  Eetoproeta, 
in  which  it  lies  outside  this  circle.  In  the  former  division,  the 
genus  Loxosoma*  which  attaches  itself  to  Sertularians  and 
to  other  Polyzoa,  is  particularly  noteworthy.  It  is  a  small 
stalked  animal,  and  the  superior  wider  end  of  the  body  is 
an  obliquely  truncated  disk,  the  margins  of  which  are  elon- 
gated into  ten  ciliated  processes.  The  mouth  is  a  trans- 
versely elongated,  slit-like  aperture  on  the  lower  side  of 
the  tentacular  circlet.  A  long  oesophagus  connects  this 
with  a  globular  caecal  gastric  sac.    From  the  midst  of  the 

•  Kowalewsky,   '<  Beitra^e  zur  St.  Petenboarg,'    1866).    Oscar 

Anatomie   und     F.ntwickclungs-  Schmidt.    ^^  Die   Gattang  Loxo- 

geteMehte  det  Lozosoma  neapoU-  anma  *'  r  Archiv  fur  Mikr.  Anat.* 

*'  CM6n.  de  TAcad.  de  1075). 


■>  i. 


THS  POLTZOA.  459 

disk,  a  oonical  prominence,  the  summit  of  which  bears  the 
anus,  is  situated.  The  sexes  are  united,  the  OTaries  and 
testes  being  situated  on  each  side  of  the  stomach,  and  the 
spermatozoa  pass  directly  into  the  ovaries.  No  nervous 
system  has  jet  been  made  out  in  Laxosoma,  The  animal  is 
fixed  bj  the  truncated  extremity  of  its  narrow  stalk-like 
end;  and  this  stalk  contains  a  gland,  the  duct  of  which 
ox>ens  in  the  centre  of  the  face  of  attachment. 

Loxasoma  appears  to  multiply  by  budding,  but  the  appa- 
rent buds  are  really  one  of  two  kinds  of  embryos  developed 
from  the  impregnated  ova.  The  other  kind  of  embryo  be- 
comes a  gastrula,  with  a  large  post-oral  ciliated  disk,  like 
a  mesotrochal  annelid  larva,  and  its  ultimate  fate  has  not 
yet  been  traced. 

The  Ectoprocta  are  divided  into  the  OymnoloBmaia,  which 
have  a  circular  lophophore,  and  no  epistoma ;  and  the  Phy^ 
ladolcBmata,*  which  possess  an  epistoma,  and  usually  have 
the  lophophore  prolonged  into  two  lobes,  so  as  to  be  horse- 
shoe-shaped ;  whence  the  term  hippocrepian  applied  to  such 
Polyzoa, 

Among  the  OymnolasnuUa  are  distinguished;  the  Cydo- 
giomaia,  in  which  the  opening  of  the  cell  is  round  and  has 
no  opercular  structures ;  the  Ctenastomaia  {auprd),  and  the 
CheilogtonuUa  {sfuprd). 

All  the  Phylactolcemata  are  inhabitants  of  fresh  water; 
while  all  the  OyrivnolcBmataf  except  PahuUcella,  are  marine. 

The  polyzoarium  of  Cristatella  is  free  and  creeps  about  as 
a  whole ;  and  that  of  LtmulUes  is  free,  at  any  rate  in  the 
adult  condition. 

In  the  fresh-water  Polyzoa,  the  impregnated  ovum  gives 
rise  to  a  saccular  planuliform  embryo,  which  is  covered 
externally  with  cilia.  From  one  end  of  this  cyatid,  one  or 
more  polypides  are  developed  from  thickenings  of  the  wall 
of  the  sac. 

•See     Dumortier    and     Van  Bruxelles,' 1850);  the  monograph 

Beneden,  **  Histoire  Naturelle  d.  of   Allman    cited    above ;    and 

Polypes  composeefl  d'eau  douce  *'  Nitsche's  "  Beitrage." 
('Bfem.   de   TAcad.    Royale  de 


460       THE  ANATOMY  OF  nTYEBTEBRATBD  AKIMAIiS. 

In  the  Gymnolsematous  genera  Bugvla,  ScrupoeeUaria, 
and  BiceUaria,  the  embryo  is  ciliated,  and  provided  with  a 
mouth  and  with  eje-spots.  After  swimming  about  for 
some  time,  it  loses  its  cilia,  fixes  itself,  acquires  a  chitinoiis 
outer  coat,  and  becomes  a  mere  sac  or  cystid,  in  which  a 
poljpide  is  developed  bj  gemmation,  and  gives  rise  to  the 
first  cell  of  the  poljzoarium. 

Schneider  *  has  shown  that  the  anomalous  Chfphonautes, 
which  he  considers  to  resemble  Aetinotrocha,  and  which  is 
enclosed  in  a  bivalve  shell,  is  the  larva  of  Metnbranipora 
pUosa,  It  is  provided  with  an  intestine,  and  with  largelj 
developed  ciliated  motor  bands.  But  when  it  attaches  it- 
self, all  these  organs  disappear,  and  the  larva  passes  into 
the  condition  of  a  cjstid,  from  which  a  poljpide  is  de- 
veloped, as  in  the  foregoing  cases. 

Hence,  it  has  been  pointed  out  that  the  characteristic 
poljpide  of  the  ectoproctous  Polytoa  is  a  structure  developed 
from  the  cjstid,  in  much  the  same  waj  as  the  Tcenia-head 
is  developed  from  its  saccular  embr jo ;  or  as  the  Cerearia 
is  developed  from  the  sporocjst  or  Bedia;  the  cjstid  of 
the  Phylactolcemata  being  comparable  to  a  sporocjst,  and 
that  of  Menibranipora  to  a  Bedia,  But,  without  altogether 
denjing  the  justice  of  this  comparison,  it  maj  be  suggested 
that  the  cjstid  is  comparable  to  a  vesicular  morula,  and 
that  the  mode  of  development  of  the  alimentarj  canal  of 
the  poljpide  corresponds  with  that  of  the  formation  of  an 
alimentary  sac  bj  invagination.  If  this  view  of  the  case 
be  correct,  the  perivisceral  cavitj  in  the  Polyzoa  is  a  bias- 
tocoBle,  more  or  less  modified  bj  the  development  of  the 
mesoderm. 

The  onlj  known  representative  of  the  genus  Bhabdo* 
plewraf  is  an  aberrant  Poljzoon  which  presents  manj  in- 
teresting peculiarities.  The  poljzoarium  consists  of  a 
creeping  stem  from  which  erect  branches,  each  of  which 


*  **Zar  Entwickelangsgeschi-  f  See  the  papers  of   Allman 


THE  BRAOHIOPODA.  461 

ends  in  a  circular  aperture  and  constitutes  the  cell  of  a 
poljpide,  arise.  The  cavity  of  the  stem  is  divided  bj 
transverse  septa,  and  its  centre  is  traversed  bj  a  hollow 
chitinoas  cord,  which  passes  through  and  is  attached  to  the 
septa. 

The  lophophore  resembles  that  of  the  hippocrepian  Phy* 
IcietolcBnuUa  in  being  produced  into  two  arms,  fringed  with  a 
double  series  of  tentacula.  These  arms  are  longer,  narrower, 
and  more  cylindrical  than  in  any  other  Polyzoa,  and,  thus 
far,  approach  the  arms  of  the  Brctchiopoda.  Furthermore  the 
tentacula  are  confined  to  the  arms,  which  are  very  flexible. 
Between  the  bases  of  the  arms  there  is  a  rounded  or  pen« 
tagonal  disk  with  raised  and  ciliated  edges,  which  occupies 
the  place  of  the  epistoma  in  the  phylactolsBmatous  Polyzoa, 
The  mouth  is  situated  beneath  the  free  margin  of  this  disk, 
on  the  opposite  side  to  the  anus,  and  to  that  towards  which 
the  arms  are  turned.  The  animal  is  attached  to  the  bottom 
of  its  cell,  or  rather  to  the  endosarc  of  the  stem,  by  means  oi 
a  long  contractile  pedicle,  by  which  its  retraction  is  effected. 
According  to  Sars,  it  protrudes  itself  by  climbing  up  the 
wall  of  its  tubular  cell  by  means  of  the  disk.  Professor 
Lankester's  comparison  of  the  polypide  of  Bhahdopleura  to 
the  embryo  Piaidium,*  appears  to  me  to  be  fully  justified. 
The  branchisB  of  Nucula,  in  form  and  position,  present  no 
little  resemblance  to  the  arms  of  Bhahdopleitra,  though 
these,  like  the  arms  of  the  Brachiopoda,  are  probably  more 
strictly  comparable  to  the  labial  palpi  of  the  I^unelli- 
branchs. 

Polyzoa  occur  in  the  fossil  state  from  the  Silurian  epoch 
to  the  present  day,  and  the  oldest  forms  are  referable  to  the 
groups  which  now  exist. 

The  Bbaghiopoda. — The  Brachiopoda  are  all  marine 
animals  provided  with  a  bivalve  shell,  and  are  usually  fixed 
by  a  x>€duncle  which  passes  between  the  two  valves  in  the 

*  '*  On  the  developmental  history  of  the  Mollusca.*'  C  PKVI.Ttvsa! 
1874.) 


462       THE  AKATOMT  OF  INTBBTBBBATBD  AHDEALS. 

centre  of  the  binge  line,  or  the  region  which  answerB  to 
it,  in .  those  Brachiopods  which  have  no  proper  hinge. 
Thej  never  multiplj  bj  gemmation,  nor  give  rise  to  oom- 
ponnd  organisms.  The  shell  is  always  inequivalye  and  equi- 
lateral; that  is  to  saj,  each  yalve  is  symmetrical  within 
itself  and  more  or  less  nnUke  the  other  yalve.  The  shell 
is  a  cnticolar  stmctore  secreted  by  the  ectoderm,  and  con- 
sists of  a  membranous  basis,  hardened  by  the  deposit  of 
calcareous  salts,  sometimes  containing  a  large  propcurtion 
of  phosphate  of  lime  {Lingula). 

In  many  Brachiopods,  varionsly  formed  calcareons  spi- 
cnla,  or  minute  plates,  are  f  onnd  in  the  walls  of  the  peri- 
visceral cavity,  and  of  the  greater  sinuses;  and  also  in 
the  arms  and  cirri,  and  sometimes  these  unite  together  so 
as  to  form  an  almost  continuous  skeleton.* 

The  body,  or  rather  that  part  of  it  which  contains  the  chief 
viscera,  is  often  small  relatively  to  the  valves  of  the  shell, 
and  the  integument  is  produced  into  two  broad  lobes,  which 
line  so  much  of  the  interior  of  the  valves  as  the  visoenJ 
mass  oes  not  occupy.  The  free  edges  of  these  lobes  are 
thickened,  and  are  beset  with  numerous  fine  chitinous  sets 
like  those  found  in  Annelids,  and  Hke  them  lodged  in  sacs. 
Between  the  two  lobes  of  the  mantle,  or  paUium,  is  the 
pallial  chamber,  bounded  behind  by  the  anterior  wall  of 
the  visceral  mass.  In  the  middle  line,  this  wall  presents 
the  oral  aperture,  which  is  seated  in  the  midst  of  a  wider  or 
narrower  area,  the  margins  of  which  are  provided  with 
numerous  ciliated  tentacula. 

In  Argiope,  the  oral  area  occupies  a  large  part  of  that 
lobe  of  the  mantle  which  is  ordinarily  termed  dorsal,  and 
its  margins  are  simply  indented  by  three  deep  "Tinatioiig 
In  Thecidium,  the  sinuations  are  deeper,  and  the  folds  of 
the  oral  area  thus  produced,  narrower.  But  in  most 
Brachiopods  the  oral  area  is  narrowed  to  a  mere  groove,  and 
18  produced  on  each  side  of  the  mouth  into  a  long  spirally- 

*Tlicte  have  been  described  by  champs,  *Becherohee  ear  For- 
Woodwaid,  Leosae-Ihithiert  mod  nnisatioD  du  BCanteeu  ches  lee 
<yedaHy   by   Eudct   Beilmi^      Bmohiopodes  artieiiMe,'  1864. 


THS  BIU.CHIOPODA.  463 

coiled  arm,  fringed  with  tentacles;  whence  the  name  of 
Bra4:hiopoda,  applied  to  the  group. 

In  this  case,  the  tentacnla  disappear  from  the  anterior 
margin  of  the  oral  disk  in  the  region  of  the  mouth,  and  are 
replaced  bj  a  lip-like  ridge.  Each  arm  contains  a  canal, 
which  ends  in  a  sac  at  the  side  of  the  mouth. 

In  Waldheimia  (Fig.  116),  the  two  arms  are  united  together 
and  their  distal  portions  coiled  into  a  horizontal  spiraL 
In  many  genera,  the  margins  of  the  oral  area  or  arms  are 
fixed  to  processes  of  the  dorsal  valve  of  the  shell.*  In  this 
case  the  arms  are  not  protrusible ;  but,  according  to  the 
observations  of  Morse,t  they  can  be  straightened  and 
extended  beyond  the  shell  in  Bhynehonella,  which  has  no 
brachial  skeleton,. 

The  alimentary  canal  consists  of  an  oesophaguB,  a  stomach, 
provided  with  hepatic  follicles,  and  an  intestine.  In  the 
majority  of  existing  genera  the  latter  is  short,  and  ends  in  a 
csecimi  in  the  middle  line  of  the  body  {e.g,  WaMkeimia) ;  in 
others  it  is  long,  and  opens  into  the  pallial  chamber  on  the 
right  side  of  the  mouth  {e.g.  Lingula,  Diseina  and  Crania), 

The  alimentary  canal  is  invested  by  an  outer  coat — the 
so-called  peritoneum, — by  which  it  is  suspended,  as  by  a 
mesentery,  in  a  spacious  "  perivisceral"  cavity.  The  walls 
of  this  cavity  are  provided  with  cilia,  the  working  of  which 
keeps  up  a  circulation  of  the  contained  fluid.  Lateral 
processes  of  this  coat — the  gcutro^parietal  and  ileo-parietal 
banda — connect  the  gastric  and  intestinal  divisions  of  the 
alimentary  canal  respectively,  with  the  parietes.]: 

From  the  perivisceral  cavity,  sinus-like,  branched  pro- 
longations extend  into  each  lobe  of  the  mantle,  and  end 
csBcally  at  its  margins.    The  lobes  of  the  mantle  are  pro- 

■*  See,  for  excellent  figures  of  Natural  History,  1873.) 

,  these  arrangements,  and  for  the  {  Huxley,  **  Contributions    to 

shells  and  external  form  of  the  the   Anatomy   of  the   Brachio- 

body    in    genenU,   Woodward's  poda'*  (Proceedings  of  the  Royal 

*  Manual  of  the  Mollusca.'  Sodetv,    1854);   and    Hancoek, 

t  **  On  the  systematic  position  '*  On  tne  organisation  of  the  Bra- 

of  the  Brachiopoda."    (Proceed-  chiopoda"  Q  PhU.  Trans.'  1858). 
ingg  of  the  Boston   Society  of 


THE  AXATOKT  OF  IVTXBTBBBATED  AXI1LLLS. 
V\g.  111. 


.  — LaMrkl  tItw  of  the  viicen  of  WaUkcimiii  a< 
BwMoek,  '  On  the  Orgaolution  of  the  Braobiopodi,' 
I9S8).— «,'doTMt'  Ujd  of  vuali«',  b,'*entral'  Itjtti  < 


I  WlT 


THS  BBA.OHIOPODA.  465 

walls  of  the  body  between  the  mantle  lobes;  d!,armB;  0,  gullet;  a, 
stomach  with  cut  biliary  ducts  of  the  left  side ;  r,  nght  hepatic 
mass ;  «,  intestine  ending  csecally  below ;  v,  so-called  *'  auricles  "  ;  o, 
the  right "  pseudo-heart,"  the  left  being  almost  wholly  removed ;  w. 
pyriform  vesicle  fixed  at  the  back  of  the  stomach ;  2,  oesophageal 

Sanglia;  t, j\ adductor ;  k,  divaricator;  l,  adjustor  muscles;  M9 pe- 
uncles. 

bably,  together  with  the  ciliated  tentacnla,  the  seat  of  the 
respiratory  function.  The  sinuses  of  the  pallial  lobes  of 
Lingula  give  rise  to  nnmerous  highly  contractile,  teat-like, 
processes,  or  ampvlloB,  During  life  the  circulating  fluid 
can  be  seen  rapidly  coursing  into  and  out  of  oach  ampulla 
in  turn  (Morse,  Ix.  p.  33). 

The  perivisceral  cavity  communicates  with  the  pallial 
chamber  by  at  fewest  two,  and  sometimes  four  {Bhynchonella) 
tubular  organs,  which  have  been  described  as  hearts,*  but 
are  now  known  to  have  no  such  nature. 

Each  of  these  organs  is  shaped  like  a  funnel,  the  wide 
portion  which  opens  into  the  perivisceral  cavity,  being 
much  plaited  and  folded,  and  separated  by  a  constriction 
from  the  narrower  part,  which  answers  to  the  pipe  of  the 
funnel.  The  latter,  passing  obliquely  through  the  anterior 
wall  of  the  visceral  chamber,  ends  by  a  small  aperture  in  the 
pallial  cavity.  Prof.  Morse  has  observed  the  passage  of  the 
eggs  through  these  organs  in  Terebratulina  septerUrionalis, 
They  are  drawn  into  the  open  end  of  the  funnel  by  the 
action  of  the  cilia  with  which  its  surface  is  covered,  and  enter 
the  pallial  cavity  by  the  aperture  just  mentioned.  It  is 
probable  that  these  "  pseudo-hearts  "  subserve  the  function 
both  of  renal  organs  and  of  genital  ducts ;  and  that  they 
are  the  homologues  of  the  organs  of  Bojanus  of  other 
moUusks,  and  of  the  segmental  organs  of  worms. 

Between  the  ectoderm  and  the  lining  membrane  of  the 
prolongations  of  the  perivisceral  cavity  in  the  mantle ;  and 
between  the  endoderm,  the  ectoderm,  and  the  lining  mem- 
brane of  the  perivisceral  cavity  itself,  there  is  an  inter- 

*  Owen,'"Lettre  sur  rappareil       nodes."    (*  Annates  des  Sciences 
de  la  circulation  chez  les  Alol-       jSaturelles,'  1845."^ 
lusques  de  la  classe  des  Brachio- 


^66       THB  ANATOMY  OF  IKYEBTSBBATBD  AKIMALS. 

space,  broken  up  into  many  anastomocdng  canals,  wbich 
I  conceive  to  represent  a  large  part  of  the  proper  blood 
system. 

Yesicolar  dilatations  of  the  walls  of  these  canals  found 
at  the  back  of  the  stomach,  and  in  some  other  localities, 
in  the  Brachiopods  with  articulate  shells,  have  been  regarded 
as  hearts,  but  observations  on  the  living  animals,  made 
by  various  investigators,  show  that  they  are  not  contractile 
and  their  function  is  unknown.  Although  the  existence  of 
a  direct  communication  between  the  perivisceral  chamber 
and  the  blood  canals  has  not  been  demonstrated,  it  is  veiy 
probable  that  the  perivisceral  chamber  really  forms  part 
of  the  blood- vascular  system. 

Muscles  for  the  adduction  and  divarication  of  the  valves 
of  the  shell,  and  for  effecting  the  other  movements  of  the 
animals,  are  well  developed  in  the  Brctchiopoda.*  They  are 
to  a  great  extent  striated. 

The  nervous  system  of  the  articulated  Brachiopods,  in 
which  it  has  been  best  made  out,  consists  of  a  relatively 
thick  ganglionic  band  on  the  ventral  side  of  the  mouth,  the 
ends  of  which  are  united  by  a  commissural  cord,  which 
surrounds  the  gullet,  and  bears  two  small  ganglionic  enlarge- 
ments. The  latter  probably  answer  to  the  cerebral,  the 
former  to  the  pedal,  ganglia  of  the  LameUibranchiaia, 
Immediately  behind  the  pedal  mass,  from  which  two  large 
nerves  to  the  dorsal  or  anterior  lobe  of  the  mantle  are  given 
off,  are  two  elongated  ganglia,  connected  by  a  commissure 
of  their  own,  which  possibly  correspond  with  the  parieto- 
splanchnic  ganglia  of  the  higher  Mollusks.  The  nerves 
to  the  ventral  lobe  of  the  mantle  and  those  to  the  pedunde 
arise  from  these  ganglia. 

In  the  inarticulated  Brachiopods,  our  knowledge  of  the 
nervous  system  is  very  imperfect.  In  Lingula,  Professor 
Owen  has  described  two  lateral  nerve  cords,  and  the  obser- 
vation has  been  confirmed  by  Gratiolet  and  Morse.    The 

*  See  Hancock  (1*  c.).  Owen,  Palseontographical  Soeie^,  end 
Introdaotion  to  Davidson's  <  Fos-  Transactions  of  the  Zoological 
tii  ArMhiopoda '  (MeiaQlit «{ \1»      ^wafity  of  London,  18S5>. 


THE  DEYBLOPMENT  OF  THB  B&AOHIOPODJL 


467 


latter  anatomiBt  finds  similar  cords  in  Diacina,  and  Gratiolet 
has  described  an  oBsopbageal  ring  in  Lingtda,* 

The  reprodnctive  organs  are  lodged  in  the  periyisoeral 
cayitj  or  its  prolongations,  and  are  apparently  always  con- 
tained in  processes  of  the  lining  membrane  of  that  cavity. 
It  is  not  clear  whether  hermaphrodism  is  the  rale  or  the 
exception.  ThecidiiMn,  however,  has  been  shown  by  Lacaze- 
Duthiers  to  be  dicecions ;  and,  according  to  Morse,  the  sexes 
are  distinct  in  Terebraiulma  and  Digcina, 

The  development  of  the  Braehiopoda,  notwithstanding 
the  important  observations  of  F.  Muller,t  Lacaze-Dnthiers,^ 
and  especially  of  Mor8e,§  stood  mnch  in  need  of  farther 
elucidation  (especially  in  regard  to  the  earlier  conditions  of 
the  embryo),  nntil  quite  recently,  when  the  investigations  of 
Kowalewsky  ||  filled  up  the  hiatus  in  our  knowledge  for  the 
genera  Argiope,  Hiecidivm,  TerebrctMa,  and  TerebroMina. 
The  egg  becomes  converted  into  a  vedcular  morula,  in 
which  an  alimentary  sac  is  developed  by  invagination,  and 
this  sac  gives  off,  as  in  Sagitta,  two  diverticula,  which 
become  shut  off  from  the  alimentary  canal,  and  are  con- 
verted into  the  perivisceral  cavity.  The  latter,  therefore, 
is  an  enterocoele.  The  embryo  elongates,  and  constrictions 
divide  it  into  three  segments,  of  which  the  anterior  becomes 
fringed  with  long  cilia,  and  developes  eye-spots.  Thus  the 
young  Brachiopod  acquires  a  great  resemblance  to  an  ordi- 
nary Annelid  larva.  The  resemblance  is  increased  by  the 
appearance  of  four  bundles  of  set»  on  the  middle  segment, 
which  becomes  produced  into  a  sort  of  hood,  the  free 
edges  of  which  are  at  first  turned  backwards  and  bear 


•  **  Recherches  Pour  servir  a 
I'histoire  des  &rachiopodeg.*' 
(*  Journal  de  Conchyliologid, 
1860.) 

t  ^  Beschreibung  einer  Bra- 
ehiopoden-larra."  (*Arcbiv  fur 
Anat.,'  I860.) 

L^'Histoire  de  la  Thecidee.*' 
in.  d'Bitt.  Nat.,'  1861.) 
^  **  On  the  early  stages  of  7>re- 
bratulma   $eptetUrioHali$ "   ('  Me- 


moirs of  the  Boston  Society  of 
Natural  History,'  1869),  and  the 
memoir  already  cited« 

t  Contained  in  a  memoir,  pub- 
ed  at  Moscow  in  1874,  for 
which  I  am  indebted  to  the 
courtesy  of  the  author.  It  is  in 
Uussian ;  but  I  have  been  able  to 
acquaint  myself  with  its  contents, 
to  some  extent,  by  the  aid  of  a 
friend. 


468       THB  ANATOBiT  OF  TNYKBTEBBATBD  AKIMAJJI. 

these  setffi.  As  the  hirva  grows,  the  third  segment  beoomee 
truncated  at  the  end,  and  furnishes  a  surface  (proTided 
with  a  shell  gland?  infra),  by  which  the  larva  attaches 
itself.  At  the  same  time,  the  first,  or  prsestomial  segment, 
atrophies,  and  the  setigerons  liood  developed  from  the 
middle  segment  is  retroverted,  rapidly  grows,  and  gives  rise 
to  the  lobes  of  the  mantle,  on  which  the  valves  of  the  shell 
are  developed. 

The  resemblance  of  the  larval  Brachiopod  to  a  Poljzoon, 
and  especially  to  Loxoaoma,  is  stiiking,  and  fully  bears  out 
the  conclusion  as  to  the  affinity  of  the  Polyzoa  vnth  the 
Brachiopoda  which  results  from  the  study  of  their  adult 
structure.  On  the  other  hand,  the  development  of  the  Bra- 
ehiopoda  no  less  strongly  testifies  to  their  close  relations 
with  the  Worms.* 

In  the  course  of  the  previous  pages  the  terms  dorsal  and 
ventral  have  been  employed  in  the  sense  in  which  they  are 
conventionally  used  by  conchologists.  But  an  interesting 
question,  and  one  not  easy  to  settle  is,  what  relation  do 
these  dorsal  and  ventral  regions  of  a  Brachiopod  bear  to 
the  neural  and  haemal  regions  of  a  Polyzoon,  or  to  those 
of  a  Lamellibranch,  or  of  a  Gasteropod  P 

If  we  compare  one  of  the  articulated  Brachiopods,  such  as 
Waldheimiat  in  its  shell,  with  a  polypide  of  a  Cheilostomatous 
Polyzoon  in  its  cell,  the  dorsal  valve  will  appear  to  answer 
to  itie  operculum,  and  the  ventral  valve  to  the  cell.  If  this 
comparison  be  just,  the  two  lobes  of  the  mantle  of  the 
Brachiopod  must  both  belong  to  the  dorsal  or  hsemal  aspect 
of  the  body;  that  which  corresponds  with  the  so-caUed 
dorsal  valve  of  the  shell  being  the  anterior,  and  that  which 
lines  the  ventral  valve  of  the  shell  being  the  posterior  lobe. 
And  the  region  of  the  anterior  wall  of  the  pallial  cavity 

*  The  acceptance  of  the  view  ton  Society  of  Natural  Historyy 

originallv  propounded  by  Steen-  1 873),  does  not  to  my  mind  weaken 

■trup  and  lo  ably  ur^ed  by  Pro-  the  opinion  I  have  always  held 

feasor  Morse,  respecting  the  afii-  as  to  tneir  affinities  with  the  Fo^- 

idtiei  of  the  Brachiopods  with  20a,  on  the  one  hand,  and  with 

tiis  Worms  (Proceedings  of  Bos-  the  higher  MoHuteojOn  ^e  other. 


THB  BSAOHIOPODA.  dOO 

which  lies  behind  or  below  Iho  mouth,  will  anawcr  to  the 
neural  aspect  of  the  Polyzoon. 

On  the  other  hand,  if  the  segments  of  the  body  of  the 
larval  Brachiopod  are  true  somites,  and  the  discoidal  sur- 
face of  the  hindermost  corresponds  with  the  similarly 
formed  end  of  the  larva  of  iMcinulatia,  as  Professor  Morse 
suggests,  the  dorsal  lobe  of  the  mant  ie  will,  as  before,  repre- 
sent part  of  the  hsemal  surface  uf  tlic  body,  but  the  ventral 
lobe  will  belong  to  its  neural  saifae<2 — and  can  no  longer 
properly  be  termed  mantle,  but  will  rather  answer  to  the 
foot  of  one  of  the  higher  Mollusca. 

The  Brachiopoda  are  distinguiHhable  into  two  groups, 
the  ArtieidcUa  and  the  Inarticulata,  In  the  Articulaia,  the 
two  valves  are  united  by  a  hinge,  and  the  ventral  valve 
is  usually  provided  with  teeth,  which  are  received  in  sockets 
of  the  dorsal  valve.  The  gullet  ascends  in  the  middle  line 
towards  the  dorsal  valve,  and  the  intestine  descends  to- 
wards the  opposite,  or  ventral,  valve,  and  there  ends  in  a 
c£8cum.  The  dorsal  valve  often  gives  rise  to  spiral  or 
looped  shelly  processes  to  which  the  arms  are  attached.  The 
valves  are  brought  together  by  a  pair  of  adductor  muscles, 
which  pass  directly  from  valve  to  valve;  and  they  are 
separated  by  divaricator  muscles,  which  run  obliquely  from 
the  ventral  valve  to  a  median  process  (the  cardinal  process) 
of  the  hinge-line  of  the  dorsal  valve.  The  impressions  of 
the  attachments  of  these  muscles  on  the  inner  surfaces  of 
the  valves  have  considerable  systematic  importance.  Very 
often  the  ventral  valve  is  produced  into  a  sort  of  spout, 
through  which  passes  the  peduncle  by  which  the  animal 
is  attached  to  rocks.  At  the  sides  of  the  visceral  chamber 
the  thickened  edge  of  the  dorsal  lobe  of  the  mantle  passes 
into  that  of  the  ventral  lobe. 

The  substance  of  the  shell  is  very  often  traversed  by 
numerous  canals  perpendicular  to  its  surface,  which  contain 
prolongations  of  the  mantle.* 

*  The  structure  of  the  shell  has  Association,'  1844-1847,  and  In- 
been  psrtioalarly  studied  by  Car-  troduction  to  Davidson's  '  Fossil 
penier.    (*  Reports  of  the  British      Brachiopoda.')     See  also  King, 


470       THB  ANATOMY  OF  IKYEBTEBSATED  AKIMALS. 

This  diyision  containB  the  families  of —(1)  The  Tere5ro- 
kdicUp,  (2)  the  SpiriferidcB,  (3)  the  BhynehoneUidoB,  (4)  the 
Orthidoe,  and  (5)  the  Productidoe,  of  which  the  second,  fourth, 
and  fifth  are  extinct  and  almost  wholly  paUdozoic,  no  species 
extending  beyond  the  lias,  while  the  majority  of  the  species 
of  the  other  two  families  are  also  extinct. 

The  family  of  the  Terebratulidce,  \diich  is  not  certainly 
known  to  occur  in  formations  older  than  the  Deyonian,  is 
the  only  one  in  which,  since  the  end  of  the  palsBOzoic  epoch, 
numerons  new  generic  types  appear.* 

The  Inarticulata  have  no  hinge ;  the  intestine  opens  into 
the  cavity  of  the  mantle,  the  margins  of  the  lobes  of  which 
are  completely  separate.  Some  have  a  long  pednnde 
{Linffula),  others  are  fixed  by  a  plug  idiich  passes  through 
an  aperture  or  notch  of  one  valve  (Discina),  or  by  the  sur- 
face of  one  valve  (Crania),  There  is  no  brachial  skeleton, 
and  the  arrangement  of  the  muscles  is  in  many  respects 
different  from  that  which  obtains  in  the  articulated  division. 

Species  of  all  these  families,  except  the  8piriferid4B, 
OrthidcBy  and  ProducHdcB,  exist  at  the  present  day,  but  they 
are  also  represented  in  the  older  palseozoic  epochs,  and 
LingulcB  are  among  the  oldest  known  fossils,  f 

The  MoLLUSCA. — The  term  MoUusca  may  be  used  as  a 
convenient  denomination  for  the  Lamellibranehiata  and 
Odontophora  (=  Gasteropoda,  Pteropoda,  and  Cephalopoda,  of 
Ouvier),  which  can  be  readily  shown  to  be  modifications  of 
one  fundamental  plan  of  structure.  This  may  be  represented 
by  a  body,  symmetrical  in  relation  to  a  median  vertical 
plane,  at  one  end  of  which  is  the  oral,  and  at  the  other  the 
anal  aperture  of  the  alimentary  canal.  In  the  body  a 
ventral,  or  neural,  face,  an  opposite  dorsal,  or  hcemdl,  face, 
and  a  right  and  left  side  may  be  distinguished.  The 
neural  face  usually  gives  rise  to  a  muscular  foot.  The  in- 
tegument of  the  haemal  face  is  generally  produced  at  its 

'  Trans.  Royal  Irish  Academy,'  f  ^^  Davidran's  *  Monographs 

1869.  of  British    Fossil   Brachiopoda,' 

*  Saess,  '*  IJeber    die   Wohn-  in    the    Palseontographical    So- 

dtMe  der  Brachiopoden  "  (*  Sitzb.  ciety's  publications. 
it  Wiener  Akad.;  \%bl). 


*  *, 


THB  XOLLUBOA.  471 

edges  into  a  free  fold,  and  the  term  mantle,  or  paUiwn, 
is  applied  to  the  region  of  the  integument  thus  circnm- 
scribed^  Between  the  free  portion  of  the  mantle  and  the 
reet  of  the  body  is  a  cayity,  the  p(iUi4d  chamber,  from  the 
waUs  of  which,  processes  which  sabeerre  respiration,  the 
branehioB,  may  be  developed. 

In  the  medkn  line  of  the  surface  of  the  mantle  of  the 
embryo,  a  sheU  gland  is  very  generally  formed,  and  from 
the  surface  ol  the  mantle  a  cuticular  secretion,  the  eheU,  is 
produced. 

A  systemic  heart  usually  exists,  and  when  present,  is 
situated  in  the  middle  of  the  posterior  haemal  region,  and 
consists  of,  at  fewest,  two  chambers,  an  auricle  and  a  ven- 
tricle. Arterial  vessels  often  ramify  extensively  through 
the  body,  but  more  or  fewer  of  the  venous  channels 
remain  in  the  condition  of  lacunss.  The  blood  corpuscles 
are  colourless  and  nucleated.  Distinct  respiratory  organs 
may  be  absent,  or  they  may  take  the  form  of  branchis  or 
pulmonary  sacs.  When  present,  they  lie  in  the  course  of  the 
blood  which  is  returning  to  the  heart.  Beside  the  heart 
and  the  intestine  are  situated  the  renal  organs,  which,  on 
the  one  side,  open  externally,  and  on  the  other,  communi- 
cate with  the  blood  system. 

The  nervous  system  consists  of,  at  least,  one  pair  of  ganglia 
(cerebral)  at  the  sides,  or  on  the  haemal  aspect  of,  the  mouth, 
and  of  two  other  pairs  of  oesophageal  ganglia  (pedoZ  and 
parieiO'Splanehnic).  The  latter  are  situated  at  the  sides, 
or  on  the  neural  aspect,  of  the  alimentary  canal,  and  are 
connected  by  commissures  with  the  former. 

In  the  majority  of  the  JtfoUiMca,  the  embryo  passes  through 
a  stage  in  which  it  is  provided  with  bands  of  dlia  or  with 
a  simple,  bifid,  or  multifid  fold  of  the  integument  {velvm), 
the  edges  of  which  are  ciliated,  developed  on  the  hsemal 
aspect  of  the  cephalic  region  of  the  body,  in  front  of  the 
pallial  region. 

The  special  peculiarities  of  the  different  groups  of  the 
MoUueca  result  chiefly — 

1.  From  the  form  of  the  pallial  regioii,  «isA^(^<b  ^tXass^  ^ 
the  mantle-lobes  relatively  to  t\iA\KA^. . 


472       THB  AKATOXY  OF  IKYBBTEBRATBD  AJflMALB. 

2.  From  the  number  and  arrangement  of  the  pieces  of  the 

shell  to  which  the  mantle  giyes  rise. 

3.  From  the  prox>ortional  size  and  the  form  of  the  foot 

and  the  production,  or  non-production,  of  chitinoiiB, 
or  shelly,  matter  by  it, 

4.  From  the  deyelopment  of  sense-organs  on  the  anterior 

end  of  the  body,  and  the  absence  or  presence  of  a 
distinguishable  head. 

5.  From  the  disproportionate  growth  of  the  hamial  re- 

gion of  the  body  into  a  visceral  aac,  followed  bj  a 
change  in  the  primitiYe  direction  of  the  intestine,  and 
often  accompanied  by  asymmetrical  lateral  distortion. 

The  Lamellibbanchiata.* — In  these  MoUusVs  there 
are  always  two  large  pallial  lobes,  the  margins  of  which  are 
deroid  of  set® ;  and  which  are  lateral,  or  right  and  left,  in 
relation  to  the  median  plane.  Each  lobe  gives  rise  to  a 
piece,  or  valve j  of  the  shell ;  and  to  these,  accessory  pieces, 
developed  upon  the  median  hsenud  face  (FhoUu)  or  the  pos- 
terior end  of  the  mantle  (Teredo) ^  are  in  some  cases  added ;  or, 
in  addition  to  its  valves,  the  mantle  may  secrete  a  shelly  tube 
(Teredo,  Aapergillum).  The  shell  itself  consists  of  super- 
imx>oBed  lamellse  of  organic  matter,  hardened  by  the  deposit 
of  calcareous  salts.  It  is  a  cuticular  excretion  from  the 
surface  of  the  mantle,  and  never  presents  any  cellular 
structure.  But  from  the  disposition  of  its  lamells,  and  from 
the  manner  in  which  the  calcareous  deposit  takes  place  in 
them,  it  may  present  varieties  of  structure  which  have  been 
distinguished  as  nacreous,  prismatic,  and  epidermic.f 

The  two  valves  are  generally  united  over  the  median  line 
of  the  hffimal  surface  of  the  body  by  an  uncalcified  chitinous 
cuticular  matter,  termed  the  ligament,  which  is  usually  veiy 
elastic,  and  is  so  disposed,  that,  when  the  valves  are  closed,  it 
18  either  stretched  or  compressed.    In  either  case,  it  an- 

*  For  a  detcriptioii    of   the      of  Animal  Life.' 
tomv  of  a  Lamellibranch  in  f  See  Carpenter,  article** Shell,' 


d$iailf  the  itodent  is  referred  to      Todd's   *  Qrclopedia.'     Huxley, 
Btudty  and  Mart&n,  *  Elemcmtsry      ^^  Te^asfAuXKri  Qft^kaa^"  ibid. 
r/  and  RoUMton,  ^  BoTma 


THE  LAMBLLIBSUrOHIATA.  473 

tagonises  the  action  of  the  adductor  muscles  and  divaricates 
the  valTes  when  these  muscles  are  relaxed.  Conchologists 
commonly  draw  a  distinction  between  an  internal  and  an 
external  ligament ;  but,  in  relation  to  the  body  of  the  animal, 
all  ligaments  are  external,  and  their  intemalitj  or  exter- 
nality is  in  respect  of  the  hinge  line,  or  the  line  along  which 
the  edges  of  the  valres  meet.  In  symmetrical,  or  eqmvalve, 
Lamellibranchs,  each  yalre  is  concave  internally  and  convex 
externally;  it  has,  in  fact,  the  form  of  a  very  depressed 
cone,  the  apex  of  which,  termed  the  vmbo,  is  incurved  and 
is  situated  on,  or  projects  beyond,  the  hsemal,  or  as  it  is 
termed,  dorsal  edge  of  the  valve.  Moreover  it  is  usually 
inclined  forwards,  and  situated  nearer  the  anterior  than  the 
posterior  end  of  the  valve.  Sometimes  the  umbonic  cone 
is  prolonged  and  bent  inwards,  or  may  even  form  a  short 
spiral  turn  {Isocardia,  Dicerae),  so  that  the  valve  acquires  a 
certain  resemblance  to  the  shell  of  some  gasteropoda.  As 
the  shell  of  a  Lamellibranch  increases  in  thickness  by 
the  deposition  of  new  layers  on  the  interior  face  of  the  old 
ones ;  and,  in  area,  by  the  extension  of  the  new  layers  beyond 
the  old  ones,  the  summit  of  the  umbo  represents  the  original 
shell  of  the  embryo,  and  the  outer  surface  is  usually  marked 
by  concentric  lines  of  growth,  which  indicate  the  boun- 
daries of  the  successively  added  new  layers  of  shell  sub- 
stance. 

The  applied  edges  of  the  two  valves  are  very  often  pro- 
duced into  elevations  and  depressions  which  interlock  with 
one  another.  The  form  and  arrangement  of  these  teeth 
and  sockets  are  of  much  use  in  systematic  conchology. 

The  muscles  which  are  attached  to  the  valves,  viz.,  the 
adductors,  retractors  of  the  foot  and  pallial  muscles,  give 
rise  to  impressions  on  the  inner  faces  of  the  valves,  which 
are  very  obvious  when  the  latter  are  removed  and  cleaned. 
With  the  growth  of  the  animal,  the  distance  of  these  im* 
pressions  from  the  hinge  line  and  from  one  another  is 
necessarily  increased,  and  it  is  not  difficult  in  some  cases 
(e.g.  Anodonta)  to  trace  a  faint  triangular  mark,  which  has 
its  base  in  each  adductor  impreadon  ttad\\A  «i?g«ss.YDL*OE^^T£a^c^. 


iJ*      THX  UIATOn  or  nmKTSBSl.TBD  AKIMAIA 

and  wliioh  indicates  Ute  saooeaeir«  ahiftinga  of  pomticm  of 
the  muscle. 

Fig.  117. 


FIr.  in.— SmHoiwI  diagiwn  of  ■  frohmter'MBMel  MiwdD-to}.— A  A, 
muilla,  the  right  lobe  of  which  la  cut  »w«t  ;  B,  foot ;  C,  bnnebi»l 
ohambarofthv  mantle  OTity;  D,  >n>l  ehombfr;  I.mnterioraddDctoT 
■  nmiols;  II,  pcMterior  adduotor  mnaele;  III,  retnelor  miuola  of 
the  fbot;  o,  mouth;  i,  atomach;  c,  inteatlDc,  the  turoi  of  which  ara 
anppDtod  to  be  teen  through  the  aide  walla  of  Ilic  mewaoma;  ^ 
netom;  i,  ansa;  /,  Tantricle;  g,  auiida;  k.  gilla,  except  i,  right 
■itarnal  Kill,  largely  cut  kway  and  tamed  back;  ll,  labial  palpi: 
^  embrS;  at,  pedal;  >,  parieto-aplanehDia  ganglia;  <\  apotan  of 
tti  UdiW7  ot  organ  oi  Bo^aiuu-,  p,Y»^"**^™^ 


\t. 


THB  LAMXLLIBSUrOHIATA.  475 

In  some  cases  {e.g,  Lima)  a  LameUibrancli  may  perform  a 
sort  of  aquatic  flight  by  the  flapping  of  the  yalyes  of  its 
shell. 

The  hard  and  sharp  edged  yalyes  of  the  shell  in  Teredo 
are  probably  the  agents  by  which  the  mollnsk  caryes  its 
passages  through  the  wood  which  it  inhabits.  Whether 
the  yalyes  of  the  shell  of  the  Pholades  and  Samiecmce  are 
the  instrnments  by  which  they  excayate  their  bnrrows  in 
hard  rock,  or  whether,  as  has  been  suggested,  the  foot,  armed 
with  sand,  is  the  boring  instrument,  is  a  question  which  has 
been  much  discussed,  but  hardly  brought  to  a  satisfactory 
decision. 

The  hsemal  face  of  the  body  is  either  flat  or  slightly 
arched,  whence,  in  side  yiew,  the  hsemal  contour  is  either 
straight  or  conyex.  In  most  Lamellibranchs,  the  body  is 
symmetrical  in  relation  to  the  median  plane,  but  in  those 
which  haye  inequiyalye  shells,  as  the  Scallop  {Pecten)  and 
the  Oyster  {Ostroea),  the  one  half  is  more  conyex  than  the 
other.  No  Lamellibranch  has  a  distinct  head ;  but  in  those 
which  possess  two  adductor  muscles  (e.g.  AnodotUa),  the 
region  in  which  the  anterior  adductor  lies  and  which  is 
situated  in  front  of  the  month,  may  be  distingniBhed  as 
the  prosoma,  from  the  middle  region  {mesosoma)  which 
giyes  rise  to  the  foot ;  while  the  part  which  lies  behind  the 
foot  and  contains  the  posterior  adductor  may  be  termed  the 
metasoma. 

The  foot  may  be  rudimentary,  but  it  is  usually  large, 
flexible,  and  employed  as  an  organ  of  locomotion.  The 
posterior  face  of  the  foot  not  uncommonly  presents  a  gland 
which  secretes  a  chitinous,  or  shelly,  substance— the  byssus. 

From  the  sides  of  the  mesosoma,  close  to  the  attachment 
of  each  mantle-lobe,  the  branchise  project  into  the  pallial 
cayity. 

In  its  simplest  form,  the  branchia  of  a  LameUibranch  con- 
sists of  a  stem  fringed  by  a  double  series  of  filaments  {e.g. 
Nucula).  The  next  degree  of  complication  arises  from 
these  filaments  becoming  as  it  were  doubled  upon  them- 
selyes  at  their  free  ends,  the  reflected  i^qx^oiaVxc^^sc^^^ 


476   THB  ANATOKY  OF  IKTEBTBB&ATKD  AKIXALS. 

outer  side  of  the  outer,  and  on  the  inner  side  of  the  inner, 
series  of  primary  filaments.  Bnt  the  free,  or  l»gmMtl^  ends 
of  the  reflected  filaments  contract  no  adhesion  either  with 
the  mantle  on  the  outer  side,  or  with  those  of  the  opposite 
gill  on  the  inner  side.  Delicate  hands  stretch  from  the 
primary  to  the  reflected  filaments  across  the  interspace  which 
they  enclose  {MytUus,  Pecten).  In  most  Lamellibranchs, 
the  gills  are  four  elongated  plates,  each  of  which  is  in  fact 
a  long  and  narrow  pouch,  with  its  open  end  turned  towards 
the  hflBmal  face  of  the  body.  Two  pouches  are  situated 
on  each  side  of  the  mesosoma;  one  of  these  pouches  is 
internal,  the  other  extemaL*  Their  walls  are  united  by 
transrerse  septa ;  they  are  richly  ciliated,  and  are  perforated 
by  numerous  apertures.  As  the  outer  wall  of  each  pouch  is 
united  with  the  mantle,  and  the  inner  with  its  fdlow  of  the 
opposite  side,  behind  the  foot,  the  whole  branchial  apparatus 
forms  a  siere-like  partition  extended  between  the  mantle  and 
the  foot  (Fig.  117),  and  thus  divides  the  pallial  cavity  into  a 
supra-branchial  and  an  infra-hranehicd  chamber.  Inasmuch 
as  the  hsemal  edge  of  the  inner  wall  of  each  inner  bran- 
chial pouch  is,  for  the  greater  part  of  its  extent,  not  united 
with  the  mesosoma,  but  only  closely  applied  against  the 
latter,  the  supra-branchial  and  infra-branchial  chambers  may 
communicate  by  the  cleft  thus  formed,  as  well  as  by  the 
apertures  in  the  lamellar  waUs  of  the  branchial  pouches.  The 
anterior  part  of  the  supra-branchial  chamber  is  divided  into 
a  right  and  left  cavity  by  the  interposition  of  the  mesosoma, 
on  the  sides  of  which  the  apertures  of  the  renal  and  genera- 
tive organs  are  situated.  The  products  of  these  organs 
therefore  readily  pass  into  these  right  and  left  cavities.  The 
posterior  part  of  the  supra-branchial  chamber,  into  which 
these  two  lateral  divisions  open,  contains  the  termination  of 
the  rectum,  and  receives  the  faeces,  as  well  as  the  urinary 
and  generative  products :  it  is  therefore  a  sort  of  cloaca. 
Its  external  opening  is  usually  termed  the  anal  opening  of 

*  The  external  gill  pouch  is      and  TeUma  only  one  gill  poach, 
4)fteD  mailer  than  the  internal.       the  internal,  is  preaent. 
Jb  Ijpidef  of  lAcmOf  Cytkerea^ 


THE  LAMELLTBRAyCHIATA,  477 

the  mantle  cavitj.  The  margins  of  this  opening  may  be 
produced  into  a  tube  which  is  termed  the  anal  siphon.  In 
front  of  the  anal,  or  rather  cloacal,  opening,  the  margins  of 
the  mantle  may  be  completely  disunited.  Yery  frequently, 
however,  they  are  conjoined,  so  as  to  leave  only  an  opening 
for  the  exit  of  the  foot,  and  another  behind  this,  which  is 
termed  the  branchial  opening.  The  edges  of  this  aperture 
maybe  prolonged  into  a  tube,  which  is  termed  the  branchial 
siphon.  When  a  Lamellibranch  is  in  its  natural  element 
and  undisturbed,  the  valves  of  the  shell  gape  sufficiently  to 
allow  of  the  free  entrance  or  exit  of  water,  to  or  from  the 
pallial  cavity ;  or,  when  siphons  exist,  they  are  fully  pro- 
truded. The  cilia  with  which  the  branchise  are  beset,  work 
in  such  a  manner  as  to  drive  the  water  from  the  infra- 
branchial  chamber,  through  the  openings  of  the  branchisD, 
into  the  supra-branchial  chamber.  From  hence  its  only 
way  of  exit  is  by  the  cloaca  and  the  anal  siphon,  when  the 
latter  exists.  In  order  to  make  up  for  the  water  thus  driven 
out,  a  new  supply  of  water  enters  by  the  interspace  between 
the  lobes  of  the  mantle,  which  bound  the  infra-branchial 
chamber,  or  by  the  branchial  siphon.  These  currents  may 
readily  be  made  obvious  by  allowing  a  stream  of  finely- 
divided  colouring  matter  to  pass  slowly  towards  the  bran- 
chial siphon  of  a  Lamellibranch.  It  will  be  seen  to  be 
swiftly  sucked  in,  and  after  a  very  short  time  a  coloured 
stream  will  flow  out  of  the  anal  siphon.  The  same  agency 
brings  the  nutritive  matters  suspended  in  the  water  within 
reach  of  the  labial  palpi,  by  which  they  are  guided  to  the 
mouth. 

Whatever  form  the  branchise  may  possess,  they  are  sup- 
ported by  a  chitinouB  skeleton,  in  the  form  of  a  partial  or 
complete  investment  to  the  transverse  branchial  vessels. 

The  mouth  is  bounded  by  lips,  the  angles  of  which  are 
usually  produced  on  each  side  into  two  hibial  palpi.  Some- 
times the  lips  are  represented  by  a  circular  fold  produced 
into  numerous  tentacula  {Pecten),  There  are  no  organs  for 
the  prehension  or  mastication  of  food.  A  wide  and  short 
gullet  leads  into  a  stomach  surroundedib^  V^[v<^>^^st^^^t>c^^t^ 


478       THB  AKATOMT  OF  IKYBBTXBSATBD  AHIKALS. 

consists  of  nmnerous  c»ca  united  into  ducts  wliich  open 
into  the  stomach.  Yery  generally  a  diyerticulum  of  the 
pjloric  end  of  the  stomach  contains  a  transparent  rod-like 
body — ^the  crystalline  style. 

The  intestine  usually  makes  many  conTolutions,  bat» 
finally  reaching  the  middle  line  of  the  dorsal  region  of  the 
body,  it  terminates  by  the  anus  in  the  posterior  part  of  the 
pallial  chamber.  The  heart  lies  in  the  region  traversed  by 
the  termination  of  the  intestine.  It  consists  of  an  auricle 
and  a  yentricle,  or  of  a  ventricle  and  two  auricles,  or  may 
be  divided  into  two  separate  auricles  and  ventricles  {Area). 
Aortic  trunks  distribute  the  colourless  blood  to  the  body, 
whence  it  is  carried  to  a  large  median  venous  sinus ;  fron^ 
this  it  passes  through  the  walls  of  the  renal  organs  to  the 
gills,  and  is  returned  from  these  to  the  auricular  division 
of  the  heart.*  Very  generally  the  ventricle  invests  the 
rectum,  but  in  Ostrcea,  Teredo,  and  Anomia  the  ventricle  is 
quite  detached  from  the  intestine. 

The  renal  organs,  or  organs  of  Bojanus,  are  usually  two 
in  number,  often  more  or  less  united  together,  of  a  dark 
colour,  situated  beneath  and  behind  the  pericardium  and  in 
front  of  the  posterior  adductor  muscle,  extending  forwards 
on  each  side  of  the  mesosoma,  and  traversed  by  such 
numerous  blood-channels  that  they  have  a  spongy  texture. 
The  walls  of  the  cavernous  blood  sinuses  are  lined  with 
cells  which  secrete  the  urinary  matters  from  the  blood. 
These  take  the  form  of  calcareous  concretions  containing 
uric  acid.  The  gland  communicates  at  one  extremity  with 
the  pericardium ;  at  the  other,  it  either  opens  directly  on  to 
the  surface  of  the  body,  or  into  a  vestibular  cavity  which 
has  an  external  aperture. 

In  Chtrcea  and  Teredo  the  renal  organ  seems  to  be  present 
in  only  a  very  rudimentary  f orm.t 

The  mesodermal  region,  between  the  endoderm  and  the 

*  The   circulatory  organs    of  demie,'  1855  and  1856.) 

the  freshwater  Mussel  have  been  f  See  for  the  stractore  of  the 

very  fully  desciibed  by  Lancer.  rena    organs    and    manv   other 

(*  Aenksehriftea  der  Wiss.  Aka-  points  connected  with  ue  ana- 


TBI  LAICILLIBBJJIOHUTA.  479 

ectoderm,  is  for  the  mort  part  occnpied  by  TMcolar, 
coimeotive,  and  moBcnlar  tiaaneB,  and  bj  the  reproductive 
organa,  ao  that  there  ia  no  lafge  periTiaoeml  apace.  But 
there  is — 1.  The  large  median  eiiina  alreadj  mentioned, 
which  receives  the  blood  retnmed  from  all  parta  of  the 
bodj,  and  is  commonlj  termed  theoena  cava.  2.  A  apadone 
pericardial  chamber  which  enclosea  the  heart.    It  is  in 


Fig.  118. 


Fig.  IIS.— j^KOdoKfa.— Tertleal  tnd  tmwvene  wctlan  of  tbe  bodj 
uirDugb  Ibebcart;  /,TeDtricJe;  p.iurlclca;  c.reotum',  p,DtritMi' 
dlmu;  h,  inner,  pouter  gill;  a*  veitibnie  of  q,  the  orgui  of  Bojuiiu; 
B,  foot,  A.  A,  Duitle  lobci. 

commiinicatioli  with  the  venoaa  ayatem,  and,  OOIMeqiiently, 
directly,  or  indirectlj,  with  the  vena  cava.  3.  The  osTitiea 
of  the  renal  organs,  which  naoally  freely  commtmicftte  with 


tomf  of  tha  LameUStnfftthiatit,  tlie 
■criet  of  Tdiuble  papen  of  Lk- 
cue-Duttiian.      (>  Auualei    dw 


+80       THE  ANATOMY  OF  INTEBTEBBATBD 

one  another,  while  they  open  into  the  pericardinm  oi 
one  blind,  ajid  on  the  e»teriur  of  the  body  on  the  t 
4-.  In  flomc  Lumellilrranekiaia.  canaia  open  on  the  exi 
of  the  b'jdy.  especially  on  the  Burtace  of  the  foot.  Ii 
way  the  blood  ajHt^m  is  placed  in  direct,  thongh  circu 
(?omniimieation  with  the  surrounding  water.  Tbee 
colled  tcat(v-rei8eU  communicate  internally  with  the  rt 
Byatem,  of  whit'b,  indeed,  tbey  seem  to  form  a  part. 
probable  that  all  these  cavitiea,  taken  together,  repr 
the  pcriviai.-erul  cavity,  pallial  ainiiBes,  and  pseitilo-heaj 
a  Brachiopod. 

Sti'ong  bundles  of  muscular  fibres,  usuallj  nnBtriated. 
tranHversely  from  one  valve  of  the  shell  to  the  other 
brin^i  them  together;  while  they  are  divaricated  bj 
elastic  reaction  of  tbo  ligament.  Of  Buch  addiKtor  mi 
there  may  be  either  one  or  two.  When  there  are 
ilHnnjariai,  the  anterior  adduetar  lies  in  front,  and  o 
htK'mal  eiile  of.  the  tcsophagus ;  while  the  ponterior  odd 
iica  in  front,  but  on  the  neural  aide,  of  the  rectum.  E 
the  alimentary  canal,  as  a  whole,  lies  between  these 
muadca.  When  only  one  adductor  mnacle  eiiste  |J 
s  the  poaterior. 


TRB  ULMBLLIBSAKOHIATA. 


481 


inUgropMiaie  and  tinupaUiaie  as  applied  to  LameUibrancliB 
which  haye  the  pallia!  line  erenlj  rounded  or  notched. 

The  cerebral  ganglia  lie  at  the  sides  of  t^e  month,  and 
are  connected  by  a  commissure,  which  passes  in  front  of  it. 
Thej  gire  branches  to  the  anterior  region  of  the  mantle, 
to  the  gills,  to  the  anterior  adductor  muscle,  to  the  labial 
palpi,  and  to  the  parts  about  the  mouth.  The  j^edal 
ganglia  are  situated  in  the  foot ;  or  in  the  corresponding 
region  on  the  neural  side  of  the  alimentaiy  canal,  when 
no  foot  is  dereloped.  Each  is  united  by  a  commissure 
with  the  cerebral  ganglion  of  the  same  side,  and  gives  off 
branches  to  the  muscles  of  the  foot.  The  parieto-splanehnie 
ganglia  lie  on  the  neural  face  of  the  posterior  adductor 
muscle.  The  long  commissures  which  unite  them  with  the 
cerebral  ganglia  usually  trayerse  the  renal  organ,  and  lie 
beneath  the  floor  of  the  pericardium.  Each  of  these 
ganglia  giyes  off  a  nerye  to  the  branchia  of  its  side,  and 
supplies  the  posterior  and  middle  part  of  the  mantle. 
This  posterior  pallial  nerye  may  anastomose  with  the 
anterior  pallial  nerye  from  the  cerebral  ganglion.  The 
ganglia  also  furnish  neryes  to  the  posterior  adductor 
muscle,  to  the  heart,  to  the  rectum,  and  to  the  nrasclee  of 
the  siphons,  when  the  latter  are  present.  Eyes  are  neyer 
developed  in  the  cephalic  region  of  the  LamelHbranchs, 
but,  in  many  {e,g,  Fecten)  numerous  simple  eyes  terminate 
papillsB  of  the  margins  of  the  mantle.  Auditory  sacs  are 
almost  inyariably  attached  by  longer  or  shorter  pedimcles 
to  the  pedal  ganglia. 

The  Lamellibranchiaia  are  usually  dioecious,  but  some- 
times hermaphrodite*  {e,g.  Cyclas,  some  species  of  Cardium 
and  Pecten,  Odroea,  ClavageUa  and  Pandora),  The  genera- 
be  either  almost  all  ovigeroas  or 
almost  all  spermigeroos :  and  it 
appMrs  probable  that  toe  pre- 
dominantly male,  precedes  the 
predoninantlv  female,  condition. 
See  Lacase-Dathiers.  **Organea 
genitanx  dea  Ac^halea  Lamelll- 
branehes "  ('  Ann.  das  Scienoet 
NatiireUef,'1854). 

2x 


*  The  testes  and  ovaria  are 
distinct  in  the  hermaphrodite 
Pectines.  In  Cardhan  terratum. 
adjacent  c®ca  of  the  sexual  glaml 
contain  spermatosoa  or  ova,  or 
both  products  may  be  developed 
in  the  same  omcum.  In  the  eoa- 
mon  Oyster  the  genital  cseea  in 
any  given  individoai  are  found  to 


480       THB  AKATOMT  OF  INYEBTBBSATBD  AKOCALS. 

one  another,  while  thej  open  into  the  pericardiom  on  the 
one  hand,  and  on  the  exterior  of  the  body  on  the  other. 
4.  In  some  Lamellibranchiata,  canals  open  on  the  exterior 
of  the  body,  especially  on  the  surface  of  the  foot.  In  this 
way  the  blood  system  is  placed  in  direct,  though  circuitous 
communication  with  the  surrounding  water.  These  so- 
called  toater-vessels  communicate  internally  with  the  renous 
system,  of  which,  indeed,  they  seem  to  form  a  part  It  is 
probable  that  all  these  cavities,  taken  together,  represent 
the  perivisceral  cavity,  pallial  sinuses,  and  pseudo-hearts  of 
a  Brachiopod. 

Strong  bundles  of  muscular  fibres,  usually  unstriated,  pass 
transversely  from  one  valve  of  the  shell  to  the  other,  and 
bring  them  together;  while  they  are  divaricated  by  the 
elastic  reaction  of  the  ligament.  Of  such  adductor  muscles 
there  may  be  either  one  or  two.  When  there  are  two 
(Dimyaria),  the  anterior  adductor  lies  in  front,  and  on  the 
hsemal  side  of,  the  oesophagus ;  while  the  posterior  adductor 
lies  in  front,  but  on  the  neural  side,  of  the  rectum.  Hence 
the  alimentary  canal,  as  a  whole,  lies  between  these  two 
muscles.  When  only  one  adductor  muscle  exists  (Mono- 
myaria),  it  is  the  posterior. 

The  foot  is  retracted  between  the  valves  of  the  shell 
by  two  or  three  pairs  of  retractor  muscles,  of  which  the 
anterior  and  posterior  pairs  are  usually  attached  to  the 
shell,  close  to  the  anterior  and  posterior  adductor  im- 
pressions. The  protraction  of  the  foot  appears  to  be 
effected  by  the  compression  of  the  blood  by  tiie  intrinsic 
muscles  of  the  walls  of  the  mesosoma  and  of  the  foot 
itself. 

Each  lobe  of  the  mantle  is  attached  to  the  corresponding 
valve  of  the  shell  by  a  series  of  muscular  fibres,  the  attach- 
ments of  which  give  rise  to  a  linear  impression,  which  runs 
from  one  adductor  to  the  other,  and  constitutes  the  paUial 
line.  When  the  siphons  are  largely  developed  they  have 
retractor  muscles,  the  insertions  of  which  are  so  disposed 
as  to  cause  the  posterior  part  of  the  pallial  line  to  be  more 
or  less  deeply  curved  or  angulated.     Hence  the  distinction  of 


THE  LAMBLLIBSAKOHIATA. 


481 


integropalliaie  and  sinupdUiaie  as  applied  to  LamellibrancliB 
which  haye  the  pallial  line  erenlj  rounded  or  notched. 

The  cerebral  ganglia  lie  at  the  sides  of  the  month,  and 
are  connected  by  a  commissure,  which  passes  in  front  of  it. 
They  giye  branches  to  the  anterior  region  of  the  mantle, 
to  tiie  gills,  to  the  anterior  adductor  muscle,  to  the  labial 
palpi,  and  to  the  parts  about  the  mouth.  The  pedal 
ganglia  are  situated  in  the  foot ;  or  in  the  corresponding 
region  on  the  neural  side  of  the  alimentaiy  canal,  when 
no  foot  is  deyeloped.  Each  is  united  by  a  commissure 
with  the  cerebral  ganglion  of  the  same  side,  and  giyes  off 
branches  to  the  muscles  of  the  foot.  The  parietO'Splanchnie 
ganglia  lie  on  the  neural  face  of  the  posterior  adductor 
muscle.  The  long  commissures  which  unite  them  with  the 
cerebral  ganglia  usually  trayerse  the  renal  organ,  and  lie 
beneath  the  floor  of  the  pericardium.  Each  of  these 
ganglia  giyes  off  a  nerye  to  the  branchia  of  its  side,  and 
supplies  the  posterior  and  middle  part  of  the  mantle. 
Thia  poeterior  pallial  nerve  may  anastomose  mth  the 
anterior  pallial  nerye  from  the  cerebral  ganglion.  The 
ganglia  also  furnish  neryes  to  the  posterior  adductor 
muscle,  to  the  heart,  to  the  rectum,  and  to  the  nrascles  of 
the  siphons,  when  the  lattar  are  present.  Eyes  are  neyer 
deyeloped  in  the  cephalic  region  of  the  Lunellibranchs, 
but,  in  many  {e.g.  Fecten)  numerous  simple  eyes  terminate 
papillsB  of  the  margins  of  the  mantle.  Auditory  sacs  are 
almost  inyariably  attached  by  longer  or  shorter  pedimcles 
to  the  pedal  ganglia. 

The  Lamellihranchiata  are  usually  dioecious,  but  some- 
times hermaphrodite*  {e.g.  Cyclae,  some  species  of  Cardium 
and  Pecten,  Ostroea,  ClavageUa  and  Pandora),    The  genera- 


*  The  testes  and  ovaris  are 
distinct  in  the  hermaphrodite 
Pectmes.  In  Cardium  terratunu 
adjacent  c®ca  of  the  sexual  gUnd 
contain  spermatoaoa  or  ova,  or 
both  products  Biay  be  developed 
in  the  same  caecum.  In  the  com- 
mon  Oyster  the  genital  cseea  in 
any  given  indiyidoai  are  found  to 


be  either  almost  all  ovigerous  or 
almost  all  spermigerous :  and  it 
appears  probable  that  toe  pre- 
dominantly male,  precedes  the 
predosnioantlv  female^  condition, 
bee  Laoaae-Dathiers,  '*Organes 
g^nitaux  des  Ao^phales  Lamelli- 
branches "  (*  Ann.  det  Sciences 
Naturelles,'  1854). 

2x 


482   THB  ANATOMY  OF  IKTEBTEBSATKD  AHIMALS. 

tiye  organs  are  ramified  glands  of  simple  straotore  and 
similar  in  both  sexes,  the  ducts  of  which  open  into,  or  dose 
to,  the  renal  organs. 

The  process  of  yelk-division  *  nsnally  gives  rise  to  smaller 
and  larger  blastomeree,  of  which  the  former,  as  an  epiblast, 
invest  the  latter  as  a  hypoblast.  At  the  o^halic  end  of  the 
embryo  of  most  Lamellibranchs,  a  velum,  or  disk  with 
richly  ciliated  edges  and,  nsuaUy,  a  central  toft  of  longer 
cilia,  ii9  formed.  On  the  dorsal  face  of  the  embryo  the 
integument  rises  into  a  patch  with  raised  edges,  which 
is  the  rudiment  of  the  mantle.  The  separation  of  the  shell 
into  twa  valves,  united  by  an  uncalcified  hinge,  must  pro- 
bably be  ascribed  to  the  manner  in  which  the  calcareous 
matter  subsequently  added  to  the-  shell  is  deposited.  The 
foot  appears  as  a  median  outgrowth  of  the  neural  face  of 
the  embryo  behind  the  mouth.  The  branchis  have,  at 
first,  the  form  of  separate  filamentous  processes,  which 
are  developed  from  the  roof  of  the  anterior  part  of  the 
pallial  cavity,  at  the^  point  of  junction  of  the  mantle  vritii 
the  mesoeoma,  and  gradually  increase  in  number  from 
before  backwards.  Jn  those  Lamellibranchs  which  have 
pouchlike  gills,  it  appears  that  the  processes  which  are  first 
formed  become  the  outer  lamella  of  the  inner  g^-plate, 
their  free  ends  uniting  together;  the  inner  lamella  of  this 
plate  is  produced  by  the  upgrowth  of  a  thin  lamina, 
which  subsequently  becomes  perforated,  from  the  united 
ends  of  these  processes.  The  inner-  lamella  of  the  outer 
gill  is  formed  of  branchial  processes,  which  grow  out  from 
the  attached  ends  of  the  first  set;  and  the  outer  lamella 
of  this  gill  is  produced  in  the  same- fashion  as  the  inner 
lamella  of  the  inner  gill.f 

Recent  observations  tend  to  show  that  in  these,  as  in 
other  Invertebraia,  the  nervous  ganglia  are  modified 
ingrowths  of  the  epiblast. 

*  See  Love'n,  'Archiv  fur  Na-  f  Lacaie-Ihithien^  <'Sur  lede- 

tnrgeeohichte,'  1849.   De  Quatre-  veloppement  dea  branehies  des 

^'Memoires  sur  TEmbrvo-  Molfusques    aoephalea   Lamelli- 

des  Tareto  **  (*Anii.  dea  So.  branchea  "  O  ^nn*  dea  Seienoat 

1849).  Naturelles,*  4,  iv.). 


THB  DETSLOPMBITT  OF  LAMBLLIB&AHCHB.         483 

The  simplest  form  of  development  of  the  LameUibranehu 
aia  has  been  observed  in  Pitidiwn.*  Bj  the  prooess  of 
cleavage,  the  yitelliis  is  divided  into  a  number  of  equal 
blastomeres.  The  morula  thus  formed  undergoes  invagi- 
nation, and  is  converted  into  a  gastrula.  The  blastopore, 
or  aperture  of  invagination,  closes,  and  the  epiblast,  or 
ectodermal  layer  of  the  embryo,  growing  much  faster  than 
the  hypoblast,  or  endodermal  layer,  the  latter  forms  a  small 
shut  sac,  the  primitive  alimentary  sac  (or  (Mrchenteron) 
attached  to  one  point  of  the  inner  surface  of  the  much 
larger  ectodermal  sac.  The  mesoblastic  cells  appear  to  be 
derived  both  from  the  epiblast  and  the  hypoblast. 

The  mouth  is  formed  by  a  depression  of  the  ectoderm  at 
the  anterior  end  of  the  body,  which  grows  towards  and 
opens  into  the  archenteron.  The  anus  is  developed  at  the 
opposite  end,  in  the  region  of  the  primitive  invagination. 
On  the  neural  face  of  the  embryo,  the  foot  grows  out, 
while  the  mantle  appears  on  the  opposite  face ;  and,  in  the 
centre  of  the  mantle,  a  transversely  oblong  depression  lined 
by  elongated  cells  is  the  'shell  gland.'  In  the  median 
line  this  answers  to  the  ligament,  and,  at  the  sides,  to  the 
middle  region  of  the  future  valves  of  the  shell ;  but  the 
precise  share,  if  any,  which  it  takes  in  the  formation  of 
these  parts  does  not  appear.    Piaidium  has  no  velum. 

The  development  of  one  of  the  fresh-water  Mussels  (Unto 
pidorwn)  has  recently  been  worked  out  very  fully  by 
BabLt  The  vitellus  divides  into  two  unequal  masses,  of 
which  the  larger  is  termed  by  Babl  the  'vegetative'  and 
the  smaller  the '  animal '  cell,  somewhat  inconvenient  names 
which  may  be  replaced  by  '  macromere  *  and '  mieromere.* 
Each  of  these  becomes  subdivided,  partly  by  ordinary  fission, 
partly,  as  in  the  case  of  the  macromere,  by  a  process  of 
budding,  intoblastomeres,  of  which  those  which  proceed  from 
the  macromere  long  remain  larger  and  more  granular  than 
those  which  proceed  from  the  micromere.    The  blastomeres 

*  Lankester"  On  the  Develop-  t  C.  Rabl,  *Ueber   die   Ent- 

nental  History  of  the  MoUasca."      wickelungtgeschichte  der  Hsler- 
(*  FhiL  Trane.'  1874.)  muscheV  JeD««  1876. 

2  I  2 


484       THE  ANATOMY  OF  INYEBTBBRATBD  AKOlAIiS. 

arrange  themselyes  into  a  hollow  sphere — ^the  hkuiosphere. 
This  is  a  yesicular  morula,  composed  of  a  single  lajer  of 
blastomeres,  of  which  those  of  one  hemisphere  have  pro- 
ceeded from  the  micromere,  and  those  of  the  other  from 
the  macromere.  Two  blastomeres  of  the  macromenJ  hemi- 
sphere remain  much  larger  than  the  rest.  The  macromeral 
hemisphere  next  undergoes  invagination,  and  its  invagi- 
nated  part  becomes  the  hypoblast.  The  two  large  blasto- 
meres  just  mentioned,  which  are  disposed  symmetricallj, 
one  on  each  side  of  the  median  plane  at  the  anterior  margin 
of  the  area  of  inyagination,  become  enclosed  be^een  the 
hypoblast  and  the  epiblast,mnd  by  their  division  give  rise 
to  the  mesoblast.  This  last,  therefore,  may  be  regarded 
as  an  indirect  product  of  the  hypoblast. 

The  endoklermal  sac  formed  by  the  hypoblast  now  loses 
its  connection  with  the  region  of  the  embryo  of  which  it  is 
an  invagination,  and  applies  itself  to  the  anterior  wall  of 
the  body,  where  an  involution  of  the  ectoderm,  which  gives 
rise  to  the  oral  cavity,  takes  place.  The  gre&ter  part  of  the 
mesoblastic  cells  become  the  adductor  muscle,  which  is  at 
first  single  and  answers  to  the  posterior  adductor  of  the 
adult.  There  seems  to  be  no  shell  gland.  The  shell  appears 
at  first  as  a  membranous  cuticula,  continuous  from  side  to 
side,  and  therefore  undivided  into  two  valves.  Subsequently 
it  becomes  calcified  and  bivalve.  The  byssus  gland  is 
developed  as  an  involution  of  the  ectoderm  at  the  posterior 
end  of  the  body ;  and  the  ventral  hemisphere,  or  that  oppo- 
site the  shell,  becomes  divided  by  a  deep  median  fold  into 
the  two  lobes  of  the  mantle  on  which  the  characteristic 
pencil-like  papillae  appear.  In  front  of  the  rudimentary 
mouth  are  two  ciliated  depressions  of  the  ectoderm,  which 
are  possibly  the  rudiments  of  the  nei'vous  ganglia. 

In  Unio  and  Anodonta  the  young  are  hatched  in  the  outer 
gill  pouches  of  the  parent,  from  which  they  are  so  dis- 
similar that  they  were  at  one  time  considered  to  be  parasites 
(Olochidivm),  The  valves  of  the  shell  are  triangular  and 
have  incurved  and  serrated  apices,  by  the  help  of  which  the 
Urvm,  after  they  leave  the  parent,  attach  themselves  to 


THB  LAMXLLIBRAirGHIATA.  485 

fisliee  and  other  floating  bodies.  In  this  position  they 
undergo  a  sort  of  metamorphosis,  and  eyentuallj  fall  off  and 
sink  to  the  bottom  as  minnte  fresh- water  Mnssels. 

On  comparing  the  LameUibranchiata  with  the  Brtxehiopadaf 
it  is  obvious  that  the  two  have,  in  common  with  one  another 
and  with  the  Annelida,  the  ciliated  or  veligerous  larval 
form.  If  the  shell  gland  is,  as  Mr.  Lankester  suggests, 
the  homologue  of  the  peduncular  gland  of  LooB08oma  and 
of  the  Brachiopod  larvs,  it  follows  that  the  peduncle  of 
the  Brachiopod  corresponds  with  the  centre  of  the  pallial 
surface  of  the  Lamellibranch,  and  that  the  so-called  dorsa^ 
and  ventral  lobes  of  the  mantle  in  the  Brachiopod  corre« 
epond  with  the  anterior  and  posterior  halves  of  the  mantle 
in  the  Lamellibranch.  The  Brachiopod  hinge  will  there- 
fore  be  transverse  to  the  axis  of  the  body,  while  the 
Lamellibranch  hinge  is  parallel  with  it.  If  this  comparison 
be  just,  however,  the  three  segments  of  the  Brachiopod 
larva  cannot  answer  to  the  segments  of  an  Annelid  larva, 
but  the  two  posterior  segments  of  the  Brachiopod  larva 
must  represent  an  outgrowth  of  the  hsBmal  side  of  the  bodj; 
and  this  would  correspond  very  well  with  the  arrangement 
of  the  intestine  in  the  articulated  Brachiopoda, 

In  the  simplest  forms  of  the  LameUibranchiata,  as  Trigonia, 
Nucula,  and  Pecten,  the  mantle-lobes  are  almost,  or  com- 
pletely, disunited  with  one  another  and  with  the  branchiie, 
and  the  latter  are  either  simple  plumes  or  have  undergone 
but  little  modification.  The  haemal  face  of  the  body  is 
short  relatively  to  its  vertical  height. 

In  most  Lsmaellibranchs  the  haemal  face  of  the  body  is 
longer;  the  gills  are  lamellar,  and  the  mantle-lobes  are 
united  with  one  another  and  with  the  gills,  so  as  to  sepa- 
rate a  supra-branchial  from  an  infra-branchial  chamber 
(Anodonta).  In  yet  others,  the  posterior  margins  of  the 
mantle  are  produced  backwards  into  short  siphons,  but  the 
mantle-lobes  remain  separate  for  the  rest  of  their  extent 
{Cardivm);  in  others,  the  siphons  are  greatly  elongated  and 
the  ventral  margins  of  the  mantle-lobes  unite,  so  as  to  leave 
only  a  small  median  aperture  for  the  foot  {Pholas),    In  the 


4S6       THE  ANATOMY  OF  HTYEBTSBRATBD  ANIMALS. 

most  modified  forms,  the  body  becomes  more  and  more 
elongated,  until,  in  Teredo^  it  is  completely  vermiform,  and 
the  valyes  of  the  shell  cover  but  a  very  small  portion  of 
the  body. 

The  foot  is  wanting  as  a  distinct  stmctnre  in  CMroea; 
while  in  Cardium  and  Trigonia  it  is  a  large  mnscnlar 
organ,  by  the  aid  of  which  the  animal  is  able  to  leap  for 
some  distance.  The  byssns  may  be  present  in  the  yonng 
and  absent  in  the  adult  [e.g.  AnodorUa).  It  may  have  the 
form  of  strong  chitinous  filaments  {Mytihts)  or  of  a  plate 
of  homy  or  shelly  texture  {Area,  Anomia).  The  inequality 
of  the  valves  attains  its  maximum  in  the  HippuriHdcB,  in 
which  one  valve  may  have  the  form  of  a  long  cylinder,  or 
cone,  while  the  other  is  a  flattened  plate.* 

The  shells  of  Lamellibranchs  are  among  the  most 
abundant  of  fossil  remains  in  all  epochs  of  the  world*s 
history.  In  the  Palaeozoic  formations,  however,  the  pro- 
portion of  these  moUusks  relatively  to  the  Brachiopoda  is 
the  reverse  of  what  obtains  at  the  present  day,  the  latter 
being  very  numerous,  while  the  Lamellibranchs  are  com- 
paratively scanty.  The  integropalliate  are  far  more  nume- 
rous than  the  sinupalliate  forms  in  the  older  rocks.  The 
HippurUidoi  of  the  Cretaceous  epoch  is  the  only  family  of 
ancient  Lamellibranchs  which  is  extinct  at  the  present  day ; 
and  the  only  one  which  diverges  to  any  considerable  degree 
from  existing  forms. 

The  Odontophoka. — In  the  Mollusks  which  belong  to 
this  division,  the  mantle,  always  present  in  the  newly 
hatched  young,  may  abort  in  the  adult  condition.  It  is 
never  divided  into  two  lobes,  though  it  may  be  slit  or  per- 
forated where  it  forms  the  waU  of  the  branchial  chamber 
(Hdliotia,  Fisswrella). 

Yery  generally,  the  prosoma  bears  tentacula  and  eyes ; 
and  a  distinct  head  being  thus  recognisable,  these  Mollusks 

*  For  an   exoeUent  Account   of  the  LamelUbramekiaia  finom    the 
ooaeMogieal  tide,  te«^ood^tx^'%^'^«>iv^ui^^t  xSu^lAoUnMa.' 


THS  ODONTOPHOIU.  487 

have  been  named  Cephalophora,  in  OQntradistinotiQn  to  the 
acephalous  Lamellibranchs  and  Brachiopods. 

The  mantle  commonlj  gives  rise  to  a  shell ;  which  may 
either  be  a  more  or  less  calcified  cnticidar  product  of  the 
epidermis,  covering  the  onter  surface  of  the  mantle,  when  it 
constitutes  an  external  shell,  as  in  the  LaimMibranchiaia 
and  Brachiopoda ;  or  it  may  be  developed  within  a  sac  in 
the  interior  of  the  mantle,  as  an  internal  shell.  In  neii&er 
of  these  cases  is  it  ever  a  bivalve  shell  divided  into  two 
lateral  portions.*  Usuallj  it  is  in  one  piece  (uivalve),  but 
in  one  group,  the  ChUonidce,  it  consists  of  a  number  of 
pieces  (not  exceeding  eight),  arranged  in  longitudinal  series 
along  the  middle  line. 

Calcareous  matter  is  very  commonly  diffused,  in  the  form 
of  granules,  through  the  connective  tissue,  and  often  takes 
the  form  of  spicula  (e.^.  Doris), 

The  mesosoma  is  generally  prolonged  into  a  muscular 
foot,  which  may  be  provided  with  lateral  appendages,  the 
epipodia.  And,  on  the  hsmal  aspect  of  the  posterior  portion 
of  the  foot,  a  chitinous  or  shelly  plate,  termed  the  operculum^ 
may  be  developed.  This  operculum  appears  to  be  the 
analogue,  if  not  the  homologue,  of  the  byssus  of  the  LameUi- 
branchs;  and  is  certainly  not  homologous  with  either  of 
the  valves  of  the  shell  of  the  latter,  which  are  pallial  struc- 
tures. The  edge  of  the  mantle  forms  a  free  fold  which 
nearly  or  entirely  surrounds  the  mesosoma;  and  in  one 
genus,  Denialium,  the  margins  of  the  mantle  unite  for  the 
greater  part  of  their  length :  in  all  the  rest  they  remain 
free.  A  space  is  enclosed  between  the  lobes  of  the  mantle 
and  the  mesosoma.  Usually  this  space  is  much  larger  on 
one  face  of  the  body,  and  constitutes  the  pallial  chamber. 
As  a  rule,  the  branchiffi  are  lodged  in  this  chamber,  and 
the  anus  opens  into  it. 

In  a  very  few  Odoniophara,  the  symmetry  of  the  body  is 

*  The  singular  bivalve  plates,  homologous   with   the   shell    of 

termed  Aptvckusj  which  occur  in  ordinary  Mollusks,  which  is  re- 

the  AmmomuidtBy  whatever  their  presented  by  the  chambered  shell 

nature  may  be,  are  obviously  not  of  the  cephalopoda 


488       THI  ANATOMY  OV  INYSBTSBRATED  AKIMAUB. 

undisinrbed ;  that  is  to  say,  the  month  and  the  anna  are 
sitnated  at  opposite  ends  of  the  axis  of  the  body,  and  the 
hsmal  face  is  not  produced  into  a  Tiscend  sac  (e.g.  ChUon^ 
DenUUiwn).  Bnt,  in  the  great  majority,  such  a  TiBceral  sac 
is  formed.  In  the  Cephalopoda,  it  co-existB  with  bilateral 
symmetry,  inasmnck  as  the  mantle  and  the  anns  lie  in  the 
plane  which  divides  the  body  into  two  similar  halves.  Bnt, 
in  most  OdotUophora,  the  anus  is  twisted  to  one  side  (nsnally 
the  right),  and  in  many,  it  is  situated,  together  with  the 
pallial  chamber  in  which  it  is  contained,  on  the  anterior 
face  of  the  body. 

The  mouth  lies  at  the  anterior  end  of  the  body,  on  the 
haemal  side  of  the  anterior  part  of  the  foot  (except  in  the 
Cephalopoda),  It  may  be  provided  with  variously  dispoeed 
jaws,  or  cutting  plates,  of  a  chitinous  or  calcified  substanoa 
But  the  structure  which  is  most  characteristic  of  the  Odo%' 
tophora,  and  which  is  absent  in  only  very  few  genera  (e.g. 
Teihys,  Doridium,  Bhodope),  is  a  peculiar  rasping  and  some- 
times prehensile  apparatus,  the  odowtophore,  or  as  it  is 
often  termed,  the  tongue,  which  is  attached  to  the  floor 
of  the  mouth  (Fig.  119, 120). 

This  apparatus  consists  of  a  skeleton;  of  a  eubradular 
membrane,  ^i4nch  is  continuous  with  the  lining  of  the  oral 
carity ;  of  the  radula ;  and  of  intrineie  and  extrinsic  muscles. 

The  skeleton  is  composed  of  two  principal  masses  of  par- 
tially fibrous,  or  completely  cartilaginous  tissue  {odonto^ 
phoral  cartUages),  which  may  be  more  or  less  confluent,  and 
are  further  xmited  together  in  the  middle  line  by  fibrous 
and  muscular  tissue.  Their  anterior  ends  and  oral  faces 
are  free  and  smooth,  and  are  usually  excavated  so  as  to 
present  a  trough-like  surface  to  the  subradular  membrane* 
which,  rests  upon  them.  Accessory  cartilages  may  be 
added  to  these.  Behind,  the  subradular  membrane  is  con- 
tinued into  a  longer  or  shorter  sac,  lined  by  a  continuation 
of  the  buccal  epithelium.  The  radula  is  a  cuticular  chitinous 
product  of  the  epithelium  of  the  subradular  membrane.  It 
.]•  anned  with  tooth-like  processes  arranged  in  one  or  many 
[;  and  addiUona  aro  cons^aai^lL^  bein^  made  to  its  pos- 


THS  ODOKTOPHORA. 


489 


terior  end,  wliich  ie  lodged  in  the  sac  of  the  sabradolar 
membrane.  Thus  the  teeth  are  replaced  from  behind,  as 
fast  as  they  are  worn  away  by  friction  against  the  food 
which  thej  rasp,  at  the  anterior  end  of  the  ribbon. 

The  intrinsic  muscles  oi  the  odontophore  are  attached,  on 

Fig.  119. 


Fig.  U9,—Biiecmwm  undatitm.—A^  radol*;^  B,  one  of  the  transyerte 
rowf  of  teeth,  a,  anterior,  b,  posterior  end ;  c,  central,  I,  lateral 
teeth.    (After  Woodward^  *  Manual  of  the  MoUusca.*) 

Fig.  120. 


Fig.  120. — A^  T^ockuM  einerarimt ;  the  median  tooth  and  the^teeth  ot 
the  right  half  of  one  row  of  the  radula.  B,  C^nta  .EWrqpoo,  one 
row  of  teeth  of  the  radula.   (Woodward,  ibid.) 

the  one  hand,  to  the  posterior  and  nnder  faces  of  the  odonto- 
phoral  cartilages,  and,  on  the  other,  to  the  subradular  mem- 
brane, some  being  inserted  into  its  posterior  and  lateral 
portions,  and  others  into  its  anterior  extremity,  after  it 
has  tnmed  over  the  anterior  extremities  of  the  principal 
cartilages.      Certain   of   the  mnscnlax  \>\m!3\«&  «x^  ^J^oi^ 


490       THE  ANATOMY  OV  XNTBBTEBRATED  AHIMAL8. 


attaclied  to  the  fore  part  of  the  odontophond  cartilages 
themselves.  The  contraction  of  these  muscles  must  tend  to 
cause  the  subradular  membrane,  and  with  it  the  radula^  to 
travel  backwards  and  forwards  over  the  ends  of  the  car- 
tilages in  the  fashion  of  a  chain-saw,  and  thus  to  rasp  any 
body  against  which  the  teeth  may  be  applied.  When  xm- 
disturbed,  the  radula  is  concave  from  side  to  side,  and  the 
teeth  of  the  lateral  series,  being  perpendicular  to  the  sorfaoe 
to  which  they  are  attached,  are  inclined  inwards  towards 
one  another.  But  when  the  intrinsic  muscles  come  into 
action,  the  radula,  as  it  passes  over  the  ends  of  the  car- 
tilages, becomes  flattened,  and  the  lateral  teeth  are  con- 
sequently erected  or  divaricated.  The  extrinsic  muscles  pass 
from  the  odontophore  to  the  lateral  walls  of  the  head,  and 
protract  or  retract  the  whole  apparatus.  They  may  give  the 
protruded  extremity  of  the  radula  a  licking  motion,  which 
is  quite  independent  of  the  chain-saw  action  doe  to  the 
intrinsic  muscles.* 

The  odontophore  is  developed  very  early,  and  it  would  be 
interesting  to  know  whether  it  exists  in  the  young  of  those 
few  Odontophora,  in  which  it  is  wanting  in  the  adult 
state. 

Salivary  glands  are  very  generally  present  in  the  Odontih 
phora,f  and  the  liver  is  usually  large. 

As  in  the  MoUusca  in  general,  the  blood  corpuscles  are 


*  In  my  memoir  *'  On  the  mor- 
phology of  the  Cephalous  Mol- 
luBca"  rPhil.  Trans.  1852),  1  de- 
scribed the  chain-esw  action  of  the 
odontophore,  as  I  observed  it  in 
the  transparent  i^o&>u2e<  and  At- 
laiUa,  while  living.  But  as  Troschel 
has  remarked  in  his  excellent 
monograph  (*Das  Gebiss  der 
Sehneeken,'  erste  Lieferung,  pp. 
19, 20, 1856),  I  did  not  sufficiently 
dwell  on  tlie  frequency  and  im- 

Sortanee  of  the  licking  action  pro- 
ueed  by  the  extrinsic  muscles.  I 
am  atill  of  opinion,  however,  that 
this  aotioii  cannot  be  rightlv  de- 
•oribady  M  a  inovtiaeia  of  t^ 


radula  following  secondarily  upon 
that  of  the  cartilages,  inasmuch 
as  it  is  a  motion  of  the  whole 
odontophore.  On  the  other  hand, 
it  maybe,  as  has  been  suggested 
to  me  by  Mr.  Geddes,  who  at  my 
suggestion  has  undertaken  a  re- 
examination of  the  structure  of  the 
odontophore,  that  the  flexure  of 
the  anterior  ends' of  the  odonto- 
phoral  cartilages,  by  the  intrinsic 
muscles  inserted  into  them,  plays 
an  important  part  in  the  motion 
of  the  radula. 

t  In  IJolium  the  salivary  secre- 
tion contains  free  sulphuric  acid. 


THB  ODONTOPHORA.  491 

coloorlees  and  nucleated.  The  blood  plasma  is  red  in 
Planorbis. 

The  heart  maybe  wanting  {Dentalium)  or  it  maj resemble 
that  of  the  Lamellibranchs  in  having  two  anricles  {Chiton, 
HalioHs),  and  even  in  being  perforated  by  the  rectom 
(HalioHSf  IStrhOy  Neriia);  most  commonly  it  consists  of  a 
single  anricle  and  a  single  ventricle.  In  the  Oephalopods,  it 
is  hard  to  say  whether  the  two  or  four  branchio-cardiac 
tronks  which  open  into  the  ventricle  should  be  regarded 
as  veins  or  as  auricles.  An  accessory  "  portal "  heart  has 
been  described  in  Doris.*  Special  respiratory  organs  may 
be  wanting,  their  place  being  taken  by  processes  of  the 
body,  or  by  the  walls  of  the  mantle  cavity,  or  by  the  general 
surface. 

The  branchise,  when  present,  are  numerous  lamellar  pro- 
cesses, or  from  one  to  four  plume-like  gills.  Aerial  respira- 
tion is  effected  by  the  walls  of  a  pulmonaiy  sac,  which  is 
a  modification  of  the  pallia!  cavity. 

The  presence  of  renal  organs,  in  the  form  of  one  or  more 
sacs  situated  close  to  the  heart,  open  to  the  exterior  on  one 
side  and,  on  the  other,  in  relation,  usually  by  means  of  a 
glandular  structure,  with  the  returning  current  of  blood,  is 
very  general ;  and,  in  many  cases,  these  renal  sacs  communi- 
cate directly  with  the  blood  sinuses  through  the  pericardium. 
In  many  Pteropods  and  Heteropods  they  are  rhythmically 
contractile. 

As  in  the  LameUibranehiata,  so  in  many  Odoniophora, 
simple  or  branched  canals  traverse  the  substance  of  the  foot 
and  open  externally  by  a  more  or  less  conspicuous  pore, 
which  is  usually  situated  upon  its  inferior  face.  These 
ctquiferoua  canals,  as  they  have  been  termed,  appear,  in  many 
cases,  to  open  by  their  inner  ends  into  the  blood  sinuses, 
and  thus  to  establish  a  direct  communication  between  the 
blood  and  the  surrounding  water.  In  species  of  Pyrula, 
Agassiz  found  that  coloured  fluids  ii^'ected  into  the  pore 
passed  into  and  filled  the  blood  vessels  generally.    But  it 

*  Hancock  and  Embleton,  « On  the  Anatomy  of  lyorii.**  Q  PhlL 
Trans.'  1852.) 


4d2       THX  ANATOMY  OF  HTVIBBTBBRATED  ANIMALS. 

may  be  donbted  whether  these  canals  should  be  regarded  as 
a  special  system  of  yessels,  rather  than  as  blood  giimaes 
which  open  extemallj. 

The  arrangement  of  the  centres  of  the  nenrons  system  in 
Dentaliwn  *  most  nearly  approaches  that  which  exists  in  the 
Lattiellihranchiata.  Two  cerebral  ganglia  lie  close  together 
on  the  haemal  side  of  the  oesophagns.  A  long  commisBiiral 
cord  connects  each  of  them  with  one  of  the  pedal  ganglia, 
which  are  also  closely  nnited.  A  second  long  commissore 
passes  backwards  from  the  cerebral  ganglia,  and  often 
presents  a  ganglionic  enlargement  at  its  origin.  It  unites 
with  one  of  two  ganglia,  situated  close  to  the  anns,  and  con* 
nected,  in  front  of  it,  by  a  rather  long  transverse  commissure. 
The  nerves  distributed  to  the  posterior  half  of  the  mantle 
are  given  off  from  these  ganglia,  and  those  to  its  middle  region 
from  the  anterior  end  of  the  commissure  or  its  ganglionic 
enlargement.  There  seems  no  reason  to  doubt  that  the 
ganglia  close  to  the  anus,  together  with  the  ganglionic 
enlargements  at  the  anterior  ends  of  the  commissures 
which  connect  them  with  the  cerebral  ganglia,  correspond 
with  the  parieto-splanchnic  ganglia  of  the  Lamellibranchs, 
and  that  the  cerebral  and  pedal  ganglia  are  the  homolognes 
of  those  so  named  in  the  latter  Mollusks. 

In  addition  to  this  approximation  of  part  of  the  gan- 
glionic mass  of  the  parieto-splanchnic  system  to  the  cerebral 
ganglia,  Dentalium  differs  from  the  Lamellibranchs  and 
resembles  other  Odontophorat  in  the  possession  of  a  system 
of  bucccU  nei'ves,  which  arise  from  the  cerebral  ganglia,  and 
in  which  minute  ganglia  are  developed.  The  nerves  which 
proceed  from  the  buccal  ganglia  are  distributed  to  the 
odontophore  and  its  muscles. 

In  other  Odontophora,  the  two  cerebral  and  two  pedal 
ganglia,  with  their  commissures,  are  always  to  be  recog- 
nised ;  but  the  number  of  the  ganglia  which  represent  the 
parieto-splanchnic  system  may  be  increased,  and  the  anterior 
ganglia  of  this  system  may  attain  a  large  size,  and  may 

•  See  Lacaxe-Du\YAcr%,  ^  OT^jKn\%^\Xwi  4Ax\i«aUle.* 


THE  ODOXTTOPHOIU.  493 

come  into  close  relation  not  only  with  the  cerebral  bnt  with 
the  pedal  ganglia. 

In  Lymnceus  pcdustris*  for  example,  there  are  fiye  such 
ganglia  situated  close  to  the  cerebro-pedal  ring.  The  most 
anterior  of  these,  on  each  side,  is  nnited  with  both  the 
cerebral  and  the  pedal  ganglion  of  its  side ;  and  appears, 
indeed,  like  an  enlargement  npon  a  second  commissure 
between  those  two  ganglia.  The  ganglia  which  constitute 
the  second  pair  are  united,  in  front,  by  a  short  commissure, 
with  the  preceding;  and,  behind,  with  the  fifth  or  azjgos 
ganglion.  The  second  pair  of  ganglia  give  off  the  nerves 
to  the  right  and  left  sides  of  the  mantle  respectively. 

In  Limax,  and  apparently  in  the  terrestrial  PulmoruUa 
generally,  the  arrangement  is  essentially  the  same,  except 
that  all  the  ganglia  of  the  parieto-splanchnic  system  co- 
alesce into  one  mass ;  between  which  and  the  pedal  ganglia, 
the  aorta  passes. 

In  HalioiiStf  on  the  other  hand,  while  the  anterior  parieto- 
splanchnic  ganglia  are  situated  close  to  the  pedal  ganglia 
and  are  connected  with  them  and  with  the  cerebral  ganglia, 
in  such  a  manner  as  to  give  rise  to  an  apparent  second 
cerebro-pedal  commissure,  the  ganglia  which  represent  the 
second  pair  in  Lymnceus,  are  situated  at  the  base  of  the 
branchia)  and  are  united  by  a  long  commissure  with  one 
another,  and  also  with  the  anterior  parieto-splanchnic 
ganglia.  Of  the  latter  commissures,  that  from  the  left 
branchio-pallial  ganglion  goes  to  the  right  anterior  parieto- 
splanchnic  ganglion,  and  viee  versa. 

With  respect  to  the  position  of  the  cerebral  and  pedal 
ganglia  in  the  Odontophora,  the  commonest  arrangement  is 
that  in  which  the  cerebral  ganglia  are  supra-oesophageeal, 
and  are  connected  by  two  longer  or  shorter  commissures, 
on  each  side,  with  the  pedal  and  anterior  parieto-splanchnic 

*   Compare     Lacaze-Duthien,  ganglia  of  the   nervous  system 

« Du  systeme  nerveuz  des  Mol-  given    in    his    memoir    on    the 

lusques    gast^podes    pulmonis  otocjrsts.  (Ibid.) 

aquatiques  **  (*Arch.  de  Zoologie/  f  See   Lacase>I>athier8,    "  Snr 

1872),  and  the  numerous  figures  le  syst^e  nerveox  de  UalictldA" 
of  the  anrnngemeut  of  the  oerebnl 


4d4       THE  ANATOMY  OF  nrVEBTBBRATED  AKIMAIiS. 

ganglia,  both  of  which  are  infra-  or  po6t-0B8ophi^;8eaL  But 
in  many  cases  (most  Nudibranehicttd),  the  pedal  and  parieto- 
gplanchnic  ganglia  are  approximated  to  the  cerebral  gang^ 
(the  latter  being  snpra-cesophagaRal ),  and  are  united  bj  long 
sub-OBSophagseal  commissures.  In  others,  as  in  most  Plero* 
poda,  the  pedal  and  parieto-splanchnic  ganglia  are  sab- 
OBSophagBBal ;  while  the  cerebral  ganglia,  brought  close  to 
them,  are  united  by  a  supra-<Bsophag8Bal  commissure. 

Accessory  ganglia  are  frequently  developed  in  the  region 
of  the  heart  and  branchise,  on  tbe  nenres  of  the  parieto- 
splanchnic  system. 

A  complicated  system  of  visceral  nerves  is  distributed 
over  the  whole  length  of  the  alimentary  canal,  the  genital 
organs,  and  various  parts  of  the  vascular  system,  in  many 
Odantophora,* 

Two  auditory  vesicles  usually  exist,  and  very  generally 
appear  to  be  sessile  upon  the  pedal  ganglia.  In  the 
Heieropoday  in  many  Nudibranchi4ita,  as  shown  by  Hancock, 
and  in  numerous  genera  of  Branchuh  and  Pulmo^gcuieropoda^ 
which  have  been  carefully  examined  by  Lacaze-Duthiers^t 
however,  there  seems  to  be  no  doubt  that  the  auditoiy 
nerves  arise  from  the  cerebral  ganglia,  even  though  the 
vesicles  may  be  situated  close  to  the  pedal  ganglia. 

Olfactory  organs  certainly  exist  in  the  C^htUopoda  in 
the  form  of  saccular  involutions  of  the  integument  near  the 
eyes;  and  it  is  very  probable  that  the  integument  of  the 


*  See  especially  Hancock  and 
Embleton,  **The  Anatomy  of 
Doris"  (Phil.  Trans.,'  1852). 

t  *'  Otocystes  dea  Mollusques.** 

(*  Archives  de  Zoologie  Experi- 

mentale,'  1872.)    In  the  memoir 

the  origin  of  the  acoustic  nerves 

from  the  cerebral  ganglia  is  deter- 

mineil  in  so  many  Puhmopastero' 

poda  (Limaxj  Arkm^    TetiaceUoj 

CtausUicu  ZonkeMy  Helix,  Sucemea, 

PhytOy   LymnauSj  Aneyhu)  and 

Branc/uo^oMtercpoda,      {NerHinay 

jPalmdmay    Cffclodoma^    FUeopau^ 

Cafyptrtta,  i^otioa,  Nasta,TVochiM^ 


JIfvrer,  Casaidaria^  Pwrptaray 
Patdla,  Haiioiis,  Philme,  Af*fyua, 
LameUaria),  that  there  is  a  large 
basis  for  the  generalisation  that 
this  mode  of  origin  is  imivenal. 
Moreover,  aooording  to  Lacftse- 
Duthiers,  the  same  law  holds  good 
for  the  Cephalopoda,  Sach  being 
the  case,  the  question  suggests 
itself  whether  the  eonnexioo  of 
the  nerves  of  the  otoeysts  with 
the  pedal  ganglia,  which  obtains 
universally  among  the  Lamelli> 
branchs  indicates  their  real  or 
Qn^^  ^^DA^K  v^'\ax«ai  origin. 


THE  ODOirrOPHORA.  495 

tentacula,  or  of  the  lips,  maj  subBerve  the  same  function 
in  the  Gkuteropods. 

£  jee  are  generally  present,  and  are  limited  to  two,  situated 
in  the  head.  They  resemble  the  vertebrate  eye  in  stmctnre, 
so  far  as  they  possess  a  concave  retinal  expansion  and 
usually,  in  front  of  this,  a  vitreous  humour,  lens,  and  cornea. 
But  they  differ  from  the  eyes  of  Vertebrataj  and  resemble 
those  of  other  invertebrated  animals,  in  that  the  structures 
which  answer  to  the  rods  and  cones  are  situated  on  that 
face  of  the  retina  which  is  turned  towards  the  light,  while 
the  fibres  of  the  optic  nerve  traverse  the  pigment  layer  to 
reach  them. 

The  reproductive  organs  of  the  Odoniophora  present 
very  great  diversities  of  structure.  They  may  be  either 
dioecious  or  monoecious,  and  each  type  of  reproductive 
organs  may  present  various  degrees  of  complexity.  Of  the 
dioecious  reproductive  organs,  there  are  two  chief  forms; 
the  one  in  which  the  duct  of  the  ovarium  or  testis  is  con- 
tinuous with  the  gland ;  and  the  other  in  which  the  duct 
opens  into  a  sac,  into  which  the  ova  or  spermatozoa  are 
set  free  by  the  dehiscence  of  the  follicles  in  which  they 
are  developed.  The  latter  arrangement  is  met  with  in  the 
Cephalopoda ;  the  former  appears  to  prevail  among  all  the 
other  dioecious  Odoniophora. 

In  these,  the  racemose  generative  gland  is  usually  situated 
close  to  the  liver.  In  the  female,  the  oviduct  ordinarily 
presents  a  uterine  dilatation  towards  its  termination,  which 
is  generally  situated  in  the  pallial  cavity  on  the  right  side  of 
the  body.  In  some  rare  cases  (PahuLina,  Neritina),  a  dila- 
tation or  a  special  vesicular  api>endage  of  the  uterus  may 
serve  as  a  vesicula  aeminalis ;  and,  in  Paludina,  according 
to  Leydig,  an  albumen  gland  opens  into  it. 

A  penis  is  not  always  present.  When  it  exists,  it  is  a 
muscular  process  of  the  mesosoma,  to  which  the  semen  may 
be  led  from  the  opening  of  the  vas  deferens  by  a  groove ;  or 
it  may  be  traversed  by  the  vas  deferens  which  opens  near,  or 
at,  its  apex. 

In  all  the  moncecious  Odoniophora  which  Wi^  ^a^  '^^\. 


496       THB  ANATOMY  OV  INYBBTBBRATBD  AHIMALS. 

been  thoroughlj  examined,  there  is  a  generatiTe  gland 
termed  the  ovotesHs,  in  which  both  spermatozoa  and  o?a 
are  produced.  Only  in  the  anomalous  genua  Bhodepe, 
(Kolliker),  are  the  spermatozoa  and  ova  formed  in  distinet 
c»ca;  in  all  the  rest,  each  csBcum  is  hermaphrodite,  the 
spermatozoa  and  the  ova  being  usually  developed  in  dif- 
ferent parts  of  the  csdcum.  The  duct  of  the  OYotestia  may 
remain  single  to  its  termination  at  the  genital  aperture ;  or 
become  only  incompletely  divided  into  two  semicanala 
{Pteropoda,  Pleurophyllidia,  Umbrella,  Aplysia) ;  or  it  may 
become,  at  first,  partially,  and  then  completely,  divided  into 
an  oviduct  and  a  vas  deferens  (Nudibranchiaiaf  I^leuro* 
hranchiaf  Pulmonata). 

In  the  former  case,  there  is  but  one  genital  aperture.  The 
common  duct  usually  receives  the  secretion  of  a  uterine 
gland  which  may  take  the  form  of  a  special  albumen  gland* 
and  a  spermatheca  opens  into  it  near  its  outer  extremitj ; 
while,  on  the  male  side,  a  vesicula  seminalis,  and  an  eversible 
penis  may  be  added. — The  penis,  however,  may  be  distant 
from  the  genital  opemng,  and  then  a  groove  on  the  side  of 
the  body  leads  to  it  {Aplysia),  In  the  latter  case,  there  are 
two  genital  apertures,  one  for  the  male  and  one  for  the 
female  organs,  though  they  may  open  into  a  common  ves- 
tibule. The  penis  is  an  eversible  involution  of  the  integu- 
ment, on  which  the  vas  deferens  opens.  A  prostate  gland 
is  usually  connected  with  the  latter,  and,  near  its  opening, 
there  may  be  a  saccular  appendage,  in  which  a  hard  pointed 
body,  the  tpiculum  amoria,  is  contained  (Doris,  Helieida), 
An  albumen  gland  opens  into  the  uterus,  and  a  spermatheca 
is  connected  with  the  vagina. 

Spermatophores,  by  the  aid  of  which  the  spermatozoa  are 
transferred  into  the  female  organs,  occur  in  the  Cephalo- 
poda, and  in  the  Pulmonata.  In  the  latter  they  are  grooved 
bands,  or  incomplete  tubes  of  hardened  mucus  secreted  by 
the  penis,  which  become  fiHed  with  spermatozoa  during 
copulation ;  while,  in  the  former,  they  are  closed  cases  which 
may  have  a  very  complex  structure. 

Li  the  great  majority  of  the  Odoniophora,  the  young 


THS  DSTXLOPlCXirT  OF  THX  ODOVTOPHOR4.        497 

res  the  egg  as  a  veliger  reij  nxnilar  to  that  of  the 
mdlibranehiatci.  The  ▼eltun  usuallj  becomes  bilobed, 
I  aometiinee  (Heteropoda),  its  tnargins  are  produced  into 
aj  tentacnliform  processes;  and,  in  all  Pieropoda  and 
mehiog<uteropod(i^  whether  the  adnlt  possess  a  mantle 
i  a  shell  or  not,  the  larva  is  provided  with  both,  the  shell 
ig  at  first  a  simple  conical  symmetrical  cap,  developed 
the  middle  line  of  the  mantle.  The  eyes  make  their 
earance  behind  the  velnm,  and  the  tentacles  in  front 
or  upon  it. 

Hiile  the  course  of  the  development  of  the  embryo  in 
Odaniophora  presents  a  general  uniformity,  there  are 
e  differences  in  detail. 

a  PcUudina,*  the  blastomeres  produced  by  yelk  division 

of  equal  size.    They  arrange  themselves  into  a  vesicular 

Tila,  which  undergoes  invagination  and  becomes  a  gas- 

a  of  the  simplest  type.    Hie  aperture  of  invagination 

ttopore)  becomes  the  anus,  while  the  mouth  is  formed 

«  involution  of  the  ectoderm  of  the  anterior  end  of  the 

,  which  extends  towards  and  eventually  opens  into,  the 

end  of  the  archenteron  or  primitive  alimentary  sac. 

lated  velum  is  developed  on  the  hsemal  side  of  the 

I ;  and  a  '  shell  gland '  appears  in  the  centre  of  the 

hich  gives  rise  to  the  mantle. 

'^ymncBUStf  also,  cleavage  ends  in  the  production  of 

leres  of  equal  size,  whether  with  or  without  a  tran- 

tage  of  inequality,  and  the  vesicular  morula  under- 

Tagination  to  give  rise  to  the  archenteron.     The 

nre  is  elongated,  and  it  appears  to  be  likely  that 

ior  and  posterior  ends  may  coincide  with,  if  they 

ve  rise  to,  the  mouth  and  anus  respectively. 

t  OdorUophora,  the  process  of  yelk  division  goes  on 

,  and  results  in  the  production  of  large  and  small 

ter,  *'On  the  coinci-  the   development   of  the   Pond 

'he   bUstopore     and  Snail"    (^Qaarterly  Journal   of 

?ahidina     vivipara"  2dicro9Copical  Science,'  1874),  and 

Journal  of   Micro-  C.  Rabl,  **I>ie  Ontogenie  der  Siiss- 

see,'  1876.)  wasser  Pulmonatan"  ('Jen.  Zeit- 

r,  **  Ohaervationt  on  ichrifV  1875). 

2  K 


498       THS  AKATOHY  OF  INVEBTEBRATBD  AKIMAIJB. 

blastomeres  (macromeres  and  micromeree).  The  latter 
form  a  layer  which  graduallj  extends  over  the  macromeret 
and  encloses  them.  Ob^onslj  this  comes  to  the  aame 
result  as  invagination ;  and  the  included  macromeres  and 
their  progeny  either  become  converted  into  the  archenteron 
with  its  appendages,  and  more  or  less  of  the  mesoblast ;  or 
a  portion  of  them  may  serve  as  food  yelk. 

In  the  Pteropoda  and  Heteropoda*  and  in  Ncu9a,  NaUoa, 
and  Fu9U8,f  the  blastopore,  or  aperture  circumscribed  by 
the  edges  of  the  micromeral  layer  as  it  grows  round  the 
macromeres,  closes,  but  corresponds  in  position  to  the  in- 
vagination of  the  ectoderm  which  gives  rise  to  the  future 
mouth ;  and  the  anus  is  a  new  formation. 

In  such  land  PtUmonata  as  Idmax,  the  process  of  yelk 
division  gives  rise  to  macromeres  and  micromeres,  and  the 
latter  enclose  the  former.  What  becomes  of  the  blastopore 
is  not  clear,  though  I  am  inclined  to  think  that  it  conre* 
spends  in  position  with  the  mouth.  The  latter  is  seen  very 
early  as  a  funnel-shaped  invag^ination  of  the  epiblast 
bounded  by  lateral  lips.  Behind  it,  the  foot  grows  out  and 
rapidly  attains  a  considerable  size.  Its  posterior  extremity 
becomes  flattened  from  above  downwards,  and  converted 
into  an  orbicular  appendage,  the  opposite  walls  of  which 
are  connected  by  reticulated  muscle-cells.  This  appendage 
undergoes  rhythmical  movements  of  dilatation  and  contrac- 
tions. The  macromeres  form  a  large  mass  enclosed  within 
a  spheroidal  dilatation  of  the  greater  part  of  the  hsemal 
wall  of  the  body,  which  deserves  the  name  of  yelk-sac 
even  better  than  the  structure  so  named  in  the  Cephalopoda, 
inasmuch  as  it  more  nearly  corresponds,  morphologicaUy, 
with  the  vitelline  sac  of  vertebrated  animals.  Between  this 
sac  and  the  foot,  the  small  remainder  of  the  haemal  wall 
becomes  converted  into  the  mantle. 

The  walls  of  the  vitelline  sac  undergo  contractionB  which 

*  Fol,  **  Etudes  but  le  develop-  f  Bobretsky,   <'  Studien   liber 

pementdes  MollosqueB."  (*Arch.  dieembryonaie  Entwiokelungdar 

de  Zookwie  ezperimentale/  1875,  Gastropoden."  (*Ai«hiv iMikr. 

1876.)  Anat.,'  1876.) 


THB  DBYSLOPMBNT  OF  THX  ODONTOPROBA.    499 

sometimes,  but  not  always,  alternate  with  those  of  the  pedal 
appendage.  On  each  side  of  it  appears  the  "  primitive  kid- 
ney," consisting  of  a  cnrved  elongated  series  of  cells  within 
which  concretions  are  developed,  and  terminating  in  a  dnct 
which  opens  on  the  posterior  face  of  the  vitelline  sac,  «close 
to  the  mantle.  The  exact  mode  of  origin  of  the  alimentary 
canal  has  not  been  made  out ;  but,  in  any  case,  oidy  a  very 
small  portion  of  the  endodermal  cells  can  take  part  in  its 
formation,  and  the  archenteron  is,  at  first,  a  sac  which  nearly 
fills  the  small  projection  formed  by  the  rudimentary  mantle. 
The  oral  involution  of  the  ectoderm  gives  rise  to  the  odon- 
tophore,  and  extends  across  the  base  of  the  foot  to  open, 
eventually,  into  the  archenteron. 

The  fold  of  the  mantle  which  overhangs  the  ree^nratory 
aperture,  makes  its  appearance  very  early ;  and  immediately 
behind  it,  the  intestine  is  visible  as  a  short  tube,  which 
extends  from  the  archenteron  to  the  surface,  but  does  sot, 
at  first,  open  there. 

As  development  proceeds,  a  movement  of  the  macromerie 
part  of  the  vitellus  takes  place  in  exactly  the  opposite  direc- 
tion to  that  of  the  food  yelk  of  the  Cephalopoda ;  that  is  to 
say,  from  the  vitelline  sac  into  the  constantly  enlarging 
foot.  The  alimentary  canal  accompanies  it,  the  anus  alone 
remaining  in  its  primitive  position.  The  constantly 
lengthening  alimentary  canal  becomes  disposed  in  folds ; 
between  these,  the  macromeric  part  of  the  vitellus,  which 
gradually  forsakes  the  diminishing  \itelline  sac,  disposes 
itself  around  the  coils  of  the  intestine.  Eventually,  for  the 
most  part,  it  becomes  converted  into  the  liver. 

The  rudimentary  shell  first  makes  its  appearance  in  the 
form  of  a  few  subcrystalline  calcareous  plates,  on  the  inner 
side  of  the  ectoderm.* 

The  development  of  Helix  is  similar  to  that  of  Liinax ; 
but  the  intestine  passes  into  the  large  visceral  sac  instead 
of  into  the  cavity  of  the  mesosoma.  The  shell  is  stated  by 
Gegenbaur  to  be  at  first  internal,  as  in  Limax.    In  neither 

*  Compare  Gegenbaur,  **  Zar  Entirickelangtgeschichte  der  Land- 
Gasteropoden."    ('  ZeiUchrift  fijr  Wisi.  Zoologie,*  1^52.) 

2  K  2 


l 


1 


which  the  rudiments  of  the  tentacula 
while,  at  the  sides,  a  longitudinal  ri< 
of  the  mantle,  and  marks  off  the  mor 
from  the  flat  foot.     No  shell  is  forme 
In  Lymn<BU8,f  as  has  been  alrea( 
undergoes  complete  division,  and  t 
morula  undergoes  invagination  to  p 
Only  the  middle  part  of  the  archeni 
mentarj  canal,  however.    The  latera 
on  the  form  of  rounded  sacs,  maj  no 
Brachiopods,  give  rise  to  the  perii; 
this  has  not  been  proved.    The  mo\ 
formation  of  an  opening  in  the  cc 
ectoderm,  at  a  point  near  the  ant 
Upon  each  side  of  the  month  a  trai 
the  ectoderm  is  developed,  and  rej 
Telom  in  other  mollnscan  embryos, 
opposite  side  of  the  embryo  to  that 
1 1   '  placed,  a  raised  patch  of  the  ectoden 

The  foot  commences  as  a  papilla 
month.    An  involution  of  the  centr 
gives  rise  to  a  shell-gland,  but  the  j 
kidependently  of  this,  as  a  cutiou 


THK  POLYFI.^COPHOBA.  501 

the  Telnm  (onlesB  it  be  represented  by  the  ant«riaT  contnc* 
tile  sac)  nor  the  external  embryonic  shell. 

The  development  of  the  Cephalopoda  is  vtxy  nnlike  that 
of  other  HoUosks,  and  will  be  dealt  with  under  the  head 
of  that  gronp. 

Fig.  121. 


Fig.  131.— I.  CUbM  WufHaiMtkU.    (AfMr  U 

11.  ChitiM  diMeeted  to  show  o,  the  mauth  :  p,  the  nerrtnuniiB;  so.  me 

■oru;  c,  tha  Tcntrjela;  c',  %a  uirlde;  br,  tlialeft  bianohlB;  m^  the 

ovIducU.     (AttsT  Cuvier.) 
miV.  V.  StigMofddvelopnientof  C*i««»iMr«u.    (AfUrLoT^n.) 

The  lowest  forma  of  the  Odtmtophora  are  the  PolypUieo- 
phara,  or  ChUomda,  and  the  Beaphopoda,  or  DrntaUdce. 
The  bilateral  STnunetr;  of  the  body  is  completely  or  almost 
completely,  nndistorbed,  whjle  the  hsmal  wall  is  flat,  oe 
nearly  eo,  and  there  is  n      ' 


502       THE  ANATOMY  OF  INTBSTBBSATSD  AKHCALS. 

The  POLYPLACOPHOBA.— The  Chitons  (Fig,  121,  I.)  aie 
elongated,  sluglike  ajiimals,  having  the  month  at  one  end  of 
the  body,  and  the  anus  at  the  opposite  extremity.  A  ronnded 
lobesurmounts  the  mouth,  but  it  bears  no  eyes  nor  tentacola* 
and  there  is  no  definite  head.    The  edges  of  the  mantle  are 
thickened,  but  little  prominent,  so  that  the  pallial  cavity 
is  not  much  more  than  an  elongated  groove,  beneath,  and 
internal  to,  the  thickened  edge,  which  is  sometimes  beset 
with  setffi.    In  the  region  in  which  these  sets  occur,  the 
surface  of  the  mantle  is  covered  by  a  thick  cnticnla.    The 
setsB,  which  may  be  merely  chitinons  or  completely  calcified, 
or  partly  in  the  one  and  partly  in  the  other  condition,  are 
developed  in  sacs  lined  by  the  cells  of  the  ectoderm.*    In 
the  pallial  groove  lie  the  short  lamellar  processes  which  re- 
present the  branchifB.    The  shell  ia  unlike  that  of  any  other 
Mollusk.  It  consists  of  eight,  transversely  elongated,  symme- 
trical pieces,  arranged  one  behind  the  other,  overlapping  in 
such  a  manner  that  the  posterior  edge  of  the  one  covers  the 
anterior  edge  of  the  next,  and  articulated  together.     Some- 
times the  valves  are  partially  or  completely  enclosed  in  the 
mantle.    The  heart,  composed  of  a  single  median  ventricle 
and  two  lateral  auricles,  is  placed  in  the  middle  line,  above 
the  rectum,  at  the  posterior  end  of  the  body.    The  aorta 
is  continued  forwards  from  its  anterior  end,  while  the  anri- 
cles  receive  the  blood  from  the  branchise.    In  Chiion  pieeut, 
according  to  Schiff,t  each  auricle  communicates  by  two 
openings  with  the  ventricle,  and  the  two  auricles  are  united 
behind.    The  reproductive  organ  is  median  and  symme- 
trical, and  its  two  ducts  open  on  each  side  of,  and  not  far 
from,  the  anus. 

The  embryo  leaves  the  egg  as  an  oval  body,  surrounded 
near  its  anterior  end  by  a  circular  ciliated  band,  behind 
which  an  eye-spot  appears  on  each  side  (Fig.  121,  III.).  The 
segments  of  the  shell  appear  while  the  young  Chiion  is  still 
locomotive,  and  the  disk  in  front  of  the  ciliated  band 

*  Relncke,  <<  Beitiage  lar  Bil-      Mnschaftliehe  Zooloeie.') 
dnngigssehichte    der    ftUyaVv^Vu,         t  ^ZeitBehriftfurWiBsenchaft- 


THB  80APHOPODA.  503 

becomes  oonverted  into  the  lobe  above  the  mouth 
(Fig.  121,  lY.  v.).  The  Chitons  have  existed  from  the 
Silurian  epoch  to  the  present  day,  apparently  with  very 
little  modification. 

The  ScAPHOPODA.* — ^In  Dentaliwn,  the  shell  is  elongated, 
conical  and  curved,  like  an  elephant's  tusk,  with  the  apex 
broken  off,  and  it  is  open  at  both  ends.  The  animal  has 
a  large  mantle  corresponding  in  form  with  the  shell,  and 
also  open  at  both  ends,  the  margins  of  the  anterior,  larger, 
aperture  being  much  thickened.  The  mouth,  placed  at  the 
extremity  of  a  sort  of  cup,  the  margin  of  which  is  fringed 
with  papillse,  is  situated  far  behind  the  anterior  opening 
of  the  mantle.  Behind  the  oral  cup,  where  the  body  joins 
the  mantle,  is  a  transverse  muscular  ridge,  from  which  pro- 
ceed a  great  number  of  long  tentacles.  These  protrude 
through  the  anterior  opening  of  the  mantle,  and  play. the 
part  of  prehensile  organs.  Behind  and  below  the  oral  cup 
the  very  long  subcyHndrical  foot  proceeds.  Near  its  ex- 
tremity are  two  lateral  fleshy  lobes  which  perhaps  corre- 
spond with  the  epipodia  of  other  Mollusks.  The  oral  cup 
leads  into  a  buccal  chamber  containing  the  odontophore, 
-whence  the  oesophagus  passes  to  the  stomach.  The  liver 
consists  of  two  symmetrically-branched  divisions ;  and  the 
intestine,  after  becoming  coiled  upon  itself,  ends  in  a  pro- 
minent anal  papilla,  in  the  median  line,  behind  the  root  of 
the  foot.  There  is  no  heart,  but  the  blood  fills  spacious 
sinuses.  There  are  no  special  respiratory  organs  distinct 
from  the  wall  of  the  pallial  cavity.  The  two  renal  organs 
open  one  on  each  side  of  the  anus.  The  renal  blood 
sinos  communicates  directly  with  the  pallial  cavity  by 
two  apertures,  situated  close  to  those  of  the  renal  organs. 
In  the  nervous  system,  the  conmiissures  of  the  parieto- 
splanchnic  ganglia  pass  directly  to  the  cerebral  ganglia,  as 
in  the  Lamellibranchs.    The  sexes  are  distinct  and  the 

*  A  very  complete  and  acearate  toire  de  rorganisation,  da  dtfve« 

account  of   the  organisation  of  loppement,  des  mceon  et  des  rap- 

2/entaUuM  is  given  in  the  mono-  ports  loologiqaes  des  I>entalea^" 

graph  of  Lacaze-Duthiors,  **  Hitr  IS5^. 


504       THB  ANATOMY  OF  INTBBTEBIIATED  AKIMAIiS. 

genital  gland  is  single  and  symmetrical,  thongh  ita  duct 
opens  into  the  right  renal  organ.  The  embijo  is  at  fizst 
surrounded  by  a  number  of  ciliated  rings,  its  anterior  end 
presenting  a  toft  of  long  cilia.  By  degrees,  the  cilia 
become  restricted  to  the  edges  of  a  disk,  into  whicb  the 
anterior  end  of  the  embryo  expands,  and  which  represents 
the  prse-oral  ciliated  velnm  of  the  Lamellibrancha.  The 
mantle  now  appears  on  the  dorsal  aspect  of  the  bodj, 
behind  this  disk.  Its  ventral  edges  are  free,  and  it  secretes 
a  shelly  plate  of  corresponding  form.  But,  as  development 
advances,  the  edges  of  both  mantle  and  sheU  unite  in  the 
median  ventral  line,  leaving  the  anterior  and  the  posterior 
ends  open. 

The  Scaphopoda  are  an  ancient  group,  remains  of  them 
occurring  as  far  back  as  the  Devonian  Epoch. 

The  higher  Odontophora  (or  the  Chsteropada,  Pteropoda^ 
and  Cephalopoda  of  Cuvier)  fall  into  two  divisions,  according 
to  the  structure  and  arrangement  of  the  parts  of  the  foot. 
In  the  one  division  (the  Gasteropoda  and  Pteropoda)  it  maj 
be  a  simple  disk,  or  it  may  be  divided  into  three  portions — 
an  anterior  (the  propodivm),  a  middle  (the  megopodiwm), 
and  a  posterior  (the  metapodiwm) ;  and  it  may  be  still  further 
complicated  by  the  development  from  its  sides  of  muscular 
expansions — the  epipodia.  But  whatever  the  shape  of  the 
foot  in  these  Mollusks,  its  margins  are  not  produced  into 
prehensile  processes,  and  its  antero-lateral  portions  do  not 
extend  beyond  the  sides  of  the  head,  and  imite  in  front  of 
the  mouth. 

In  the  other  division  (the  Cephalopoda),  the  margins  of 
the  foot  are  produced  into  prehensile  processes  or  arms,  and 
the  antero-lateral  regions  of  the  foot  extend  over,  and 
unite  in  front  of,  the  mouth,  in  such  a  manner  that  the 
latter  is  placed  in  the  centre  of  the  disooidal  foot.* 

*  See  for  a  valuable  discusdon  fiMtorily,    controverted,     Gren- 

ofthehomologiesoftheariDiaiid  aoher,   **Zar    Entwiokelnns^e- 

the  Amnel  of  the  C^)halopoda^  in  schichte     der     Cephalopoden." 

nUoh  tiM  view  h«re  taken  U  C  ZeitMhrift  fOr  WIm.  Zookwie.' 


THE  GASTEBOPODA  AH]>  PTSBOPODA.  505 

In  the  former  division,  tliat  is  in  all  Pterapoda,  in  all 
those  Cfaaieropoda  which  breathe  the  air  dissolved  in  water 
Branehiogcuteropoda),  and  in  some  of  those  which  breathe 
ur  directlj  (Ftdmogcuieropoda)  the  embryo  is,  as  in  the 
Scaphopoda  and  Polyplaeophoraf  a  veliger ;  or,  at  any  rate, 
it  has  ciliated  bands  which  subserve  locomotion.  Bnt,  in 
the  Cephalopoda^  no  such  velum  is  formed,  and  the  animal 
acquires  the  general  characters  of  the  adult  before  leaving 
the  egg. 

A  shell-gland  is  often,  if  not  always,  present  in  the  embryo 
of  the  higher  Odontophora ;  and,  in  all  Pteropods  and  Bran- 
chiogasteropods,  the  mantle  secretes  a  cuticular  shell,  which, 
however,  may  exist  only  during  the  larval  condition. 

If  the  arrangement  of  the  alimentary  canal  in  a 
Gephalopod,  or  a  Pteropod,  be  compared  with  that  which 
obtains  in  such  a  Branchio-gasteropod  as  Atlanta,  it  will 
be  observed  that,  in  the  former,  the  oesophagus  enters  the 
outgrowth  of  the  haemal  region  of  the  body  which  con- 
stitutes the  visceral  sac,  to  reach  the  stomach ;  and  that  the 
intestine  passes,  at  an  acute  angle  with  the  anterior  portion 
of  the  alimentary  canal,  along  the  posterior  face  of  the 
visceral  sac,  to  end  in  the  pallial  chamber,  which  is  situated 
on  the  posterior  face  of  the  body.  The  pedal  ganglia  con- 
sequently lie  between  lines  traversing  the  anterior  and  the 
posterior  divisions  of  the  alimentary  canal  respectively;  and 
hence  the  alimentary  canal  has  a  neural  flexurey  or  is  bent 
towards  the  neural  face  of  the  body. 

In  Atlanta,  on  the  other  hand,  the  intestine,  when  it  leaves 
the  stomach,  x>a8se8  along  the  anterior  face  of  the  visceral 
sac,  to  reach  the  pallial  cavity,  which  is  situated  on  the 
anterior  face  of  the  body.  Hence  lines  traversing  the  two 
divisions  of  the  alimentary  canal  would  enclose,  not  the 
pedal,  but  the  cerebral  ganglia.  In  other  words,  the  in- 
testine is  bent  in  the  opposite  direction  to  that  which  it 
takes  in  the  Gephalopod,  or  has  a  hcBmal  flexure* 

The  hsemal  flexure  of  the  intestine  is  very  characteristic 

*  Huxiev  '<  On  the  Morphology  of  the  Cephalous  MoUosoa."  <^I^\V. 


506       THE  AKATOHY  OF  nTTBBTBBRATBD  AKHCAXS. 

of  the  Branehiogcaieropoda,  and  is  completed  at  an  eazij 
stage  of  their  deyelopment. 

In  such  a  slightly  modified  Odontophoran  as  ChUon,  the 
heart  presents  its  normal  position  in  the  posterior  r^on 
of  the  hsemal  face  of  the  body,  and  has  its  aortic  end 
turned  forwards.  Although  the  branchiaa  are  situated  at  the 
sides  of  the  body,  the  blood  which  passes  through  them 
must  take  a  backward  course  to  reach  the  heart ;  and  thus 
the  branchise  may  be  said  to  be  virtually  behind  the  heart ; 
and  the  animal  is  truly  opisthohranchiaie.  It  appears  to 
be  otherwise  with  such  a  Gasteropod  as  Buccinwn^  in 
which  the  gills  lie  actually  in  front  of  the  heart ;  and  the 
animal  is  therefore  said  to  be  prosobranchiaie.  It  must  be 
recollected,  however,  that  strictly  speaking,  no  Odonto- 
phoran is  other  than  opisthobranchiate.  The  anns  repre* 
sents  the  morphological  hinder  end  of  the  body,  and  the 
auricle  of  the  heart,  into  which  the  current  of  blood  from 
the  branchisB  passes^  is  never,  morphologically,  posterior  to 
the  branchiae. 

This  is  perfectly  obvious  in  the  Cephalopoda.  In  the 
position  which  the  animal  frequently  assumes  and  in  which 
it  is  ordinarily  represented,  the  gills  are  in  front  of  the 
heart.  But  if  the  Mollusk  is  placed  in  its  morphologioally 
correct  position  with  the  oral  face  of  the  arms  downwards, 
it  will  at  once  be  seen  that  what  is  commonly  called  the 
ventral  face  of  the  animal  is  the  posterior  half  of  its  hsemal 
face,  and  that  the  heart  lies,  morphologically,  anterior  to 
the  branchiffi. 

In  such  Branchiogasteropods  as  are  proeobranchiate,  the 
giUs  come  to  lie  in  front  of  the  heart  in  consequence  of 
their  having  followed  the  twisted  intestine  forwards  and  to 
the  hsBmal  side  of  the  body. 

The  Ptiropoda.* — In  this  group  of  small  pelagic  n-niTwalfl 
there  is  no  distinct  head,  the  eyes  and  the  ordinary  tentacles 

*  See  Bang  and  Soulevet,  *  His-      <  Untenuchungen  uber  die  Ptero- 
loire   natiirelle  det   Mollusques      poden  und  Ueteropoden/  1855. 
Pitfrqpodes;*    and    QegenWox, 


THB  PTEBOPOBA. 


507 


remaining  mdimentary.  Anditory  sacs  are  attaolied  to  the 
pedal  ganglia.  Sometimes  {Pnewnodermon)  two  eversible 
spinoee  tentacular  organs  are  developed  at  the  sides  of  the 
month,  and,  in  addition,  two  acetabnliferons  tentacles  take 
their  origin  on  the  inner  side  of  a  cnp-like  hood,  which 
surrounds  the  anterior  end  of  the  body.*  Cymibulia  is  stated 
to  possess  no  radula.  The  epipodia  are  large  muscular  ex- 
X>ansion8,  bj  the  flapping  of  which  the  Pteropods  swim; 
but  the  rest  of  the  foot  is  always  small,  and  often  rudi- 
mentary, in  correspondence  with  the  small  size  of  the 
neural  face  of  the  body. 

The  haemal  face,  on  the  contrary,  is  always  produced,  as 
in  the  Cephalopoda,  into  a  relatively  large  visceral  sac; 
and  in  some  (the  Thecosomata)  this  visceral  sac  is  co-exten- 
sive with  the  mantle,  which  is  protected  by  a  shelL  In 
others  {GymnosoTruUa)  the  mantle  early  disappears,  and  there 
is  no  shelL  In  Cymbulia,  the  delicate  transparent  chitinous 
shell  is  internal  and  is  invested  by  an  epithelial  layer 
derived  from  the  mantle.  In  Spinalis,  the  foot  bears  an 
operculum.  Chromatophores  similar  to  those  of  the  Ce- 
phalopoda occur  in  THedemannia. 

In  the  Thecosomata,  the  free  lobe  of  the  mantle,  which 
encloses  a  spacious  x>allial  cavity,  usually  lies  on  the  posterior 
aspect  of  the  visceral  sac,  as  in  the  Cephalopoda,  and  the 
rectum  terminates  in  it,  on  one  side  of  the  middle  line. 
In  these  there  is  a  simple  neural  flexure  of  the  alimentary 
canal,  as  in  the  Cephalopods,  although  the  turning  of  the 
rectum  to  one  side  destroys  the  symmetry  of  the  body.  In 
Limacina  and  Spirialis,  the  intestine  appears  to  be  bent 
round  to  the  anterior  face  of  the  visceral  sac,  the  mantle- 
cavity  accompanying  it,  so  that  the  opening  of  the  mantle 
is  placed  on  the  anterior,  instead  of  on  the  posterior,  face 
of  the  visceral  sac.  There  are  no  distinct  gills  in  the 
Thecosomata,  but  the  lining  of  the  mantle-cavity  subserves 


*  See  for  the  somewhat  similar 
arrangements  in  C/ibN«,  Cschricht, 
*  Anatomische  Untersuchungen 
iiber  CUtmt  bonaUs,*  1858,  and 


Maedonaid,  "On  the  Zoological 
characters  of  the  living  Clvf  cau- 
data:  (*  Trans.  Royal  Society  q£ 


I 


508       THE  ANATOMY  OF  IITVISBTSBBATBD  AKOCAIiS. 

the  fnnction  of  reepiration,  and  is  sometimeB  prodnced  into 
folds,  wliich  doabtless  aid  in  the  performance  of  that  fnnc- 
tion. Processes  of  the  body,  to  which  the  office  of  gills  is 
ascribed,  are  fonnd  in  some  Chfmnosomaia  {PneMmodemum 
Spongobranchia) . 

The  heart  consists  of  a  single  anricle  and  a  single  Ten- 
tricle.  The  anricle  lies  close  to  the  pallial  cayity,  and  re- 
ceiyes  the  aerated  blood  from  its  walls.  The  yentride  is 
sometimes  directed  forwards  (as  in  all  Gymnoswnaia),  and 
sometimes  backwards,  so  that  nearly  related  foims  axe 
sometimes  opisthobranchiate,  sometimes  prosobranchiate. 
The  branches  of  the  aortic  trunk  soon  terminate  in  lacunae, 
by  which  the  blood  is  conyeyed  back  to  the  waHs  of  the 
mantle-cayity.  The  renal  organ  is  a  contractile  sac  with 
delicate  walls,  which  opens  on  one  side  into  the  pallial 
chamber,  and  on  the  other  into  the  pericardial  sinus. 

The  Theeosomaia  haye  the  principal  ganglia  concentrated 
aronnd  the  gollet — the  cerebiul  ganglia  being  lateral  and 
united  by  a  long  commissure. 

In  the  Oymnosomata  the  ganglia  are  more  scattered,  bat 
the  arrangement  of  their  neryous  system  needs  re-exami- 
nation. 

All  the  Fteropoda  are  provided  with  an  ovoUHU.  This  is 
a  racemose  gland,  in  the  ultimate  cseca  of  which  both  oya 
and  spermatozoa  are  developed.  The  spermatozoa  make 
their  appearance  at  the  closed  end  of  the  caecum  and  accumu- 
late in  its  cayity ;  the  oya  are  deyeloped  from  the  epithelial 
tissue  of  the  c»cum,  somewhat  lower  down;  neyertheless 
fecundation  does  not  take  place  in  the  oyotestis,  probably 
in  consequence  of  the  oya  and  spermatozoa  attaining 
maturity  at  different  times.  The  oyotestis  has  a  single 
excretory  duct,  the  termination  of  which  may  be  proyided 
with  a  receptaculum  seminis  and  connected  with  a  penis. 

The  young  of  the  Pteropoda  leave  the  egg  proyided  with 
a  yelum,  with  a  rudimentary  shell,  and  probably  with  an 
operculum.  In  most  of  the  Thecosomaia,  the  shell  is  re- 
tained and  forms  the  commencement  of  that  of  the  adult, 
while  the  yda  diBapi^eBx  «3A  V2i[i<^  ^^\v^A^  «ac%  deyeloped. 


THB  BIULHCHIOGASTSBOPODA.  509 

In  CynibvlM,  the  primary  external  shell  is  shed  and  the 
chitinouB  internal  shell  is  a  secondary  development.  In 
the  Qymno9omaia,  the  primary  shell  is  also  cast  off,  but 
is  not  replaced,  and  three  girdles  of  cilia  are  developed  on 
the  surface  of  the  body.* 

The  Silurian  genera  TentacuUtes,  Theca,  Pteroiheea,  Conit- 
laria,  Ecculiamphalua  are  referred  to  the  Ptercpoda,  but 
they  differ  much  from  all  existing  foims.  Unqnestionable 
Pteropoda  are  not  known  earlier  than  the  tertiary  formations. 

The  Bbancriogastebopoda. — In  all  the  members  of 
this  gronp,  the  development  of  which  has  hitherto  been 
studied,  the  intestine  becomes  twisted  round  on  to  the 
anterior  face  of  the  body,  in  such  a  manner  that  the 
alimentary  canal  has  a  completely  luemal  flexure,  even  in 
the  veligerous  embryo.  Hence,  in  the  adult,  the  intestine 
springs  from  the  hsemal  or  dorsal,  and  not  from  the  ventral 
or  neural,  aspect  of  the  stomach;  and  the  pallial  cavity, 
when  it  exists,  is  placed  upon  the  anterior  haemal  face  of 
the  body. 

In  the  embryo,  the  shell  always  makes  its  appearance  as 
a  conical,  symmetrical,  median  cap.  This  embryonic  shell 
usually  persists  at  the  apex  of  that  of  the  adult,  the  form 
of  which  is  modelled  upon  that  of  the  visceral  sac,  and 
hence,  like  the  latter,  is  usually  spiral.  The  embryo  is 
also  very  generally,  if  not  universally,  provided  willi  an 
operculum. 

The  shell  and  operculum  of  the  embryo  disappear  in  the 
naked  Branchiogasteropods ;  but  the  primitive  external 
shell  is  sometimes  replaced  by  an  internal  shell  lodged  in  a 
cavity  of  the  mantle  (e.g.  Aplyaia).  Usually,  the  Branchio- 
gasteropods possess  a  distinct  head  provided  with  a  pair  of 
tentacles  and  with  two  eyes,  which  may  either  be  sessile  or 
mounted  upon  peduncles  of  their  own. 

*  Gegenbaur,  /.  c.  j  Krohn,  Tleteropoden,"  1860;  and  Fol, 
"  Beitrage  lur  Entwickelangs-  **  Etudes."  O  Archives  de  ZooL 
geschichte  der  Pteropoden  und      Experimentsle^'  1%7^  «sisi  V^^>^ 


510       THE  ANATOMY  OF  INYEBTEBBATEB  AKOCAL8. 

The  mouth  may  be  armed  with  chitmouB  jaw-plateB,  in 
addition  to  the  radula.  The  heart  is  genen^j  composed 
of  a  ventricle  and  a  single  auricle,  but  sometimeB  there 
are  two  auricles. 

The  Branchiogasteropoda  fall  into  two  distinct  aeries,  of 
which  the  one  is  hermaphrodite  (the  genital  gland  being 
an  ovotestis)  and  invariably  opisthobranchiate ;  while  the 
other  is  unisexual  and  usually  prosobranchiate.  In  each 
series,  there  are  some  forms  which  are  provided  with  a  large 
mantle;  and  others,  in  which  the  mantle  is  altogether 
abortive  {Nudibranchiata,  Firola),  These  chlamydate  and 
achlanvydate  Branchiogasteropods  correspond  with  the 
Theco8<miata  and  fiymnosomata  among  the  Pteropods. 

The  chlamydate  Branchiogasteropods  are  usually  pro- 
vided with  branchisB,  which  either  take  the  form  of 
numeroTis  lamellse,  or  of  two  plume-like  organs,  sometimes 
reduced  to  one  functional  gill  and  a  rudiment  of  the 
second.  In  the  achlamydate  forms,  true  gills  are  usually 
absent,  though  they  may  be  replaced  functionally  by 
processes  of  the  haemal  body- wall. 

Among  the  Qpidhobranchiata,  Phyllidia  is  nearly  symme- 
trical, the  anus  being  situated  at  the  posterior  end  of  the 
body,  and  there  is  a  large  mantle,  devoid  of  a  shell.  There 
is  no  pallial  cavity,  and  the  branchiae  are  numerous  lamellsCt 
placed  on  each  side  of  the  body,  between  the  free  edge  of 
the  mantle  and  the  foot.  In  Aplysia,  the  mantle  is  rela- 
tively small,  and  possesses  an  internal  shell ;  the  branchiae, 
the  anus,  and  the  reproductive  apertures  are  placed  on 
the  right  side  of  the  body.  In  this  genus,  and  in  OoHero^ 
pteron,  there  are  very  large  epipodial  lobes,  by  the  aid  of 
which  some  species  propel  themselves  like  Pteropods. 

The  Nudibranchiata  have  no  mantle,  and  the  anus  is 
usually  situated  on  the  right  side  of  the  body ;  sometimes, 
however,  as  in  Doris,  it  is  terminal.  In  the  pelagic  Phylli- 
rhoe,  the  foot  aborts,  as  well  as  the  mantle,  and  the  body 
has  the  form  of  an  elongated  sac. 

The  gastric  portion  ol  \2iEi<^  v^imentBry  canal  becomes 


THE  PBOSOBSANCHIA.TA.  511 

complicated  bj  division  into  seyeral  portions,  some  of  which 
are  provided  with  chitinous  or  calcareous  plates,  or  teeth, 
in  Aplysia,  BuUa,  and  other  genera.  In  manj  Nndibranchs, 
as  Eolis,  the  liver  is  represented  by  a  much-branched  tubular 
organ,  the  csecal  ultimate  ramifications  of  which  end  in  the 
elongated  dorsal  papillsB,  The  apices  of  these  papillse 
contain  thread  cells. 

In  the  series  of  the  Proaohranchiata,  the  great  minority 
are  not  only  chlamydate,  but  there  is  a  spacious  branchial 
chamber,  and  the  pallial  wall  of  the  body  is  produced  into  a 
conical  visceral  sac,  which  contains  the  stomach,  liver,  and 
genital  organs.  It  is  usually  asymmetrically  <y>iled,  and  is 
protected  by  the  shell  No  Opisthobranch  possesses  a 
large  visceral  sac  of  this  kind.  On  the  other  hand,  no 
Prosobranch  is,  like  Thyllidia,  symmetrical,  with  the  anus 
at  the  posterior  end  of  the  body.  PaiteUa  and  Fissurella 
are  nearly  symmetrical,  but  the  anus  is  anterior. 

The  Tro8obr(mchiata  have,  at  most,  rudiments  of  q^podia, 
but  the  rest  of  the  foot  often  acquires  a  much  greater 
development  than  in  the  Opisthohranchiata,  and  a  chitinous 
or  shelly  plate — the  operculum — is  frequently  developed 
from  the  dorsal  or  hsBmal  aspect  of  the  metapodium.  The 
differentiation  of  the  foot  attains  its  highest  degree  in  the 
so-called  Heteropoda,  in  which  the  propodium,  mesopodium, 
and  metapodium  differ  widely  in  form, — ^the  propodium 
being  broad  and  fin-like,  and  constituting  the  chief  organ 
of  locomotion  in  these  free-swimming  oceanic  animals. 

In  the  Limpets  (Patellidai),  the  visceral  sac  forms  merely 
a  conical  projection  of  the  hflemal  surface,  and  the  numerous 
lamellar,  or  fiilamentous,  respiratory  organs,  are  lodged 
between  the  free  edges  of  the  mantle  and  the  sides  of  the 
body.  In  the  other  chlamydate  Frosobrcmehiata,  except  the 
Oyclostomaia,  there  are  two  plumose  gills  lodged  in  a  pallial 
chamber  situated  on  the  anterior  face  of  the  visceral  mass, 
which  is  usually  large  and  spirally  coUed.    Qofm^^ixs^^^^'^s^ 


512       THE  ANATOMY  OF  mYSBTEBKATBD  AKIMAIiS. 

in  the  diyision  of  the  Aspidohranehia,  the  two  branchiae  are 
equal  or  nearly  equal  in  size.  Sometimes  one  is  so  much 
smaller  than  tiie  other  as  to  be  nearly  abortiye  (Otono- 
branekia).  Am^Uaria  has  a  pnlmonarj  cayity  as  well  as 
gills.  On  the  other  hand,  the  CycloBtomakL  hare  no 
branchisB,  but  breathe  air  by  means  of  the  parietes  of  the 
pallial  chamber,  whence  they  are  ordinarily  reckoned 
among  the  Puhnonata,  which  they  resemble  in  their 
terrestrial  habits.  In  many  Prosobranchiata,  the  wall  of 
the  branchial  chamber  is  produced  into  a  muscular  spoat- 
like  prolongation,  termed  the  siphon,  which  serres  to  direct 
the  branchial  current.  The  presence  of  this  siphon  is 
usually  accompanied  by  a  notch  or  grooved  process  of 
the  shell,  and  by  carnivorous  habits. 

In  the  Heteropoda,  there  is  a  gradual  reduction  of  the 
mantle,  from  Atlanta,  in  which  the  mantle  and  shell  have  the 
ordinary  proportions,  and  the  departure  from  the  ordinazy 
Gasteropod  type  is  but  little  greater  than  that  observed  in 
Strombus  and  Pteroceras,  through  Carinaria,  in  which  the 
mantle  is  much  reduced,  and  the  shell  is  a  mere  conical 
cap,  to  Firola,  in  which  the  mantle  and  shell  are  wanting 
in  the  adult,  and  which,  therefore,  correspond  with  the 
achlamydate  Pteropoda  and  Opigthobranchiata, 

In  many  genera  of  the  Cienobranchia,  and  especially 
among  the  carnivorous  forms,  the  mouth  is  situated  at  the 
end  of  a  long  proboscis,  which  contains  the  odontophore, 
and  a  great  part  of  the  long  oesophagus.  This  proboecis 
is  protruded  and  retracted  by  special  muscles.* 

The  eggs  are  often  laid  in  capsules  secreted  by  the  walls 
of  the  oviduct.  In  NeriUna,  Purpura,  and  Buecinwni,  each 
capsule  contains  a  considerable  number  of  ova,  but  of  these 
only  a  few  (one  in  Neritina)  become  embryos,  and  devour 
the  rest.f 

*  See   the   description  of  the  na  littoralis  Norvegis,'  11.  1856), 

proboscis  of  the  Whelk  in  Cuvier's  and  Carpenter  "  On  the  develop* 

*  Me'moires  sur  lea  Mollasques.'  ment  or  the  embryo  of  PWrom 

t    Koren     and     Daniellssen,  lapillui "  (Trans.  Mior.   Roaety, 

**  Kecherches  sur   le  dcveloppe-  1854,  and  *  Annals  of  Nat.  Bitt^' 

ment  dc9  Pectimbruichtft**  (^^saxir  \^^*l^.  C\».\«xMe^  **Anatoiiiie  vnd 


THE  PULMONATA.  513 

The  parasitic  Habit  whicH  is  so  rare  among  tlie  Mollusca 
occurs  in  the  genus  Stylifer,  which  infests  Star-fishes  and 
Sea-urchins,  sometimes  imbedding  itself  in  the  perisoma ; 
and,  under  a  very  remarkable  and  not  yet  thoroughly  under- 
stood form,  in  the  singular  parasite  of  another  Echinoderm, 
Synapta  digiiaia^  termed  by  its  discoverer,  Miiller,  EntO" 
concha  mirabilis* 

In  some  few  of  the  SynaptcB  (not  more  than  one,  or 
perhaps  two,  in  a  hundred),  elongated  tubular  moUushigerous 
sacB  are  found  attached  by  one  extremity  to  one  of  the 
intestinal  vessels;  while  the  opposite  end  either  hangs 
freely  into  the  perivisceral  cavity,  or  may  be  entangled 
among  the  bases  of  the  tentacles,  at  the  cephalic  extremity 
of  the  body  of  the  Synapta.  The  sac  is  closed,  but,  at  its 
attached  end,  a  long  invagination  extends  into  its  interior. 
The  cavity  of  the  sac  beyond  the  closed  extremity  of  the 
invagination  contains  an  ovaiy ;  and,  beyond  this,  a  certain 
number  of  free  seminal  capsules.  The  ova  are  detached  from 
the  ovary,  and  undergo  their  development  in  envelopes, 
each  containing  many  ova,  which  gradually  fill  the  cavity 
of  the  molluskigerous  sac.  From  these  ova,  embryos,  pro- 
vided with  a  velum,  shell,  and  operculum  proceed.  A  large 
pallial  cavity  is  soon  apparent ;  but,  in  the  most  advanced 
stages  of  development  observed,  it  contained  no  bran- 
chifiB. 

What  becomes  of  these  larvsB  is  unknown,  nor  is  it  even 
certain  to  what  group  of  the  Odomtophoray  Enioconcha 
belongs. 

The  PuLMONATA. — These  are  odontophorous  MoUusks 
which  breathe  air  directly,  by  means  of  a  respiratory 
surface  furnished  by  the  wall  of  the  pallial  cavity. 

In  some,  such  as  the  Peroniadce  (Pig.  123)  and  Veroni- 
cellidijB,  the  body  of  the  slug-like  animal  is  very  nearly 


Fntwickelangtgeschichte        der  ken  in  Holothurien,'  1852.   Baur, 

yerUinafluviatUu:*  (*Archiv  fur  **  Ueber        Symgirta        dUgUata^ 

Anatomie,' 1857.)  (•Nova  Acta,*  xxxl.  \8ftV^ 
*  ^IHeEneagungvonScbneo- 


514       THB  ANATOMY  OV  IKYEBTEBBATBD  ANIMALS. 

symmetrical;  the  anus  and  tlie  lung-sac  being  eitiiated 
close  together  at  the  posterior  extremity  of  the  body.  The 
mantle  is  large,  and  extends  oyer  the  whole  liyBtn^l  or 
dorsal  surface.  In  all  the  other  PvInunuUat  the  pnbnonary 
and  the  anal  apertures  lie  on  the  right  side  of  the  body, 
and  the  mantle  is  provided  with  at  least  the  rudiments  of 
a  shell.  The  pallial  region  is  sometimes  very  small  in  pro- 
portion to  the  rest  of  the  body,  and  then  forms  a  flattened 
disk,  as  in  the  common  Slug ;  while,  in  some  lAmaddcB  and 
Testacellidce,  and  in  the  JaneUidcB,  the  mantle  is  so  much  re- 
duced that  they  are  almost  achlamydate.  In  the  Snails,  the 
mantle  is  large  and  is  produced  into  an  asymmetrically 
coiled  visceral  sac,  in  which  the  stomach,  liver,  and  genital 
gland  lie.  The  mantle-cavity  lies  on  the  fore  part  of  the 
sac,  and  the  anus  opens  on  its  margin.  Thus,  in  all  the 
ordinary  Pulmonata,  the  termination  of  the  intestine  is 
twisted  from  its  normal  position  at  the  hinder  end,  forwards 
to  the  right  dorsal,  or  hsemal,  aspect  of  the  body. 

When  the  pulmonary  sac  is  posterior,  and  the  pallial  re- 
gion small,  the  ventricle  of  the  heart  is  anterior,  and  the 
auricle  posterior,  and  the  animal  may  be  said  to  be  opigtko- 
pulmoncUe,  On  the  other  hand,  when  the  pallial  region  is 
large,  and  gives  rise  to  a  visceral  sac,  with  the  concomitant 
forward  position  of  the  pulmonary  chamber,  the  auricle  is 
inclined  more  or  less  forwards  and  to  the  right  side,  and 
the  apex  of  the  ventricle  backwards  and  to  the  left  side. 
The  animal  is  thus  more  or  less  prosoptUmonate, 

The  mouth  is  commonly  provided  with  a  homy  upper 
jaw,  as  well  as  with  a  well-developed  odontophore.  Large 
salivary  glands  are  usually  present. 

The  heart  consists  of  a  single  auricle  and  a  single  ven- 
tricle. The  aortic  trunk,  which  proceeds  from  the  apex 
of  the  latter,  divides  into  many  branches,  but  the  venous 
channels  are  altogether  lacunar.  A  renal  organ  lies  close 
to  the  pulmonary  sac  in  the  course  of  the  current  of  the 
returning  blood. 

There  are  usually  two  simple  eyes,  often  lodged  in  the 
jsnmmitfi  o£  TetRy(^tAl<&  Y^nW^o^au 


THB  FOUIONA.TA,  515 

The  PulmotMta  are  hermaplirodite.    The  generative  gland 
Fig.  IIS. 


Fig.  12i.— Diagram  nblbitlng  the  dispoiltion  of  theintMtine,  Derront 
»3»tem,  etc.,  In  a  cominoa  Sii^l  (Btliey—a,  mouth;  b.  tnoth;  c, 
iHionttn)hor« ;  d.  gullet;  c,  iti  dilatation  Into  a  aort  of  crop;  /, 
■tomaoh;  y,  coiled  termination  of  the  viicaral  mala:  the  latter  it 
alao  cloM  to  Iht  commeocement  of  Ihe  Intettine,  whlob  will  be  teen 
to  lie  on  the  neural  aide  of  Ihe  teaopbasui;  A,  t«cCudi  ;  t,  anna;  f, 
lanal  aao;  (  heart;  ii,  lung,  or  miidifieil  pallial  chamber;  n,  Iti 
Wteraal  aperture;  a,  thick  edge  of  the  mantle  united  with  the 
^dea  of  the  biid; ;  t>,  foot;  r.i,  cerebral,  pedal,  and  parieto-eplanchnia 
gaoglia  aggregated  round  the  gullet. 

is  an  oTotMtu,  and  is  compooed  ot  VmatnAtnSL  tc&K£a^^x<sI^ 


516       THE  ANATOMY  OF  INYEBTEBRATED  ANIMAIiS. 

the  cellular  contents  of  wliicli  both  ova  and  spermatoBoa 
are  developed  (Fig.  123,  III.). 

A  narrow  common  duct  leads  from  the  ovotestiB,  and, 
soon  dilating,  receives  the  viscid  secretion  of  a  large 
albumen  gland.  The  much  wider  portion  of  the  common 
duct  beyond  the  attachment  of  this  gland  is  incompletelj 
divided  by  longitudinal  infoldings  into  a  sacculated,  wider, 
and  a  straight,  narrower,  division.  The  former  conveys  the 
ova,  and  the  latter  the  spermatozoa.  At  the  end  of  this 
part  of  the  apparatus,  the  wider  portion,  which  represents 
the  oviduct,  passes  into  the  vagina,  which  opens  at  the 
female  genital  aperture,  while  the  narrower  portion  of  t^e 
common  duct  is  continued  into  a  separate,  narrow,  vas  de- 
ferens, the  end  of  which  opens  into  a  long  invagination  of 
the  integument — the  penis.  In  Peronia,  the  vas  deferens 
and  the  oviduct  open  together  by  the  genital  aperture,  and, 
as  in  some  Bi*anchiogasteropods,  a  groove,  along  which  the 
seminal  fluid  is  conducted,  leads  to  the  outer  opening  of  the 
eversible  penis  (Fig.  123, 1.  II.). 

In  connexion  with  the  female  genital  aperture,  there 
is  always  a  spermatheca,  or  sac  (which  is  sessile  in  the 
Slugs,  but  in  the  Snails  is  placed  at  the  extremity  of  a  long 
duct)  for  the  reception  of  the  semen  of  the  other  individual 
when  copulation  takes  place. 

The  Helicidce  alone  possess,  in  addition,  the  so-called  sac 
of  the  dart,  a  short  muscular  bag,  in  which  pointed  chiti- 
nous  or  calcified  bodies — the  spictUa  amoris — are  formed; 
and  certain  glandular  ca3ca,  generally  arranged  in  two 
digitate  bundles,  termed  mucovs  glands,  which  give  rise  to  a 
milky  secretion.  Sometimes,  progiatic  glands  are  developed 
on  the  vas  defei*ens,  which  may  be  dilated  in  part  of  its 
course  into  a  vesicula  seminalis. 

The  ova  are  impregnated  high  up  in  the  oviduct,  and  are 
invested  by  a  relatively  very  large  mass  of  albumen  and 
enclosed  within  a  thick,  sometimes  calcified  chorion.  The 
mass  enclosed  by  the  latter  may  be  a  tenth  of  an  inch  or 
more  in  diameter,  while  the  proper  ovum  may  haTe  not  m<nre 
than  a  twelfth  of  that  size. 


THE  PULMONATA. 


617 


There  is  no  tmstwortlij  evidence  of  the  existence  of  the 
opisthobranchiate  Grasteropods  before  the  epoch  of  the  Trias, 
but  it  is  to  be  remembered  that  the  great  majority  of  these 
animals  have  no  shells.  Of  the  rest  of  the  preceding  groups 
of  Odontophora,  representatiyes  are  known  as  far  back  as 
the  middle  of  the  Palseozoic  epoch,  while  Pterapoda,  HeterO' 

Fig.  128. 


Fig.  12). — I.  Peronia  verruculata, — a,  anus;/)/,  pulmonary  aperture; 
gy  genital  aperture ;  /«.  seminal  groove ;  /i,  opening  for  toe  penis. 

II.  Generative  or»:ans  of  tbe  same  animal,  the  ovotestis  being  omitted. 
gal^  gland  which  furnishes  a  glaixy  secretion ;  o</,  oviduct ;  vd^  vas 
deferens;  i,  intestine;  a,  anus;  r«,  receptaculum  seminis;  /»,  aper- 
ture of  the  penis ;  p\  penis ;  c«,  seminal  duct ;  ap.  glandular  appen- 
dage; m,  retractor  muscle  of  the  penis.    (After  Keferstein.) 

III.  Blind  end  of  a  follicle  of  the  ovotestis  of  Uetix  pomatia.  At  the 
apex  the  spermatozoa  are  seen  in  different  stages  of  development, 
the  fully  formed  spermatozoa  floaUng  in  bundles  in  the  cavity  of  the 
follicle.  Lower  down,  ova  are  developing  in  the  walls  of  the  follicle. 
(Alter  Keferstein  and  £hlers.) 

poda^  and  Prosobranchiata  occur  in  the  Silurian  formations. 
Among  the  Prosobranchiata,  the  PateUidcR  and  the  Aspido- 
branchia  are  the  characteristic  forms  of  the  older  f oi-mations, 


8 


THE  CEPHALOPODA.  519 

however,  is  not  flat,  as  in  tlie  moUosks  whicli  Have  just  been 
mentioned,  but  is  elongated  perpendicnlarlj  to  the  neura 
face,  so  as  to  form  a  sort  of  sac,  invested  by  the  mantle.    On 
the  posterior,  or  anal,  face  of  the  sac,  the  mantle  enclose 
a  large  pallial  cavity,  in  which  the  branchisB  are  pro- 
tected.   On  the  anterior  aspect  of  the  sac,  on  the  contrary 
the  mantle  may  have  no  free  edge,  or,  at  most,  forms  a 
comparatively  small  flap.* 

The  integument  is  provided  with  ehromcdophores,  which 
are  sacs  with  elastic  walls,  full  of  pigment,  and  provided 
with  radiating  muscles,  by  which  they  may  be  ditbwn  out 
to  a  size  many  times  greater  than  that  which  they  possess 
in  their  contracted  state.  In  their  dilated  condition,  the 
colour  proper  to  the  contained  pigment  becomes  plainly 
visible,  while  in  their  contracted  state  they  appear  as  mere 
dark  specks.  It  is  to  the  successive  expansion  and  con- 
traction of  these  chromatophores  that  the  Cephalopoda 
owe  the  peculiar  play  of  "  shot "  colours,  which  pass  like 
blushes  over  their  surface  in  the  living  state.  These 
blushes  of  colour  are  especially  well  displayed  by  young 
Cephalopods  just  freed  from  the  egg. 

But  that  which  particularly  distinguishes  the  Cephalo- 
pods, is  the  form  and  disposition  of  the  foot.  The  margins 
of  this  organ  are,  in  fact,  produced  into  eight  or  more 
processes  termed  arms,  or  brachia ;  and  its  antero-lateral 
portions  have  grown  over  and  united  in  front  of  the 
mouth,  which  thus  comes,  apparently,  to  be  placed  in  the 
centre  of  the  pedal  disk.  Moreover,  two  muscular  lobes 
which  correspond  with  the  epipodia  of  the  Pteropods  and 
Branchiogasteropods,  developed  from  the  sides  of  the  foot, 
unite  posteriorly,  and,  folding  over,  give  rise  to  a  more  or 
less  completely  tubular  organ — the  funnel,  or  infundibuluvi. 
The  open  end  of  the  funnel  projects  between  the  posterior 
face  of  the  body  and  the  pallial  wall  of  the  branchial 
cavity,  and  serves  to  conduct  the  water,  when  it  is  driven 

*  Cephalopoda  are  usually  de-  ber  is  placed  ventral— a  method 

scribed  as  if  the  oral  end  of  the  which  seriously  interferes  with, 

body  were  the  upper  end,  and  the  the  QomYi^«iv%\Q!tk  oS.  x^€vt  x^^*- 

lace  on  which  tie  pallial  cham-  Uoitt  wV\^  oV2k^x  VU^>&9ia&« 


520       THE  AKATOHT  Or  IHV2BTEBSATKD  ASIXAI^. 

out  of  the  latter  by  the  contraction  of  tbe  ansntte  in 
Fig.  1S5. 


Pig.  iaS.-I>l»K™inni»l!c  >eotlon  of  a  ftmale  Srpja.—a,  BacMil  nun 
(urroundMl  by  the  lips,  md  showing  ihe  homj'  ja»<  «tid  ton(iie ;  *, 
asophagua;  r;  Balivary  gluid;  i',  atoinmch;  r,  pyloric  CKCum;  f, 
thelnteiliae;  A,tlie>nui;  i,themk-bag;  *.ihe  fJiceof  thetyatooio 
hwul;  /,  Ihe  liver;  n,  Ihe  hepalio  duct  of  (he  letl  »id«;  o,theov«ry; 
p,  the  oviduct ;  o,  ont  of  the  »perlure«  by  which  the  w»ter-cl»nib«i» 
■re  placed  In  cummunicatloD  with  the  exterior ;  r,  one  of  tlic  biu- 
chiK;  (,  the  principal  gingUa  BggreKsted  round  the  ce>opb*giu;/, 
the  funnel ;  n,  the  mantle ;  lA,  the  internal  (hell,  or  outlle-bone.  I, 
a,  3,  4,  5,  the  produced  and  tnodifled  nmrgina  of  (b>  foot,  oonitital- 
ing  UMfo-««Vled  umiof  the  Srpia. 
ordinary  expuaUon-,  Miiit^isttftiftMiimji.wi.-'oa.'floa'Awaai 


THB  CEPHALOPODA.  521 

forcibly  driven  out  in  this  way  causes  it  to  dart  swiftly 
backwards. 

The  aperture  of  the  mouth  (Fig.  125,  a)  is  provided  with  a 
hard  chitinous  bea]^,  like  that  of  a  parrot,  the  two  divisions 
of  which  are  anterior  and  posterior.  Of  these,  the  anterior 
is  always  the  shorter,  and  is  overlapped  by  the  other. 

Within  the  cavity  of  the  mouth  is  an  odontophore,  with 
its  radula  (Fig.  126,  II.) ;  and  the  long  gullet  passes  back 
on  the  middle  line  to  open  into  the  stomach,  which  is 
situated  towards  the  middle,  or  the  end,  of  the  mantle-sac. 
From  the  stomach,  the  intestine,  more  or  less  bent  upon 
itself,  passes  towards  the  neural  aspect  of  the  body,  and 
ends  in  the  median  anus.  Hence  the  alimentary  canal 
has  a  well-marked  neural  flexure  (Fig.  125). 

Except  in  NatiHlus,  one  or  two  pairs  of  salivaiy  glands 
are  present  (Fig.  126,  I.  sf).  The  liver  (Fig.  126,  I.  h)  is 
always  large;  and  there  are  two  hepatic  ducts  (Fig.  126, 
I.  dh)f  beset  for  a  greater  or  less  extent  with  glandular 
follicles,  generally  considered  to  be  pancreatic  in  function. 
Very  often  a  large,  sometimes  spirally  wound,  csecum  is 
developed  from  the  commencement  of  the  intestine;  into 
this  the  hepatic  ducts  open. 

The  heart  (Fig.  127,  c)  is  placed  upon  the  posterior  face  of 
the  body  on  the  hsemal  side  of  the  intestine,  and  receives 
the  blood  by  bi*anchio-cardiac  vessels,  which  correspond  in 
number  with  the  gills ;  and,  as  they  are  contractile,  might 
be  regarded  as  auricles.  The  gills  themselves  have  no  cilia, 
and  are,  in  some  cases,  if  not  always,  contractile.  The 
arteries  end  in  an  extensively  developed  capillary  system, 
but  the  venous  channels  retain  to  a  greater  or  less 
extent  the  character  of  sinuses.*  The  venous  blood,  on 
its  way  back  to  the  heart,  is  gathered  into  a  large 
longitudinal  sinus  —  the  vena  cava  —  which  lies  on  the 
posterior  face  of  the  body,  close  to  the  anterior  wall  of 
the  branchial  chamber,  and  divides  into  as  many  afferent 

*  Mihie-Edwards, '  Rechercbei      et  experiences  sur  la  ClrouUtioa 
Anatomiqaes     et      Zoologiques.       chez  lea  Moliusques/  1845. 
Premie  parde.*    '  ObeervationB 


522       THE  ANATOMY  OF  INYEBTSBSATBD  AHUCAXS. 


branchial  vessels  as  there  are  gills.  Each  of  these  yessels 
traverses  a  chamber  which  communicates  directlj  with  the 
mantle-cavitj,  and  the  wall  of  the  vessel  which  comes  into 
contact  with  the  water  in  this  chamber  is  sacculated  and 
glandular  *  (Fig.  127,  re).  Each  chamber,  in  fact,  represents 
a  renal  organ.  The  pericardiom,  and  the  sacs  in  which  the 
teates  and  ovaria  are  lodged,  may  communicate  with  the 
pallial  cavity  either  directly  or  through  these  chambers. 
Thus  in  Sepia  officinalis^  Krohnt  observed  that  the  renal 
chambers  communicate  not  only  with  the  cavities  in  which 
the  branchial  hearts  are  lodged,  but  with  a  chamber  which 
contains  the  stomach  and  the  spiral  pyloric  appendages; 
and  that  all  these  cavities  are  distended  when  air  is  blown 
into  one  renal  chamber.  In  EledonCf  on  the  contrary,  he 
found,  and  I  have  repeated  the  observation,  that  one  renal 
chamber  can  be  fully  distended  without  the  air  passing 
into  the  other. 

In  Nautihis  pompilitis,  there  are,  as  Valenciennes  dis- 
covered, three  pairs  of  openings,  which  lead  from  the 
branchial  sac  into  chambers  contained  in  the  interior  of 
the  body.  Of  these  chambers  there  are  five;  the  anterior 
and  posterior  pairs  are  situated  on  each  side  of  the  rectum, 
and  each  has  its  own  opening ;  the  fifth,  a  very  much  larger 


*  On  account  of  the  trans- 
parency of  the  tissues  in  the 
living  Loligo  media,  this  species 
affords  an  easy  opportunity  of 
observing  the  rhythmical  con- 
tractions of  the  branchiff!  and 
their  afferent  and  efferent  vessels. 
For  this  purpose  the  mantle 
should  be  laid  open,  and  the  nidi- 
mental  glands  carefully  removed. 
The  sacculated  afferent  veins  and 
the  branchial  hearts  contract 
about  sixty  times  a  minute. 
The  pulsations  of  these  veins 
and  of  the  branchial  hearts  are 
not  synchronous.  The  branchial 
veins  and  the  lamellae  of  the 
branchite  also  contract  rhythmi- 
cally, but  1  could  observe  no  con- 
traction in  the  bTaTicV\\a\ix\«n«%. 


The  portion  of  the  branchial  vein 
which  lies  between  the  base  of 
the  gill  and  the  systemic  ventricle 
is  very  short,  and  it  is  hard  to 
say  whether  it  contracts  iode- 
pendently  or  not  Mechanical 
irritation  causes  contraction  both 
of  the  afferent  branchial  veins 
and  of  the  branchial  hearts. 

In  the  living  Eledone  eirrhosus, 
I  liave  olMerved  regular  rhythmi- 
cal contractions  of  the  vena  eava 
itself  as  well  as  of  its  divisions, 
tiie  sacculated  afferent  branchial 
Tcins,  of  the  branchial  hearts  and 
of  the  branchiocardiac  vessels. 

t  "Ueber  die  wasserfnhrende 
System  einiger  Cephalopoden." 
('  Archiv  fur  Anatomic/  1839.) 


TSB  CSFB&LOPODA. 


chamber,  has  two  openings,  one  on  each.  side.     It  is  co- 
eiteneive  with  that  part  of  the  jnanUe  which  lies  behind 


Fig.  \iS.—Seuii  officnuilii.—l.  The  >limflDtU7  ud>I  witb  the  ink  big; 
lab,  buccal  moH ;  gb.  Inferior  buccal  guiglion ;  ^,  poiterior  wliTaty 
gland*;  k,  o.'9'>phagU9 ;  h,  liver)  dh,  hepitlo  duct;  p,  ftomach;  v', 
pj'lariu  cKcum;  i,  tuieiline;  a,  auu>;  Bi,  ink  bag;  ^ap,  tplancbnlo 
rauglioa  od  Ihe  lUimach.    (jVfler  Kefentnn.) 

U.  Longitudinal  >nd  vertical  leodou  throu|;h  the  buccal  maaai  vtri, 
poateri'ir  beak ;  mn,  anteiiorbeak;mic,  buccal  membrane;  n',llp;  c, 
gmtMoTj  (?)  oriian ;  rd,  radula :   i,  uc  af  the  radula ;  i',  nXinzy 

fUnd  ;  gl,  luperior  buccal  ganglia.     (After  Kefenlein.) 
A  tingle  traaiTsne  row  ot  teeth  from  the  radula  (after  Troaohel). 

the  uuertion  at  the  shell  mnaclee  and  the  homy  band  which 
cosneote  them.    It  is  separatcid  Ixoni  tii^a  '^aAxe&.  ^OBiO^wsni 


524     THB  &NATOUT  or  iiivbbtbbka.txd  andcaia 

by  their  iimer  walls,  and  tbese  walk  are  traveraed  by  the 
afferent  branchial  Teina.  Appendagea  of  these  Teina  pro- 
ject on  the  one  hand  into  the  paired  ch&mben,  and  on  the 
Other  into  the  single  chamber.  The  latt«r  appendogoB  an 
elongated  papillte,  while  the  former  are  lamellar-  Etu^j 
concretions,  composed  m&inl;  of  phosphate  of  lune,  bat 
which  field  no  trace  of  oric  acid,  are  nsaallf  found  in  the 

Fig.  H7. 


Fig.  liT.—  S^ia  o^imtiii.—c,  ijatemlo  hekti ;  on,  anlerior  anrlB, 
uo',  pmteiior  (orto;  l,ven>  ckva;  "_  iffrifnt  hraiirhl»1  i  iiwiU,  n, 
reul  oigsni ;  i,  apuendBges  of  these  Traseli ;  9,  4,  \mxm  poeuiior 
veiulbrlngingblcwdlo  t)ieftaerentbniicbiBlveHel9;.\6,T,  eSWcnt 
bnnchlal  veiieli,  brsnchisl  veiiia,uid  braochio-euilikcarBturioulM 
tninkt.    (AAer  UuntCT.) 


The  nervous  system  in  the  Cephaiopoda,  as  in  other 
Mollatea,  consiat«  of  cerebral,  pedal,  and  parieto-splanchnic 
ganglia,  aggregated  around  the  gullet,  and  connected  by 

■Owen,     'Memoir    on     tha  poioU      in     llie     anttomjr     of 

Pau-ly      Kmtilui."        V«n     dir  Navtiha  poKpilut"     (Proeced- 

Eloeven,     "  B*itr«(t     lut     An»-  ingi    of  the    LianMn     Saelcl7, 

Uimle  vom    A'aiiliJiu  pompilita"  IS^B).       8m      tlto      KefenteiB, 

i'Arohlr    fur    'NMUTMcaleht*,'  Bronu'i  ■KUsmd  n.  OrdnuDgai,' 

«:>.        Uuxl«;,       *0«i    wnM  W.\i.lJ.*»r^VTO>13!»0,  1819. 


THE  CEPHALOPODA.  525 

commisBTiral  cords.  In  addition  to  these,  buccal,  yisceral, 
branchial,  and  pallial  ganglia  may  be  developed  on  the 
nerves  which  sapplj  the  buccal  mass,  the  alimentary  canal, 
heart,  branchise,  and  mantle. 

In  the  Dihranchiata  (Fig.  128),  the  three  principal  pairs 
of  ganglia  are  usually  large,  and  so  closely  aggr^ated 
together  that  the  commissures  are  not  readily  distinguish- 
able. The  optic  nerves  are  very  large ;  one  or  two  nerves 
are  given  off  to  the  superior  or  anterior  buccal  ganglia, 
which  have  coalesced  into  one  mass,  and  are  united  by  com- 
missures, which  encircle  the  oesophagus,  with  the  coalesced 
inferior  or  posterior  buccal  ganglia.  The  pedal  ganglia 
lie  on  the  posterior  side  of  the  gullet,  and  supply  the  large 
nerves  to  the  arms,  and  those  to  the  funnel,  while  the  auditory 
nerves  are  immediately  connected  with  them.  Each  parieto- 
splanchnic  ganglion  gives  off  a  nerve  which  runs  along  the 
shell-muscles  to  the  anterior  wall  of  the  mantle,  and  there 
enters  a  large  ganglion,  the  ganglion  gteUcttwn,  A  large 
median  branch,  or  branches,  from  the  parieto-splanchnic 
ganglia,  accompanies  the  vena  cava,  and  is  distributed  to 
the  branchise  and  sexual  organs.  The  inferior  buccal  gan- 
glion sends  a  recurrent  nerve  along  the  oesophagus,  which 
ends  in  a  ganglion  on  the  stomach.* 

The  nervous  system  of  NatUilus  differs  in  some  important 
particulars  from  that  of  the  Dibranchiata.  The  cerebral 
ganglia  are  represented  by  a  thick  transverse  cord,  which 
lies  in  front  of  the  oesophagus,  and  from  the  outer  angles  of 
which  the  optic  and  olfactory  nerves  are  given  off,  while 
nerves  to  the  buccal  mass  proceed  from  its  anterior  edge. 
The  pedal  ganglia  lie  close  to  the  cerebral  ganglia,  and 
are  tmited  by  a  slender  commissure,  which  passes  behind  the 
gullet.  They  supply  all  the  brachial  processes  and  the 
funnel  with  nerves,  and  the  short  auditory  nerves  are  con- 
nected with  them.  The  parieto-splanchnic  ganglia  are,  like 
the  cerebral  ganglia,  elongated,  and  together  constitute  a 
thick  cord,  which,  tmited  at  each  end  with  the  cerebral  gan- 

*  8e«  Hancock,   *'  Anatomy  of  the   nervoas  fjTBtem  of  Ommasin'' 
phet."     (<  Ann.  ^mt  Hiitory/  1852.) 


526       THE  AN1.TOHT  OrjIlIVEBTEBEATXD  AIIIIUL8. 

glia,  forms  a  hoop  roond  the  gnllet,  distiiict  from  the  pedal 
nerre-arch,  and  separated  from  it  bj  a  proceas  of  tlie  caitUa> 
ginons  skeleton.  The  largeet  nerree  giren.  off  from  theH 
ganglia  are  those  which  go  to  the  hi^nchise. 

Ejea,  olfactory  org&na,  and  auditor;  Baca  are  ^w^a 
present.  The  ejea  of  the  Cephalopoda  ma;  beloved  in  orbitel 
canttea  at  the  sides  of  the  head,  as  ia  all  the  Dibranehiala : 
or  ma;  be  pednncnlated,  aa  in  Nautiba.  In  the  former 
usae,  the  eje  is  enclosed  partly  b;  the  cephalic  cartilage,  to 

Pig.  128. 


tig.  IBS.— 5910  qffai%alu.~The  narrodi  miM  ohiob  mnonnds  th* 
gnlUt ;  N,  Ihe  rerebrmi;  N',  tba  pedal;  N",  Uir.  parielo-splknchnic, 
ganglion  ;  w.  the  aorta :  or.  the  trsophiiga* ;  a',  buccal  nervaa  ;  P*, 
narrea  to  the  anui;  U.nalllal  nerrai;  g,  luperior;  y',  iafcrloc 
boocal  ganglion.    (AJIer  Garner.)* 

which  sometimes  special  orbital  cartilages  are  added,  and 
parti;  b;  a  fibrous  capsole  continaoos  with  these.  The 
fibrons  capsule  becomes  tranaparent  otbt  the  eye,  ajid  givea 
rise  to  what  is  variotiBl;  interpreted  aa  the  representatiTO 
of  the  cornea,  or  as  that  of  the  e;elidH  of  vertebrated 
animals.  This  tmisparent  coat  is  Bometimea  entire,  or 
presents  onl;  a  small  perforation  (Octopui,  Septa,  LoKgo, 
and  the  other  Myopsidte  of  D'Orbign;)  ^  sometimea  it  has  a 
*  Ttana.  'Unxxwa^oiMq ,  ISaS. 


THB  CEPHALOPODA.  527 

wide  opening,  throngli  which  the  cxTstalline  lens  may  pro- 
ject (Loligophes,  Ommastrepsis  and  the  other  Oigopsidce  of 
D'Orbigny);  and  Bometimes  it  is  altogether  absent,  and 
the  capsule  of  the  eye  becomes  an  open  cnp  (Nautikui), 

In  the  DihranchicUa,*  a  great  part  of  the  chamber  of  the 
capsule  of  the  eye  is  occupied  by  the  ganglion,  into  which 
the  optic  nerve  enlarges  after  entering  it ;  by  muscles ;  and 
by  a  peculiar  white  glandular  substance.  Lining  the  capsule, 
but  not  adhering  to  its  inner  surface,  in  front,  is  the  silvery 
tapetum^  formed  of  two  layers.  These  pass  into  one  another 
at  the  edges  of  the  free  prolongation  of  the  tapetum,  which 
forms  the  iris.  Longitudinal  muscular  fibres  are  interposed 
between  the  two  layers  of  the  tapetum.  Under  the  tapetum 
is  a  layer  of  cartilage,  which  forms  the  inner  eapnUe  of  the 
eye,  extends  as  far  as  the  iris  externally,  and  is  perforated 
by  the  fibres  of  the  optic  nerve  on  its  inner  side.  The 
free  edge  of  the  inner  capsule  gives  attachment  to  a  thick 
rim  of  connective  tissue,  containing  muscular  fibres.  This 
so-called  ciliary  body  enters  the  deep  groove  which  sur- 
rounds the  lens ;  the  latter  is,  in  fact,  made  up  of  layers  of 
structureless  membrane,  which  are  cuticular  productions 
of  the  ciliaiy  body.  In  shape,  the  lens  is  elongated  in  the 
direction  of  the  axis  of  the  eye,  so  as  to  be  almost  a  cylinder 
with  convex  ends,  and  thus,  with  its  deep  equatorial  groove, 
into  which  the  ciliary  body  fits,  it  has  a  wonderful  resem- 
blance to  a  Coddington  lens.  The  vitreous  humour  is  a 
transparent  fluid.  The  retina  lines  the  inner  capsule,  and 
may  be  divided  into  an  outer  and  an  inner  stratum,  separated 
by  a  pigment  layer.  The  inner  stratum  is  formed  of  pris- 
matic or  cylindrical  rods,  the  outer  ends  of  which  abut 
upon  the  pigment,  while  their  inner  ends,  turned  towards 
the  cavity  of  the  eye,  are  covered  by  a  thick  hyaloid  mem- 
brane. The  outer  stratum  contains  the  plexus  of  the  fibres 
of  the  optic  nerves,  and  numerous  cells  (ganglionic),  sup- 
ported by  connective  tissue.  The  terminations  of  the  nerves 
therefore  must  traverse  the  pigment  layer  to  reach  the  rods. 

*  See  Hensen,  *'  Ueber  d>B  Ange  einiger  Cephslopoden."    Q  Zeit- 
schrift  f&r  WissenMilisltUelM  Zootogle,'  1865.) 


528       THE  ANATOMY  OF  INYEBTEBBATED  ANIMALS. 

It  will  be  observed  that  tbe  apparent  reeemblanceB  be- 
tween tbe  cephalopodons  and  tbe  vertebrate  eye  are  merely 
guperficial,  and  disappear  on  detailed  comparison. 

In  Nautilus^  tbe  eye  bas  neitber  cornea,  lens,  nor  TitreonB 
bumonr,  bnt  is  a  mere  cnp,  lined  by  tbe  retina.  Tbe  aper- 
ture for  tbe  admission  of  ligbt  is  exceedingly  small. 

Tbe  olfactory  organs,  tbe  true  nature  of  wbicb  was 
discovered  by  Kolliker,*  are  sometimes  pits,  sometimes 
papilla  of  tbe  integument,  situated  bebind  or  above  tbe 
eyes.  In  tbe  Teuthidce  and  SepiadcB  tbey  are  depreesions 
above  tbe  eyes ;  in  tbe  Octopoday  tbey  are  eitber  depressions 
or  papilla)  {Argonauta  and  Tremoctopus)  in  tbe  same  position, 
but  nearer  tbe  anterior  face  of  tbe  body.  In  NauHhu, 
tbey  are  elongated,  tentaculif  orm,  and  situated  immediately 
bebind  tbe  eyes. 

In  tbe  Dibranchiata,  tbe  auditory  sacs  are  lodged  in 
cavities  of  tbe  cepbalic  cartilage,  and  contain  a  single  large 
otolitb,  composed  of  carbonate  of  lime,  and  of  rounded  or 
irregular,  but  definite  and  cbaracteristic  form.  In  Nautihu, 
Dr.  Macdonald  discovered  tbat  tbe  auditory  sacs  areattacbed 
to  tbe  pedal  ganglia,  and  are  not  lodged  in  tbe  cranial  car- 
tilage.   Tbey  contain  numerous  otolitbs. 

An  endoskeleton  formed  of  true  cartilage  is  developed  in 
tbe  region  of  tbe  principal  ganglia,  and  sometimes  fumisbes 
tbem  witb  a  complete  investment.  It  gives  attacbment  to 
tbe  most  important  muscles.  In  some  Cepbalopods  addi- 
tional cartilages  appear  in  tbe  mantle  and  in  tbe  fnnneL 
Tbe  muscular  fibres  of  tbe   C^halopoda  are  imstriated. 

Tbe  sexes  are  distinct,  and  tbe  reproductive  organs  are 
unlike  tbose  of  otber  Mollusks.  Tbey  consist,  in  botb  sexes, 
(Fig.  129)  of  lamellar  or  brancbed  organs,  tbe  cellular  con- 
tents of  wbicb  are  mctamorpbosed  into  ova  or  spermatozoa, 
and  wbicb  are  attacbed  to  one  point  or  line  of  tbe  wall  of 
a  cbamber,  wbicb  communicates  v^tb  tbe  pallial  cavity  by 
two  symmetrically  disposed  oviducts,  in  tbe  females  of  some 
species ;  but,  in  most  female  and  almost  all  male,  Oepbalo- 

-*  '  Fintw\oke\ung^g2e&OQ\c\i\ft  d«t  Ce^halopoden,*  1841,  p.  107. 


THB  CKPHAI.OPODA.  629 

pods  *  it  liaa  onlj  one  duot,  the  temunfttion  of  whicli  is 
UBiiallj  eittUited  on  the  left  side,  Imt  may  be  se*r  the  middle 
line  (male  Nautiltu),  or  even  on  the  right  side  (femde  Ifau- 
ahu).  In  the  female,  the  ovidact,  or  ondDcta,  present 
glandular  enlai^emente.  In  addition,  two  la-wlla-T-  nida- 
mmital  gland*  are  dereloped  upon  the  walls  id  the  ImtnchiaL 
cavity,  and  to  theee  aceeeserj  glands  may  be  added.  These 
Fig.  139. 


Fig.  ti9.—Sipia  offiemaHt.—  i.  nale  OTgaiu,!, 
n,  valcots  Kiiiln>Jii ;  pr,  pnwiat* ;  Aq*,  n 
phom  1  ji,  penii  with  the  gcniUI  ■pertqre.     (After  DoTerDOji.) 


r..j 


glands  secrete  a  viscid  fliud,  which  inrests  the  ova,  and 
connects  them,  when  laid,  into  varionaly  shaped  aggrega- 
tionH.  In  the  male,  a  prostatic  gland  furnishes  the  material 
of  the  cases,  or  tpermaiophoTei,  in  which  packets  of  s| 


880      THE  AKATOmr  OF  lyVBKTEBBATgP  AITIMALS. 


tozoa  are  contamed,  and  wBicH  sometimes  possess  a  rery 
complicated  structure. 

In  the  Dibranchiata,  tbe  spermatop&ores  are  slender 
ejlindrical  bodies  wiiicH  may  reacli  half  an  incli  in  length. 
They  have  an  external  structur^ess  case,  thinner  at  one 
end  than  the  other,  and  often  ending  in  a  fine  filament  at 
^e-  thin  end.  Within  this  case,  filling  its  thicker  end, 
and  as  much  as  half  or  two-thirds  of  the  rest  of  its  cavity, 
is  a  delicate  sac  full  of  spermatozoa* 

The  rest  of  the  case  is  occupied  by  a  very  singolar  elastic 
body,  in  form  somewhat  resembling  the  sponge  of  a  gon 
with  a  spiral  screw  turned  on  the  handle.  The  enlarged 
'  sponge'  end  of  this  body  iis  fastened  by  a  d^cate  pro* 
longation  to  the  spermatic  sac,  while  the  '  handle^*  being 
too  long  to  lie  straight,  is  coiled  up  at  the  end  opposite 
to  the  sponge  and  then  fastened  to  the  outer  case.  When 
these  bodies  come  into  contact  with  water  they  nndergo 
strange  contortions,  and  finally,  the  thin  eud  of  the  case 
giving  way,  the  spring  frees  itself,  starts  out  of  the  case 
and  drags  with  it  the  spermatic  sac.* 

In  NauHlue,  according  to  Yan  der  Hoeven,  the  spermato- 
phores  have  a  much  simpler  structure. 

Th&  male  Cephalopods  are  distinguished  from  the  females 
by  the  asymmetry  of  their  arms,  one  or  more  of  which,,  on 
one  side,  are  peculiarly  modified,  or  heetocotylised. 

Some  Cephalopods  are  devoid  of  any  shell,  but  most 
possess  a  pallial  shell,  which  iis  either  external  or  intemaL 
In  the  former  case,  the  visceral  sac  is  lodged  within  that  part 
of  the  cavity  of  the  shell  which  lies  nearest  its  open  end,  and 
the  rest  of  the  cavity  iis  divided  into  chambers,  which 
contain  air,  by  transverse  sepia.  The  septa  are  perforated, 
and  a  prolongation  of  the  mantle — the  siphuncle — is  con- 
tinued through  the  series  of  perforations,  as  far  as  the 
apical  chamber  of  the  shell.     The  internal  sheUs  of  the 


•  For  the  minute  structare  of 
these  ourioufl  spermatic  cart* 
ridges,  see  Milne-fedwards'  elabo- 
rate essay,  '*  Observations  snr  les 


Spermatopbores  des  Mollosqnes 
Cephalopodes  "  (^  Annalea  dtf 
.Sciences  Maturelles,'  18  K)). 


THB  OBPHALOPODA.  531 

CepludopodB  may  h&Ye  very  yariouB  forms,  and  may  eyen 
be  chambered  and  sipbnncnlated ;  bnt,  in  this  case,  the 
chamber  nearest  the  month  of  the  shell  is  small,  and 
incapable  of  lodging  the  viscera. 

Onr  knowledge  of  the  development  of  the  Oephalopods 
is  confined  to  that  of  the  Dibranchiata,^  In  these,  the 
yelk  undergoes  partial  division,  and  the  blastoderm,  formed 
upon  one  face  of  it  by  the  smaller  blastomeres,  spreads 
gradually  over  the  whole  ovum,  enclosing  the  larger 
and  more  slowly  dividing  blastomeres.  The  mantle  makes 
its  appearance  as  an  elevated  patch  in  the  centre  of 
the  blastoderm,  while  the  future  arms  appear  as  sym- 
metrically disposed  elevations  of  the  periphery,,  on  each 
side  of  the  mantle.  Between  these  and  the  edge  of  the 
mantle,  two  longitudinal  ridges  mark  the  rudiments  of  the 
epipodia,  while  the  mouth  appears  in  the  middle  line 
in  front  of  the  mantle,  and  the  anus,  with  the  rudiments 
of  the  gills,  behind  it.  The  rest  of  the  blastoderm  forms 
the  walls  of  a  vitelline  sac,  enclosing  the  larger  blasto- 
meres. 

The  paUial  surface  now  gradually  becomes  more  and  more 
convex,  the  posterior  margin  of  the  mantle  growing  into  a 
free  fold,  which  encloses  the  pallial  chamber  and  covers  ova 
the  gills. 

The  internal  shell  is  developed  in  a  sac  formed  by  ac 
involution  of  the  ectoderm  of  the  mantle.  The  epipodia 
unite  behind,  and  give  rise  to  the  funnel,  while  the  antero- 
lateral portions  of  the  foot  grow  over  the  mouth,  and  thus 
gradually  force  the  latter  to  take  up  a  position  in  the 
centre  of  the  neural  face,  instead  of  in  front  of  it.  The 
yelk-sac  gradually  diminishes,  and  the  contaiaed  blastomeres 
are  finally  taken  into  the  interior  of  the  visceral  sac,  into 
which  the  alimentary  canal  is  gradually  drawn. 

•  Rdlliker,      <  Entwiekelimgt-  Wira.  Zoologie,'  1876).  Lankester 

geschicbte   der     Cephalopoden,'  '*  ObBcrvatioiiB  on  the  develop- 

]841.     Grenacher.     **Ziir    £nt-  ment     of    the      Cephalopoda." 

wickelimgaffescbicnte     der    ۥ-  (*  Quarterly    Journal    of    Mler. 

pbalopoden/'    C  ZeitschriA    fur  Seieuce/  1875.) 

2x2 


532      THB  ANATOMY  OF  INTBBTBB&ATBB  AHIXALS. 

The  Cephalopoda  are  diyided  into  two  yerj  distbict 
groups,  the  Tetrdbranehiata  and  the  Dibranehiata, 

The  TetrahrandUata  possess  an  external  chambeored  si- 
phnncnlated  shelL  The  terminal  chamber  is  much  larger 
than  any  of  the  rest,  and  the  bodj  of  the  «^tiit«i^i  can  be 
almost  completely  retracted  into  it.  When,  as  in  the  only 
existing  genus,  Nautihu  *  (Fig.  130),  the  shell  is  coiled  into 
a  flat  symmetrical  spiral,  its  apex  lies  on  the  anterior  face 
of  the  body,  and  the  outermost  chamber,  into  which  the 
whole  body  can  be  retracted,  is  consequently  posterior  to 
the  axis  of  the  helix.  In  NautiUtt,  the  brachial  processes 
are  short,  and  possess  no  acetabula  such  as  exist  in  the 
Dibranchiaia,  but  the  margins  of  the  foot  are  produced 
externally  into  a  sort  of  sheath,  which,  in  front,  has  the 
form  of  a  broad  hood  with  a  tuberculated  surface ;  while, 
at  the  sides,  it  is  diyided  into  many  processes  of  unequal 
lengths.  Behind,  the  halves  of  the  sheath  are  separated 
throughout  the  greater  part  of  their  length  by  a  wide 
interval,  but  are  united  above  by  a  thick  muscular  isthmus. 
The  central  portion  of  the  sheath  is  a  broad  triangular 
hood-like  plate,  the  apex  of  which  is  free.  It  contains  two 
long  narrow  cavities,  each  of  which  lodges  a  tentacle. 
The  tentacle  consists  of  a  slender  stem,  on  which  are  set 
a  great  number  of  transverse  plates,  in  such  a  manner 
that  the  axis  of  the  stem  passes  through  the  centre  of 
the  plates.  The  anterior  and  lateral  regions  of  the  hood 
are  completed  by  two  narrower  processes,  each  of  which 
contains  a  similar  tentacle,  and  the  lateral  portions  of 
the  sheath  are  formed  by  sixteen  or  seventeen  smaller 
tentaculif erous  processes,  the  surfaces  of  which  are  more  or 
less  distinctly  annulated.  When  the  sheath  is  opened  out, 
there  is  seen  to  be  attached  to  its  inner  surface,  on  each 
side,  close  to  the  re-entering  angle  between  it  and  the  lip 
which  surrounds  the  beak,  and  along  the  line  of  junction 
of   the  lateral   part  of  the  sheath  with   the  isthmus,  a 

*  Owen,  'Memoir  on  the  Katurelles,'  1856.  KeferBtein, ia 
Pearly  Naatilu?,' 1832.  Yander  Bronn's  <  Klaasen  a.  Ordniuigak' 
Hoeven,  'Annales  dee  Sciences 


THI  TXTBABUVCHUTA.  533 

thin  free  qrudrato  lobe  which  oaniea  tw«lTe  tentacloB. 
The  isthmuB  joins  the  porterior  edges  of  theae  outer  fan- 
laetUiferwu  lobet,  as  well  ss  thoae  of  the  two  halves  of  the 
sheatii,  and  it  exhibits  on  its  anterior,  or  inner  snifftce, 
a  Ivoad  ares  beeet  with  delic&te  close-set  cured  Umime. 
Two  other  similar,  but  much  thicker,  imier  ieniaouli- 
feitniM  lobes,  which  also  carry  twelve  tentacles,  lie  between 
these  and  the  lip.  Thej  are  qnite  free  from  the  onter 
Fig.  lao. 


FIft.  iaO.—yaiililii$fiompiliiu,  fimmlc.  C,  hood;  mi, ]kwi ;  J,  ftunel ; 
p,p',vaaatie;  6r,Dranohia;  jrn,  iil<l4DieDtsl  glud ;  r',  r,  podtlon  of 
the  Tcnil  titoeadtgea ;  <mn,  horaj  line ;  a,  ihell  muacle ;  oe,  OTsn ; 
gal,  avIducaTgland ;  i/A'.  (iplnuiclc ;  a,  bUck  put  of  ths  ihcll  DHur 
the  nuntla  p',  jbt,  proeas  of  the  a>KUa(ii>oiu  tkcleloii  into  the 
funnel.    (Aftei  Kefenlelii.) 

tentoculiferonB  lobes,  and  unite  with  the  sheath  only  above 
and  behind.  Like  the  halves  of  the  sbcAth,  these  two 
lobee  are  united  behind  hy  a  thick  isthmus,  the  surface  of 
which  presenta  a  nomber  of  parallel  longitudinal  lamina. 
The  beak,  which  b  hidden  hj  the  sheath  and  the  lobes,  is 
surrounded  bj  the  >■>'■''  circular  lip  abread;  mentioned,  the 
free  margin  of  which  ia  papillose.    Besides  these,  there  is  a 


534       THB  ANATOMY  OF  INTBBTBBRATSD  ANOCAL8. 

short  conical  tentacnlif  erous  process  above  the  pednncnliite 
eye,  and  another  below  it.  In  the  male,  the  internal  tenta- 
culiferouB  lobes  are  wanting,  and  the  outer  tentacoliferons 
lobes  are  divided  into  two  portions,  an  anterior  which  bean 
eight,  and  a  posterior  with  f onr,  tentacnla.  On  the  left  sid^ 
the  four  tentacles  of  the  posterior  division  have  undergone 
much  modification,  and  are  converted  into  a  peculiar  organ 
termed  the  qMuUx,  which  bears  a  discoidal  follicular  gland 
upon  its  outer  surface.  There  is  thus  a  kind  of  hectoootj- 
lisation  in  the  Tetrahranchiata. 

The  margins  of  the  united  epipodia  are  not  united 
into  a  tubulai'  funnel.  They  constitute  a  muscular  mem- 
brane, narrow  on  the  anterior  face  of  the  body,  but  becoming 
wide,  and  folded  in  such  a  manner  that  its  posterior  edges 
overlap,  behind. 

The  mantle  has  a  broad  anterior  fold,  which  coTers  the 
anterior  convexity  of  the  shell,  and  the  region  which  it 
thus  invests  is  black.  The  pallial  chamber  does  not  extend 
for  more  than  three-fifths  of  the  length  of  the  body,  and 
is  therefore  much  less  deep  than  in  the  Dibranchiata,  The 
anus  opens  in  the  middle  line  on  the  posterior  wall  of  the 
pallial  cavity,  close  to  its  junction  with  the  anterior  walL 
The  four  branchisB  are  attached,  two  on  each  side  of  the 
anus,  to  the  posterior  wall  of  the  branchial  chamber,  and 
the  inner  branchia  is  shorter  than  the  outer.  The  nida- 
mental  glands,  composed  of  numerous  vertical  la-mftlln*^ 
partly  covered  by  a  fold  of  the  lining  membrane  of  the 
pallial  cavity,  are  situated  on  the  posterior  waU  of  that 
cavity,  almost  midway  between  its  union  with  the  anterior 
wall  and  its  tree  edge.  The  paired  renal  chambers  lie 
immediately  above  them  also,  in  the  posterior  wall  of  the 
pallial  cavity. 

The  buccal  mass  is  very  large,  its  length  amounting  to 
one-third  that  of  the  body.  The  apices  of  the  great  homy 
beaks  are  obtuse,  and  are  coated  with  a  calcareous  de- 
posit. The  oBSophagus  dilates  into  a  wide  crop  and  is 
separated  by  a  constriction  from  the  stomach,  the  chitinouB 
liniiig  oi  irhiok  ib  ^t^nic^  voii  i^i^L-^g^    The  pyloric  cecum 


THB  TBTRABRANCHIATA.  535 

is  small  and  rounded,  and  the  intestine  maJses  two  bends 
upon  itself  before  reaching  the  anus.  Salivary  glands 
appear  to  be  wanting,  unless  certain  glandular  bodies  placed 
within  the  buccal  mass  should  be  of  this  nature. 

The  liver  is  a  loosely  racemose  gland,  divided  into  four 
lobes,  and  is  lodged  in  the  anterior  part  of  the  perivisceral 
cavity.  There  is  no  ink-bag ;  and  there  are  no  branchial 
hearts.  The  quadrate  systemic  heart  is  situated  on  the 
left  side  of  the  posterior  face  of  the  body,  close  to  the  janc^ 
tion  of  the  posterior  with  the  anterior  wall  of  the  pallial 
cavity.  It  receives  four  branchio-cardiac  veins ;  and,  attached 
to  it,  is  a  pyriform  sac,  which,  according  to  Keferstein, 
opens  into  the  pallial  cavity. 

The  cartilaginous  skeleton  supports  the  pedal  and  parieto- 
splanohnic  ganglia,  but  does  not  encircle  the  gullet,  or  roof 
over  the  cerebral  ganglia.  Two  long  processes  of  the 
skeleton  pass  into  the  funnel  and  give  attachment  to  its 
muscles.  Two  large  shell  muscles  are  attached  to  it ;  and, 
passing  upwards  and  outwards,  are  inserted  into  oval  chiti- 
nous  patches  visible  on  the  outer  surface  of  the  mantle, 
and  connected  together  by  a  thin  ring  of  the  same  substance 
(the  anntUua)  which  encircles  the  mantle. 

The  oviduct  does  not  arise  directly  from  the  sac  in  which 
the  ovary  is  lodged,  but  from  a  distinct  chamber,  into  which 
the  ovarian  sac  opens.  A  large  albumen  gland  pours  its 
secretion  into  the  ovarian  sac.  The  vaa  deferens  similarly 
takes  ita  origin,  not  from  the  sac  of  the  testis,  but  from 
a  smaller  chamber  communicating  therewith.  The  com- 
mencement of  the  vas  deferens  is  enlarged  and  glandular. 
Nothing  is  known  of  the  development  of  the  Teirdbran' 
chiata. 

The  only  existing  representatives  of  the  Tetrabranehiaia 
are  the  different  varieties  of  "  pearly  nautilus "  (NautUua 
pom^itu),  which  are  found  in  the  Southern  seaa,  living 
at  the  bottom  at  a  considerable  depth.  The  genus  is 
one  of  the  oldest  in  existence,  since  it  is  traceable  through 
the  whole  series  of  f ossiliferous  rocks  as  far  back  as  the 
Silurian  epoch. 


536       THE  ANATOMY  OF  IKTBBTBB&ATBn  AHIKALS. 

Along  with  it,  in  the  Palasozcic  formatiaiiB,  oooiur 
nomeroas  closely  allied  forms,  which  differ  from  KauUiMM 
mainly  in  the  different  oorvature  {LUwUes,  QyrooenUf  2Vo* 
choeeras)  or  straightness  {Chihoeercu,  Chsmphoeenui)  of  the 
shell,  and  in  the  varying  position,  proportions,  and  d^;Tee 
of  calcification  of  the  siphoncle. 

In  the  middle  of  the  Palseozoic  strata  (Deyonian),  Tetra- 
branchs  {AmmanitidoB)  appear,  in  which  the  margins  of  the 
septa  are  strongly  bent,  whence  their  edges  appear  as  zigzag 
transverse  lines,  folded  into  lobes  and  MULdles,  when  the 
outer  layer  of  the  shell  is  worn  away  (ChniaiiieM,  Cera- 
titea) ;  and,  in  the  Mesozoic  epoch,  the  lobes  and  saddles 
become  extremely  complicated,  while  the  shells  maj  be 
straight,  simply  carved,  or  bent,  or  turbinated  {AmmonUeB^ 
BaculUes,  TurrUUes),  The  Ammonitidm  are  extraordinarilj 
numerous  in  the  Mesozoic  epoch,  but  no  trace  of  them  has 
been  found  in  tertiary  or  quaternary  formations. 

Associated  with  Ammonites,  and  not  unfrequently  lodged 
in  the  terminal  chamber  of  the  shell,  are  the  so-called 
Aptyehi.  These  are  plates  of  a  shelly  substance,  three- 
sided,  with  rounded  off  angles,  and  applied  together  bj 
their  straighteet  edges  so  as  to  resemble  bivalve  shells. 
They  consist  of  two  layers,  an  inner  and  an  outer,  of  which 
the  inner  presents  lines  of  growth,  concentric  with  the 
angle  of  each  plate  which  is  situated  on  that  side  of  its 
broad  end  which  is  applied  to  its  fellow.  The  outer  layer 
is  composed  of  many  laminsB,  and  is  traversed  by  pores. 
Its  free  surface  frequently  presents  longitudinal  ridges. 
The  heart-shaped  plates,  undivided  by  a  suture,  which  are 
found  in  some  Ooniatites  and  Ammonites,  are  termed 
Anaptychi, 

The  Aptyehi,  when  undisturbed,  occupy  the  middle  of  the 
posterior  wall  of  the  terminal  chamber  of  the  Ammonite, 
and  have  their  bases  towards  its  mouth.  Nothing  is  cer- 
tainly known  as  to  the  nature  of  the  Aptyehi  or  Anaptyehi^ 

*  See  the  diaeiiMion  of  this  qoeetion  by  Keferstein,  in  Bnmn's 
•  Thierreioh.' 


THB  DIBIUJrOHIATA.  537 

In  the  Dibranchiata,  the  margins  of  the  foot  are  produced 
into  not  fewer  than  eight,  nor  more  than  ten,  arms,  which 
are  provided  with  aceiabula  or  suckers.  Each  acetabulum 
is  a  sessile  or  stalked  cup,  from  the  bottom  of  which  rises  a 
plug,  which  nearly  fills  the  cup,  but  can  be  retracted  by  the 
action  of  muscular  fibres  attached  to  it.  When  the  margins 
of  the  acetabulum  are  applied  to  any  surface,  and  the  plug 
is  retracted,  a  partial  vacuum  is  created,  and  the  acetabulum 
is  caused  to  adhere  to  the  surface  by  atmospheric  pressure. 
The  edges  of  the  acetabula  are  frequently  strengthened  by 
chitinous  rings,  and  these  may  be  serrated  (Fig.  124,  B), 
and  are  sometimes  produced  into  long  curved  hooks. 

The  margins  of  the  united  epipodia  are  not  only  folded 
inwards,  but  coalesce  so  as  to  give  rise  to  a  tubular  funnel, 
through  which  the  water  taken  into  the  branchial  sac  for 
respiratory  purposes  is  ejected.  Yery  often,  a  valve  which 
prevents  the  flow  of  water  back  into  the  mantle  cavity  is 
developed  within  the  funnel.  There  are  two  branchisB,  and 
the  anus  terminates  between  them  in  the  anterior  wall 
of  the  branchial  sac,  on  which  also  the  nidamental  glands 
are  situated.  The  apices  of  the  homy  beaks  are  acutely 
pointed,  and  not  ensheathed  in  calcareous  matter.  The 
liver  is  usually  a  compact  mass.  A  peculiar  gland,  which 
secretes  an  extremely  dark  fluid — ^the  so-called  ink, — and 
has  the  form  of  an  oval  or  pyriform  sac  (the  ink-hoig), 
with  a  long  duct  which  opens  into,  or  close  to,  the  rectum, 
is  lodged  sometimes  in  the  Hver,  sometimes  further  back 
(Fig.  126, 1).  The  ink  is  ejected  when  the  animal  is  alarmed, 
and  gives  rise  to  a  dark  cloud  in  the  water,  by  which  its 
retreat  is  covered.    There  are  two  branchial  hearts. 

The  eye  is  lodged  in  an  orbit  and  is  provided  with  a  lens. 
The  cartilaginous  endoskeleton  forms  a  ring  surrounding 
the  gullet  and  enveloping  the  principal  ganglia.  There  is 
usually  an  internal  pallial  shell.  It  may  be  chambered 
and  siphunculated,  but  in  this  case,  the  last  chamber  is 
small  and  hardly  larger  than  the  others. 

The  Dibranchiaia  are  divided  into  the  Octopoda  and  the 
Decapoda.    The  Octopoda  have  eight  nxma,  «aii^^gK3«aR»^  t^^ 


538     THX  AKATomr  o 

pallial  shdL  Bnt,  Id  the  female  of  one  genoa  (Aryommla, 
tlie  "paper  Nautilus,"  Fig.  131),  the  extremities  ol  tlie 
anterior  pair  of  anus  ore  greatly  expanded,  and,  bong  tamed 
back  over  the  mantle,  secrete  an  elegant  ahellj  a 
which  oorera  the  bodj,  and  Berrea  for  the  a " 

Fig.  IS1. 


FiK-  \%l.—Argomaiita  argo.~i.,  female  with  the  eipandcd  Bmi 
iheir  u&turkl  podtlon,  embneing  tba  thtll  b ;  d,  Ibe  othar  lis  m 
a,  the  fUBoel.    B,  KcUbulA. 


Fig.  133. — Argonauta  argo,  male,  wiUi  the  Htctocotglur 

the  egga.  In  thia  genns,  and  in  aome  other  Octopoda 
(Otioput  eonna,  TmnodopuM  noloonw  and  T.  QvoyaiMM), 
the  male  ia  rerj  much  •mailer  than  the  female,  and  giTca 
Xiw  to  ft  flNtoeotighu. 


THZ  DIBBAHCHUTA.  S39 

Id  Argonauta  argo  {Figa.  132,  133)  it  is  Ute  third  aim 
on  the  left  side  which  becomes  thus  modified.  At  first, 
it  has  the  form  of  a  sac,  within  which  the  slender  ter- 
minal part  of  the  arm  is  ooUed  np  (Fig.  133,  B>.  The  sac 
splits  to  give  exit  to  the  latter  (Fig.  132],  and  its  two  halves 
reunite  on  the  outer  face  of  the  base  of  the  arm  to  form  a 
chamber,  which  becomes  filled  with  spermatophores  in  a 
manner  not  jet  understood.     Dnring  boiubJ  onion,  the  arm 

Fig.  153. 


t'ig.  \Xi.~Arginvnda  argo.^'R,  nwte,  with  the  heCtoeoCrllMd  srm 
enclcnediii  iu  uc  ;  I ,  S,  3, 1,  thi  other  umi  of  the  right  aide;  Uiil 
1',  3',  *',  tboM  of  the  left  ride.    A,  the  hectoeotyliu  deuwhed. 

thus  chafed  with  eemeu  is  detached  and  left  in  the  mantle 
cavitj  of  the  female  (Fig.  133,  A).  When  first  discovered, 
it  was  regarded  as  a  parasite  and  termed  Ttitiwc^hahia 
aedabularit  bj  Delle  Chi^'e,  while  the  correeponding  bod; 
found  in  an  Otiiy^  was  called  Re/dooolyhu  octopodii  hj 

In  ZVomodopw,  it  is  the  tlkird  axm.  cm  <i^  t^^A.  <gAa 


540       THE  ANATOMY  OV  XNYBBTBBRATBD  AVnCAUB. 

which  becomes  the  Hectocatyhu,  In  other  Odopodt*  one 
or  other  arm  is  peculiarly  modified,  but  does  not  become 
detached,  or  serve  as  a  receptacle  for  the  spermato- 
phores. 

The  Decapoda  have  ten  arms,  two  of  which  are  tisnally 
much  longer  than  the  rest,  and  can  be  protruded  from,  or 
retracted  into,  sockets.  The  acetabula  have  homj  rims, 
which  may  take  on  the  form  of  hooks. 

Hectocotylisation  does  not  go  further  than  a  modification 
of  the  form  of  one  of  the  arms.  There  is  always  an  internal 
shell,  which  is  either  a  pen,  a  sepiastaire,  a  phroffmocone, 
or  a  combination  of  the  latter  with  a  pen. 

The  TeuihidoB,  or  Squids,  are  characterised  by  possessing 
a  pen.  This  is  a  lamellar  chitinous  body,  strengthened  by 
one  or  more  longitudinal  ridges,  which  lies  in  a  sac  lodged 
in  the  anterior  wall  of  the  body,  by  the  lining  membrane  of 
which  it  IB  secreted.  The  posterior  end  of  the  pen  is  com- 
monly broad,  and  its  sides  may  be  infolded  so  as  to  form  a 
conical  cup  {Ommagtrephes), 

In  the  SeputdcBf  or  Cuttle-fishes,  the  sepiostaire,  or  **  cuttle 
bone,"  which  occupies  the  same  position  (Fig.  125,  «A),  is 
composed  of  a  broad  plate  answering  to  the  pen,  and  like- 
wise infolded  at  its  apex  so  as  to  give  rise  to  a  short  cone, 
but  calcified.  On  the  inner  face  of  this  plate,  a  great 
number  of  delicate  calcified  laminse,  connected  by  numerous 
short  columns,  form  a  spongy  tissue,  which  is  full  of  air.* 

In  the  £^rttZi<^,  represented  by  the  solitary  genus  £[ptru2a,t 
which  is  among  the  rarest  of  animals  in  museums,  though 
its  shells  are  found  piled  up  in  countless  millions  on  the 
beaches  of  the  islands  of  the  Pacific,  the  shell  is  spirally 


•  Steenatrup, "  Die  Hectocoty- 
len-bildung  bei  Argonauta  und 
Tremoctf^pat  erklart  durcb  Beob- 
aditungen  abnlicber  Bildungen 
bei  den  Cephalopoden."  (*Archiv 
fOr  Nftturgeschichte,'  1856.) 

t  The  planet  of  the  tuperim- 
poted  parallel  lamina  form  an 
aonte  aa^e  with  thai  oi  t]bA  '^tm- 
ttijpal   plate   of  the  «epV)«X«it^ 


The    connecting    eolamns 

f placed  perpendicularly  to  the 
aminee  between  which  they  are 
interposed,  and  nay  be  simple  or 
branched.  When  the  young  8eg^ 
leaves  the  egg,  the  sepiottaire 
already  contains  air. 

t  Owen,       'Zoology    of    the 
Samarang,^  1848. 


■  DIBKUiaBUTA. 
Fig.  134. 


j.lM^Bd™i«»,wllhthBrraMlniofthebodTofUie»iiliiiJ  /F™, 
»  ipidmn  in  tlw  Mixmin  of  PrwHcml  oJlwrvT^i  iJS 


542       THE  ANATOMY  OF  DnrBBTBBRATSD  AHIXALS. 

coiled  and  divided  by  septa,  perforated  by  a  sipliimcle,  into 
cbamberB.  The  last  chamber  of  this  phragmocone,  however, 
is  no  larger  than  its  predecessor,  and  the  shell  is  held  in 
position  by  lateral  processes  of  the  mantle,  which  are  nnited 
over  it,  and  probably  represent  the  waUs  of  the  sac  in 
which  the  shell  was  primitively  formed.  The  last  chamber 
of  the  shell  lies  in  front  of  the  axis  of  the  helix ;  the  shell 
is  therefore  coiled  in  the  opposite  direction  to  that  of 
Nautilus, 

In  certain  extinct  genera  {e,g.  SpiruliraHra),'^  shell,  like 
that  of  Spirula,  is  enclosed  in  a  dense  and  laminated  pointed 
sheath,  like  the  hinder  end  of  a  sepiostaire,  or  of  the  pen  of 
an  Ommastreplies. 

In  the  BelemnitidoB  (Fig.  134),  which  abounded  in  the 
Mesozoic  epoch,  but  have  been  extinct  since  that  time,  a 
straight  phragmocone  is  enclosed  within  a  more  or  less 
conical  calcified  laminated  stractnre,  the  guard  or  rostrum, 
which  is  continued  forwards  into  a  variously-shaped,  usually 
lamellar,  pro-ostracum.  The  pro-oetracum  and  the  rostrum 
together  represent  the  pen  in  the  TeuthidoB. 

The  rare  specimens  of  Belemnitidce  in.  which  the  fossilised 
soft  parts  are  retained,  show  that  the  arms  were  provided 
with  hooks,  and  that  there  was  a  large  ink-bag.* 

The  genus  Acanihoteuthisf  {Belemnoteuthis,  Pearce)— one 
of  the  BelemnitidcB,  in  which  the  guard  is  almost  rudimen- 
tary, while  the  pro-ostracum  is  large  and  penlike — occurs 
in  the  Trias,  and  is  the  earliest  known  Dibranchiate  Cepha- 
lopod.  The  ordinary  BelemnitidcB  abound  from  the  Lias  to 
the  end  of  the  Mesozoic  period,  after  which  they  disappear. 
The  Sepiadce  first  appear  in  the  latter  half  of  i^e  Mesozoic 
epoch ;  while  the  Teuthidca  are  represented  by  genera  closely 
allied  to  existing  forms  (Teuthopsis,  Belemnosepia)  as  early 
as  the  Lias. 

♦  Huxley.  "The  structure  of  t  Owen,    "A    descriptloii   of 

Belemnites."     (*  Memoirs  of  the  certain  Belemnites,**  &o.  Q  PhiL 

Geological  Survey  of  the  United  Trans/  1844.) 
Kingdom/  1864.) 


THE  BCHINOBBSXATA.  543 


CHAPTER  IX. 

THE  ECHIKODBBMATA. 

The  Ecbinoderms  are  exclusivelj  marine  animals.  They 
are  always  provided  with  a  skeleton,  composed  of  calcareous 
spicula,  which  commonly  unite  into  networks,  and  give 
rise  to  definite  skeletal  plates.  These  generally  become 
connected  with  one  another  by  joints  or  sntnres,  bnt  some- 
times remain  distinct.  A  more  or  less  spacious  peritoneal 
cavity  separates  the  walls  of  the  body  from  those  of  the 
alimentary  canaL  The  nervous  system,  in  those  Echino- 
derms  in  which  it  has  been  most  satisfactorily  made  out, 
presents  a  ring,  which  surrounds  the  guUet,  and  gives  off 
radiating  longitudinal  cords.  A  remarkable  system  of 
vessels,  termed  amhulaeral,  which  also  form  a  ring  around 
the  gullet,  is  highly  characteristic  of  the  EchinodermcUa, 
The  most  conspicuous  and  familiarly  known  Echinoderms 
— the  Star-fishes  {Asteridea),  Brittle-stars  {Ophittridea),  Sea- 
urchins  {Echinidea)t  and  Feather-stars  (Crvnaidea) — have  a 
marked  radial  symmetry;  similar  parts,  usually  to  the 
number  of  five,  being  arranged  around  a  central  axis ;  and 
the  body  is  spheroidal,  discoidal,  or  stellate.  The  Sea- 
cucumbers  and  Trepangs  (Holothuridea)  are  elongated  and 
vermiform ;  but  the  radial  symmetry  is  still  traceable  in 
the  arrangement  of  the  oral  tentacula,  the  nervous,  and  the 
ambulacral  systems.  It  is  to  be  remarked,  however,  that, 
in  many  Echinoderms,  the  radial  symmetry,  even  in  the 
adult,  is  more  apparent  than  real ;  inasmuch  as  a  median 
plane  can  be  found,  the  parts  on  each  side  of  which  are 
disposed  symmetrically  in  relation  to  that  plane.  With  a 
few  exceptions,  the  embryo  leaves  the  e^  «a  ^\s^a^«sc^^SS::« 


544       THK  AII1.T0KT  Or  DnriBTIBBAnD  UltMilM. 

Bjmmetrical  l&ira,  prorided  with  ciliated  bands,  and  oUier- 
iriae  Bimilar  to  a  worm-larra,  which  maj  b«  tonaed  u 
Eekiitop<Bdium.  Th«  convereioii  of  the  Echinopcediiua  into 
an  Echinoderm  is  effected  bj  the  developm^tt  ot  an  ta- 
Fig.  135. 


Fig.  135. — Dlagnm  cihibiting  the  geaenl  plui  of  tha  deTctopmoat  of 
at  EMnodcrmt  (kftet  Hullci).— A,  common  fom  whcBO*  tia 
Termlfonn  Bolottinrid  (B,  B')  and  (he  platcifoim  OpUorid  m 
EehiDid  (C,  C)  Iuvb  ire  derived ;  D,  D',  joongcr  and  Bsn 
■dTinced  bM£««  of  ths  Aiteild  (SipnuFw)  Jkirn;  a,  mouth;  i^ 
■tomuii ;  c,  inteatins  :  d,  *diu  ;  >,  ciliaUd  bud ;  c',  waond  or  uti- 
rloi  ciliated  circlet  of .  ~ 


teroctele,  and  its  couvenion  into  the  peritoneal  caTitj  and 
tJie  HnbolacEal  vj^uan  ^1  ^ew^  «nd.  neireai  and  tij  At 


,  -  *" 


THE  HOLOTHITBIDEA.  545 

metamotpliosis  of  the  mesoderm  into  radially  dieposed 
antimeres,  the  result  of  which  is  the  more  or  less  complete 
obliteration  of  the  primitive  bilateral  symmetry  of  the 
animal. 

1.  The  HoLOTHXTBiDEA.  The  stady  of  the  stmctore  of 
the  Echinoderms  may  best  be  commenced  with  the  members 
of  this  division,  which,  in  many  respects,  deviate  least 
from  such  worms  as  the  Oephyrea, 

In  the  SynapUB,  for  example  (Fig.  136),  the  body  is  greatly 
elongated  and  cylindrical,  the  mouth  being  placed  at  one 
end,  and  the  anus  at  the  other.  The  oral  aperture  is  situated 
in  the  centre  of  a  circle  of  tentacula,  and  the  gullet  leads 
from  it  to  an  alimentary  canal,  without  marked  distinction 
of  stomach  and  intestine,  which  extends  through  the  body, 
and  is  connected  by  a  mesentery  with  the  parietes  of  the 
latter.  The  waU  of  the  alimentary  canal  presents  external 
circular,  and  internal  longitudinal,  muscular  fibres,  and  its 
cavity  is  lined  by  a  cellular  endoderm. 

The  body- wall,  or  perisoma,  consists  of  an  external  cel- 
lular ectoderm,  covering  a  layer  of  connective  tissue  within 
which  are  circular  and  longitudinal  muscular  fibres.  The 
latter  are  disposed  in  five  bands,  attached  anteriorly  to  a 
corresponding  number  of  the  pieces  of  a  calcareous  ring 
which  surrounds  the  gullet  (Fig.  136,  E).  The  separate 
ossicles  which  compose  this  ring  are  usually  ten  or  twelve 
in  number,  and  the  five  to  which  the  longitudinal  muscles 
are  attached  are  notched  or  perforated  for  the  passage  of 
the  ambulacral  nerves,  which  proceed  £rom  the  circum- 
oesophageal  nerve  to  the  parietes  of  the  body. 

The  integument  contains  numerous  perforated,  flat,  cal- 
careous plates,  to  which  protruding  anchor-like  hooks  of 
the  same  substance  are  attached  (Fig.  136,  F).  According 
to  Semper,  these  anchor-like  bodies  are  developed  in  special 
sacs  with  an  epithelial  lining.* 

A  spacious  peritoneal  cavity  lies  between  the  parietes 

•  See,  on  this  and  all  points  ArebipelderPhilippinen."(*Wis- 
relating  to  the  stmetore  of  the      senschaftliche  BmoI^^^  "^^  V.\ 


foioikwrkUa.  the  beaotiful  mo-       ffoloCfciinea.') 
ocraipb  bjaem 


iper;''jBeifeiiim 


546       THB  ANATOMY  OF  IVYSBTSBBATSB  AVIMAIiS. 

of  the  body  and  the  alimentaiy  oanal,  and  the  oeDs  which 
line  it  are  more  or  less  extensively  ciliated.  Pedunculated 
ciliated  cups  are  attached  to  the  mesentery. 

The  circtdar  vessel  of  the  ambnlaoral  system  snrronnda 
the  gullet  below  the  calcareous  ring  (Fig.  1S6,  E,  k).  Pos- 
teriorly, it  gives  off  various  csecal  prolongations,  whidi  de- 
pend freely  into  the  peritoneal  cavity.  Some  of  these— the 
Polian  vesicles — are  mere  cseca;  but,  in  addition,  there  are 
one  or  more  tubular  prolongations,  the  perforated  ertremi- 
ties  of  which  are  invested  by  a  calcareous  network,  and  are 
termed  the  madreporie  caruils.  Through  the  openings  in 
the  free  end  of  the  madreporie  canal,  the  interior  of  the 
ambulacral  system  communicates  with  the  peritoneal 
cavity.  Anteriorly,  the  circular  vessel  gives  off  branches 
to  the  tentacula.  These  pass  between  the  calcareons  ring 
on  the  outer  side,  and  the  anterior  end  of  the  alimentary 
canal  and  the  nerve  ring,  on  the  inner  side.  As  each  enters 
its  tentacle,  it  dilates  and  sends  down  a  short  csBcal 
prolongation  on  the  outer  side  of  the  calcareons  ring. 
The  ambulacral  vessels  are  filled  with  a  fluid  containing 
numerous  nucleated  cells. 

Contractile  vessels,  which  accompany  the  intestine  and  lie 
on  opposite  sides  of  it,  filled  with  a  similar  corpnsculated 
fluid,  seem,  notwithstanding  the  difference  in  their  contents, 
to  represent  the  pseud-hromal  vessels  of  the  AtiTi<»l|^iy 
These  vessels  do  not  extend  into  the  parietes  of  the  body. 

The  nervous  system  consists  of  a  ring  which  lies  superficial 
to  the  circular  water- vessel,  and  from  which  five  principal 
equidistant  cords  proceed.  These  pass  through  the  apertores 
or  notches  in  the  circnm-oesophageal  plates  already  men- 
tioned, and  each  proceeds  along  the  middle  line  of  one 
of  the  longitudinal  muscular  bands,  to  the  opposite  extre- 
mity of  the  body. 

The  ambulacral  nerves  appear  to  be  hollow ;  or  perhaps 
it  would  be  more  correct  to  regard  them  as  thickenings  in 
the  wall  of  a  neural  canal,  as  they  are  in  the  Agteridea,* 

*  AocoTdingtoGreeff^Ueber      der    Gesellschsft    lu    Marbuf^ 
den    Bau    der    Ec^\iiQd«tm«Ti^'      X^l'IV  vckAtJber  csnal  lies  sniMr-    j 
3te  MittheUimg,^itLun«i>MTvc^XA      ^\»i  Na  ^^  v>^»^atfa^^«c<r«  is    I 


v^tll 


THB  HOLOTHUBIDIA.  547 

The  genital  gland  is  single,  and  opens  near  the  oral  end 
of  the  body,  in  the  line  of  the  attachment  of  the  mesentery. 
The  branched  cecal  tabuU  of  which  it  is  composed  contain 
both  OTa  and  spermatozoa,  so  that  the  SynaptcB  are  her- 
maphrodite. In  the  majority  of  the  Holothwridea,  how- 
eTer,  the  sexes  are  distinct. 

In  other  Holothwridea,  the  skeleton  may  attain  a  mnch 
greater  development,  and  even  take  the  form  of  conspicuous 
overlapping  plates  (Psohia),  Moreover,  the  circular  vessel 
of  the  ambulacra]  system  not  only  gives  origin  to  Polian 
vesicles,  madreporic  canals,  and  tentacular  vessels,  but  five 
canals  proceed  from  it,  pass  through  holes  or  notches  in 
those  circum-OBsophageal  plates  to  which  the  longitudinal 
muscles  are  attached,  together  with  the  nerves,  and  run 
backwards,  along  the  centre  of  the  area  occupied  by  these 
muscles,  on  the  deep  or  inner  side  of  the  longitudinal 
nerve.  These  are  the  rcLdial  ambulaercd  vesseU,  In 
the  higher  Holothwridea,  each  radial  ambulacral  vessel 
gives  off  many  lateral  branches;  these  enter  contractile 
processes  of  the  body- wall,  which  subserve  locomotion,  and 
are  the  ambtdacralfeet,  auckers,  or  pediceU.  In  accordance 
with  the  disposition  of  the  ambxdacral  vessels,  the  pedicels 
are  usually  disposed  in  five  longitudinal  bands,  which  are 
the  ambulacra.  Sometimes  {Psolua)  the  pedicels  are  sup- 
pressed in  two  of  the  five  ambulacra,  and  the  other  three 
are  disposed  upon  a  flattened  surface  upon  which  the  animal 
creeps. 

In  the  higher  Holothurids,  the  intestine  terminates  in  a 

distinct  cloaca,  into  which  two  hollow  ramified  organs,  which 

lie  in  the  perivisceral  cavity,  open.    The  ramifications  of 

one  of  these  are  received  between  the  meshes  of  a  special 

plexus  of  the  psend-hsBmal  vessels.    Water  is  taken  into, 

and  expelled  out  of,  the  cloaca  and  these  appendages,  which, 

doubtless,  subserve  an  excretory  function,  and  are  commonly 

called    respiratory    trees.     It    seems    probable    that    the 

the  Hdothuridea ;  and  represents  ('  Jenaische    Zeitschrift.'    1^76^, 

the  ambulacral  groove  of  the  star-  however,    maintains     that    this 

fishes.    Teuscher,  **  Beitr&ge  sur  superficial  canal  ta  axL  «sVS&s^'«^ 

Anatomle   der   £chinodermen "  product. 


648       THK  AMATOKt  OW  IVTEBTIBXATtD  *»TTIiM. 
Fig.  188. 


A.  Lun  with  the  UlaUnl  eiUMed  Iwnd,  ud  whMt-ilu^  od- 
tsracMU  i^mtM.  Vantnl  Tlsir.  a,  moath  sad  guUat ;  fr,  ttf^mfii : 
*  "  BdMn  tar  ttitsitiMRhlchte  da  E^n^ita  difOalm."    (•  Hon 

A«US'  lUd^  lau.) 


THE  HOLOTHITBIDBA.  549 

c,  intestine  And  aniu ;  <f,  mci  of  the  enteroooele  (mnamge  ehaped 
bodies)  at  the  sides  of  the  stomach ;  e,  rudiment  of  the  ambulacral 
vascular  system.  B.  Farther  advanced  condition  of  the  larva  in 
which  the  oral  aperture  is  obsolete  (the  so-^salled  ^  pupa-stage  *'\ 
and  the  cilia  are  arranged  in  zones,  i,  tentacula ;  A,  Polian  vesicle ;  ^ 
the  longitudinal  muscles  of  the  body-wall.  C,  a  young  ^fnapta,  in 
which  the  ciliated  sones  have  disappeared ;  with  its  five  tentacles 
and  the  wheel- shaped  calcareous  bodies  at  its  hinder  end.  si,  the 
madreporic  canal  which  now  opens  into  the  cavity  of  the  body.  D,  a 
young  ^fnapta  mJuerent  with  anchor^shaped  calcareous  spicula,  except 
at  the  hinder  end  of  the  body,  where  they  are  small  and  polygonal. 
£.  Longitudinal  section  of  the  anterior  end  of  the  body  of  an  adult 
Synapta  digitata.  a,  perisoma  with  the  longitudinal  muscles  and 
radial  nerve  trunks ;  6,  calcareous  plates  which  surround  the  gullet ; 
e,  tentacular  canals:  d^  oesophagus;  e,  radiating  muscles  of  the 
pharynx;  g,  divided  ends  of  the  ctrcum-oral  nerve;  K,  circular 
ambulacral  vessel  with  Polian  vesicle :  i,  cavity  of  a  longitudinally 
divided  tentacle,  into  which  a  tentacular  canal  opens ;  k^  generative 
caeca;  /,  mesentery  with  the  dorsal  blood-vessel;  oi,  *  auditory 
vesicle '  on  the  radial  nerve ;  n,  longitudinal  muscles :  o,  tentaculi^ 
pedicels ;  /»,  oral  disk.  F.  Calcareous  plate  and  anonor  of  Sjfiutfia 
ttUuerem, 

ultimate  branches  of  these  organs  open  directly  into  the 
periyisceral  cavity.* 

The  Cwnerian  organs  are  simple  or  branched  appendages 
of  the  cloaca,  the  function  of  which  is  unknown.  The  in- 
terior of  these  organs  is  occupied  by  a  solid  substance, 
sometimes  of  a  viscid  nature.  In  some  Holothwridea,  the 
anal  aperture  is  provided  with  a  circlet  of  calcareous  plates. 

In  many  of  the  higher  Holothurids  the  pseud-hsmal 
vascular  system  attains  a  great  complexity,  and  its  branches 
not  only  extend  over  the  alimentary  canal,  but,  as  has 
been  said  above,  closely  embrace  one  of  the  branched 
excretory  organs. 

The  most  aberrant  form  of  this  group  at  present  known 
is  the  genus  Bhopalodina.  According  to  Semper,  the  body 
is  flask-shaped,  and  at  the  narrow  end  of  the  flask  are  two 
apertures.  One  of  these — the  mouth — ^is  surrounded  by 
ten  tentacula;  the  other,  which  is  the  anal  aperture,  is 
encircled  by  ten  papillsB,  and  by  as  many  calcareous  plates. 
A  spacious  cloacal  cavity,  provided  with  excretory  organs, 
traverses  the  neck  of  the  flask,  and  opens  by  the  anal 

*  Semper,  loe.  cU,  Heft  iv.,^,  Y^l^ 


550       THB  AKATOICT  OF  IVYXBTSBBJLTBD  ▲]riMAI& 

aperture.  The  gullet  is  stirroanded  bj  a  ring  of  ten 
calcareous  plates.  The  genital  duct  is  situated  between 
the  cloaca  and  the  gullet.  Ten  ambulacra  diyerge  from 
the  centre  of  the  enlarged  aboral  end  of  the  bodj,  and 
extend,  like  so  many  meridians,  to  near  the  commencement 
of  the  neck  of  the  flask.  In  correspondence  with  each 
ambulacrum  is  a  longitudinal  muscular  band ;  and  it  is  an 
especial  peculiarity  of  Bhopdlodina  that  five  of  these  are 
attached  to  the  anal  circlet,  and  five  to  the  circnm-OBsopha- 
geal  circlet.  Until,  howeyer,  it  has  been  shown  that  the 
circular  ambulacra!  vessel  encloses  the  cloaca,  as  well  as  the 
oesophagus — which  is  highly  improbable, — ^it  is  justifiable 
to  assume  that  the  anus  of  Bhopododina  is  really,  as  in  the 
Crinoidea,  interradial  in  position. 

The  development  of  the  Holothuridea  is  extremely  instmo- 
tive.  Yelk-division  gives  rise  to  a  vesicular  momla,  which 
undergoes  invagination,  and  becomes  converted  into  an  oval 
ciliated  gastrula.  The  opening  of  invagination  becomes 
the  anus,  while  a  mouth  and  gullet  are  produced  by  an 
invagination  of  the  ectoderm,  near  the  anterior  end  of  the 
body,  which  unites  with  and  opens  into  the  blind  end  of 
the  endodermal  sac,  or  archenteron.  The  completed  ali- 
mentary canal  is  thus  composed  of  a  gullet,  a  rounded 
stomach,  and  an  intestine ;  and  the  cilia  of  the  ectoderm 
usually  become  restricted  to  a  single  band,  bent  upon  itself, 
though  its  general  direction  is  transverse  to  the  axis  of  the 
1^>o^7  (^g*  135,  B ;  Fig.  136,  A).  At  a  subsequent  period, 
this  single  band  may  be  replaced  by  a  series  of  hoops  of 
cilia  (Fig.  136,  B).  According  to  Kowalewsky*  the 
embryo  of  Pentada  doliolum  does  not  become  ciliated 
at  all,  and  that  of  Psolinus  passes  from  the  conditioa  in 
which  the  cilia  are  dispersed  over  the  surface,  directly 
into  one  in  which  it  is  provided  with  five  zones  of  cilia, 
between  two  of  which  the  mouth  opens.  In  this  condition 
it  singularly  resembles  the  embryo  of  Comatula,  And. 
indeed,  in  the  further  advanced  condition  of  the  PsoItiHit, 
the  oral  end  oi  the  body,  surrounded  by  triang^nlar  eal- 


THE  BIVXLOPKXKT  OF  THB  HOLOTETaBIBEA.       551 

careouB  plates,  withm  which  the  tentacles  take  their  origin, 
has  a  striking  resemblance  to  the  oral  end  of  the  young 
Pentacrinoid  larva  of  Conutiula, 

The  peritoneal  cavity  and  the  ambulacral  vessels  take 
their  origin,*  in  a  very  remarkable  manner,  from  the 
archenteron,  before  the  oesophageal  invagpjiation  reaches  it. 
The  anterior  part  of  the  archenteron  gives  off  a  cscal  process, 
which,  becoming  a  sac,  is  constricted  off  from  the  archenteron 
as  what  Salenka  terms  a  vaao-perUoneal  vende.  This  vedde 
changes  its  position  to  the  left  side  of  the  alimentary  canal, 
and  then  sends  a  narrow  duct-like  diverticulum  towards 
the  dorsal  region  of  the  ectoderm,  which  eyentually  coalesces 
with  the  latter,  the  cavity  of  the  diverticulum  opening  on 
the  exterior  by  a  rounded  pore.  The  vaso-peritoneal  yesicle 
now  divides  into  two  portions,  one  of  which,  the  ambulaeral 
9ae,  remains  connected  with  the  exterior  by  the  duct,  and 
constitutes  the  foundation  of  the  whole  of  the  ambulacral 
system  of  vessels ;  while  the  other,  the  peritoneal  eae,  gives 
rise  to  the  peritoneum.  The  former  becomes  five-lobed, 
grows  round  the  gullet,  and  gives  rise  to  the  tentacular  and 
ambulacral  canals  with  the  Polian  vesicle,  or  yesicles ;  while 
the  duct,  detaching  itself  from  the  dorsal  wall,  becomes 
the  madreporic  canal. 

The  latter  divides  into  two  vesicles,  which  arrange  them- 
selves at  the  sides  of  the  stomach.  The  stomach  takes  on 
a  more  cylindrical  shape,  and  these  Tesides  become  the 
"sausage-shaped  bodies"  (wiirstformige  Korper),  observed 
by  Mtdler  (Fig.  136,  A).  They  gradually  increase  in  size, 
and  growing  round  the  alimentary  canal,  unite  above  and 
below  it.  Thus  a  cylindrical  cavity  with  a  double  wall 
is  formed,  between  tiie  endoderm  and  the  ectoderm.  The 
inner  waU  of  the  cavity  applies  itself  to  the  alimentary 
canal,  and  aided  by  the  mesoblastic  cells  which  appear  to 
be  developed  frx>m  the  endoderm,  becomes  the  muscular 

*  See  Metfehnikoir,  **8tadien  the  very  ■atisfaetory  memoir  of 

Uber  die  Entwickelnng  der  Echi-  Salenka,  ^  Zor  Entwickelang  der 

nodermen     and     Memertinen  **  Holothurien  *'  (*  Zeitsohrift  fur 

(<  Mem.  de  F  Acad,  de  St.  Patera-  Wiia.  Zoolog^a^  VQ^i«^« 
boQif ,  ziv.,  1869) ;  and  eapociaUy 


and  peritoneal  coat  of  that  Tiaom ;  wliile  Die  outer  walli 
attacbmg  itself  to  the  eotoderm,  or  to  the  meaobbwtio  cdU 
which  line  it,  ie,  with  Ihem,  conrerted  into  tlie  moaealar 
and  peritoneal  inveetment  of  the  parietea  of  Uie  body. 
The  interapaoe  between  the  two  ia  the  peritoneal  cari^. 


Fig.  IST.-DeTelopment  of  ft  Bololbnrid  (■Rer  Mulliir).— A,  Eart; 
condition  of  the  larva  (Aurinlnria) ;  g,  the  dorsal  pom  trf'  h,  Iki 

— V..1 ■ r,    1-. . '^  lolMtino;  p,  donal  poco  ;/,/", 

Ita  prolongatioiia ;    i,  caler— — 
Ircnlu  cllUtad  bands  ;  g,  i 


ambulMral  nc;  B,  Ut«T  atage 
oiroular  ambulftcral  Totsel  wit 
body ;  C,  yoong  Uaiotkwia  wltl 


nal  i  f,  P 

In  the  meanwhile,  the  bodj  of  the  embiro  elongate*,  the 
tentaciila  are  deTeloped  around  the  monUi,  the  ciliated  baad> 
diaappear,  and  the  Holothniid  Echinoderm  is  complete. 

Thna  it  is  clear  that  the  peritoneal  cavity  of  the  Hole- 
thnrid  ie  an  enteroccele,  and  that  it  answers  to  the  peri- 
visceral  cavitj  of  SagiHa,  or  of  the  Brachiopoda ;  and 
further,  that  the  amhulacral  Tesaels  are  also  modific»ti<mi 
of  the  enteroccele.  UoreoTer,  it  ia  obvious  that  tlie  atone- 
turea  which  are  developed  between  the  ent«roccele  and  the 
ectoderm  and  endoderm,  answer  to  those  which  az«  evolTsd 
from  the  mesoblast  in  other  aniniBla ;  and  that  the  adoU 
Echinoderm  stands  in  the  some  relation  to  tbe  JSjAmo* 
•pvedium  as  an  AimeUd  does  to  its  embryo ;  the  adnlt  f onn 
being  due  to  the  peculiar  arrangement  of  the  parte  de- 
reloped from  ^ mewAAaiA..  '^Iti-^axV.A^liABciiliiopBdiwa 


VBM  ASTBBIDaA.  553 

oast  off  in  the  oonne  of  the  deyelopment  of  the  HolO' 
vridea, 

I.  The  AsTBBiDEA. — A  Star-fish  is  comperable  to  a 
dothoiid,  the  ambulacra  of  which  are  restricted  to  its 
il  half,  flattened  out  so  as  to  have  a  very  short  axis; 
ile  its  equatorial  diameter  is  greatly  increased,  and 
xluced  in  directions  corresponding  with  each  ambu<- 
rum.  The  result  would  be  a  disk,  having  the  form  of  a 
itagon,  or  of  a  five-rajed  star,  with  ambulacra  only  on 
kt  face  of  the  disk  which  bears  the  mouth.  Hence  the 
bulaeral,  and  the  opposite,  or  antambulaoral,  faces  are 
equal  extent. 

iiost  Atieridea  are  like  five-rayed  stars,  but  some  are 

itagonal  disks  (Ooniaaier),  and  some  few  {SoUuter)  have 

tre  than  five  rays.    In  Britinga,  the  rays  are  much  more 

erent  from  the  disk  than  usual,  and  the  genus  thence 

aires  an  outward  resemblance  to  an  Ophiurid. 

11  the  Atieridea  are  provided  with  a  skeleton  made  up 

•lates  or  thick  rods,  composed  of  a  dense  calcareous 

t>rk.    A  deep  groove,  radiating  from  the  mouth  to  the 

)f  the  ray,  marks  the  position  of  each  ambulacrum, 

he  sides  of  this  groove  are  supported  by  two  series  of 

^4Uind  osndea,  which  meet  and  articulate  together  in 

iddle  line  or  roof  of  the  gproove.    The  ambulaoral 

uid  canal  lie  superficial  to  these  ossicles.    There  are 

I  tentacula. 

five-rayed  body  of  the  commonest  of  British  Star- 

the  Fivefinger  (Urtuier,  or  AHerticanthion,  rubens), 

I  an  oral  face,  in  the  centre  of  which  the  mouth  is 

and  an  opposite  or  ahoral  face.    The  hardly-dis- 

anal  aperture  is  situated  not  exactly  in  the  centre 

%ce,  but  close  to  it.    The  mouth,  which  varies  very 

size,  lies  in  the  middle  of  a  soft  membranous  oral 

deep  furrow,  the  ambulacral  groove,  occupies  the 

the  oral  surface  of  each  ray,  and  is  nearly  filled 

e  Hoffhiann,  '*  Zur  Anatomie  der  Att«rlden."    Q  ISUd^t- 
z«hiv;  Bd.  ii.  1874.) 


£64       THE  A.SATOHT  OP  IHVEBI8BKATBD  AKtlUl^.  ^ 

hj  contractile  sacker-like  pedicels,  with  cirenlar  diacoj'ltkl 
Olds,  apparently  amuiged  in  tour  loDgitudioal  a«ri«K.  Tbi: 
deepest  part  at  the  groove  is  at  ite  central  end.  where 
ita  lioing  passes  iato  the  oral  membrane.  The  sfa&Uo«reBt 
part  IB  at  Ita  dintal  end,  where  it  tra'iuinat^a  agaLuBt  ■ 
median  projection,  the  peduncle  of  the  eye.  on  the  aboikl 
Bide  uf  which  is  the  single  median  ovular  ttfalarU.  Lines 
drawn  from  the  muutli  along  ea«b  ambuliicrutn  tu-e  termed 
radii,  nnd  the  regions  oocnpied  bj  the  ambniacra  are  Buid 
to  be  radiid.  The  parts  of  the  body  situated  between  the 
ambulacra  are  inlerradial.  The  lateral  woUb  of  the  unbu- 
kcral  grooves  of  adjiu^nt  ambulacru  unite  at  the  cirooin. 
ference  of  the  oral  disk,  and  give  rise  to  &re  atl«rraMal 
aaglee.  On  one  side  of  the  aboral  face  of  the  centre  of  the 
body,  between  the  origins  of  two  of  the  rajs,  and  then^uri; 
interradial  in  posHiou,  ia  an  oial  or  somewhat  pentagonal. 
eligbtly  convex,  porousplate,  the  eurfaceof  which  is  covered 
with  uiuTow  meandering  grooves.  Tbia  it  the  madrtpcHe 
tiAerde  or  ttiatireporite. 


THB  ASTBlUDaA.  555 

tached  to  tlie  oencola  by  ligamentous  fibres  at  one  end, 
id  free  at  the  other ;  and  the  calcareons  stroctazes  oon- 
ined  in  the  pedieeUarieB.    On  the  antambtdacral  wall  of 
le  body,  the  osaicnla  are  elongated  rods  of  very  unequal 
Qgths,  united  together  in  such  a  manner  as  to  leave  poly- 
>nal,  rounded,  or  elongated,  meshes.    The  sides  and  roof 
each  ambulacral  groove,  however,  are  bounded  by  two 
lies  of  regularly  disposed  and  similar  ambtUaerdl  omHcUs, 
bich  lean  against  one  another  in  the  middle  line  above, 
verge  so  as  to  enclose  the  ambxdacral  gproove,  and,  at 
leir  outer  ends,  abut  upon    thick   short   adamMaeral 
Mdcles,  which  lie  at  the  sides  of  the  groove  (Fig.  1S9,  B). 
Between  every  two  ambulacral  ossides  in  the  same  half 
!  the  ambulacrum  there  is  a  canal,  formed  by  the  junction 
!  notches  in  the  oral  and  distal  faces  of  the  two  ossicles, 
onsequently  there  is  a  half -pore  on  the  oral,  and  another 
df-pore  on  the  distal  face  of  each  ossicle.    The  half- 
re  on  the  oral  face  is  always  internal  in  position  to 
)  half -pore  on  the  distal  face,  and,  as  the  part  of  the 
bulaoral  ossicle  which  lies  between  the  two  is  thin, 
row  of  pores,  though  it  is  really  single  and  bent  in 
harp  zigzag,  appears  at  first  sight  to  be  double.    The 
ts  which   connect   the    ambulacral  vesicles  with  the 
eels,  traverse  these  pores ;  and  the  comparatively  large 
very  flexible  and  extensile  pedicels  are  thus  so  closely 
ed  together,  that  they  appear  to  form  a  double  row, 
«ch  side  of  the  middle  of  the  ambulacrum, 
the  circumference  of  the  oral  disk,  the  ossicles  of  the 
\aora,  diminished  in  size  and  closely  united  together, 
i  pentagon,  the  angles  of  which  answer  to  the  ends  of 
ibnlaoral  gprooves,  round  the  oesophagus.    The  oon- 
oater  ends  of  the  pair  of  ambulacral  ossicles  nearest 
ath  project  on  the  oral  face,  outside  the  buccal  mem- 
as  five  vertical  crests,  armed  with  strong  spines, 
are  beset  with  pedicellarise.     In  correspondence 
ese,  five  falciform  folds  of  the  perisoma,  more  or 
ified,  project  into  the  cavity  of  the  body.    They  are 
al  in  position,  and  extend  xip  \a  \2kift  ^iX)^T«^^«iS^.. 


556      THB  ANATOMY  OF  nrYBBTSBSATSD  AXIMAIM. 

Their  inner  edges  are  free,  and  look  towaids  the  ■fawMA. 
with  one  of  them,  the  madreporic  canal  and  the  nuns 
which  accompanies  it,  are  closelj  connected. 

The  tpines  are  more  or  lees  moveablj  united  with  the 
oesicola,  but  there  are  no  such  regolar  joints  mm  aie  met 
with  in  the  .EeAiaidea.  The pedicettarice  are  snpportednpoa 
short  flexible  peduncles.  The  skeleton  of  each  consists  of 
two  blades  articulated  with  a  basal  piece.  From  the  centre 
of  this  Tciy  strong  adductor  muscles  proceed  to  the  inner 
faces  of  the  blades,  and  weaker  fibres,  attached  to  the  exterior 
and  to  the  outer  faces  of  the  bases  of  the  blades,  act  as 
divuricators. 

The  guUet  opens  into  a  wide  stomach  produced  into  five 
large  cardiac  mcs^  the  walls  of  which  are  subdiyided  into 
many  sacculi.  Each  cardiac  sac  is  radial  in  position,  and 
may  extend  a  short  way  into  the  cavity  of  the  aim  to 
which  it  corresponds.  On  the  aboral  side  of  these  mum, 
the  alimentary  canal  suddenly  narrows,  and  then  dilatfs 
again  into  a  shallow,  but  wide,  pentagonal  pyloric  sac,  the 
angles  of  which  are  produced  into  five  tubes.  Each  of 
these  passes  along  the  middle  of  the  aboral  face  of  a  ray, 
and  divides  into  two  branches,  which  run  parallel  with  one 
another  through  half  or  two-thirds  the  length  of  the  r^j, 
and  end  blindly.  The  branches  give  off  numerous  ceeosl 
dilatations,  arranged  in  pairs  on  opposite  sides,  and  these 
hang  down  into  the  cavity  of  the  ray.  The  edges  of  the 
pentagonal  pyloric  sac  and  the  aboral  faces  of  its  saocnlated 
branches  are  connected  by  mesenteric  folds  with  the  abonl 
perisoma.  The  oral  faces  of  the  cardiac  sacs  are  similarly 
connected  by  pairs  of  mesenteric  folds  with  the  sides  of 
the  corresponding  series  of  ambulacral  ossicles.  The 
aboral  face  of  the  pyloric  sac  presents  an  aperture  closed 
by  projecting  valvular  folds,  which  leads  into  the  short 
tubular  intestine.  The  latter  terminates  in  a  minute 
anal  pore,  situated  nearly  in  the  centre  of  the  aborsl 
face  of  the  body.  The  intestine  receives  the  duct  of  a 
cfficum  divided  into  two  main  branches,  each  of  which 
hfw   many  minoT  a\)\>diNmoi^.    M.  \2[^  ^•n-imf^]^  having 


THI  A8T1BIDBA.  557 

its  month  downwards,  is  divided  into  two  ludres,  by  a 
yertical  plane  passing  throngh  the  month,  the  central 
point  of  the  aboral  face,  the  madreporic  tubercle,  and 
the  middle  line  of  the  raj  opposite  to  the  tubercle;  and 
if  this  ray  is  anterior ;  then  the  anns  opens  into  the  left 
posterior  interradial  space,  and  the  cseca  lie  partly  in  this 
and  partly  in  the  left  anterior  interradial  space. 

The  nervous  *  and  vascular  systems  of  the  Star-fish  are 
so  closely  related  to  one  another  that  they  may  be  best 
considered  together,  and  as  there  is  least  difficulty  in 
malring  out  their  arrangement  in  the  ambulacra,  the  study 
of  them  may  be  commenced  in  this  region. 

When  the  suckers  of  an  ambulacrum  are  carefully  cut 
away,  a  longitudinal  ridge  is  seen  to  lie  at  the  bottom  of 
the  groove  between  their  bases.  This  ridge  is  the  ambula' 
eral  nerve.  Followed  to  the  apex  of  the  ray,  it  ends  upon  the 
eye  and  its  tentacle ;  in  the  opposite  direction,  it  reaches  the 
oral  disk,  at  the  periphery  of  which  it  divides,  and  skirting 
the  margins  of  the  disk,  joins  the  branches  formed  by  the 
bifurcation  of  the  adjacent  ambulacral  nerves,  thus  giving 
rise  to  a  subpentagonal  ring  round  the  mouth. 

The  eye  f  is  a  thick  cushion-like  expansion  of  the  ectoderm 
continuous  with  the  ambulacral  nerve.  In  it  are  imbedded 
many  dear  oval  bodies  surrounded  by  pigment,  which 
appear  to  represent  the  crystalline  cones  of  a  compound 
eye. 

The  tentacle  which  lies  on  the  aboral  side  of  the  eye, 
resembles  one  of  the  pedicels  in  structure,  but  has  no 
terminal  sucker ;  its  function  appears  to  be  tactile. 

In  a  good  transverse  section  of  one  of  the  arms  or  rays 

of  the  Star-fish,  the  nerve  is  seen  to  be  a  band-like  thicken- 

fng  of  the  ectoderm,  the   cells  of  which    have   become 

peculiarly  modified,  but  which  is  continuous  laterally  with 

the  ordinary  ectodermal  covering  of  the  pedicels.     This 

band-like  nerve  constitutes  the  superficial  wall  of  a  canal, 

*  See  Wilson,  "  The   nervous  Teuscher  cited  below, 

system  oftheAsterida^C  Trans.  f  Conf.    Uaeokel,    *Zeit   fur 

Linnean  Soeietv,'  1862),  and  the  Wiss.  Zoologie/  18GQ. 
later  eontribotions  of  Professor 


558       THB  AKATOXT  0¥  IVTXBTBB&iLTSD  AVIMAIiB. 

which  extends  through  the  whole  length  of  the  ambnlacniiii 
and  may  be  termed  the  amhulacral  neural  eandL  It  is 
diyided  by  a  longitadinal  septum.  At  its  oral  end,  as  has 
been  seen,  each  ambolacral  nenre,  when  it  reaches  the  onl 
membrane,  diyides  into  two  divergent  branchiea,  whidi 
unite  with  the  corresponding  branches  of  the  other  amba- 
lacral  nerves  to  form  the  oral  ring.  Answering  to  the 
latter  is  a  wide  circular  neural  canal,  into  which  the  ambu- 
lacral  neural  canals  open. 

In  the  transverse  section  of  the  arm,  a  second  and  mnch 
larger  canal  is  seen  to  lie  between  the  conjoined  ends  of 
the  ambulacral  ossicles  and  a  strong  septum,  containing 
transverse  fibres,  which  separates  it  from  the  neural  ^hm>^1 
This  is  the  radial  canal  of  the  ambulacral  system  of 
vessels.  At  its  oral  end  it  opens  into  the  eurcmnorel 
ambulacral  vessel  which  lies  close  to  the  ossicles  to  whidi 
the  margins  of  the  oral  membrane  are  attached.  Ftom 
opposite  sides  of  the  radial  canal,  short  branches  are  given 
off,  which  pass  between  the  ambulacral  ossicles,  and  ea^ 
opens  into  the  neck  of  a  relatively  large  sac,  with  nraacakr 
walls  {ambulacral  vesicle),  which  lies  on  the  aboral  face  6L 
the  ambulacral  ossicles  in  the  interior  of  the  ray.  Hk 
neck  of  the  ambulacral  vesicle  passes  in  the  opposite 
direction  into  one  of  the  pedicels.  Thus  the  ambnlacnl 
vessel  communicates  with  the  cavities  of  all  the  pedioelf 
on  the  one  hand,  and  with  the  cavity  of  the  ciixmmcnBl 
ambulacral  vessel  on  the  other.  Five  pairs  of  wwall 
eminences,  consisting  of  caeca  which  open  into  the  dr- 
cumoral  vessel,  are  seated  upon  it;  and  from  one  part 
of  it,  opposite  one  of  the  interradial  falciform  folds  alrady 
mentioned,  springs  a  canal,  which,  taking  a  sinuous 
passes  to  the  aboral  face  and  terminates  beneath  the 
dreporie  tubercle;  this  is  the  madreporic  mn^  It  jg  not 
a  simple  tube,  but,  as  Sharpey  first  observed,  its  waUs  ait 
doubly  involuted  so  as  partially  to  obstruct  its  cavity,  ani 
it  is  strengthened  by  annular  (^deifications.  The  poies  d 
th«  madreporic  tubercle  place  the  cavity  of  the  aadxepoiie 
oamil  in  yKmTftTiT\\oA\.\aa.-^V^>3tvfe.  es^xscvor^  whence  it  foUowi 


^ 


THS  ASTSBIDSA. 


559 


that  the  cayities  of  the  whole  ambolacral  ayBtem  mnBt  he 
directly  acoeaaihle  to  the  sea-water  in  which  the  Star-fish 
lives.  The  madreporio  canal  is  invested  by  the  lining  mem- 
brane of  the  peritoneal  cavity.  This  indoses  a  sinus, 
which  aooompanies  the  madreporic  canal,  and  into  the 
interior  of  which  a  fold  projects. 

There  is  no  great  difficulty  in  ascertaining  the  existence 
of  the  structures  which  have  now  been  described,  and 
all  anatomists  are  agreed  as  to  the  nature  of  the  ambu- 
lacral  system.  But  whether  the  neural  canals  are  to  be 
considered  as  a  special  system  of  blood-vessels,  and  the 
sinus  which  accompanies  the  madreporic  canal,  a  heart,  as 
is  usually  assumed,  appears  to  me  to  be  very  doubtful.*  I 
am  disposed  to  think,  in  fact,  that  not  only  these  canals, 
but  the  circular,  or  rather,  pentagonal  vessel  which  has 
been  described  as  situated  on  the  aboral  face  pi  the  body, 
around  the  anus,  giving  off  various  branches  to  the  viscera 
and  communicating  with  the  so-called  heart,  are  mere  sub- 
divisions of  the  interval  between  the  parietes  of  the  body 
and  those  of  the  alimentary  canal,  arising  from  the  dis- 
position of  the  ambulacral  vessels  and  that  of  the  walls 
of  the  peritoneal  cavity ;  both  of  which,  as  their  development 
shows,  are  the  result  of  the  metamorphosis  of  saccular  diver- 
ticula of  the  alimentary  canal,  which  have  encroached  upon, 
and  largely  diminished,  the  primitive  perivisceral  cavity 
which  exists  in  the  embryo. 

The  peritoneal  cavity  of  the  body  and  rays  is  filled  with 

it  and  with  the  nearal  canslf. 


*  Since  Tiedemann't  time,  the 
presence  or  absence  of  a  blood- 
vaicular  system  in  the  Starfishes 
has  been  attemately  asserted  and 
denied.  The  recent  investiga- 
tions of  Oreef,  **  Ueber  den  Ban 
der  Eohinodermen  **  (*  Marburg 
Sitsunesberichte,'  1871-2X  Ho£ 
man  (1.  c),  and  of  Tensoher, 
**  Beitrage  sur  Anatomic  der 
Eohinodermen  "  Q  Jenaisehe  Zeit- 
■chrift,'  Bd.  X.),  are  in  fkvonr  of 
the  existence  of  the  '  anal  ring,' 
and  of  an  extensively  ramified 
system  of  canals,  ooiinected  with 


But  it  does  not  appear  to  me  that 
the  facts,  as  they  are  now  known, 
Justify  tike  assumption  that  these 
canals  constitute  a  distinct  system 
of  blood-vessels.  Injections  show 
that  an  these  canals  communicate 
with  the  ambulacral  vessels,  and 
with  the  exterior,  by  means  of 
canals  in  the  madreporic  tubercle 
which  open  partly  outwards, 
partly  into  the  madreporic  canal, 
and  partly  into  the  sinus  which 
accompanies  it,andcomraunieat«& 
with  the  QVxc;!QkmoTiXxA!<Q3niiL^^»MS^« 


560       THE  AKATOMY  OT  IFYXBTSBRATED  ▲KIMAI.8. 

a  watery  oorpusculated  fluid ;  a  similar  fluid  is  found  in  the 
ambulacral  vessels,  and  probably  fills  all  tbe  canals  whicb 
liave  been  described.  The  corpuscles  are  nii<deated  oells, 
wHich  exhibit  amoeboid  movements ;  and  the  fluid  bo  ob- 
vionsly  represents  the  blood  of  the  higher  animal  it,  that  I 
know  not  why  the  preposterous  name  of  "  ohylaqueous 
fluid"  should  have  been  invented  for  that  which  is  in  no 
sense  "  chyle/'  though,  Uke  other  fluids  of  the  living  body, 
it  contains  a  good  deal  of  water.  As  the  cavities  of  the 
tubular  csBca  of  the  perisoma  communicate  freely  with  the 
general  cavity,  and  their  walls  share  in  the  general  ciliation 
of  the  lining  of  the  cavity,  it  is  very  probable  that  they 
may  subserve  the  function  of  respiration. 

The  genital  glands  are  situated  in  pairs,  interradially,  at 
the  junction  of  the  body  with  the  rays.  Each  gland  is 
divided  into  a  number  of  elongated  processes,  the  common 
base  of  which  is  attached  to  the  face  of  one  of  the  inter- 
radial  septa,  while  the  processes  project  freely  into  the 
cavities  of  the  arms.  According  to  Hoffmann  and  Greef, 
the  inner  cavities  of  the  genital  processes  are  filled  when 
the  vascular  system  is  injected.  It  is  possible,  therefore, 
that  the  genital  glands  are  merely  processes  of  the  meso- 
dermal layer,  in  the  walls  of  which  the  genital  products  are 
developed ;  in  which  case  there  would  be  a  close  approxi- 
mation between  the  genital  glands  of  the  Star-fishes  and 
those  of  the  Crinoids.  According  to  Greef,  the  external 
openings  of  the  genital  glands  are  visible  in  UraHer,  in  tiie 
breeding  season ;  in  other  Star-fishes,  they  are  conspicuous 
in  the  interradii  of  the  aboral  face  of  the  body.  In  LuideOy 
Ophidiaster  and  some  other  genera,  the  glands  extend  far 
into  the  interior  of  the  arms,  and  Prof.  G.  O.  Sars*  has 
pointed  out  that,  in  Brisinga  endecacnemos,  the  genitalia 
are  numerous  distinct  glands,  arranged  in  two  series,  one 
on  each  side  of  the  middle  line  of  the  central  half  of 

*  *  Researches    on    the  Struc-  proves   that   BrUmga  is  a  troe 

tore  ftnd  AflBnity  of  the  genus  Asterid,  and  not,  as  has  been  siip> 

Britmga^    1870.     In    this    im-  posed,  a  transitional  fonn  beiwesa 

portant    memoli    ^e      vqAiot  >3[i<^  AsCeriofea  and  the  Opkimnim, 


tarn  ssWiOPiuKT  or  tbx  UTnnm.        561 
encb  ra;.    Each  of  theae  OTories  or  tcatea  has  «  separate 

Id  Bome  Star-fiehea,  ae  in  some  Holothoridi,  the  embryo 
possea  into  the  Star-fish  fonn  withont  anj  free  lairal  stage. 
Bat,  more  naualfy,  an  Echinopndiom  is  tonoed  in  the  same 
wBj  BM  in  the  Holothorians,  though  it  presents  diSerencea 
In  the  arrangement  of  it«  ciliated  bands,  and  especially  in 
their  prolongation  into  nomennw  lobex  or  narrow  processes. 
ua  in  the  remarkable  ferm  originally  named  Bipinnaria. 
(Fig.  135,  D  D',  and  I^g.  138.)  It  baa  no  calcareous 
skeleton. 

Fig.  138. 


ria,  BfMr  MuUer).— A, 

,  _____ ^ ■£»):  C,  09)B«Hina  with 

rudiment  of  tht  Stu-Sih,  a,  moaih;  t,  <Eaop)uga>|  c,  itonueh: 
b',  inteitine ;  o,  snui ;  s,  iraatnl;  jr,  don«l  (ld«  of  the  Mitaiior  end 
of  the  body;  d,  f.  ellUled  buidi ;  k,  iuboI  divertiaulum  fbrmlog 
the  rudimeDt  of  the  unbnlunl  viacalar  ■jstem,  uid  opening  ti- 
ternnU]'  by  the  pore  jr. 

Ancerdiug  to  Uie  obaarTationa  of  Prof.  A.  Agassiz,*  which 
have  been  confirmed  bj  MetochnikofT  and  Greef,  the  ambn- 
lacral  veasela  commeDoe  aa  diverticnla  of  the  stomach, 
which,  beconung  detached  from  the  alimentary  canal,  giye 
rise  to  the  peritoneal  cavity,  and  to  all  the  snbstance 

DMDt  of  wblah  U  detcribed  in  tbli 
Inportant  memoir,  ue  .^Mmun- 
OuiMpcUlidiu  ukd  A.  iotUiHU. 


•  "Embr 
toh."('Con 


Uw«lKT< 

ieM.>Thi 


of  lb*  Dailad  Bute*,' 
■pedei,  the  develop- 


562       THE  ANATOMY  OF  DfYBBTBBBATKD  AinXALS. 

of  the  body  between  the  endoderm  and  the  ectoderm.* 
A  portion  of  one  of  these  diverticohi,  howerer,  sep&rates 
itself  from  the  rest,  opens  externally  by  a  pore,  and  becomes 
metamorphosed  into  the  ambnlacral  yessels.  But  this 
ambulacral  diverticnlum  does  not  surround  the  gallet»  and 
consequently  a  new  mouth  is  developed  in  the  centre  of  the 
ambulacral  ring.  The  lanral  mouth  and  g^nllet  are  abolished, 
and  the  greater  part  of  the  body  of  the  Echinopsedinm  is 
separated  from  that  portion  which  contains  the  stellate 
Echinoderm.  The  latter  results  from  the  metamorphosis 
of  the  mesoderm,  which  is  modelled  upon  the  different 
divisions  of  the  enterocoele,  and  encloses  the  middle  portion 
of  the  alimentary  canal.f 


The  Ophiubidka. — The  brittle  Stars,  thongh  they  re- 
semble the  ordinary  Star-fishes  in  form,  differ  essentially 
from  them,  not  only  in  the  structure  of  their  skeleton,  but  in 
the  characters  of  the  Echinopsedium.  The  ambulacra  ai« 
confined  to  the  oral  aspect  of  the  body,  so  that,  as  in  the 
Asteridea,  the  ambulacral  and  oral,  the  antambulacral  and 
the  aboral  surfaces,  respectively  coincide.  The  mouth  is 
situated  in  the  centre  of  the  oral  face,  but  no  grooves 
radiate  from  it  along  the  ambulacra,  which  are  covered  hj 
a  series  of  plates  of  the  skeleton.  The  alimentary  caiud 
is  a  simple  gastric  sac  without  cseca,  and  has  no  intestine 
or  anus.  In  contradistinction  from  the  Star-fishee,  the 
prolongations  of  the  peritoneal  cavity  into  the  rays  are 
very  narrow. 

The  typical  Ophiuridea  possess  a  very  complete  calcareooi 
skeleton ;  which,  on  the  body  and  on  the  exterior  of  the 
rays,  has  the  form  of  plates.  On  the  body,  the  disposition 
of  these  vanes  much ;  but  five  of  them,  which  are  situated 


♦  Probably  independently  de- 
^loped  mesoblastic  cells  contri- 
ate  to   the  formation    of   the 

metodenn  as  in  the  Holothorids. 
t  Greef  (/.e.)has  worked  out  the 

devetopment  of  Uratter  {Astera- 


cttHthton)  rubeju^  the  larval  ftta 
of  which  resembles  the  B^mmarit 
and  Braddolaria  of  HeUinxloiii 
described  by  M&ller.     ParSess- 

genesis  appears  to  oooor  ia  tkii 
tar-fish. 


THX  OPHIT7BIDBA. 


563 


interradially  in  the  neigHbourhood  of  the  mouth,  are  often 
larger  than  the  others,  and  are  termed  »cuia  huecalia. 

Each  ray  contains  an  internal  solid  axis,  composed  of  a 
single  series  of  quadrate  cueial  ossicles  (Fig.  139,  C,  a),  each 
consisting  of  two  lateral  halves  united  by  a  longitudinal 
suture  and  articulated  together  by  tenon  and  mortice  joints 
ux>on  their  terminal  surfaces.  Each  of  these  ossicles  (which 
are  sometimes  termed  verie&roZ)  is  surrounded  by  four  plates ; 
one  median  and  antambulacral  (Fig.  139,  0,  h),  two  lateral 
(Fig.  139,  B,  c)  and  one  median  and  super-ambulacral  (Fig. 

Fig.  139. 


Fig.  139.— A,  ventrtl,  B,  lateral,  views  of  a  ray  of  Ophiura  texhtrata 
(after  Miiller).  C,  transverse  section,  a,  axial  or  ^'rertebrar* 
ossicle  of  ray ;  6,  antambulacral  plate ;  c,  lateral  plate ;  d,  ventral  or 
superambulacral  plate.  D,  section  of  a  ray  of  an  Asterid,  Attro- 
peeten  aurantiacut  f after  Gaudry).  a,  ambniacral  or  **  vertebral  *' 
ossicles ;  6,  adambuiacral  ossicles ;  c,  c',  marginal  ossicles ;  d,  paxillse 
of  antambulacral  surface. 

139,  A,  d).  The  lateral  plates  may  meet  in  the  middle  line  on 
both  the  ambulacral  and  the  antambulacral  faces.  Between 
the  lateral  plates  are  the  apertures  by  which  the  pedicels 
make  their  exit.  The  oral  aperture  is  surrounded  by  five 
^cU  angles,  each  of  which  consists  of  five  pieces.    The  two 

2  O  2 


564       THS  AKATOMT  OF  INTBBTBBRATBD  AHI1CAL8. 

oonstitaents  of  the  axial  oesiole  whicli  lies  at  the  <nral  end 
of  a  ray  become  moveably  articulated  with  one  another, 
while  each  ankyloses  with  an  interambulacralpieoe.  Trans- 
yerse  muscles  connect  the  two  interambulacral  piecea,  the 
oral  edges  of  which  are  articulated  with  a  long  narrow 
plate,  the  torus  angularis  (Fig.  140,/).  The  free  anrlace  ol 
the  tarua  angularia  lies  in  the  walls  of  a  sort  of  Testibiile  in 
front  of  the  mouth.  A  number  of  short  flat  proccnaeo,  the 
pcdcB  angulares,  are  articulated  with  it  and  moved  by  special 
muscles.  They  doubtless  perform  the  function  of  teeth. 
Rudimentary  representatives  of  the  calcareous  ring  of  the 
Hohthuridea  and  of  the  parts  of  the  lantern  of  the  Sehinidea 
exist  as  delicate  calcareous  plates,  which  lie  on  the  cixxsular 
ambulacral  vesseL  The  latter  is  usually  provided  with 
CflBcal  appendages,  or  Polian  vesielea.  The  madreporic  canal 
ends  on  the  surface  of  one  of  the  tenia  buecaUa ;  the  radial 
ambulacral  vessels  run  in  the  arch  between  the  axial  oasicles 
and  the  super-ambulacral  plates.  The  nerve  lies  superficial 
to  the  super-ambulacral  vessel,  but  is  also  covered  by  the 
super-ambulacral  plate.  A  neural  canal  lies  between  the 
nerves  and  the  ambulacral  vessels.  The  pedicelB  are  tenta- 
culif  orm,  and  have  no  vesicles  at  their  bases.  The  genital 
glands  are  lodged  in  the  disk,  and  pour  their  products  into 
the  peritoneal  cavity,  which  communicates  freely  with  the 
exterior  by  verticidly  elongated  apertures  placed  inter- 
radiaUy  on  its  margins.*  According  to  Metschnikoff, 
Ophiolepis  aquamaia  is  hermaphrodite. 

The  early  conditions  of  the  embryos  of  most  Ophwmridm 
are  similar  to  those  of  other  Echinoderms,  and  acquire  the 
characteristic  bilateral  ciliated  zone;  but  in  some,  the 
embryo  does  not  become  an  Eehinopcedium,  but  pannnn 
directly  into  the  adult  condition.    Thus  Krohn  discovered 

*  Muller,  '*  Ueber  den  Bau  der  Apparently  cecal  divertieiila  cf 

Echinodennen"(Abh.Berl.  Akad.  the    circular   ambulacral  canal, 

1853) ;  Teuscher  (1.  c);  Simrock,  and  of  the  necks  of  the  PtoUaa 

^Anatomic  und  SchUogonie  der  vesiclei  (iNua  €mbuiacrttiia  coai) 


riaeiii  vtrau"     (*  Zeitschrift      which    traverse    the   peritoaeal 
Wiss.  Zoologie,*  1876).    The      cavity  in  aU  directiona. 
latter  writer  describes  numerous 


TKt  OPRmslDIA.  565 

that  the  eiiibi70  of  OphiolepU  eiliata  it  developed  within 
the  bodj  caritf  of  the  {lorent,  to  whioh  it  odhereB  b;  a 
bind  of  pedicel.  Where  an  Eehinopeedivm  etage  ezista,  the 
larra  is  a  Pluieus  (Fig.  135,  0  C).  The  donal  wall  of  the 
boc^  of  the  embrjo  exhibits  •  median  oonioal  ontgrowtlt ; 
along  the  ooone  of  the  ciliated  band  BjmmetrioaUj'  dia- 
poaed  proceases  are  developed;  and  these  oatgrowiha  ore 
supported  bj  a  oalcoieooa  skeleton,  which  ia  ^ao  bilaterall; 
ajmrnetricaL  Uetechnikoff  *  has  made  the  interesting  ob- 
serration  that  in  an  Ophiorid  (probablj  OphiothriafragUu) 
the  whole  aTstem  of  periTisceral  and  ainbnlacral  cavities 

Fig.  1«. 


Fix.  140.— A,  Ophhirplj  ciiiala,  oral  ikeletoa  tmta  within  (Bftfr 
Hiillst). — B,  dorsal  mkrgiiial  pUtes;  b,  ventral  platat;  d,  vartebral 
owicles;  c,  intcrunbulacral  piecn  of  oral  uigle ;  /,  tonu  uigu- 
laria  ;  g,  apirturee  for  oral  bmtaclei ;  h,  poiltlon  of  nBrvoui  eollu' ; 
t,  linpr««*ion  of  circular  unbolacral  vesul ;  i,  oriflcs  In  tha  firtt 
ambalacral  platg  for  the  tcntseolar  branch  of  the  oral  venal ;  o, 
pals  anKalare*.  B,  AMiropSjrIm,  oral  ikelelon  leen  from  wtthiu 
(after  Muller)  :  ■•  n,  periiiomial  platei ;  other  iMtars  ■•  In  A. 

arises  from  two  bodies,  one  aitoated  on  each  side  of  the 
gullet,  which  are  solid,  Qiough  it  is  possible  that  Uiej  may 
primitively  have  been  hollow  diverticula  of  the  archenteron. 
Two  cellular  masses  become  detached  &om  thwe  bodies, 
applj  themselves  to  the  sides  of  the  stomach,  and  are  con- 


566       THE  ANATOMY  OF  INYEBTBBRATBD  ANXMALS. 

verted  into  disks,  from  which  the  parietal  and  Tiaceral 
walls  of  the  peritoneal  cavity  take  their  origin.  The  rest 
of  the  solid  body  on  the  left  side  of  the  gollet  aoqniree  a 
vesicular  character,  opens  by  a  dorsal  pore,  and  grows 
i*ound  the  gullet,  to  give  rise  to  the  circular  ambnlacral 
vessel.  The  other  solid  body  disappears.  The  mouth  of 
the  Echinopeedium  becomes  that  of  the  Ophiurid. 

It  cannot  be  doubted  that  these  solid  bodies  take  their 
origin,  in  the  same  way  as  in  other  Echinopsedia,  from  the 
hypoblast ;  and  thus  the  question  arises,  how  far  does  the 
mesoblast  thus  formed  differ  from  that  which  arises  by 
the  mere  outgrowth  of  cells  from  the  hypoblast,  as  in  the 
Dog-fish,  and  how  far  does  thia  case  tend  to  render  it 
probable  that  a  schizocoele  is  only  a  modification  of  an 
enterocoele  P 

The  EoHiNiDEA. — An  ordinary  Sea-urchin  is  comparable 
to  a  Holothuri  J,  with  the  body  distended  into  a  more  or  less 
globular  form,  and  with  a  skeleton  in  the  form  of  regular 
plates  arranged  in  meridional  series;  those  plates  which 
correspond  with  the  ambulacral  vessels  being  superficial  to 
the  latter,  and  consequently  x>erf  orated  by  the  canals  which 
pass  from  the  ambulacral  vessels  to  the  pedicels. 

In  the  Echinidea,  as  for  instance  in  the  ordinary  Echintu 
or  Sea<urchin,  the  perisoma  round  the  mouth  {perigiame) 
is  usually  strengthened  for  some  distance  by  irregular  oral 
plates.  In  addition,  ten  rounded  plates  are  placed  in  pairs 
close  to  the  lip ;  these  support  as  many  pedicels  and  are 
perforated  by  the  canals  of  the  latter.  A  much  smaller 
space  around  the  anus  (periproct)  is  similarly  protected  by 
anal  plates.  The  rest  of  the  body  is  supported  by  a  eon- 
tinuous  wall  made  up  of  distinct,  more  or  less  penta- 
gonal plates,  iisually  firmly  united  by  their  edges,  which 
is  called  the  corona.  Of  these  plates  there  are  twenty 
principal  longitudinal  series,  constituting  the  great  mass 
of  the  corona ;  and  ten  single  plates,  which  form  a  ring 
around  ita  aboral  or  apical  margin.  The  twenty  series 
of  longitadinal  ^AsA^ea  «iX^  ^Y^«ft^\s^\/^^  double 


THB  BcanipB^  . 


567 


five  ambalacntl,  (tod  fire  inter-ambiilacral— alternating  witK 
one  another  throt^hont  tbe  circn  inference  of  the  corona. 
Sach  double  eeriee  of  plates  presents  a  zigzag  suture  in 
tbe  middle  line,  formed  bj  the  alternating  arrangement  of 
tbe  triangular  extremities  of  its  component  elements.  The 
antoree  between  tbe  reapeotiTO  series  of  ambulacral  and 
interambolacral  plates,  on  the  other  hand,  are  less  obvions 

Fig.  1*1. 


Fig.  141.— Di*gnin  exhibiting  tbe  relBtiom  of  the  different  ijelemt  of 
ornni  in  ka  £cAJiH(.— a.  Dtouth;  b,  teeth;  e,  lipi;  d,  alieoli;  (, 
fslcet :  /.  Mirieate ;  g,  relnotor,  and  h,  prolrkolor  muules  of  leatem ; 


*piii( 


A,  prolrkolor  muules  of  leatem ; 
.  ._.i — Ml ;  i, polUn  veriele  J 

I,  tubercle  to  vhich  It  f«  krliculated;  t,  pediecUariiE i   h, 
,  madreiiaria  tubercle ;  z,  oculer  tpot. 


and  more  straight.  Each  ambulacral  plate  is  sabdivided 
bj  a  great«r  or  less  number  of  snturee,  which  traverse  it 
obliquelj,  into  a  corresponding  number  of  minor  plates; 
and  these,  inasmuch  as  thoj  are  perforated  b;  tbe  canela 


569      THB  AKATOXT  OT  nrYBBTEBKlLTSB  LVTMAUL 

or  poree,  which  give  exit  to  the  twoTesaels  whereby  each 
pedicel  is  placed  in  commnnication  with  ite  baaal  Tesielee 
and  with  the  ambulacral  reesel,  are  called  pore  pUttm, 
Throaghx>ut  the  greater  part  of  the  leagth  of  an  ambnlA- 
crum  of  the  common  Echinus  tpheera  (Fig.  142,  A)  each 
ambolacral  plate  is  thus  divided  into  three  pore  plates, 
traversed  altogether  by  six  pores  or  short  canals.  The 
outer  openings  of  these  canals  are  arranged  dose  together 
in  pairs  upon  little  excavated  shield-shaped  elevations^  or 
umbanes,  sculptured  on  the  outer  or  interambulacral  half 
of  the  face  of  the  ambulacral  plate;  but  their  inner 
extremities  are  much  wider  apart.  A  pore  plate,  or  sab- 
division  of  the  ambulacral  plate,  thus  corresponds  with 
each  pair  of  pores,  and  therefore  with  each  pediceL 
Lov^n  *  has  shown  that  the  pore  plates  are  the  primitive 
ambulacral  ossicles  in  the  Echinoidea.  At  its  apical  ex- 
tremity, in  fact,  the  ambulacrum  is  composed  of  only 
two  small  ossicles  which  meet  in  the  middle  line.  Each 
of  these  primitive  ambulacral  ossicles  is  perforated  by 
a  single  or  double  pore  for  the  pedicel  which  it  bears. 
But  as,  in  the  course  of  the  growth  of  the  corona,  new 
primitive  ambulacral  ossicles  are  added  between  the  ocular 
plate  and  those  already  formed,  the  latter  shift  towards 
the  oral  end  of  the  ambulacrum  and  grow,  in  correspondence 
with  the  larger  space  which  they  have  to  filL  But  thej 
grow  unequally ;  and  while  all  retain  their  primitiTe  con- 
nexions with  the  adjacent  interambulacral  plates,  some 
lose,  while  others  retain  their  median  union  with  the 
corresponding  ossicles  of  the  same  ambulacrum.  The  former, 
therefore,  are,  as  it  were,  pushed  away  from  the  middle  line 
by  the  union  of  their  encroaching  predecessors  and  suc- 
cessors. Groups  of  the  primitive  ambulacral  plates,  thus 
modified,  enter  into  close  union,  and  constitute  the  complex 
ambulacral  plates  of  the  fully  developed  ambulacrum. 

In  the  genus  Cidaris,  the  primitive  ambulacral  plates 
enlarge,  but  do  not  coalesce  into  secondary  ambulacral 

*  ^  Etudes  sur  les  Eehinoidto."   (*  Kongl.  Svenska  Vetentk-Aktd. 
Handlingar;  Bd.  U ,  \^1^.^ 


THI  MCBOriDIA.  869 

plates;  Iiaiioe  tiie  distinction  between  Bmbalaonl  i^tes 
and  pore  i^tea  Tanishes.  The  ambtUacnl  pUtea  are  ooa- 
tinned  on  the  peristome  to  the  margins  of  the  month, 
and  here  th^  become  somewhat  altered  in  fonn  and  their 
edges  overlap. 

In  the  living  genns  Agthmumoma,  and  in  certain  extinct 
Eehinidea  {Lapidoeaninu,  EchinoOmria),  the  plates  of  the 
corona  are  loosel;  united  and  overlap  one  another;  while, 
in  the  extinct  pabeozoic  Frri»ehoeehinidtB,  there  are  more 
than  two  series  of  interambnlaoral  plates,  those  in  the 
middle  of  each  interambidacmm  being  hexagonal. 

Fig.  143. 


Fig.  Ui.  (After  Hfiller.)— A.  Thnw  Knbatecnl  plitci  of  fcAhw 
^hrra,  sihibillni  Ihe  auiurn  of  the  pora  )>latei  of  which  tush 
■mbulaoni  plate  u  compoted.  B.  fart  of  Uie  petaloid  aalnilBeruDi 
■>r>  CJypcutrold. 

In  Eekinut,  the  apical  extremities  of  the  ambulacra  abnt 
npou  the  five  smaller  of  the  ten  single  plates  which  snrronnd 
the  periproct.  Each  of  these  is  perforated,  and  supports 
the  ejeepot ;  it  is  thence  called  an  ocular  plaia.  The  apical 
extremities  of  the  interambnlacra,  on  the  other  hand,  cor- 
respond with  the  five  larger  plates,  which  alternate  with 
the  ocular  plat«B,  and,  like  them,  are  perforated.  The 
aperture  is,  however,  larger,  and  constitutes  the  exit  for 
the  generative  products.  One  of  these  five  genUal  plates  is 
lai^er  than  the  others,  and  presente  a  peculiar  porous 
convex  surface,  which  is  the  madreporic  tubercla  Qi  rnodRi- 


570       THE  ANATOMY  OF  UfYEBTBBBATBD  AKIM ALS. 

porite.    The  latter  is  therefore  interambulacnil  in  pontioiiy 
as  in  the  Star-fish. 

Compariaon  with  the  elongated  Echinoderma  ahowa  that 
the  madreporite  lies  in  the  right  anterior  inter-radina  of 
the  sea-urchin,  so  that  the  anterior  ambolacmiii  is  that 
which  lies  to  the  left  of  the  madreporite,  when  the  latter 
is  directed  forwards.  In  consequence  of  being  able  to  dia- 
tingaish  this  odd  or  anterior  radios,  it  is  possible  in  any 
of  the  Echinidea,  to  separate  the  three  anterior  ambulacra, 
as  the  trivivfii,  from  the  two  posterior,  the  hivium ;  and  in 
the  fossil  genus,  Dysaster,  this  separation  of  the  ambulacra 
into  trivium  and  bivium  exists  naturally.  MiiUer  has 
pointed  out  that  in  all  the  flattened  Echinidea^  with  a 
special  ambulatory  surface,  the  latter  is  formed  by  the 
bivial  ambulacra  and  interambulacra,  while,  in  the  similarly 
modified  Holothuridea,  the  animal  rests  upon  the  trivium. 

Within  the  circle  formed  by  the  genital  and  ocular  plates 
the  x>eriproct  presents  a  variable  number  of  calcificiutionB, 
of  which  one,  the  anal  plate,  is  larger  than  the  rest.  The 
anus  lies  excentrically,  between  this  plate  and  the  poeterior 
margin  of  the  periproct. 

With  the  exception  of  certain  palaeozoic  forms  (Palachi' 
nus),  the  composition  of  the  skeleton  of  the  Echinidea  is 
always  essentially  similar  to  that  which  has  juat  been  de- 
scribed ;  but  the  form  of  the  body  and  the  relative  positions 
of  the  anal  and  oral  apertures  may  vary  very  much.  In  the 
Echinoida  (Cidaris,  Echiniu)  the  body  is  spheroidal,  and  the 
oral  and  anal  apertures  are  opposite  and  central,  or  veiy 
nearly  so.  In  the  Clypeastroida  {Clypeader,  Echinocyamui) 
the  form  of  the  body  varies  from  a  spheroidal  to  an  ex- 
cessively flattened  and  even  lobed  shape.  The  mouth  re- 
mains central,  but  the  anus  varies  in  position,  from  the 
apical  surface  to  the  margin,  or  even  to  the  oral  aurface,  aa 
iu  Echinaeyamus.  In  the  remaining  division  of  the 
Echinidea,  the  Spatangoida  (Spatangus,  Amphidotugf  Anan-^ 
chyles),  the  form  is  usiudly  a  somewhat  depressed  oval,  and 
both  the  oral  and  the  anal  apertures  are  excentric.  The 
madraporite  asoid  tVie  g<^mtal  and  ocular  plates,  on  the  other 


.*'  M 


THB  BCHIHIDBA.  571 

hand,  remain  in  the  centre  of  the  ahoral  region  in  all  the 
Echinidea, 

The  amhulacra  present  important  variationB  in  the  three 
divisions  of  the  Echinidea,  In  the  Echvnoida  they  are  ho- 
mogeneofiu,  presenting  the  same  composition  from  their 
oral  to  close  to  their  apical  extremities,  and  haying  the 
pores  and  pedicels  similar  throughout.  Furthermore,  the 
ambulacra  are  widest  in  the  middle,  and  taper  gradually 
to  each  extremity  {Echinus),  or  are  of  nearly  the  same  size 
from  one  end  to  the  other  {Cidaria), 

In  many  Clypeasiroida,  on  the  contrary,  the  oral  and  the 
apical  portions  of  each  ambulacrum  differ  very  widely,  or 
are  heterogeneous.  The  apical  moiety  is  usually  very 
wide  in  the  middle  and  tapers  to  a  point  marginally,  where 
it  joins  the  oral  portion.  Hence  there  is  an  appearance  of 
five  petals  diverging  from  the  apex ;  and  such  ambulacra 
are  called  petaloid  (Fig.  142,  B).  In  the  oral  portions  of  the 
ambulacra,  on  the  contrary,  the  pores  are  either  scattered 
widely  over  the  ambulacral,  and  sometimes  over  the  inter- 
ambulacral,  plates,  forming |>or6-arece ;  or  they  are  arranged 
in  bands  which  ramify  over  the  inter-ambulacral  as  well  as 
the  ambulacral  plates,  giving  rise  to  what  Miiller  has  termed 
pore  fascuB,  In  the  Spatangoida  (Fig.  143)  the  ambulacra 
commonly  present  the  same  heterogeneous  character ;  but 
the  oral  portions  are  not  arranged  in  fascia ;  and  it  not 
unfrequently  happens  that  the  anterior  ambulacrum  becomes 
more  or  less  abortive,  so  that  only  four  petals  are  obvious 
on  the  apical  surface,  instead  of  five. 

The  growth  of  the  shell  of  the  Echinidea  is  effected  in 
two  ways ;  partly  by  addition  to  the  circumference  of  the 
existing  plates,  partly  by  the  interpolation  of  new  ambu- 
lacral and  inter-ambtdacral  plates  at  the  apical  end  of  each 
series  between  it  and  the  ocular  or  genital  plate,  as  the  case 
may  be.  New  plates  are  never  added  to  the  oral  extremity 
of  the  corona  proper. 

The  surface  of  the  plates  of  the  corona  in  the  Echinidea 
is  covered  with  minute  rounded  elevations,  or  tubercles, 
to  which  are  articulated  the  spines  so  charaAtAxv^^^  ^1  K^<^ 


572       THE  AyATOMY  OF  IKYBBTEBRATED  AKIMAIiB. 

group.  The  tabercle  may  be  either  simple  or  marked  by  a 
central  pit,  into  which  and  a  corresponding  pit  on  the  head 
of  the  spine  a  ligament  of  attachment  is  inserted.  Further- 
more, capsular  muscular  fibres  connect  the  neck  of  the 
spine  with  the  base  of  the  tubercle,  and  effect  the  Taried 
movements  of  which  the  organ  is  capable.  The  spines  of 
the  Eehinidea  vary  very  much  in  form  and  size,  from  the 
close-set  yelvety  pile  of  Souiellay  or  the  delicate  spoon- 
shaped  blades  of  Amphidotus,  to  the  long-pointed  lances  of 
Echinus  and  the  great  clubs  of  Cidaris,  Even  on  the  same 
Echinoderm  the  spines  may,  as  in  the  two  latter  genera,  yaiy 
very  much  in  appearance ;  and  it  becomes  necessary  to  dis- 
tinguish those  large  ones  which  form  a  continuous  series 
from  one  end  of  an  ambulacrum  or  inter-ambulacrum  to  the 
other,  as  primary  spines,  from  the  other  less  complete 
aeeandary  and  tertiary  series. 

Lov^n  *  has  drawn  attention  to  the  existence  in  all  the 
Eehinidea,  except  Cidaris,  of  certain  minute  spheroidal 
bodies,  rarely  more  than  y^  of  an  inch  long,  which  he 
terms  ephceridea.  They  occur  upon  the  ambulacral  plates, 
and  especially  upon  those  nearest  the  mouth.  Each  contains 
a  calcareous  and  more  or  less  dense  and  glassy  skeleton, 
which  is  articulated  with  a  corresponding  tuberde  as  if  it 
were  a  miniature  spine.  In  some  genera,  these  sphoBrtdeOf 
to  which  Loven  ascribes  a. sensory  function  (probably 
auditory),  are  sunk  in  fosssa  of  the  plate  to  which  they 
are  attached. 

Scattered  among  their  spines,  the  Eehinidea  poasosi 
pedicellarice,  which  are  usually  provided  with  long  slender 
stems,  terminating  in  oval  heads,  divided  into  three  jaw*like 
processes.  The  latter  are  strengthened  by  calcaz«oi» 
ossicles,  which  articulate  with  an  ossicle  contained  in 
the  basal  part  of  the  head,  and  a  calcareous  rod  is  iiaoally 
developed  in  the  stem. 

In  the  Spatangoida,  when  the  skeleton  is  cleaxied«  its 
surface  is,  in  many  cases  {Amphidotua,  Briseue,  Spaiem^ru), 
marked  by  one  or  more  symmetrical  bands  of  doee-aet, 

*  ^l.\xi!ieAvaT\«&^f3t\T«ir\\^*  NATS, 


TBI  lOHiniDKA. 


minato  tnberdeB  (Fig.  143,  e,/,  9).  During  life,  slender  Bpines 
Are  attached  to  tlieM  tubercles,  the  caloareona  skeleton  of 


Fig.  la.—AmBhiihtv  cordalti.—X.  Viswed  flvm  Bbovfl.  B.  Fmn 
beblnd.  a,  M.  Trivium,  or  uiMrior  and  uit«roUtenl  ambnlAim. 
cc.  BiriuTD,  or  posMroLstenl  uubulacn.  d.  Mkdreporio  tabercla, 
•nrrouoded  by  the  genitnl  tperturei.  t,  Intr»-pet*loiu  KwUta.  f, 
Circun^aal  Kmila.  jr.  Sub-uil  KMdtd.  k.  Amu.  t,  Intn-*emltkt 
poretorbivlftl  uabuUcra.  C.  Sginlta m&gulfled.  a.  Semilal  Mber- 
clea.  b.  Ordinary  taberclai.  D.  Semltal  (pint.  a.  Teimliud  co- 
ittgad,  noa-dltetad  porUcn.    i.  CUlstod  tlMn. 


fitfciolei.  Scmitce  lie  oeue&u.  u^_  . 
Bomc  Renern.  and  iire  called  evb-a: 
otiicra  aiirniiind  the  outer  extremitii 
biila«ra,  and  are  Urmed  peripetahus, 
the  inner  taimiDations  of  their  an 
{Ataphidotaa)  (Pig.  143.  A,  B}. 

If  we  tnm  to  the  interior  of  the  i 
we  find  in  the  Eehinoida,  that  unfa 
(Cidarit)  intenunbnlaoral,  plates  of  t 
corona  are  ptodoced  into  fire  per 
procesaes,  whiah  arch  over  the  amb 
the  aurteula. 

Besides  these,  processe*  are  dere^ 
lacral  plates  in  Cidarii,  which  form 
etde  of  the  ambnlacral  canal,  but  d 
Clypeeuter,  aiinilar  procesees  form 
in  Uie  flattened  ClTpeaatroid,  Scufej 
walla  of  the  corona  are  united  toget 
cul»,  eo  that  the  cavity  of  the  bod 
Bmall  epace. 

The  Bpatangoida  present  neithf 
internal  processes. 

la  the  Eckinidea,  the  <S8oph^nB 
tuvnnd  a  CEecal  diverticnlnm  in  i 


middle  Un«,  while  each  half  again 
Fig.  IM. 


ists  of  a.  Ruperior 


—A.  Dentirf  >p|Hnihu  of  ■  Clyptatlrid  (mfler  MQIIer),-  a. 
ohu.  dl  Rotnlft.  s.  Tooth.  B,C,  U.  t>(iitarrippantna(Am- 
■  Untero)  of  ErJwt<a  iplvrra.  B.  Two  of  the  flre  chief  com- 
it  p«rtj  of  tha  lantern  appoaed  and  Tieirad  laterally.   C.  L»Ier»l 

--■  "    *--■-  -■-<•  of  a  ihigle  pert.    o.    Prinolpal 


Tiew,  and  D.  back  tIcit  o 


„      .  «lp«l  1 

_'.  iSutara  wilb  iU  fallow,    b.  Eplphrili.    V.  Satore  of 

flplphyiii  with  piineipkl  piece,    ir,  Kotnla.    a.  Badioa  OTOomfwHi. 
•.  Tooth. 


576       THE  ANATOMY  OF  XNYXBTEBRATBD  AJriMAL8. 

epiphysis,  and  an  inferior  principal  portion,  united  together. 
Each'alyeolns  serves  as  the  socket  for  a  long  tooth  (e),  shaped 
somewhat  like  the  incisor  of  a  Bodent,  harder  externally 
than  intemallj,  so  as  always  to  develope  a  sharp  edge  with 
wear.  The  tooth  constantly  grows  from  its  upper  extremity, 
while  its  lower  half  becomes  united  with  the  wall  of  the 
alveolus.  The  five  alveoli,  if  fitted  together,  form  a  cone, 
the  applied  surfaces  of  which  are  united  by  strong  trans- 
verse muscular  fibres,  while  superiorly,  the  epiphysee  of 
each  pair  of  alveoli  are  connected  by  long  radial  piecee — 
the  rotulcs  (c)  articulated  with  their  edges.  To  the  inner 
extremity  of  each  rotula,  finally,  a  slender  arcuated  rod, 
presenting  in^cations  of  a  division  in  the  middle  of  its 
length,  is  articulated,  and,  running  outwards  parallel  with 
the  rotula,  terminates  in  a  free  bifurcated  extremity.  This 
is  the  rekfittff  {d). 

Altogether,  then,  the  Lantern  consists  of  twenty  prin- 
cipal  pieces — five  teeth,  five  alveoli,  five  rotnlsa  and  five 
radii;  of  which  the  alveoli  are  again  divisible  into  four 
pieces  each  and  the  radii  into  two,  making  a  total  of 
forty  pieces.  In  their  normal  position,  it  must  be  re- 
membered  that  the  alveoli  and  teeth  are  intenunbolacral, 
while  the  radii  and  rotulsB  are  ambulacral.  BesideB  the 
inter-alveolar  muscles  already  described,  this  complex  ap- 
paratus has  protractor  muscles  arising  from  the  intcr- 
ambulacral  region  of  the  oral  edge  of  the  corona,  and 
inserted  into  the  upper  part  of  the  alveoli;  alender 
oblique  muscles,  with  a  similar  origin,  but  inserted  into 
the  radii ;  transverse  muscles  connecting  the  radii  together: 
and  retractor  muscles  arising  from  the  arches  of  the  auri- 
culse,  and  inserted  into  the  oral  ends  of  the  alveoli. 

A  similar,  but  less  complex,  oral  skeleton  exists  in  most 
Clypeastroida  (Fig.  144  A),  but  nothing  of  the  kind  has  yel 
been  discovered  in  the  Spatangoida, 

In  the  Echinidea,  the  circular  ambulacral  Tessel  liei 
between  the  oesophagus  and  the  alveoli,  and  is  nsoally  pro- 
vided with  five  sacculated  polian  vesicles.    There  is  a 


THB  BCHINIDBA.  577 

in  Ou2a9*M,  wliicli  extends  nearly  in  the  axis  of  the  body 
from  the  circular  Teasel  to  the  madreporic  tubercle.  Five 
radial  ressels  ran  up  the  middle  of  the  inner  surface  of 
the  ambulacral  plates,  which  thej  reach  bj  passing  from 
the  circular  canal,  outwards,  beneath  the  rotuba,  when 
these  exist ;  next,  downwards,  external  to  the  inter-alveolar 
muscles;  and  then,  outwards,  through  the  arches  of  the 
auriculffi:  these  give  off  branches  on  each  side  to  the 
pedicels,  the  bases  of  which  open  into  large  ambulacral 
vesicles.  The  circular  ambulacral  vessel  of  the  Spaian* 
goida  has  no  polian  vesicles,  and  no  vesicular  appendages ; 
in  the  Clypeasters  there  are  many  vesicular  appendages, 
but  no  polian  vesicles.  In  most  Echinaida,  all  the  i>edicel8 
are  expanded  into  sucking-disks  at  their  extremities,  and 
are  here  strengthened  bj  a  calcareous  plate  or  plates ;  but, 
in  Echinocidaris  and  some  other  Echinoida,  the  pedicels  of 
the  oral  portion  of  the  ambulacra  onlj,  have  this  structure, 
vehile  those  of  the  apical  portion  are  pectinated,  flattened, 
ajid  gill-like.  Again,  in  the  heterogeneous  ambulacra  of 
the  Clypeastroida  and  Spatangoidaf  the  forms  of  the  pedicels 
▼ary  much.  Thus  Miiller  distinguishes  four  kinds  of  pedi- 
cels in  the  Spatangoida — simple  and  locomotive  pedicels, 
without  anj  sucking-disk;  locomotive  pedicels,  provided 
vnth  terminal  suckers,  and  containing  a  skeleton ;  tactile 
pedicels,  with  papillose  expanded  extremities ;  and  gill-like 
pedicels,  triangular,  flattcDcd,  more  or  less  pectinated 
lamelke.  Two  or  three  of  these  kinds  of  feet  may  occur  in 
anj  given  ambulacrum,  and  those  which  lie  within  a  semita 
are  always  different  from  the  others. 

In  the  Clypecuftroida,  the  petaloid  x>ortion8  of  the  ambu- 
lacra x>08ses8  branchial  pedicels,  interspersed  with  delicate 
locomotive  pedicels,  provided  with  a  calcareous  skeleton  and 
with  a  terminal  sucker.  The  latter  kind  alone  extend  on 
to  the  oral  portions  of  the  ambulacra. 

The  circimioral  nerve  of  Eekinus  surrounds  the  OBSopha- 
^us  near  the  mouth.  It  has  a  pentagonal  form,  and  is 
enclosed  bj  the  alveoli,  between  which  the  ambulacral 
nerves  pass,  over  the  peristome  and  throag,h  tK^  ^ac^^^  ^V 


J 


ends  of  the  ambiilacral  nen'es. 

The  peritoneal  space  is  fllleil  bj 
which  is  kept  conslantly  in  motion  I 
the  parietcs  and  the  contained  visi 
this  fluid  appears  to  be  facilitated 
except  Cuiaru,  by  five  pairs  of  sp 
developed  from  the  perietome;  whi 
and  Spatangoida,  which  poesera  the 
monly  termed  ambulacra!  gille,  ther 

In  the  Echinidea,  a  circular  p«ei: 
branches  are  given  off  to  the  genit 
the  Uina.  The  alimentary  canal 
vesaela,  one  on  the  side  of  the  meee 
on  tlie  free  aide  (ventral),  which  com 
network  in  its  walla ;  and  besidea 
nuining  parallel  with  the  madrep< 
ing  inferiorlj  in  a  circnlar  vessel 
circular  ambnlacral  vessel,  around 
detoribed  as  a  '  heart't 

^le  genital  oi^ans  are  aa^ciilate 
large  size  in  the  breeding  season 
the  porea  on  the  genital  plates,  t 
dnota  are  extruded.  Hoffmann  I 
doid  of  the  males  fnll  of  apermato 

In  tho  Eehinidea,  aa  in  the  Ophv 
i»  a  Plvieai,  and  has  a  skeleton  f< 


I  DBTSLOPmtHT  07  THE  ICBIItlDSA, 
Fig.  145. 


45.— Derelapumit  of  tn  Ediiiud.  (After  MQIIer.)— A.  Echfno- 
inni  of  KdkSim  piMielhu  In  ths  sutruU  itage.  B.  Fnllj  de- 
ped  EgblmnwdlDDi  {PlMtm)  of  the  wne  apecle* ;  a,  mouth  ; 
omMh  Bad  IntcMliie ;  c,  UDi ;  A  P,  proeeMes  of  (he  body  Into 
:h  prolonnUoni  of    tbe    lotenul  ikelatoo  eitand.      C.  The 


which  prohmgftUoni  of  tie  lotenul  ikelatoo  eitand.  C.  The 
EehiDopBdimn  of  an  Eohinld  la  whloh  the  Eohlnodenn  ti  n  fu 
•dTanoedaattiMipfDWipedleali,  >BdIl«dleri)]Bi■lwmVlliia^A.  "%• 


580       THB  ANATOMY  OV  IKTEBTSBBATSB  AVIMAIiB. 

EchinofMedium  of  EduHus  Ihndiu :  a,  moath ;  J  gnllet :  6,  staOMfih ; 
b\  intestine ;  c,  rudimentary  Echinoderm ;  c',  the  mmlmiAcrmI  sae ; 
c",  the  external  opening  of  its  duet  \  a  ti,  ff,B,  the  ptoec«es  of 
the  body. 

which  support  the  processes  into  which  the  body,  in  the 
region  of  the  ciliated  bands  and  elsewhere,  is  prolonged. 

The  origin  of  the  ambulacral  system,  before  it  has  the 
form  of  a  caecum  with  a  dorsal  pore,  has  not  been  made  out. 
The  blind  end  of  this  csecum  lies  on  the  left  aide  of  the 
alimentary  canal,  and  is  connected  with  a  discoidal  body, 
which  is  situated  on  the  left  side  of  the  stomach ;  a  similar 
body  appears  on  the  right  side.  Doubtless  these  discoidal 
bodies  answer  to  the  peritoneal  diyerticula  of  the  alimen- 
tary canal  of  the  EchinopsBdium  in  other  Echinoderma. 

The  blind  end  of  the  tube  enlarges,  and  giyes  rise  to  a 
rosette,  whence  the  ambulacral  vessels  proceed;  and  a 
depression  of  the  integument  of  the  larva,  forming  the 
so-called  wnbo,  extends  inwards  to  this.  At  the  bottom 
of  the  umbo,  a  new  mouth  opens  through  the  centre  of 
the  rosette  into  the  gastric  cavity  of  the  larva,  the  primitive 
oesophagus  being  abolished.  The  larval  skeleton  undergoes 
resorption,  but  the  rest  of  the  Echinopsediimi  paases  into 
the  Echinoderm.* 

Loven  has  recently  drawn  attention  to  the  fact  that,  in 
young  Echinids^t  the  plates  of  the  apical  region  are  not 
only  more  conspicuous  in  relation  to  the  corona,  bat  differ 
somewhat  in  their  arrangement,  from  those  of  the  adult. 
Thus  the  anus  is  at  first  wanting,  and  the  anal  plate,  which 
occupies  the  centre  of  the  apical  area,  is  relatively  large ; 
it  is  united  by  its  edges  with  the  five  plates,  which,  im- 
perforate in  the  young,  will  become  the  genital  plates  in  the 
adult.      The  five  ocular  plates  are  also  imperforate,  and 

*  See,  in  addition  to  the  me-  A.  Agassis,    'Revision    of   the 

moirs  of  MfiUer  and  Metschnikoff  Echini,*  published  in  the  '  lUoi- 

already  cited,  A.  Agassis,  **  On  the  trated  Catalogue  of  the  Mnseini 

Embryoloffy    of    Echinoderms.**  of  Comparative  Zoolofnr  at  Har> 

O  Menu  Ameriean    Academy  of  vard  ('oHege,'  is  also  mU  of  ia- 

Scienoei.*  1864.)  formation  respeotinff  tba  joog 

f  The  adnAitUle  hmmi^^  oi  itaJiei  of  the  Eehinm. 


THS  CBXKOIDBA.  581 

are  disposed  in  a  circle  outside  that  formed  by  the  genital 
plates,  their  inter-spaces  being  occupied  bj  interambu- 
lacral  plates.  The  apical  region  of  an  Echinid  has  thus,  as 
LoT^  points  out,  a  most  striking  resemblance  to  the  cal  jx 
of  a  Crinoid ;  the  anal  plate  representing  the  boidUa ;  the 
genital  plates,  the  parahasalia ;  and  the  ocular  plates,  the 
first  rctdialia. 

The     Obinoidea.  —  This     remarkable    group,    which 

abounded  in  former    periods  of    the  world's  history,  is 

represented  at  the  present  daj  only  by  the  genera  Antedan 

{ComahUa),  AcHnometra,  Comader,  Fentacrinua,  Bhuocrinus 

and  Holopus, 

The  first  three  genera  are  capable  of  locomotion,  while 
the  next  two  are  attached  by  long  articulated  stems  to 
submarine  bodies.  Holopus,  which  is  but  imperfectly 
known,  appears  to  be  fixed  by  a  short  thick  unjointed 
prolongation  of  its  base. 

Bhizoorinvs  lofotenaU  (Fig.  14f6),  which  has  been  yery 
carefully  and  elaborately  described  by  Sars,*  is  a  small 
animal  which  does  not  attain  more  than  three  inches  in 
length,  and  lires  at  great  depths  (100-^300  fathoms  or  more) 
in  the  sea.  It  consists  of  a  relatively  long,  many-jointed 
stem,  from  many  of  the  articulations  of  which,  branched, 
root-like  filaments,  or  cirri,  are  given  off;  at  the  summit  of 
this  is  seated  a  cup-shaped  body,  the  calyx,  from  the  margins 
of  which  5-7  arms  {brachia)  radiate.  To  each  arm  is 
attached  a  double  series  of  alternating  pinnuUB,  The 
mouth  is  situated  in  the  centre  of  that  part  of  the  perisoma 
which  forms  the  surface  of  the  calyx  opposite  to  the  stem. 
The  oral  aperture  is  circular,  but  five  (or  sometimes  only 
four)  triangular  lobes  of  the  perisoma,  with  rounded  free 
ends,  project  over  it,  and,  when  shut,  dose  it  like  so  many 
valves.  From  the  intervals  between  these  oral  valves  five 
(rarely  four)  grooves  traverse  the  oral  surface  of  the  calyx, 
and  extend  thence  throughout  the  whole  length  of  each 
arm,  giving  offsets  as  they  go  to  the  pinnules.    Thus  the 

*  '  M^moires  poor  lervir  Ik  It  eonnilttance  des  Crinoldeft  xiWD&j^  >M(Ak. 


582     TH*  i.trATOMT  or  nrrxBTiBRiTiD  asihaia. 

oral  anrface  ctf  mcb  arm  and  of  eaoh  piiuitil«  i>  deeplj 
«xoavat«d. 

Betweem  Uie  oiroolar  lip  and  the  oral  Talvea,  aoft  flexible 
tontaouliform  p«dioela  are  attached  in  a  siiigie  aeriM.  Two 
pairs  of  pedioela  correspond  to  erei;  valve,  each  pair  aiiaiiig 
oppoeiU  the  basal  angle  of  a  vtlre.  Tbeae  pedioela  are 
liollow,  their  surface  is  papillose,  and  the  onter  or  radial 
pedicel  of  each  pair  is  veij  contractile.    Pedicels  of  tlie 

Fij.  146. 


Fig.  l«.-J(*itt«riMH  lofiiUiuu.    (After  8»r».> 

I.  AAitocmiu  entire ;  a,  enltrsed  upper  Joint  of  the  stem ;  i 
JoinU  of  llM  ■lem  ;  c,  cirri ;  rf,  br«hU, 

II.  Caljx  and  trms,  wiUi  tha  ■uminic  of  the  ■ten  of  k 

having  fire  well-developed  bnchia;  n,  u  before;  i,  flnt  iwluH; 
r>,  H,  Mcond  and  third  rsdialg ;   b',  flnt  brublftl ,  s,  p,  piiuinlea. 

III.  Upper  part  of  the  ■tern  ud  oral  &oa  of  the  oaljx,  Tiewrd 
obliquely  ;  v,  lower  part  of  visceral  mis ;  «,  r,  teDlacnlai  eroomi 
0,  oral  valve* ;  t,  oral  lentaclee  ;  an,  aDOi. 

same  general  character    are    continned    througboat    the 
braohial  and  piminlar  grooves. 
The  uva  u  ntaBtodk  «X  %b  ood.  of  a  conical  pnanineoce 


THB  CBINOIDSA.  583 

between  two  of  the  grooves  on  tlie  oral  face  of  the  calyx, 
and  is  therefore  interraddal  in  position  (Fig.  146,  III.  an). 

The  skeleton  consists  of  very  numerous  pieces  resulting 
from  the  calcification  of  the  perisoma.  In  the  stem  thej 
hare  the  form  of  elongated,  sabcjlindrical,  or  hourglass- 
shaped,  joints  {artieuli),  the  opposed  faces  of  which  are 
united  by  strong  elastic  ligamentous  fibres.  The  centre  of 
each  is  traversed  by  a  longitudinal  axial  canal,  which  ex- 
tends  through  the  whole  length  of  the  stem  and  is  occupied 
by  a  soft  but  solid  substance.  The  distal  joint  of  the  stem 
is  not  directly  fixed  to  the  surface  to  which  the  Crinoid  is 
attached,  but  is  connected  therewith  by  the  branched  cirri 
which  proceed  from  it.  Each  cirrus  has  a  skeleton  com- 
posed of  joints  or  artieuli,  somewhat  like  those  of  the  stem 
and  traversed  by  a  prolongation  of  the  axial  canaL  Similar 
cirri  are  developed  from  a  larger  or  smaller  number  of  the 
artieuli  of  the  distal  portion  of  the  stem. 

The  proximal  joints  become  gradually  shorter  in  pro- 
portion to  their  length,  until  they  assume  a  discoidal  form. 
It  appears  that  new  artieuli  are  continually  added  at  that 
end  of  the  stem  which  lies  nearest  the  calyx. 

The  summit  of  the  stem,  or  the  base  of  the  calyx,  is 
formed  by  an  enlarged,  solid,  pear-shaped  ossicle,  which  is 
probably  formed  by  the  coalescence  of  several  artictUi, 
Upon  tiiis  follow  five  pieces  (first  rcicUalia)  closely  united 
together  and  with  a  central  piece,  which  probably  represents 
the  hamilia  of  other  Grinoids.  The  first  radial  corresponds 
in  direction  with  the  origin  of  one  of  the  arms,  and  is 
followed  by  a  second  and  third  radial.  With  the  third 
radial  is  articulated  the  first  of  the  brachial  ossicles,  which 
constitute  the  skeletal  support  of  the  unbranched  brachia. 
The  pinnules  are  also  supported  by  a  series  of  elongated 
calcified  joints,  the  basal  joint  being  articulated  with  a 
brachial  ossicle  and  the  distal  joint  pointed. 

The  axial  canal  dilates  in  the  enlarged  pyrif  orm  ossicle 
above-mentioned ;  and,  from  the  dilatation,  branches,  which 
traverse  the  radial  and  the  pinnular  ossicles,  are  given  off. 
There  is  a  calcareous  plate  in  the  substance  of  eaAk  cst^ 


584       THE  ANATOMT  OF  INYEBTEBBATBD  AVIMALS. 

Talve,  and  minute  reticulated  calcifications  are  aoattered 
through  the  perisoma  of  the  oral  face  of  the  disk. 

The  sides  of  the  radial  grooves  are  provided  thronghout 
with  a  double  series  of  oval  calcareous  plates — ^the  margindl 
lamelloR — which  are  disposed  transversely  to  the  groove^ 
those  of  opposite  sides  alternating  with  one  another.  They 
can  be  erected  or  depressed ;  and,  in  the  latter  case,  overlap 
one  another  like  tiles. 

In  Pentacrinus,  the  long  stem  is  fixed  by  its  distal  end, 
and  the  pentagonal  articuli  of  its  skeleton  give  off,  at 
intervals,  whorls  of  unbranched  cirri.  No  distinct  basal 
piece  is  known,  but  the  calyx  appears  to  begin  with  the 
five  first  radialia.  At  the  third  radiate,  the  series  bifurcates 
into  two  series  of  brcuihialia,  and  these  again  bifurcate 
to  give  rise  to  the  palmaria,  which  support  the  free  arms. 
There  are  marginal  lamellae  along  the  sides  of  the  tentacular 
grooves,  and  a  longitudinal  series  of  calcareous  ossicles 
occupies  the  fioor  of  each  groove.  The  anus  is  situated 
upou  an  elevated  interradial  cone. 

The  body  of-  an  adult  ComcUula  (Antedon)  answers  to 
the  calyx,  with  its  brachia,  in  other  Crinoids. 

The  centre  of  the  skeleton  is  constituted  by  a  large 
centrO'dorsal  ossicle,  articulated  with  the  aboral  face  of 
which  are  the  numerous  cin*i,  by  which  the  ArUedon  ordi- 
narily grasps  the  bodies  to  which  it  adheres,  though  it  ie 
able,  on  occasion,  to  swim  freely  about.  This  centro-dorsal 
ossicle  appears  to  be  the  homologue  of  the  nppermott 
part  of  the  stem  in  the  PerUcusrinus.  There  are  five 
divergent  series  of  radialia^  each  containing  three  oeaicles. 
The  first  radials,  or  those  nearest  the  centro-dorsal  plate, 
are  closely  adherent  to  one  another  and  to  the  centro-doml 
plate,  and  are  not  visible  on  the  outer  surface  of  the  calyx. 
The  space  left  between  the  apices  of  the  five  first  radials  is 
occupied  by  a  single  plate,  the  rosette*  which  is  formed  by 
the  coalescence  of  the  five  hcisalia  present  in  the  larva. 

The  anatomy  of  the  soft  parts  of  the  Crinoidea  hsf 

*  CarpenteT,  'On  the  Struoture,  Physiology,  and  DevelopaieBt  «f 


^THX  CBIKOIDBA.. 


585 


been  most  thoronglilj  inTeetigated  in  tlie  genos  (hmattUa 
(ArUedon)* 

The  month  leads,  by  a  short,  wide  gullet,  into  a  spacionB 
sacculated  alimentary  canal,  which  is  coiled  nx>on  itself 
in  such  a  manner  as  to  make  about  one  turn  and  a  half 
around  the  axis  of  the  body ;  and  then  terminates  in  the 
projecting  rectal  cone  which,  as  has  already  been  seen, 
is  situated  interradially,  on  the  oral  face  of  the  calyx. 
The  central  cavity,  included  by  the  coil  of  the  alimentary 
canal,  is  occupied  by  a  sort  of  core  of  connective  tissue,  and 
has  received  the  name  of  eolwmella,  but  it  must  be  under- 
stood that  it  is  not  a  distinct  structure.  Bands  of  con- 
nective tissue  connect  the  outer  periphery  of  the  alimentary 
canal  with  the  perisoma. 

The  five  triangular  lobes  of  the  perisoma,  which  surround 
the  mouth  like  so  many  valves,  contain  no  calcareous 
skeleton  in  the  adult  Antedon.  Within  these  lobes,  attached 
to  the  oral  membrane,  there  is  a  circle  of  tentacula.  From 
the  interval  between  each  pair  of  oral  valves,  a  groove 
radiates  outwards  over  the  surface  of  the  calycine  perisoma 
and  speedily  bifurcates;  one  branch  goes  to  the  oral 
surface  of  each  of  the  arms  and  runs  along  it  to  its  ex- 
tremity, giving  off  alternate  lateral  branches  to  the  pinnules 
in  its  course. 

These  grooves  are  the  ambulacral  grooves.  Their  sides 
are,  as  it  were,  fenced  by  small  lobed  processes  of  the  peri- 
soma ;  and,  on  the  inner  sides  of  these  processes,  groups 
of  minute  pedicels  take  their  origin  from  the  sides  of  the 
floor  of  the  groove.  A  thickened  band  of  the  ectoderm 
occupies  the  middle  of  the  floor,  and  so  strikingly  resembles 


♦  E.  Perrier,  "  Recherchei  but 
rAnatomie  de  la  Comatula 
rotacea**  ('Aroh.  de  Zoologie 
Experimentale/  1873).  Semper, 
*'Kurze  anatoinisohe  Bemerkun- 
gen  iiber  Comatula**  (*  Wfinburg 
Arbeiten,'  1874).  Ludwig. ''  Ztir 
Anatomie  der  Crinoideen " 
('Z«itschrift  fur  Wis*.  ZooL' 
1876).   Carpenter**  On  the  Struo- 


tore,  Phvsiology,  and  Develop- 
ment of  Antedon"  (*  Proc.  Royal 
Society,*  1876).  Greef,  **Ueber 
den  Ban  der  Crinoideen  **  (*  Mar- 
burg SiUiingBberichte,'  1876). 
P.  M.  Carpenter,  **  Remarks  on 
the  Anatomy  of  the  Arms  of  the 
Crinoids  "  (*  Journal  of  Anat.  and 
Physiology,'  1876). 


586       THB  ANATOMY  OF  INYEBTBBRATBD  AKIKALS. 

the  ambolacral  nerve  of  the  Star-fish,  that  the  homology  cf 
the  two,  first  asserted  by  Lndwig,*  cannot  be  doubted. 
Immediately  beneath  it  runs  a  small  canal,  discovered  bj 
Dr.  Carpenter,  and  termed  by  him  the  teniaeular  oonol, 
which  gives  off  lateral  branches  to  commnnicate  with  the 
cavities  of  the  pedicels.  A  second  much  wider  canal — ^the 
suMeniacular  canal — lies  beneath  this,  and  is  divided  by  a 
longitudinal  septum.  But  the  septum  is  incomplete  at 
intervals,  and  thus  the  two  canals  communicate.  A  third, 
still  larger,  cceliac  eanal,  is  interposed  between  the  floor  of 
the  subtentacular  canal  and  the  axial  skeleton  of  the  arm. 

Where  the  arm  joins  the  calyx,  the  tentacular  canals  run 
beneath  the  ambulacral  groove  to  the  gullet,  around  which 
they  are  united  by  a  circular  canal,  from  which  numerous 
short  diverticula,  resembling  the  vasa-  ambuUMcraUa  cavi 
in  the  Opjiiurids,  described  by  Simrock  (l.c,\  depend. 
The  subtentacular  and  cceliac  canals  communicate  with 
channels  in  the  perivisceral  tissue,  on  the  oral  or  the  abonl 
face  of  the  visceral  mass;  and  these  channeki  appear, 
eventually,  to  open  freely  into  the  cavities  by  which  the 
columella  is  traversed. 

In  the  partition  between  the  subtentacular  and  the 
coeliac  canals  there  lies  a  cellular  cord,  or  rachis,  which  can 
be  traced  back  into  a  reticulation  of  similar  tissue  in  the 
visceral  mass.  The  genital  glands,  contained  in  the  pin- 
nules, are  enlargements  of  lateral  branches  of  this  zadiit. 
But  the  rachis  is  apparently  only  an  extension  of  tbe 
mesodermal  tissue  of  the  visceral  mass,  comparable  to  that 
in  which  the  genitalia  are  lodged  in  the  Star-fiahes ;  and 
the  multiplication  of  the  genital  glands  may  be  regaided 
as  a  further  extension  of  the  structure  which  obtains  in 
Brisinga.  Thus  it  would  seem  that  the  position  of  the 
genital  glands  in  the  Grinoids  is  not  so  anomalous  as  it  at 
first  appears  to  be. 

The  centre-dorsal  tubercle  contains  a  cavity,  with  whii^ 
the  canals  which  travei*se  the  osaicula  of  the  cirri,  the 
calyx,  the  brachia  and  the  pinnules  communicate.    Thii 

•  *lA\a^\iTMlt^^W«a.'&»W  1876. 


THS  DBYUiOPMBHT  OV  THB  CBIHOIDEA.  587 

waa  cozLBidered  by  Mailer  to  be  a  heart.  It  proTes, 
<er,  to  be  largely  filled  by  solid  tissue,  whicb  is  con- 
L  not  only  into  all  the  canals  which  trayerse  the 
la»  bat  also  into  the  colamella,  or  tissae  which 
ies  the  centre  of  the  coils  of  the  alimentary  canal. 
Carpenter  *  is  of  opinion  that  so  mach  of  this  axial 
as  occupies  the  cavity  of  the  central  tubercle,  and  is 
Lued  throughout  the  ossicula  of  the  calyx  and  arms, 
proper  central  organ  of  the  nervous  system ;  f ound- 
is  opinion  partly  upon  the  fact  that,  when  this  mass 
bated  in  a  living  AntecUm,  a  sudden  contraction  of  all 
nacles  of  the  arms  takes  place ;  and  partly  ux>on  the 
)ution  of  the  ultimate  ramifications  of  the  axial 
in  the  arms.  Qreef ,  on  the  contrary,t  affirms  that 
eee  tracts  can  be  injected,  and  retains  the  name  of 
» *  for  the  cavity  of  the  centro-dorsal  tubercle. 
I  perisoma  of  the  oral  surface  of  Comaiula  exhibits  a 
number  of  minute  circular  x>ores,  with  thickened 
ir  margins.  Greef  has  discovered  that  these  are  the 
lal  apertures  of  canals,  with  ciliated  walls,  which 
into  the  body  cavity,  and  readily  allow  fluids  to  pass 
>r  out  of,  that  cavity. 

h  mature  ovary  of  Antedon  has  a  distinct  aperture, 
3fh  wbich  the  ova  are  discharged,  and  to  which  they 
3  for  some  days  like  bunches  of  g^pes.  The  testis 
^pes  no  special  aperture,  but  the  spermatozoa  appear 
discharged  by  dehiscence  of  the  integument. 
se  the  discovery  by  Yaughan  Thompson  that  Comaiula 
\  through  a  Pentacrinoid  larval  condition,  the  develop- 
of  the  free  Grinoids  has  been  the  subject  of  various 
igations,^  and  the  following  results  may  be  regarded 
iblished. 
nplete  yelk-division  takes  place.     The  morula  ac- 

roceedings  of  the  Royal  Trans.'      1865),       Metschnikoff 

,'  1876.  0  Bulletin   de  I'Acad.  Imp.  des 

Teber  daa  Hen  der  Crl-  scienoes    de     Si.    Petenlx>arg,' 

"     ('Marburg    Sitzunga-  1871),    and      especially      GOtte 

«,M876).  ('Archiv     fOr     Mikroskopiscbe 

WyviUe-ThomK>n  ('  P^U.  Anatomia,'  1876V 


588       THS  AKATOMT  OF  IHYBBTSBSATBD  ANIMALS. 

quires  an  oval  form,  and  developes  four  hoop-like  bands  of 
cilia,  with  a  tuft  of  cilia  at  the  hinder  end.  Between  the 
third  and  fourth  bands  of  cilia,  counting  from  the  anterior 
end  of  the  Echinopsddium,  the  blastoderm  becomes  in- 
vaginated,  and  gives  rise  to  an  archenteron.  In  the  in- 
terspace between  this  blind  sac,  the  wall  of  which  is  the 
hypoblast,  and  the  epiblast,  constituted  by  the  rest  of  the 
blastoderm,  a  mesoblast  composed  of  reticulated  cells 
makes  its  appearance.  The  blastopore  closes,  while  the 
archenteron  detaches  itself  from  its  attachment  to  the 
posterior  ventral  face  of  the  larva,  and  becomes  connected 
with  an  oesophageal  involution  formed  at  its  anterior  end. 
The  archenteron  next  throws  out  three  diverticula,  of  which 
two  are  lateral,  and  one  is  ventral.  The  lateral  diverticula 
enlarge,  and  apply  themselves  to  the  rest  of  the  archenteron* 
now  become  the  intestine,  from  which  they  are  soon  com- 
pletely shut  off,  and  converted  into  peritoneal  sacs.  The 
left  sac  thus  formed  lies  on  the  ventral  side  of  the  intestine^ 
the  right  sac  on  its  dorsal  side.  The  walls  of  the  two  sacs 
become  applied  together,  and  form  a  circular  mesentery. 
The  peritoneal  sac  of  the  aboral  side  sends  a  prooess  into 
the  hinder  end  of  the  body,  which  has  begpin  to  elongate, 
in  order  to  give  rise  to  the  stem  of  the  Pentacrinoid  form. 

The  third,  or  ventral,  diverticulum  is  shut  off  from  the 
alimentary  canal  much  later  than  the  other  two.  It  grows 
round  the  mouth,  and  gives  rise  to  the  circular  ambolacrdL 
vessel,  whence  the  tentacular  canals  are  given  off. 

Ten  plates,  each  consisting  of  a  calcareous  network  and 
arranged  in  two  rows  of  five  each,  next  appear  in  the 
substance  of  the  EchinopaBdium  around  the  alimentaiy 
canaL  From  the  centre  of  the  posterior  row,  eight  calcareone 
rings  extend  through  the  length  of  the  body  of  the  larfii 
enclosing  the  backward  prolongation  of  the  aboral  peii* 
toneal  sac ;  and  the  series  terminates  by  a  broad  disocudil 
network  which  lies  on  one  side  of  the  posterior  end  of  the 
larva.  This  discoidal  plate  is  that  which  occupies  the 
attached  end  of  the  stem  of  the  future  Crinoid ;  the  xingt 
heooanift  the  tieiis  «DdL  V2^<&  \^q  ^ixcles  of  plates  the  hssil 


THS  DETBLOPMBKT  OF  THE  CBIirOIDEA.  589 

tl  ossicula  of  the  calyx,  respectiyely.  As  the  stem 
tes,  new  rings  (ariiculi)  are  added  at  the  junction  of 
m  with  the  calyx. 

larva  now  fixes  itself  by  the  discoidal  end  of  its 
irhich  becomes  relatively  longer  and  narrower ;  while 
rt  of  the  body  which  contains  the  basal  and  oral  plates, 
to  be  converted  into  the  calyx,  remains  thick  and 
Its  broad  end  becomes  five-lobed,  each  lobe  answering 
oral  plate.  These  plates  separate  like  the  petals 
lower  bnd,  and  discover,  in  the  centre,  the  wide  per- 
t  oral  aperture.  Between  the  margins  of  this  and 
al  plates,  tentaonliform  pedicels,  at  first  only  five, 
entoally  arranged  in  groups  of  three,  between  every 
!  oral  plates,  make  their  appearance, 
alimentary  cavity  is  still  a  mere  sac,  without  intestine 

I  radial  plates  next  appear  in  the  wall  of  the  calyx 
m  the  basal  and  the  oral  plates,  and  alternating  with 
and,  in  correspondence  with  them,  the  arms  grow 
1  rapidly  elongating  processes,  in  which  the  other 
1  are  successively  developed.  The  entire  zone  of  the 
which  is  occupied  by  the  oiigins  of  the  arms,  at 
me  time  widens,  so  that  the  oral  plates,  which  remain 
the  mouth,  and  the  basal  plates,  which  encircle  the 
become  widely  separated.  The  intestine  grows  out 
diverticulum  of  the  alimentary  cavity  and  opens 
interradial  elevation  of  the  calyx,  in  which  an  anal 
is  developed,  nrhe  young  Echinoderm  has  now 
I  into  the  stalked  Fentacrinoid  stage. 
hmatttla,  the  oral  and  anal  plates  disappear  altogether, 
lie  basals  coalescing  into  the  rosette,  are  hidden  by 
rst  radials,  on  the  one  hand,  and  the  centro-dorsal 
de,  which  represents  coalesced  joints  of  the  stem,  on 
her.  The  arms  bifurcate  and  acquire  their  pinnules ; 
he  calyx,  with  its  appendages,  eventually  becomes 
led  from  its  stem  as  a  free  Comaiula,  In  the  exist- 
alked  Crinoids,  such  as  Penio/crinm,  on  the  other 
the  segments  of  the  stem  acquire  whoT^  ^1  ^\srcv^^^ 


590       THE  AKATOmr  OF  nfYBBTBBSATXD  ASUUkLA. 


intervals,  and  no  such  modification  of  the  uppermost  seg* 
ments  into  a  centro-dorsal  tubercle  takes  place. 

On  comparing  the  facts  of  stmcture  and  development 
which  have  now  been  ascertained  in  the  five  existing 
groups  of  the  Eehinodermata,  it  is  obvious  that  they  are 
modifications  of  one  fundamental  plan.  The  segmented 
vitellus  gives  rise  to  a  ciliated  morula,  and  this,  by  a 
process  of  invagination,  is  converted  into  a  gastrola,  the 
blastopore  of  which  usually  becomes  the  anus.  A  mouth 
and  gullet  are  added,  as  new  formations,  by  invagination  of 
the  epiblast.  The  embryo  normally  becomes  a  free  Echi- 
nopsedium,  which  has  a  complete  alimentary  canal,  and  is 
bilaterally  symmetricaL  The  cilia  of  its  ectoderm  dispose 
themselves  in  one  or  more  bands,  which  surround  the  body; 
and,  while  retaining  a  bilateral  symmetry,  become  varioudy 
modified.  In  the  Holothwridea,  Aateridea,  and  CWnotdeo, 
the  larva  is  vermiform,  and  has  no  skeleton;  in  the 
Echinidea  and  the  Ophiuridea  it  becomes  pluteiform,  and 
developes  a  special  spicular  skeleton. 

If  an  EchinopsBdium  were  to  attain  reproductive  organs, 
and  reproduce  its  kind,  I  think  that  it  cannot  be  doubted 
that  its  nearest  allies  would  be  found  among  the  TwrMiant^ 
the  Eotifera,  the  Chphyrea  and  the  Enieropneutta,*  But 
that  which  characterises  the  Echinodertrutta  is  tlie  ta/i 
that  the  alimentary  canal  of  the  Echinopsddinm  gives 
rise  to  an  enterocoele,  which  again  is  subdivided  into  two 


**  In  a  report  upon  the  *  Re- 
searches of  Prof.  Miiller  into  the 
anatomy  and  development  of  the 
Echinoderms,'  published  in  the 
'Annals  of  Natural  History'  for 
July  1851,  I  drew  attention  to 
the  affinities  of  the  Eobinoderms 
with  the  Worms ;  and  in  a  paper 
on  Ltiuiuularia  BocialU^  read  be- 
fore the  Microscopical  Society  in 
the  same  year,  I  expressed  the 
view  that  the  Rctifera  *  are  the 
ssimmwttqnnioi  Echinoderm 
iHrvtti  tad  Md  \Ytt  wBft  i^is^^ 


to  the  Echinoderms,  that  tke 
Bydriform  Polypi  hold  to  the 
Medusae/  and  that  they  *  oooBset 
the  Echinoderma  wiUi  the  Kf" 
matidK  and  the  Kematsid 
Worms.'  When  they  wen  pob- 
lished,  those  who  did  not  inoit 
these  vieiit's,  ridiculed  xttm. 
Nevertheless,  thoush  aoiMwIiit 
crudely  expressed,  I  think  it  vffl 
be  admitted  they  have  been  n^ 
Btantially  justified  by  the  uiognsi 
of  knowledge  durmg  tM  Itft 
^s^oaxlcs  of  a  centuiy. 


THS  AVFINITIBS  OF  THE  ECHDrODBBMATA.  591 

syBtems  of  cayities,  one  ambulacral  and  tlie  other  peritoneal, 
and  that  the  mesoblaat  becomee  modified  in  accordance 
with  the  arrangement  of  these  BystemB.  The  enterocoele 
may  be  formed  by  one  diyerticalam  or  by  three.  In  the 
former  case,  the  first  formed  becomes  subdivided  into  three, 
of  which  one  is  anterior,  and  two  lateral,  as  in  the  latter 
case.  The  lateral  diverticula  give  rise  to  the  peritoneal 
cavity  and  its  lining :  the  median  diverticulum  is  converted 
into  the  circular  ambulacral  vessel  and  its  dependencies ; 
and  it  is  in  consequence  of  the  radiating  disposition  of  the 
latter,  and  of  the  nerves  and  muscles  which  are  related  to 
it,  that  the  Echinoderm  possesses  so  much  radial  Sjrmmetry 
as  it  displays.  It  is  clear,  therefore,  that  the  radial  sym- 
metry of  the  Echinoderm  results  from  the  secondary  modi- 
fication of  an  animal,  which  is  primitively  bilaterally 
symmetrical ;  and  that  the  apparently  radiate  Echinus  or 
Star-fish  is  a  specially  modified  '  Worm,'  (using  that  term 
in  its  widest  sense)  in  the  same  sense  as  the  apparently 
radiate  Corantda  is  a  modified  Arthropod. 

Haeckel  goes  further  than  this,  and  supposes  that  each  ray 
of  a  Star-fish  or  Ophiurid,  for  example,  represents  a  Worm, 
and  that  the  Echinoderm  consists  of  coalesced  vermiform 
buds,  developed  in  the  interior  of  the  Echinopsedium.  I 
must  confess  my  inability  to  see  that  this  hypothesis  is 
supported  by  valid  reasons.  On  the  contrary,  the  more 
closely  one  compares  the  structure  of  the  ray  of  an  Echino- 
derm with  the  body  of  any  known  Annelid,  the  more 
difficult  does  it  appear  to  me  to  be  to  find  any  real  likeness 
between  the  two. 

In  order  to  find  any  analogy  for  the  production  of  the 
Echinoderm  within  the  Echinopsedium,  on  the  contrary,  it 
appears  to  me  that  we  must  look  to  the  lower  and  not  to 
the  higher  morphological  types.  Among  the  Hydrogaa, 
nothing  is  commoner  than  the  distribution  of  the  functions 
of  life  between  two  distinct  zooids,  one  of  which  alone 
developes  reproductive  organs.  In  the  former,  the  hydranih, 
radial  symmetry  is  often  hardly  discernible  (e.g,  Calyeo- 
j^Ufridod) ;  in  the  latter,  the  meduBoid^  it  ia  vearj  xdk^^^ 


592       THE  AKATOmr  OF  nrYSBTEBSATBD  AXULkLB. 

and  especially  characterises  the  arrangement  of  the  gaatfo- 
vascnlar  canals;  which  are  offshoots  of  the  alimentary 
cavitj,  and  if  they  hecame  shut  off  therefrom,  would  answer 
to  the  enterocoele  of  the  Echinoderm. 

Suppose  that  from  a  hydronth  such  as  that  of  a  Diphfei, 
a  medusoid  were  developed,  and  that  instead  of  projecting 
from  the  exterior  of  the  body,  it  remained  hypodermic, 
spreading  out  between  the  ectoderm  and  the  endoderm  of 
the  hydroid,  and  consequently  superinducing  a  very 
marked  radial  symmetry  upon  it.  The  resulting  form 
would  give  us  a  Ccelcnterate  which  would  be  a  close  analogue 
of  an  Echinoderm. 

In  a  certain  sense,  an  Actinozoon  may  be  fairly  regarded 
as  such  a  combination  of  a  hydroid  with  its  medusoid;  and, 
hence,  it  must  be  conceded  that  the  parallel  between  the 
gastro-yascular  system  of  the  Ctenophora  and  the  ambn- 
lacral  system  of  the  Echinoderms,  instituted  by  the  elder 
Agassiz,  was  well  worthy  of  consideration.  Shut  off  the 
gastro-yascular  canals  of  a  Cydippe  from  the  alimentary 
canal,  and  they  become  an  enterocoele,  of  which  the  pro- 
longations along  the  stomach  may  be  compared  with  the 
peritoneal  sacs,  and  those  beneath  the  paddles  with  the 
ambulacral  vessels  of  the  Echinoderm. 

But  there  is  a  long  step  between  the  admission  of  the 
force  of  these  analogies,  and  the  conclusion  that  the 
Echinoderms  and  the  Ccdenteraia  are  so  closely  allied  as 
to  be  properly  associated  in  one  natural  assemblage  of 
"  Radiate  "  animals.  On  the  contrary,  the  Echinoderm,  hj 
its  Echinopssdium  stage,  shows  an  advance  in  organisation, 
far  beyond  anything  known  in  the  CcelerUeraia ;  and  in  the 
highly  characteristic  mode  of  development  of  its  entexooode 
(the  elucidation  of  which  in  the  Star-fishes  by  Prof.  A- 
Agassiz,  is  the  most  important  advance  in  our  knowledge 
of  the  Echinoderms  made  since  the  time  of  Miiller),  the 
Echinoderm  agrees  with  the  hi^er,  and  not  with  the  lower 
Metazoa, 

JBbfciiiodermaia  «\xrosi^  Vn  ^&i&  fossil  state.    Calcanout 


THS  OTSTIDSA.  598 

plates,  referred  to  tlie  HohMhuridea,  oconr  in  the  meeozoio 
rocks,  but  are  not  known  earlier.  The  Star-fishes  are  met 
with  in  the  older  Palffiozoio  strata,  nnder  forms  very  similar 
to  some  of  those  which  now  exist.  The  Eehinidea  abound 
from  the  Upper  Silurian  (PalcBchinus)  onwards.  The  Palffio- 
zoio  forms  are  spherical,  and  hare  multiple  interambnlacral 
plates  and  simple  ambnlacra.  Eehinidea  of  the  modem 
type  appear  in  the  Mesozoio  strata,  the  Echinoida  first; 
while  the  Spatangoida  and  Clypecuiroida  are  of  later  date. 
This  order  of  occurrence  agrees  with  the  embryonic  develop* 
ment  of  the  two  latter  groups,  which  ore  more  nearly 
spherical  when  young  than  subsequently. 

The  Orinoidea  abound  in  the  Pakeozoic  and  older  Mesozoio 
rocks,  gradually  diminishing  in  number  in  later  formations. 
The  oldest  appear  to  have  all  been  stalked,  and  of  peculiar 
and  extinct  types. 

Three  groups  are  wholly  extinct,  and  are  unknown  in 
strata  newer  than  the  Carboniferous  formation.  These  are 
the  Cystidea,  the  Edrioasterida,  and  the  BUuMdea, 

The  Ctstidea. — In  their  general  characters  the  Cystidea 
6ome  very  near  the  Orinoids.  Crypiocrinue,  the  simplest 
form  of  the  group,  possesses  a  calyx  supported  on  a 
stem,  and  composed  of  five  baealia,  five  parabiualiai,  and 
five  radialia.  An  inter-radial  aperture  is  surrounded 
by  a  cone  of  small  plates,  termed  the  pyramid.  The 
antambulacral  surface  has  no  pores,  but  these  were 
present  in  other  genera,  and  sometimes  are  scattered 
irregularly  {Caryocrinus) ;  sometimes  disposed  in  pairs 
{Sphceronites) ;  while  sometimes  they  take  the  form  of 
parallel  slits  arranged  in  '*  pectinated  rhombs."  The  arms 
were  free  (Comarocystites),  or  recurved  and  closely  applied 
to  the  calyx.  They  bore  pinnules,  which,  in  consequence  of 
the  non-development  of  the  arms,  were  sometimes  sessile  on 
the  radialia.  In  the  species  with  recurved  arms,  the  latter 
simulate  calycine  ambulacra.  There  is  an  aperture  placed 
in  the  centre  of  the  calyx  at  the  point  of  convergence  of 
the  ambulacra;  another  small  one  on  on&  ^^^  ^\  ^(k^\ 
and,  thirdly,  the  aperture  of  the  p^-waxudu    'tVift  %s^  ^'^ 


594      THE  ANATOmr  OF  nrvXBTSB&ATBD  ▲KIKAL8. 

these  ia  commonly  regarded  as  the  mouth,  the  second  as 
the  anus,  the  third  as  the  reprodnctive  apertore. 

The  Cystidea  would,  on  this  interpretation,  differ  from  all 
other  Eehinodermaiii,  except  the  Edrioasterida  and  HoUh 
thuridea,  in  the  genital  outlet  being  single ;  but  around  the 
central  aperture  five  pores  are  seen,  in  some  species  at  least, 
to  which  a  genital  function  has  been  ascribed.  In  any  case, 
the  Cyriidea  would  appear  to  come  very  close  to  the  Orinoidea, 

The  Edbioastebida. — This  gproup  contains  serend 
genera  of  extinct  Echinoderms  {Edrioaeter,  AgelacriniUt, 
HemieyHiteM),  which,  in  general  form,  somewhat  resemble 
what  the  Asterid  Chniaater  would  be  if  its  angles  were 
rounded  off.  Like  the  Cystidea,  they  possess  an  interam- 
bulacral  pyramid,  but  they  differ  from  them  in  that  they 
have  ambulacra  perforated  by  canals  which  open  directly 
into  the  cavity  of  the  calyx,  and  that  they  possess  no  aims. 
The  Edrioagierida  have  no  stem,  but  seem  to  have  been 
attached  by  the  aboral  face  of  the  body. 

The  Blastoidea. — In  PerUremites,  the  representatiYe  of 
this  order,  the  ambulacral  and  antambulacral  regions  are 
nearly  on  an  equality :  the  body  is  prismatic  or  subcylin- 
drical.  The  pedunculated  calyx  is  composed  of  three  basal 
plates,  two  of  which  are  doable.  The  aboral  plates  receiTe 
in  their  intervals  five  plates  deeply  cleft  above.  In  the 
clefts  lie  the  apices  of  the  ambulacra,  the  oral  portions  ol 
which  are  included  between  the  five  deltoid  inter^radisl 
pieces  which  surround  the  mouth.  The  cleft  plates  are  not 
radials,  but  portions  of  the  perisomatic  skeleton  of  the  abonl 
region.  Surrounding  the  central,  probably  oral,  aperture 
are  four  double  pores,  and  a  fifth  divided  into  three.  The 
median  of  these  three  seems  to  be  anal,  the  others  and  tlie 
paired  pores  being  genital.  Each  ambulacrum  is  lanceolate 
in  form,  and  presents  superficially  a  double  row  of  ossidee, 
which  meet  in  the  middle  line  and  support  pinnules  aft 
their  outer  extremities ;  beneath  them  lies  a  mngle  platob 
perhaps  the  homologue  of  the  vertebral  ossicles  in  the  Ophm- 
ridea  :  beiie&t\i  \\.  ^b^^odii  are  parallel  canals,  the  natoe  <i 
which  IB  usLkno^m. 


CHAPTER  Z. 

THI  TDHICATA   OB  A^CIDIOID^. 

:iB  remarkable  and,  ia  raaaj  respecte,  isolated  groDp  of 
Tine  animala  contains  bstlt  simple  and  composite,  fixed 
1  free  organiBins.  None  attain  a  length  of  more  than  a 
r  inchea,  and  some  are  minnte  and  almost  ffiioroMOpio. 
rhe  simplest  members  of  the  group,  and  Uiose  the  stmo- 
'eof  which  is  most  readily  comprehensible  are  the  Appm- 
ulori«s ;  minate  pelagic  organisms,  which  are  toimd  in  all 
itades,  and  are  propelled  like  tadpoles,  by  the  flapping 
a  long  caudal  appendage  at  the  snrfaoe  of  the  sea. 
ippendieuiaria  flabeUtim  (Fig.  U7)  has  an  OToid  or  flask- 
tped  body  (A),  one-sixth  to  one-fonrlh  of  an  inch  in  length. 
B  append^^  (B)  is  from  three  to  four  times  as  long  M  the 
Ij,  to  one  face  of  which  it  ia  attached  near,  but  not  at, 
I  posterior  extremity.  It  is  flattened,  and  is  supported 
a  firm  central  axis,  which  may  be  termed  tlie  uroekord 
g.  147, 1).  The  greater  part  of  the  bodj  is  usually  in- 
ted  by  a  stmctarelesa  gelatinous  tubetance.  but,  on  its 
nded  hinder  extremity,  this  ceases  to  be  distinguishable 
m  the  ectoderm. 

>n  the  caudal  appendage  the  polygonal  contours  of  the 
[s  of  which  the  ectoderm  is  composed,  are  plainly  dis* 

The  month  has  an  orerbanging  lip.  It  leads  into  a 
je  pharyngeal  sac,  the  walls  of  which  are  formed  by  the 
toderm.  Posteriorly, thissacnarrowsintotbecwophagiw, 
ich  bends  towards  the  hnmal  side  of  the  body,  and  then 
ns  into  a  epacions  stomach,  wfaich  takes  a  toanneMe 
action  and  is  dinded  into  two  lobes,  a  rig.b.A,  «jA«>^*ft^ 


596       THB  UTATOHT  OF  ntVIBTIBBATID  AJmULB. 

From  the  left  lobe,  the  mtcetine  arises;  uid,  bntding 
inwards,  turns  abruptly  forwards  in  the  middle  line,  where  it 
terminates  midwaj  between  the  oral  aperture   uad  the 
attachment  of  the  caudal  appendage.    The  inteatjne  there- 
Fig.  147. 


n.— Sida~view  of  the  bod;,  with  the  caadal  appendage  forcibiy  Ual    I 

A,  tlie  body;    B,  the  wudii  appendage;    a,  oral  aperture;  i,  d* 
phuyni;  e,  an  atrial  opening ;  d,  the  correipoadiDgaliema,  vithiM    ' 

-111-.  .  .•  — . . 1 — jg.   I   £^  stomaoh;  i,  tm^; 

leaf  the  onl  end  of  the  bob: 


.;  ff.  ifsophagus ; 
/,Dii>ehord;  n, celiulsr  paiob  at  the  lidi  ' 
II,  endoatyle ; /I,  innglion;  q,  ciliated  «  ,    ., 

nflFTB  vim  itH  gacgliB,  r ;  m^  endoderm ;  e  r,  ectodarm. 


fore  haa  a  hsmnJ  fleiare.    In  the  middle  of  its  faamil 
aspect  t^e  endo^ernv  lA  \^  '^^iB.T^ni^aal  cavity  is  raised  into  ^ 


▲PPBNDIOUIiASIA  FIiABKLLUM. 


«97 


a  fold,  which  projects  into  the  blood  cavity  contained 
between  the  endoderm  and  ectoderm.  The  walls  of  the 
bottom  of  the  fold  are  thicker  than  the  rest,  so  that, 
viewed  sideways,  it  has  the  aspect  of  a  hollow  cylinder. 
This  is  the  endottyle^    (Fig.  147,  n.) 

The  endoderm  of  the  pharynx  is  ciliated,  and  the  cilia 
are  especially  large  over  a  narrow  tract,  or  peripharyngeal 
band,  which  encircles  the  oral  aperture  at  the  level  of  the 
anterior  end  of  the  endostyle,  and  is  continued  back,  as  a 
hypopharyngeal  band,  along  the  middle  of  the  neural  face 
of  the  pharynx  to  the  oesophageal  opening. 

On  each  side  of  the  endostyle,  the  posterior  part  of  the 
hsemal  wall  of  the  pharynx  presents  two  oval  apertures  or 
stigmata  (Fig.  147  d),  encircled  by  cells,  which  are  provided 
with  very  long  and  active  cilia.  Each  stigma  leads  into  a 
funnel-shaped  oiriaZ  canal,  the  open  end  of  which  termi- 
nates beside  the  rectum.t    (Fig.  147,  c.) 

nrhe  heart  is  a  large  sac,  which  exhibits  rapid  peristaltic 
contractions,  and  is  placed  transversely  between  the  two 
lobes  of  the  stomach.  In  the  species  which  I  observed  no 
blood  corpuscles  could  be  seen,  and  the  direction  of  the 
pulsations  of  the  heart  was  not  reversed  at  intervals,  as 


*  So  described  and  n&med  in 
my  *^  Observations  upon  the 
Anatomy  and  Physiolog^^  of  Sal- 
pa  and  Pyrosoma,  together  with 
remarks  upon  Doholum  and 
Appendicularia."  (Phil.  Trans. 
1851.)  In  1856,  however,  I  sUted 
"  With  regard  to  the  endostyle,  I 
have  nothing  important  to  add  to 
m  v  previous  account,  except  that 
I  believe  it  to  be  here,  as  in  other 
ascidians,  the  optical  expression 
of  the  thickened  bottom  of  a 
fold  or  groove  of  the  branchial 
w/6**  ('Quarterly  Journal  of 
Microscopical  Sdence,'  April, 
1856.)  In  my  memoir  on  Pyro- 
soma  (Linn.  Trans.  1860,  p.  205) 
the  endostyle  is  stated  to  be  **  in 
reality  a  lon^tudinal  fold  or 
diverticulum  of  the  middle  of  the 


hsemal  wall  of  the  pharynx, 
which  projects  as  a  vertical  ndge 
into  the  hsemal  sinus,  but  re- 
mains in  free  communication 
with  the  pharynx  by  a  cleft  upon 
its  neural  side." 

t  These  stigmata  were  first  de- 
scribed bv  Ge^enbaur  (**  Bemer- 
kungen  uber  die  Organixation  der 
Appendicularien ;  *^  Zeitschrift 
fur  Wiss.  Zoologie,  1855),  who 
supposed  that  they  communicated 
with  canals  of  the  interior  of  the 
body.  However,  l>y  feeding  Ap- 
pendkularuB  with  indigo,  I  demon- 
strated  the  communication  of 
these  stigmatic  funnels  with  the 
exterior  of  the  body.  (*  Quar- 
terly Journal  of  Microscopical 
Science,*  Lc.) 


598      THB  AVATOKT  OV  imrBBTSBSATSD  AVIICAU. 

it  is  in  the  Asoidians  in  g^eraL  M.  FoU*  howerer,  states 
that,  in  other  AppendiaUaricB,  the  xeTersal  of  the  con- 
tractions of  the  heart  takes  phuse.  Like  myself  he  has 
been  unable  to  discover  anj  blood  corpuscles.  There  are  no 
distinct  vessels,  but  the  colourless  fluid  which  takes  the 
place  of  blood  makes  its  way  through  the  interspaces 
between  the  ectoderm  and  endoderm  and  the  various 
viscera. 

The  nervous  system  consists  of  a  ganglion  (Fig.  147,  p) 
situated  nearly  opposite  the  anterior  end  of  the  endostyle ; 
in  front,  this  gives  off  the  nerves  to  the  sides  of  the  mouth, 
while,  behind,  it  is  continued  into  a  long  cord  (s),  which 
runs  back  beside  the  oesophagus,  and  between  the  lobes  ol 
the  stomach,  to  the  base  of  the  appendage.  It  then  passes 
along  one  side  of  the  urochord  to  its  extremity,  giving  off 
nerves  at  intervals.  At  the  origins  of  these  nerves  aggre- 
gations of  ganglionic  cells  are  situated  (Fig.  147, 1).  The 
most  anterior  of  these  ganglia  is  the  largestf 

A  rounded  otocyst  containing  a  spherical  otolith  is 
attached  to  the  ganglion,  and  a  small  ciliated  sac,  whidi 
opens  into  the  pharynx,  is  in  close  relation  with  it  (Fig.  147, 
r,  q),  M.  Fol  describes  a  number  of  fine  tactile  sete 
situated  around  the  oral  aperture. 

The  urochord,  which  constitutes  the  axial  skeleton  of 
the  appendage,  is  transparent,  rounded  at  each  end,  and 
bounded  by  a  delicate  membrane.  The  remains  of  the  oeUs 
of  which  it  is  composed  are  to  be  seen  in  it,  here  and 
there,  as  ramified  corpuscles  lodged  in  its  periphery. 

The  only  muscles  hitherto  observed  in  Appendieuhm 
are  two  sheets  of  striped  fibres  interposed  between  ths 
urochord  and  the  cellular  ectoderm  of  the  appendage. 

The  reproductive  organs  occupy  the  rounded  projection 
formed   by  the   posterior  part  of  the  body  behind  the 


*  '  Etades  sar  les  Appendiou-  eularut,  counts  this  ss  the 

Imiros,'  1872.  ganglion  of  the  nervous  systta, 

f  '  Quarterly  Journal  of  Micro-  and  states  that  a  fine  eaaal  tia- 

scopieal  Science,'  1856,  pp.  8,  9.  verses  both  the  ganglia  aad  tht 

If.    Fol,   who    filndt    the    same  longitudinal  nerve, 
arraagtment  in  othst  ApfimdU 


APPSHDIOUULBIA  VLABBLLUX. 


599 


digestive  canal.  The  testiB  (Fig.  147,  lb)  is  a  large  oellxilar 
mass  which  fills  the  greater  part  of  the  cavity  of  this  pro- 
jection in  the  adult.  When  f ally  formed,  it  is  resolved  into 
spermatozoa  with  rod-like  heads  about  yi^th  of  an  inch 
long  and  very  fine  filiform  tails.  They  escape  by  the 
dehiscence  of  the  testis. 

I  have  never  met  with  AppendieulariaB  containing  ova, 
nor  do  any  other  observers,  except  M.  Fol.  appear  to  have 
been  more  fortunate.  The  latter,  however,  states  that  these 
animals  are  hermaphrodite  (Oikoplewra  dioiea  apparently  is 
dioBcious),  and  that  the  ovary  is  developed  later  than  the 
testis.* 

Two  singular  rounded  x>atches  of  a  cellular  structure  (Fig. 
147,  II.  m)  are  interposed  between  the  ectoderm  and  the 
endoderm  on  each  side  of  the  anterior  end  of  the  endostyle. 
Similar  bodies  occur  in  other  Ascidians,  but  their  function 
is  unknown. 

One  of  the  strangest  peculiarities  of  the  AppendicularuB 
is  the  power  which  they  possess  of  excreting  from  the  surface 
of  the  ectoderm,  with  extreme  rapidity,  a  mucilag^ous 
cuticular  investment,  in  the  interior  of  which,  as  in  a  spacious 
case,  the  whole  body  is  lodged.  This  is  what  was  originally 
described  by  Mertens  as  the  "  house  "  of  the  Appendicularia. 
It  is  obviously  the  homolog^e  of  the  test  of  other  Ascidians, 
which  is  often  adherent  to  the  ectoderm  by  only  two  or 
three  points;  but  no  cellulose  has  been  discovered  in  it. 
According  to  M.  Fol,  who  has  studied  the  formation  of  the 
**  house  "  with  great  care,  the  AppendieulatioB  have  no  proper 
test,  and  what  I  have  described  as  the  structureless  gelatinous 
investment  of  the  anterior  part  of  the  body  is  the  commence- 
ment of  the  *'  house."    It  increases,  assumes  a  peculiar 

larve,ne  me  pamtdiff^rer  en  rien 
de  oelui  dee  Ajoidies ;  et  eomme 
d'autre  part,  la  petiteaie  de  ces 
ceofB  et  la  difflonltd  qu'on  a  de  lea 
obtenir  lea  rendentpea  favorablet 
k  Tetode,  je  n*al  pas  juge  kpropos 
d'approfondir  davantage  oe  m- 
jeO^(l.  c.  p.  1.) 


*  I  must  confeBS  that  M.  Fol's 
figures  and  descriptions  of  the 
ovary  and  ova  are  not  satisfactory 
to  me,  and  his  dismissal  of  the  suli^ 
jeet  of  their  development  in  the 
following  paragraph  is  tanta- 
lising :— 

**  Le  d^veloppement,  que  j*al  pu 
juivre  jusqu'a  la  formation  de  la 


600      THB  ANATOMY  OF  IHYSBTBB&ATBB  AITIMALB. 

fibrous  stmctare,  and  in  the  course  of  an  hour,  in  a  Tigorous 
animal,  it  is  separated  as  an  envelope  in  which  the  whole 
body  is  capable  of  free  moYement.  In  front,  it  presents  two 
funnel-shaped  apertures  supported  by  a  filnrous  treUis-work, 
which  lead  down  to  the  cavity  in  which  the  body  is  con- 
tained. A  spacious  median  chamber  allows  of  the  free 
motion  of  the  tail.  After  a  few  hours  the  animal  deserts 
its  test  and  forms  another. 

In  the  great  majority  of  those  Timi4saia  which  are  fixed 
in  the  adult  state,  the  young  leave  the  egg  in  an  actire 
larval  condition,  and  resemble  Appendictdaria  in  being 
propelled  by  a  muscular  appendage  in  the  axis  of  which  lies 
an  urochord.  The  body  and  appendage,  however,  are  in- 
vested by  a  coat,  or  test,  impregnated  with  cellulose,  and  the 
former  presents  some  importuit  structural  differences  from 
that  of  AppendictUaria,  After  a  free  existence  of  a  certain 
duration,  the  body  of  the  larva  fixes  itself,  the  appendage 
withers  away,  and  the  young  animal  assumes  the  ordinary 
form  of  a  fixed  Ascidian.  It  may  remain  simple,  or  it  may 
develope  buds  and  give  rise  to  a  compound  organism  or 
Ascidiariwn,  consisting  of  many  Ascidiozooids  united  to* 
gether. 

All  the  fixed  Tunicates  present  two,  more  or  less  closely 
approximated,  apertures;  one,  oral,  leads  into  the  ali- 
mentary cavity,  the  other,  atrial,  opens  into  a  chamber, 
the  aifiwn,  into  which  the  faeces  and  genital  products 
are  poured.  During  life,  when  these  apertures  are  open, 
a  current  sets  into  the  oral  and  out  of  the  atrial  opening. 
But  if  the  animal  is  irritated,  the  sudden  contraction  of 
the  muscular  walls  of  its  body  causes  the  water  contained 
in  the  brachial  and  atrial  cavities  to  squirt  out  in  two 
jets,  while  both  apertures  are  speedily  closed. 

The  apertures  are  much  further  apart  in  some  fomii 
than  in  others,  and  in  certain  of  the  BotryUicUB  they  ait 
almost  terminal.  In  the  pelagic  genera  Pyrosama  (Fig.  150), 
Doliolwm  (Fig.  151),  and  Salpa  (Fig.  152),  the  atrial  and  oial 
apertuxea  are  at  o^i^oiatb  csada  ^1  '^'^  longest  <iii^w^^^  ^ 


THK  TVNICATA, 


the  body ;  and,  in  the  two  latter,  locomotion  is  effected  l^ 
the  contraction  of  txansrerse  mnscnlar  bands,  which  drives 


Fig-  Its— PAoZ/tuu  mattmla.—ttM  iMt  la  removed,  ukd  bwdly  more 
of  the  ■nimal  repreuuted  than  woald  be  leea  In  ■  longiludin*! 
■eedoo:  a,  onl  apertiini ;  b,  nnglion  ;  c,  elrolct  of  tentaelM;  it, 
bnachUl  lao,  the  three  rowi  of  aperturee  in  Iti  upper  part  iadieate 
butdoDOtrapreeent  the  lUgmala:  «,  the  langueU ; /,  the  (Eeopbagea^ 
opening;  g,  tbe  nomaoh ;  A,  the  luteatine:  i,  the  anw,  t,  41>ft 
atrluin ;  I,  the  atiU  ^ertore ;  wl,  the  endMqVv,  ii,<&i«\maX. 


602       THB  ANATOmr  OV  nmBBTSBRATSD  AVDIALS. 

the  water  out  of  the  one  aperture  or  the  other,  and  canaee 
the  body  to  be  propelled  in  the  opposite  direction. 

When  one  of  the  simple  fixed  AscidianB,  aaoh  as  a  Phal' 
lugia  (Fig.  148)  or  a  Cynthia,  is  laid  open  by  a  section  carried 
through  the  oral  opening,  at  right  angles  to  a  transrene 
pkme  passing  through  its  centre,  the  month  is  found  to 
open  into  a  large  pharyngeal  dilatation,  termed  the  bra^ 
ehidl  sac  (Fig.  148,  d),  A  series  of  simple  or  pinnatifid  ten- 
tacles (Fig.  148,  c)  is  seen  encircling  the  oral  aperture,  at 
some  little  distance  within  the  margin  of  the  lip,  which 
is  usually  divided,  like  that  of  the  atrial  opening,  into 
four  or  six  lobes.  Immediately  behind  the  tentacular 
circlet  is  a  ciliated  peripharyngeal  band. 

On  that  side  of  the  branchial  cavity  which  is  furthest 
away  from  the  atrial  opening,  a  pair  of  delicate  lip-like  f ddB 
ext€»ad,  parallel  with  one  another,  from  the  periphaiyngeal 
band,  along  the  middle  line  of  the  branchial  sac,  as  far  as  the 
opening  of  the  OBsophagua  at  the  opposite  end  of  the  branchial 
sac.  The  interspace  between  these  leads  into  a  fold  of  the 
endoderm,  lined  by  a  thick  epithelium  and  forming  the  endo- 
style,  and,  in  the  middle  line  of  the  peripharyngeai  hcmd,  on 
the  same  side  as  the  atrial  aperture,  there  is  a  tubercuhur 
elevation,  which  contains  a  ciliated  cavity  and  answers  to 
the  ciliated  sac  of  Appendicularia.  The  walls  of  this  sac 
are  variously  folded,  and,  consequently,  the  surface  of  the 
tubercle  presents  a  more  or  less  complicated  pattern.  Con- 
tinued backwards  in  the  middle  line,  as  far  as  the  obbo- 
phageal  aperture  on  this  side  of  the  branchial  sac,  there  are 
sometimes  one,  sometimes  two  longitudinal  1«.wip1)<p,  the 
hypopharyngeal  folds ;  or  there  may  be  merely  a  ridge  Bar- 
mounted  by  a  series  of  tentacles,  termed  langueU  (Fig.  148,  e). 
The  languct  which  is  nearest  the  ciliated  sac  is  often  the 
largest  of  the  series.  Behind  the  peripharyngeal  band,  the 
lateral  walls  of  the  pharyngeal,  or  branchial,  sac  are  perfo- 
rated by  small  elongated  apertures,  the  stigmaia^  the  edges  of 
which  are  fringed  with  long  cilia ;  and,  by  means  of  thsse 
ftperturea,  the  cavity  of  the  sac  communicates  with  the 
atrinia. 


THS  TUVICATA.  603 

The  stigpnata  are  ammged  in  transyerae  rowa  and  are 
usoallj  very  numerous.  The  retionlated  wall  of  the 
branchial  aao  may  be  streng^ened  bj  longitadinal  lameU», 
or  it  may  be  raised  into  few  and  distant,  or  many  and 
close-set  folds.  In  some  oases,  papilla  of  a  compUoated 
form  are  developed  from  the  inner  surface  of  the  sac,  and 
its  outer  wall  is  always  connected  by  Tascular  trabecule  with 
the  parietal  wall  of  the  atrium.  In  some  cases,  {Molgula) 
the  stigmata,  instead  of  being  elongated  meshes,  are  coiled 
spirally.  The  atrial  chamber  (Fig.  148,  h),  into  which  the 
branchial  stigmata  open,  is  shown  by  laying  it  open  from 
the  atrial  aperture,  in  the  same  way  as  the  branchial 
chamber  was  laid  open  from  the  oral  aperture.  The  atrial 
opening  is  thus  seen  to  lead  into  a  cavity,  interposed 
between  the  branchial  sac  and  the  parietes,  and  lined  ux>on 
all  sides  by  a  delicate  membrane  (the  ihi/rd  iwnie  of  Milne- 
Edwards)  like  a  peritoneum.  This  membrane  has  a  parietal 
and  a  visceral  layer.  The  former  is  continued  from  the 
atrial  aperture  on  to  the  parietes  of  the  body,  to  the  level  of 
the  i>eripharyngeal  band  in  one  direction,  to  a  line  par- 
allel with  the  endostyle  in  another,  and  to  the  alimentary 
and  genital  viscera  in  a  third  direction.  From  these  va- 
rious lines,  it  is  reflected  on  to  the  branchial  sac,  of  which  it 
forms  the  outer  wall.  At  the  margins  of  the  stigmata  it  is 
continuous  with  the  endoderm  of  the  pharynx,  and,  at  the 
aperture  of  the  rectum,  with  the  endoderm  of  the  intestine. 
Thus  the  atrial  membrane  forms  a  bilobed  sac,  one  lobe 
extending  on  each  side  of  the  pharynx,  and  opens  out- 
wards by  the  atrial  aperture ;  it  communicates  by  the  stig- 
mata with  the  interior  of  the  branchial  sac;  and,  by  the 
anal  and  genital  openings,  it  receives  the  faces  and  genital 
products.  The  current  which  sets  in  at  the  oral  and  out  at 
the  atrial  aperture  is  set  in  motion  by  the  cilia  of  the  stigmata. 

The  atrium  of  the  higher  Ascidians  differs  from  that  of 
Appendieularia,  not  only  in  extent,  but  in  being  single  and 
not  double ;  and  in  its  single  aperture  being  placed  upon 
the  neural  aspect  of  the  body  dose  to  the  ganglion,  while 
the  atrial  funnels  of  Appendieularick  Qf[^sB^^QS!^fso^'^kiSi^\assBDa^ 


604       THE  AKATOMT  OF  IHTKBTXBKATSD  AVIMALS. 

aspect  of  the  body.  The  development  of  the  liigiier  TmmI- 
eaioy  however,  shows  that  the  peculiarities  of  the  atiium  is 
them  are  of  secondary  origin ;  and  that,  to  begin  with,  there 
are  two  distinct  atria,  as  in  Appendieularia, 

The  oesophageal  aperture  is  nsoally  surrounded  by  a  Tailed 
lip,  and  the  short  and  wide  oesophagus  leads  into  a  dilated 
stomach,  whence  a  shorter  or  longer  intestine  pit)ceeds.  The 
alimentary  canal  is  always  bent  upon  itself  in  such  a  iw^immj* 
that  the  anus  terminatee  on  the  neural  side  of  the  bod|f, 
in  the  atrial  chamber. 

In  Clavelina,  AmoHromeium,  Didemnum,  SyniefhySf  and 
most  of  the  compound  Ascidians,  the  greater  part  of  the 
alimentary  canal  lies  altogether  beyond  the  branchial  sac, 
in  a  backward  prolongation  of  the  body  whicb  has  been 
termed  the  abdomen,  and  is  often  longer  than  all  the  rest  of 
the  body ;  the  alimentary  canal  forming  a  long  loop,  and 
the  direction  of  the  axis  of  the  branchial  sac  being  continued 
by  that  of  the  gullet,  stomach,  and  first  half  of  the  intestinei 
In  the  BotryllidcBt  however,  the  stomach  is  bent  at  right 
angles  upon  the  gullet,  as  in  Appendieularia ;  the  intestine 
almost  immediately  turns  forward,  and  then,  turning  shaiply 
upon  itself,  passes  forwards  parallel  with  the  hinder  paitol 
the  branchial  sac,  on  one  side  of  which  it  opens  into  the 
atrium. 

A  similar  arrangement  obtains  in  Perop^oro,  but  the 
branchial  sac  extends  backwards  for  a  short  distance  on  one 
side  of  the  stomach.    In  the  solitary  Ascidians,  the  stomadi 
lies  sometimes  altogether  behind  the  branchial  sac  (Peloiuns,    / 
some  Phallutice) ;  but,  usually,  the  branchial  sac  extends  so   | 
far  back  that  the  whole  alimentary  canal  lies  on  one,  usually    ] 
the  right,  side  of  it.    In  Phalluna  fiaonod^ns,  tbe  binder  end 
of  the  branchial  sac  is  recurved,  and  the  oesophageal  opening 
looks  backwards  to  the  fundus  of  the  sac,  instead  of  forwards 
to  the  mouth. 

In  many  Ascidians,  a  strong  fold  of  the  endoderm  ol  the 
intestine  projects  into  its  interior,  as  in  Liamellibraii^ 
and  in  the  Earthworm,  where  such  a  fold  oonBtitates  the 
BO-cnXled  lipklosoU. 


THB  T17KICATA. 


005 


In  the  pelagic  Tunicates,  Salpa,  Pyroaoma,  and  Doliolum, 
I  found  a  system  of  fine  tubules,*  which  ramify  over  the 
intestine  and  are  eventuaUj  gathered  together  into  a  duct 
which  terminates  in  the  stomach.  An  apparatus  of  the 
same  nature  exists  in  Phallusia,  Cynihia,  Molgula,  Perophora, 
Botryllut,  BotrylUndes,  Clavelinat  ApUdam,  and  DidemnmHtf 
and  I  have  little  doubt  that  it  is  hepatic  in  its  function. 
In  some  Cynthice,  however,  there  is  a  follicular  Uyer  of  the 
ordinary  character,  which  opens  into  the  stomach  by  several 
ducts. 

In  some  Phallu8ice,  the  alimentary  canal  is  coated  by  a 
very  peculiar  tissue,  consisting  of  innumerable  spherical 
sacs  containing  a  yellow  concretionary  matter.  In  Molgula 
(and  in  the  Ascidia  tntrea  of  Yan  Beneden)  an  oval  sac 
containing  concretions  lies  close  to  the  genital  gland,  on 
one  side  of  the  body.  As  these  concretions  have  been  shown 
by  Kupfer;^  to  contain  uric  acid,  the  organ  must  be  re<* 
garded  as  renal  in  function.  M,  Lacaze-Duthiers  §  terms 
this  sac  an  "organ  of  Bojanus;"  but,  as  he  admits,  no 
opening  is  discoverable :  it  would  probably  be  more  correct, 
therefore,  to  regard  it  as  the  representative  of  the  glandular 
part  6f  the  organ  of  Bojanus.  || 

The  heart  is  an  elongated  sac  open  at  each  end,  lodged 
near  the  stomach,  and  close  to  the  hinder  extremity  of  the 
branchial  sac.  After  a  certain  number  of  contractions  in 
one  direction,  it  stops  and  contracts  for  the  same  number 


*  Savigny  seems  first  to  have 
observed  this  orgmn,  as  would 
appear  from  his  account  of  Via- 
zona,  (*  Memoires  sur  les  Aui- 
maux  sans  vertebres/  p.  176,) 
and  the  description  of  plate  12. 
Lister  mentions  and  figures  it  in 
Perophora  (Phil.  Trans.  1834). 

t  '  Reports  of  the  British 
Association,'  1852.  Hancock  "On 
the  Anatomy  and  Physiology  of 
the  Tunicata:'  (*  Journal  of  the 
Linnean  Society,'  Vol.  IX.)  The 
development  of  these  tubules 
from  the  stomach  was  trac^  by 
Krohn  in  Phtdlusia^  and  by  myseif 


in  Pyrtmoma. 

X  **  Zur  Entwickelung  der  ein- 
fachen  Ascidien."  (*  Archly  flir 
Mikr.  Anatomic '  1872.) 

§  **Les  Ascidies  simples  des 
Cdtes  de  France."  ('  Archiyes  de 
Zoologie  ezp^rimentale,'  1874.) 
M.  Lacaze-Uuthiers  has  obtained 
murexide  by  heating  this  sub- 
stance with  nitric  acid. 

H  There  is  a  close  resemblance 
between  the  cells  of  which  this 
organ  is  composed  and  those 
wMch  constitute  the  primitiye 
kidney  in  the  PtUmonata, 


606       THB  ANXTOHT  01  IWrXXTOBSAIXD 

of  times,  in  the  opposito  direction.  The  ootine  of  the  cir- 
culation ie  thus  reveraed  with  great  regnlalitj.  The  blood 
IB  a  clear  fluid,  cofitaining  colourleaa  corpnaclea. 

ReepiRition  is  effected  in  the  nalU  of  the  bmnchial  boc 
through  which  the  blood  is  driven.  The  enpply  of  &erat«d 
water  is  kept  up  bj  the  currents  already  mentioned,  which 
BubBcrve  the  ingestion  of  food,  the  respiratory  process  and 
the  ejection  of  effete  matters,  as  well  as  the  expulsion  of  tbe 
generative  products.  The  test  in  which  the  body  ia  en- 
closed is  somtttimes  closel;  adherent  to  the  surface  of  the 
ectoderm,  but  sometimes  is  united  with  it  only  at  the  oral 
anil  atrial  upertures,  and  by  prolongations  of  the  body.  In 
(■ODsistency  it  presents  every  variety,  from  soft  and  gela- 
tinous, to  dense  and  hard  like  cartilage,  or  tough,  likefibroiu 
tissue.  In  some  cases  the  exterior  of  the  t««t  is  covered 
with  humy  spinet,  tubercles,  or  even  with  regularly  disposed 
plat«3  iCkdyoemna). 

In  texture,  the  test  may  present  merely  a  bomogeneotis 


TBI  DIVBLOPMBBT  OT  TBI 
Ftg.  1*9. 


Slg.  l*9.~Piaihak 


of  tha  lu*a.    (After  Komlcwik;.^ 


i/bla. —Varionl  lUgM  In  the  diTdopinciil 


I.  ThP  vMicQtar  moral.,  fl.tUmf 
fh.  blDaloFO'lc.     The  Urgf!  I<1iwl<>in(<ri 

tmalt  one*  the  eiiililust. 
n.  The  pnsiruU  with  Ihe  bloClnpoTe,  or  apvnioa  nf  liiv«ct>»tii>n,  m 

rh.  Ihe  hlulomerM  which  ooiuriiutv  tliB  ruiliaii<nt  of  tjw  DradWnl; 

dil,  the  rcmuning  blutompTOB  of  llic  hypablul. 
ni.  A  more  advaiiiwl  eiubiyn ;  oA,  iM,  u  bitftir*.    e,  the  ni^blnil  ,■  >, 

the  n»rvous  Ujor  of  the  neonU  oBvlty,  whioh  i>  no«  open  ©nlj  la 

rV.  An  Piabrjo  n<Ih  the  caudal  apnendagv  illillnnl.  Th*  arm  tnbf 
n  li  complete,  and  the  muMlo-fclla  a,  are  dUtliiKU>>h>b)*. 

V.  The  bndy  of  u  larva  aa  it  euape*  from  tli*  «gg.  a,  the  vy*;  fi. 
Ihe  saccular  anterior  euA  of  the  central  mrviiioi  ■pparatDi  Inin 
which  the  oinliih  projecta;  Ro.  Hm,  ill  InbnlU'  backward  prfilna- 
(Ration  •,  Chi,  colli  of  the  nrochonl ;  a,  moulh  ;  U,  atrial  ap^rtnivi 
f,  oijening  Bl  the  anterior  end  of  the  centra]  nrnroiia  avpantiu,  bj 

ment  of  the  icsuphiigui  and  aiotnach ;  n,  blmil  corpuaelf*  |   tf, 
pnnilte  bj  whieh  (he  larva  attach «  iiaelf. 

V I.  The  bndv  anil  th(>  enmmenBcmeot  of  the  Cauda]  «ppFDdag«  af  a 
free  brva  two  Uaya  i>)d  ra,  ondaatyle ;  Ju,  branohial  ne  ■  lli, 
Ui,  branchial  atlgmata;  U.  uiitrance  into  the  blood  alooa  t>M«(<a 
them ;  if,  iDiostinc ;  b,  blood  oorpuaclea  i  jiAa,  atrial  >|>(<rliir«. 


reprodactiTe  organs  ore  loilgttd  i 
atria]  cavitj,  and  their  du«U  an 


,  the  lateral  waUa  of  tli« 
dietutt  from  tbo  maa; 


THB  DEYELOPMEKT  OF  THB  T17KICATA. 


609 


is  formed  hj  the  perforation  of  a  spot  in  wliicli  the  hypo- 
blast and  the  epiblast  cohere  (Fig.  149,  YI.).  The  atrial 
cavity  is  formed  by  two  involutions  of  the  ectoderm,  which 
extend  inwards  and  apply  themselves  to  the  lateral  and 
neural  walls  of  the  branchial  sac  (Pig.  149,  VI.).  Their 
originally  separate  apertures  eventuaUy  coalesce  into  one.* 
The  atrial  tunic  thus  formed,  and  the  walls  of  the  branchial 
sac,  coalesce  and  become  perforated,  in  order  to  give  rise 
to  the  stigmata. 

The  test  appears,  at  first,  to  be  a  cuticular  secretion  of  the 
epiblast,  and  to  derive  its  cellular  elements  from  the 
wandering  into  its  substance  of  cells  derived  from  the 
epiblast. 

In  Molgtda  tubulosay  Kupfer  and  Lacaze-Duthiers  have 
observed  that  the  fecundated  eggs  are  expelled  from  the 
atrial  cavity  and  almost  immediately  become  fixed  to  the 
surface  on  which  they  fall.  Yelk-division  takes  place,  and 
after  four  nearly  equal  blastomeres  are  formed,  much 
smaller  ones  are  developed  from  one  face  of  these,  and 
increase  until  they  constitute  a  blastodermic  layer  around 


*  In  1852  Krohn  discovered  the 
fact  that  the  larva  of  PhaUuda  is 
provided  with  two  distinct  sym- 
metricallv  disposed  openings,  by 
which  the  originally  separate 
atria  open  outwards ;  and  that  the 
two  eventually  coalesce  into  the 
single  atriura  of  the  adult.  Kowa- 
lewsky,  Fol,  and  later  obser- 
vers, agree  that  these  openings 
and  the  atrial  sacs,  are  formed 
by  two  involutions  of  the  ecto- 
derm, which  apply  themselves  to 
the  sides  of  the  pharynx,  and 
coalesce  with  it  at  the  points 
which  become  perforated  by  the 
stigmata ;  of  which,  in  PhaUutiOy 
there  are  at  first  but  two  on  each 
side.  If  this  is  a  true  account  of 
the  origin  of  the  atrium,  the 
atrial  membrane  is  obviously 
part  of  the  ectoderm,  and  its 
cavity  is  analogous  to  the  pallial 
cavity  of  a  mollusk. 


On  the  other  hand,  Metschni- 
koff  and  Kowalewsky  agree  that 
in  the  buds  ofJBotryttut.  and  other 
ascidians  which  multiply  by  gem- 
mation, the  two  primitively  dis- 
tinct atrial  cavities  are  portions 
of  the  alimentary  sac,  which  be- 
come shut  off  from  It,  and  sub- 
sequently open  outwards. 

Metschnikoffr*'£ntwicke1ungs- 
geschichtliche  ^itrikge,"  '  Bulle- 
tin de  r  Acad.  St.  PetersbouiK,' 
ziii.)  therefore  compares  the 
atrium  to  the  enteroccele  of  Echi- 
noderms.  Renewed  observations 
specially  directed  to  this  point, 
which  is  of  great  morphological 
importance,  are  much  needed.  If 
the  atrial  cavity  is  really  an 
enteroccele,  it  will  answer  to  the 
perivisceral  cavity  of  the  Brachio' 
poda,  the  pseudo-hearts  of  which 
will  correspond  with  the  primi- 
tive atriflkl  ai']^«tVax%. 


.1 


of  any  candiii   appeuua;;*:.     A-.l»^.«  ^ ^ 

it. self  with  a  transparent  test,  throws  out 
prolonpitionB  of  the  eetodfrni,  and  fmall}' 
adult  condition.     Although  no  tail  is  devel 
J  uiasB  is  to  l>c  seen  in  the  same  position  as  t 

the  remains  of  this  appenila^c.  when  it  ha 
retrogressive  mctamorphoBis,  in  the  Ascidir 
larva;.  The  atrial  aperture  is  single  at  its  i 
and  no  larval  sensory  organs  are  developed. 

8eepaffe6\\, 

Ki«».  1 50. —  Pyroaoma  pigatUmm. — I.  A  vertical  secti 

Ascidiftrium  near  the  cloacal  aperture  and  in 

The  youngest  condition  of  a  bud  befure  the  et 

III.  IV.  v.,  further  stages  of  the  development  of 

I  formed  bud  with  a  second  ascidiozooid  in  course  < 

ita  peduncle. 
^  VII.  A  fcetus  with  the  blastoderm  divided  into  five 

the  cyathoxooid  (I)  is  the  largest.    VIII.  A  firt 
^  I  of  which  half  encircle  the  base  of  the  cyathozof 

K  most  advanced  stage  observed.     The  remain 

cyathoxooid  and  ovisac  are  hidden  by  the  circle 
The  letters  have  tlie  same  signification  in  all  the 
labial  process ;  a\  lip  of  the  doaoal  aperture ; 
bryonfc  test ;  e,  oral  aperture ;  />^,  atrial  ape 
P,  /*,  branchial  sac  and  stigmata ;  r,  heart ;  r', 
-  i         '  ascidiarium ;  H,  stolons  of  the  embryonic  asc 

;|    .  U  testis;  w,  u\  ovum;  w\  peduncle  of  a  bw 

^^r*\nn  nf  t.hft  endoderm  entering  into  a  bu 


■  I 
1 1 


612       TBE  ANATOKT  OF  OITXBTSBaATED  AITIHALS. 

branchcB,  which  derelope  new  ucidiozooidB,  ue  given  off  at 
intervals:  bnt,  more  commonly,  the  aacidiaritun  ia  maaaive, 
and  the  aecidiozooids  relain  no  permanent  connexion  mth 
one  another.  In  the  Botryllida,  the  zooida  are  arranged  in 
whorls  around  a  common  central  cavitj,  or  cloaca,  into 
which  the  atria  of  all  the  memhers  of  the  whorl  open.  In 
Pyrosoma,  which  is  a  eort  of  floating  Botryllut,  the  process 
of  budding  is  highlj  instmctlve,  aa  it  exemplifies  the  majmer 
in  which  gemmation  occnrs  in  the  Taiticata  in  general.* 

The  aacidiariumoi  Ptproioma  (Fig.  150, 1.) has  the  form  of 
a  hollow  cylinder,  rounded  and  closed  at  one  end,  truncated 
and  open  at  the  other,  formed  of  a  firm  transparent  test, 
in  which  the  zooida  are  arranged  in  whorls.  Their  oral 
apertures  open  on  the  exterior  enrface,  and  their  atrial 
apertures  into  the  interior  of  the  cylinder.  The  htemal 
aspect  of  each  zooid  is  tamed  towards  the  closed  end  of 
the  cylinder.  The  brsnchial  sac  has  the  ordinary  atmctare, 
and  each  7.ooid  is  provided  with  a  testisand  with  an  ovisac, 


THE  BTTBDIHa  AlTD  7188109  OV  ASCIDIAITS. 


613 


a  new  zooid  united  by  a  narrow  neok,  or  peduncle,  with  the 
parent  (Fig.  150,  lY.).  The  endostylic  cone  gives  rise  to 
the  whole  alimentary  canal  of  the  bud,  while  the  ectoderm 
of  the  latter  proceeds  from  the  ectoderm,  and  its  ovisac 
and  testis  from  the  mesoblastic  cells,  of  the  parent.  Thns 
the  organs  of  the  bud  are  all  the  direct  product  of  the 
corresponding  parts,  or  of  the  primitive  layers  of  the  germ 
from  which  they  are  derived,  in  the  parent.* 

After  the  terminal  bud  is  formed,  a  second  is  usually 
developed  immediately  below  it  (Fig.  150,  YI.)  by  the  growth 
of  the  ectoderm,  endodermal  axis,  and  mesoblastic  cells 
of  the  peduncle ;  and  it  would  appear  that  this  process  is 
frequently  repeated.  The  fully  formed  bud  becomes  de- 
tached, and  takes  its  place  among  the  other  zooids  in  the 
test,  there  to  repeat  the  process  of  gemmation. 

The  observations  of  Krohn,  Metschnikoff,  and  Kowa- 
lewsky,  have  shown  that  two  components  enter  into  the 
buds  of  ascidians  in  general ;  first,  an  outer  layer  consisting 
of  the  ectoderm  of  the  region  in  which  the  budding  takes 
place,  and  secondly,  an  inner  layer  derived  from  the  endo- 


•  In  my  second  memoir  on 
Pyrotoma  (Trans.  Linn.  Society, 
zxiU.  p.  211)  I  have  said  :— 

"Gemmation  does  not  take 
place  in  Pyrotoma  as  in  so  many 
of  the  lower  animals  (e.y.  the 
JJydrozoa  and  Pofyzoa,  or  Salpa 
and  ClaveUnOy  among  the  asci« 
dians),  by  the  outgrowth  of  a 
proce&s  of  the  body- wall  whose 
primarily  wholly  indifferent  pari- 
etes  become  differentiated  into 
the  organs  of  the  bud ;  but,  from 
the  first,  several  components,  de- 
rived firom  as  many  distinct  parts 
of  the  parental  organism,  are 
distinguishable  in  it,  and  each 
component  is  the  source  of  certain 
paru  of  the  new  being,  and  of 
them  only.  Thus  the  body-wall 
or  external  tunic  of  the  parent 
gives  rise  to  the  external  tunic  of 
the  bud :  while  a  process  of  the 
endostylic  cone  of^the  parent  it 
converted  into  the  slimentaxy 


tract  of  the  bud,  and  the  repro- 
ductive organs  of  the  latter  are 
furnished  by  a  part  of  that  tissue 
whence  the  reproductive  organs 
of  the  parent  took  their  origin." 
As  will  appear  further  on, 
however,  recent  investigations 
show  that  the  whole  process  of 
budding  in  the  great  majority  of 
the  Twucata,  and  at  any  rate  the 
first  steps  of  that  process  in  Sa^po, 
are  essentially  similar  to  those  in 
Pyrotoma;  and  it  remains  to  be 
seen  whether  there  is  any  differ- 
ence in  other  Ascidians.  And  as 
regards  even  the  Hydrozoa  the 
expression  that  the  parietes  of  a 
bud  are  at  first  *  wholly  indiffer- 
ent' in  structure  is  not  quite 
accurate,  inasmuch  as  thev  are 
composed  of  an  ectodermal  and 
an  endodermal  layer,  which  aje^ 
continnoua  n«V^  wma  ^  ""^^ 
mrenV  %ji^  ^n^  ttofe  \»  \»ssb>«*- 
loscraft  otfiMDa. 


614     Tirn  anatokt  of  ntrSBTSBBATSD  AnntkiA. 


derm  o(  II10  bmncliiiil  sac  (furnji'if'riil :  or,  Bfl  in  Bairylbu, 
aooording  to  Metschmkoff,  from  the  atrial  tuuit.*  To  th^ 
must  be  added  a  tliird  eomponeiit,  deri*od  fn»ii  thn  in- 
different  tisaae,  out  of  which  the  reprodnotive  organs  of  di* 
parent  bave  been  dereloped. 

In  Amoitroudmrt  prol^eram,  &giame.  muItiplioAtion  t&kw 
plooe  when  tbe  laj^a  has  fixed  itedf  and  grown  into  a 
aolttuiy  asi'idiim.  The  long  poat-abdumtrn  (as  die  prok^- 
gation  of  the  abdomen  bejoad  tUe  alimeDtorj  caokl  it 
termed)  Bepamtcs  itacif  from  the  body,  carrying  with  it  the 
heart,  tuid  divides  iuto  a  number  of  Be.j^eatji  which  rise  (u 
the  snmmit  of  tbe  teet  of  the  parent,  rongs  tbemaekiw 
around  it.  and  become  conTerted  into  independeot  sooidit. 
The  parent  developea  a  new  heart  and  post-abdomen.  The 
process  appears  to  be  repeated  in  the  post'Sbdomina  of  tfae 
new  zooida.     The  poet-abdomen  is  a  process  of  tfaoectodenn, 

Titr  of  which  is  divided  by  a  septum  into  twal 


cbambem,  containing  man;  fatty  ceUe.    The  septtii 


THB  DEYSLOPMBKT  OV   BOTBTLLVS,      615 

loped,  and  then  becomes  divided  by  longitudinal  partitions 
into  three  chambers,  a  median  and  two  lateral.  The  latter 
give  rise  to  the  lateral  chambers  of  the  atrium,  which 
subsequently  open  into  one  another  on  the  neural  side 
of  the  body,  and  finally  communicate  with  the  exterior  by 
a  median  atrial  opening. 

G^egenbaur  *  has  described  the  detachment  of  the  era  of 
a  species  of  Didemnwn  into  the  substance  of  the  common 
test,  where  they  are  developed  into  caudate  larvae  provided 
with  an  eye.  Before  the  development  of  the  larva  is  nearly 
complete,  a  zooid  is  formed  from  it,  so  that,  at  one  time, 
the  embryo  appears  to  have  two  branchial  sacs. 

Metflclmikoff  t  and  Krohni^  have  shown  that  the  caudate 
larvae  of  Boirylhis  are  not  composite,  as  Savigny  and  Sars 
supposed,  but  that  the  bodies  imagined  by  these  observers 
to  be  buds  are  simply  diverticula  of  the  ectoderm,  and 
become  converted  into  the  vascular  processes,  which  ramify 
through  the  conmion  test,  and  commonly  end  in  dilatations. 
In  the  adult,  the  buds  are  developed,  one,  or  sometimes  two, 
at  a  time,  at  the  sides  of  the  body,  and  consist  of  an  outer 
layer,  derived  from  the  ectoderm,  and  an  inner  layer,  which, 
according  to  Metschnikoff,  proceeds  from  the  atrial  tunic. 
From  the  inner  layer  the  alimentary  canal  of  the  bud  pro- 
ceeds, and  between  the  inner  and  the  outer  layers  the  rudi- 
ments of  the  genitalia  appear.  The  ovaria  advance  towards 
their  development  much  more  rapidly  than  the  testes.  The 
zooids  thus  developed,  as  they  enlarge,  rise  to  the  surface, 
taking  the  place  of  those  from  which  they  proceed  and 
which  die  away.  The  ova  are  impregnated  from  without, 
and  undergo  their  development  in  the  atrium  of  the  parent. 
Subsequently  the  testes  attain  their  full  development ;  and, 
at  the  same  time,  the  buds  are  formed  which  will  give  rise 
to  a  third  generation,  supplanting  the  second. 

*  "Ueber  Didemnum  geUdimo-  %  <'Ueber  die  Fortpflansungs- 

satm."  C  Archiv  fiir  Anat.,'  1862.)  verhaltnisse  bei  den  Botrylliden.'* 

t    **  EntwickelungigeschichtU-  (*Archiv    fur    Naturgeschichte,' 

ohe  Beitrage."  (*  Bulletin  de  I'A-  (1869.)      <'  Ueber    die    friiheste 

cademie  des  Sciences  de  St  Pe-  Bildung    der    BotrYlleoia^iMft^:- 

ienbourg,'  xUi.  1868.)  (^Iblvi.) 


616       THE  ANATOMT  OF  nTYXBTBBKATBD  AjriMALS. 

After  the  larva  (which  may  be  called  A)  has  attached 
itself,  the  first  sets  of  zooids  which  are  developed  are  sexlesB. 
The  first  bud  arises  on  the  right  side  of  the  bodj  of  the 
larva  (A)  in  the  neighbourhood  of  the  heart ;  as  it  increaaes 
in  size,  the  parent  withers  away,  and  the  zooid  (B)  thus  de- 
veloped takes  its  place.  Two  buds,  a  right  and  a  left,  are 
developed  from  (B)  and  become  zooids  (C,C),  B  disappearing. 
The  two  zooids  (C,  C)  are  so  disposed  that  their  atrial  ends* 
are  close  together,  and  their  oral  ends  turned  away  from  one 
another.  These  each  develope  two  lateral  buds,  which  be- 
come four  zooids  (D,  D,  D,  D).  The  zooida  C,  G  disap- 
pear as  before,  and  their  successors  arrange  themselves  in 
a  circle.  Each  of  these  developes  two,  or  sometimes  three, 
lateral  buds ;  these  grow  into  zooids,  which  supplant  their 
predecessors  and  are  themselves,  in  turn,  supplanted. 

Every  new  system  of  the  later  successions  is,  at  first,  devoid 
of  a  common  cloaca ;  and  the  zooids  which  compose  it  may 
arrange  themselves  into  one  or  several  circles,  each  of 
which  then  acquires  its  cloaca. 

It  thus  appears  that,  in  BotryUua,  the  ascidiozooid  which 
results  from  the  metamorphosis  of  the  caudate  larva  serves 
merely  as  a  kind  of  stock,  from  whence  the  other  zooids 
which  build  up  the  ascidiarium  proceed ;  and  this  leads  to 
the  still  more  singular  process  of  development  in  Pyrosoma, 
in  which  the  first  formed  embryo  attains  only  an  imper- 
fect development,  and  disappears  after  having  given  rise  to 
four  ascidiozooids. 

In  Pyrosonia,  the  ovisac  is  attached  by  a  short  oviduct  to 
the  wall  of  the  atrium,  into  which  it  eventually  opens,  and 
thus  aUows  of  the  entrance  of  the  spermatozoa. 

Of  the  process  of  yelk  division  I  could  see  nothing  in  my 
specimen,  which  was  preserved  in  spirit,  but  it  has  since 
been  traced  in  fresh  specimens  by  Kowalewsky,*  who 
compares  it  to  that  which  takes  places  in  osseous  fishes. 
The  result  is  the  formation  of  an  elongated  flattened 
blastoderm  which  occupies  one  pole  of  the  egg,   and  is 

*  **  VJcberdie'Eiitwic.VLQluii^^eftchichte  der  Pyrosoma."    (*Archiv 
flir  Mikr.  A.nalom\«;  \^1^.^. 


PTS060MA  AND  DOLIOLUM.  617 

converted  into  what  I  tenned  the  eyathozooidf  which  is 
shown  by  Kowalewskj  to  be  a  sort  of  radimentarj  ascidian 
(Fig.  150,  Ylll.).  From  this,  a  prolongation  or  stolon  is 
given  off,  which  becomes  divided  by  lateral  constrictions 
into  four  portions,  each  of  which  gives  rise  to  a  complete 
ascidiozooid.  As  these  increase  in  size,  thej  coil  themselves 
ronnd  the  cyathozooid,  with  their  oral  openings  outwards 
and  their  cloacal  openings  inwards*  and  thus  lay  the 
foundation  of  a  new  ascidiarium  (Fig.  150,  VIII.).  The 
cyathozooid  eventually  disappears,  and  its  place  is  occupied 
by  the  central  cloacal  cavity  (Fig.  150,  IX.).  Thus,  in 
Pifrosoma,  the  usual  first  stage  of  an  Ascidian — ^the  caudate 
larva — is  abortive  and  serves  only  to  found  the  colony  by 
the  buds  which  are  developed  from  it. 

In  the  pelagic  genus  Doliolwm  *  the  cycle  of  life  of  the 
species  is  represented  by  distinct  sexual  and  sexless  forms. 
The  egg  produced  by  the  sexual  form  (A)  f  gives  rise  to  a 
caudate  larva  which  passes  into  the  first  sexless  form  (B) ; 
this  gives  off  from  the  neural  side  of  the  body  an  out- 
growth or  stolon,  from  which  buds  are  developed.  These 
buds  are  arranged  in  three  rows,  two  lateral  and  one  median, 
and  grow  into  zooids  of  two  different  forms,  of  which  the 
median  may  be  indicated  by  C  m,  the  lateral  by  G  I.  All 
these  zooids  are  detached,  and  swim  about  as  independent 
organisms.  What  becomes  of  the  lateral  zooids  (C  I)  is  un- 
known. But  the  median  zooids  give  off  a  stolon  from  the 
hsemal  side  of  the  body  on  which  buds  are  developed,  which 
pass  into  the  sexual  form  (A). 

The  sexual  zooid  (A)  (Fig.  151)  is  shaped  like  a  cask  with 
an  opening  at  each  end^  these  are  the  oral  and  cloacal 
apertures.  According  to  Keferstein  and  Ehlers  there  is  no 
test,  the  outer  wall  of  the  body  being  formed,  as  in  most 
AppendicularicB,  by  the  ectoderm.    Eight  muscular  bands 

*  Huxlev,      '*  Remarks    upon  Entwickelane    von    DoUohany 

Appendicu/aria    and     DoUolum."  (*Zeit8ch.  f&  Wiss.    Zoologie,* 

(*PM1.  Trans.,'  1851.)      Krohn,  1853.) 

«« Ueber  die  Gattung   Dolhlumr  f  Keferstein  and  Ehlen,  *  Zoo- 

('Arcliiv    fur    Naturgeschiciite,'  logisclie  6eitxt^<  V^\. 
1852.)    Gegenbsur,  "*  Ueber  di« 


does  not  extend  further  forwardB  th 
the  wide  pharynx,  and  thb  is  i)crtor 
of  stigmata,  faiir  or  five  in  each.  In 
(Fig.  151),  on  the  other  hand,  the 
forwards  at  the  aides  of  the  pharjii 
and  the  nenral  side,  and  the  stigma 
Terticallj  elongated. 
An  opening  in  the  middle  line  of 

Fig.  lai. 


Fig.  \i\.—Ihllol<m  dniiailatam.—a,  gui|tli< 
opening ;  g,  (PHiphagiii ;  i,  Momseb ;    ^  i 

phaiTSX  leads,  bj  a  short  gullet,  int 
whence  the  slender  intestine  proceed 
atrial  cavity.     The  nerrone  ganglioi 


f*'.VJ 


DOLIOLUM  ASO  8ALPA.  619 

The  first  sexless  zooid  (B)  resembles  A  in  general  form, 
bat  has  nine  muscle-rings.  The  long  stolon,  which  trails  in 
the  water,  is  attached  in  the  seventh  intermuscular  space  to 
the  middle  of  the  neural  face  of  the  body.  The  stigmata  are 
arranged  as  in  the  form  A,  of  Doliolum  MiiUeri,  and  one  of 
the  antero-lateral  nerves  terminates  in  an  otolithic  sac. 
It  is  spherical  and  contains  a  single  otolith. 

The  zooids  produced  by  the  lateral  buds  of  the  stolon  (G  I) 
have  wide  oral  apertures,  and  the  body  is  shaped  somewhat 
like  the  bowl  of  a  spoon.  They  possess  neither  auditory 
organs  nor  genital  organs,  nor  have  they  been  observed  to 
develope  buds.  The  median  zooids  (G  m)  closely  resemble 
the  sexual  zooids.  The  stalk  by  which  each  is  attached, 
and  the  insertion  of  which  is  in  the  middle  line  of  the  hsemal 
face  in  the  sixth  intermuscular  space,  remains  as  a  pro- 
minence after  the  animal  is  set  free ;  and,  from  the  base  of 
this  prominence,  buds  are  developed,  which  take  on  the 
sexual  form  (A). 

In  the  ScilpcB,  the  divergence  from  the  ordinary  Tunicctta 
reaches  its  maximum.  The  oral  and  atrial  openings  are 
situated  at  opposite  extremities  of  the  body,  as  in  Pyrosoma 
and  Doliolvm ;  and  the  branchial  stigmata  are  represented 
by  wide  vacuities  at  the  sides  of  the  branchial  sac,  the  walls 
of  which  are  thus  represented  only  by  the  epipharyngeal 
folds  on  the  one  side,  and  a  narrow  trabecula,  which  occupies 
the  region  of  the  hypopharyngeal  band,  on  the  other  side. 
The  relatively  small  alimentary  and  reproductive  viscera  are 
sometimes  aggregated  into  a  mass,  the  so-called  niuHeus,  at 
the  posterior  end  of  the  hssmal  side  of  the  body.  The 
chief  muscular  bands,  by  the  contraction  of  which  the 
water  is  driven  out  of  the  branchial  and  atrial  apertures, 
and  the  propulsion  of  the  animal  is  effected,  are  transverse, 
but  do  not  form  complete  hoops,  as  in  Doliolwfn, 

In  aU  the  8alp€B,  each  species  is  represented  by  two  sets 
of  zooids,  the  one  sexual  and  the  other  sexless.  The  sexual 
zooids  are  produced  by  budding  from  a  stolon,  which  is 
given  off  from  the  body  of  the  sexless  form  in  the  immediate 
neighbourhood  of  the  heart.    When  the  sexual  "loov^  ^}K:«^s^ 


620       THE  AKATOMY  OF  INYBBTBB&ATBD  AKOKALS. 

formed  are  detached,  they  are  at  first  connected  into  chains 
of  yarions  forms,  but  these  eventually  break  up  and  the 
constituent  zooids  are  set  free.  Fig.  152  shows  the  two 
zooids  of  the  species  8alpa  denwcratuxt-mucronaia,  viz.  the 
sexless  zooid,  Scdpa  demooratiea  (Fig.  152, 1.)  and  the  free 
sexual  zooid,  8alpa  mucranaia  (Fig.  152,  II.). 

The  recent  investigations  of  Dr.  Todaro,*  in  accordance 
with  those  of  Kowalewsky,  show  that  the  stolon  is  formed, 
as  in  Pyrosoma,  by  the  conjunction  of  a  process  of  the 
endoderm  which  forms  the  extremity  of  the  endostyle,  with 
an  outgrowth  of  the  ectoderm,  and  with  certain  cells  of  the 
mesoblast.  But,  according  to  Todaro,  there  is  this  essential 
difference :  the  young  Salpa,  which  make  their  appearance 
in  double  series  along  the  stolon,  are  developed  altogether 
from  the  mesoblastic  cells.  These  cells,  in  fact,  become 
aggregated  into  masses,  of  which  four  are  arranged  in  the 
circumference  of  each  segment  into  which  the  stolon  is 
divided ;  and  two  of  these  masses,  one  on  each  side  of  each 
segment,  are  converted  into  young  Salpcs,  by  a  process 
analogous  to  that  by  which  a  morula  becomes  an  embryo. 
If  this  account  of  the  matter  be  correct,  the  agamic  deve- 
lopment  of  the  8alp<B  would  rather  resemble  that  of  the 
germ  masses  of  tiie  sporocysts  of  Tremaioda,  or  the 
pseudova  of  insects,  than  ordinary  budding. 

Each  sexual  zooid  possesses  a  testis  and  a  single  OTum.  The 
latter  is  contained  in  an  ovarian  follicle,  the  slender  duct  of 
which  is  attached  to  the  waU  of  the  atrium  and  opens  into 
the  atrial  cavity.  The  testis  attains  its  full  growth  and 
functional  perfection  only  after  the  ovum  has  undergone 
development.  It  follows,  therefore,  that  impregnation  must 
be  effected  by  the  spermatozoa  of  some  other  zooid.  The 
sexless  form  which  is  developed  from  the  egg,  goes  through 
the  early  stages  of  its  development  in  the  atrial  cavity  of  the 
parent,  to  the  walls  of  which  it  is  attached  by  a  peduncle 
(Fig.  152,  III.),  the  centre  of  which  is  occupied  by  a  diver- 
ticulum of  the  vascular  canals  of  the  parent,  enclosed  within 
a  cup-shaped  cavity  in  free  communication  with  the  blood 
*  '  So]^  \o  ^vViu^f^  «\  KsnXATiiia.  ^<(&&a  Sftlpe,'  1875. 


8ALPA  DUCOCKATICA-XirOBOHATA. 

ng.  isa. 


F»rtol 


>  lo-eBlled    ''br»nchl« ; ■  /.    l«r„        ,    ,,  ,      .  „ 

■tolon  ;  t,  viiecnl mast  or  noolmi ;  Ajmoacnlu-buidi;  M-plx 
■,  blood  tinoi ;  9,  oviuo  *nd  OTum  ;  I,  atomftch ;  v,  dll&M 
a,  celeoblut;  ■,  •clodaim  knd  teit^  p,  anAodMtllu 


022       THE  AKATOICY  OF  INYBBTBBBATBD  AKIMALS. 

Binnses  of  the  f oetuB.  It  is,  in  fact,  a  tme  placenta ;  and, 
during  life,  the  independence  of  the  foDtal  and  maternal 
circnlations  is  readily  observed,  as  the  blood  corpuscles  of 
the  two  organisms  coarse  through  their  respectiye  channels. 

The  early  stages  of  the  development  of  the  embryo 
Salpa  have  been  investigated  by  numerous  observers,  most 
recently  by  Kowalewsky,*  Todajro,  Brooks  f  and  Salensky.^ 
The  observatioDs  of  the  last-named  author  relate  chiefly  to 
Salpa  democraHea-mueronata,  and  his  account  of  the  process 
appears  to  me  to  be  the  most  satisfactory. 

The  egg  is  impregnated  in  the  ovarian  follicle,  as  in 
Pffrosoma ;  and  the  oviduct,  shortening,  gradually  draws  the 
ovarian  follicle,  with  its  contents,  into  a  sort  of  incubatory 
pouch,  which  is  a  diverticulum  of  the  wall  of  the  atrium, 
and  projects  into  the  atrial  cavity. 

For  distinction's  sake  the  incubatory  pouch  may  be 
termed  the  otjicyti.  As  the  oviduct  shortens,  it  widens  and 
constitutes,  together  with  the  ovarian  follicle,  a  single 
uterine  sac,  the  outer  or  oviducal  half  of  which  applies 
itself  to  the  wall  of  the  ovicyst,  while  the  inner  half  con- 
tains the  ovum.  The  vitellus  undergoes  complete  division, 
and  the  superficial  layer  of  blastomeres  constitutes  itself 
into  an  epiblast,  investing  the  solid  mass  formed  by  the  other 
blastomeres,  which  represent  the  hypoblast  A  mesoblastic 
layer  subsequently  appears  between  the  two.  The  nervous 
^^anglion  results  from  an  involution  of  the  epiblast,  while 
the  branchial  sac,  the  alimentaiy  canal  and  the  atrium  are 
the  product  of  the  subdivision  of  a  cavity  which  appears 
in  the  midst  of  the  hypoblast.  The  maternal  and  the 
foetal  parts  of  the  placenta  arise,  respectively,  from  the 
wall  of  the  ovarian  sac  and  &om  certain  large  blastomeres 
on  the  adjacent  hsemal  face  of  the  embryo. 

Todaro  agrees  with  other  observers  in  stating  that  the 
viteUus  undergoes  division,  and  that  a  small  celled  blasto- 

*  *  Nachrichten   der  K(inigli-  Comparative  Zoology,'  No.  U. 

Chen  Geselltchaft  xa  Gdtdngen,*  t  ^Zeitachrift  fur  Wiss.  Zoo- 

1868.  logie,'  1876. 

t  '  Bulletin  of  \3\«  14uMnm  «A 


THS  DSVBLOPXSNT  OF  THB  BALPM. 


623 


derm  invests  the  large  remaining  cells  which  he  terms  the 
germinal  mass.  But  his  account  of  the  farther  stages  of 
development  is  very  different.  A  circular  thickening  of 
the  blastoderm  separates  the  hemisphere  which  is  directed 
outwards  from  that  which  is  turned  inwards,  and  gives 
rise  to  a  lamellar  outgrowth.  It  is,  at  first,  directed  towards 
the  inner  end  of  the  ovisac,  having  reached  the  bottom  of 
which,  it  becomes  reflected;  and  the  reflected  portions 
lining  the  inner  wall  of  the  ovisac,  and  meeting  over  the 
outer  hemisphere,  form  a  sort  of  amniotiG  investment  of 
the  embryo.  It  is  the  cavity  left  between  this  '  amnion '  and 
the  inner  hemisphere  of  the  blastoderm  which  becomes  the 
parental  blood  sinus.  An  involution  of  the  outer  hemi- 
sphere of  the  blastoderm  gives  rise  to  the  alimentary  canal, 
which  becomes  shut  off*,  as  the  endoderm,  from  the  remain- 
ing blastoderm,  which  constitutes  the  ectoderm.  A  mass 
of  cells  which  appears  in  the  middle  of  the  outer  half  of 
the  embryo,  between  the  alimentary  sac  and  the  ectoderm, 
and  which  has  only  a  transitoiy  existence,  is  regarded  by 
Todaro  as  the  representative  of  the  urochord. 


^.\ 


CHAPTER  X 


THE     PEEIPATIDEA,     THE 

PHEEJSTA,  TUB  CH^;T0ONATHA,  T 
PHTBEUAKIA,  THE  ACANTHOCEP: 
HJDA. 

I  HAVE  reserved  for  discnaaion  in 
paiidta,  which  hare  heretofore  b 
authors  to  the  Annelida ;  and  certai 
Mekuoa,  the  precise  morphologic: 
are  as  jet  nnoertoin,  although  it 
sereral  of  them  are  allied  with  th 
Sol^era,  and  the  Twbtllaria.  The; 
totally  devoid  of  segmentation;  wbi 
the  ilytostomata  alone  present  ttnj 
limbs,  though  the  natore  of  these  i 
the  nerroos  eystem  ia  clearlj  made 
chain  of  poat-oral  ganglia  aa  charact< 
The  Pe&ifatidea. — At  p.  257, 
group  to  the  Arthropoda,  Mr.  Moselej 
having  left  no  doubt  npon  my  mi 
faotorilj  proved  the  justice  of  the 
afflnitiee  originally  made  by  Qerva 

hnwrnrar    tlmt.  T  Tiavfl  hnan   ftWe.  tl 


THS  PSBIPATIDSA.  625 

from  the  West  Indies,  South  America,  the  Gax>e  of  Good 
Hope  and  New  Zealand,  where  they  are  found  among  the 
decaying  wood  of  damp  and  warm  localities.  They  have 
the  curious  habit  of  throwing  out  a  web  of  yisoid  filaments 
when  handled  or  otherwise  irritated. 

The  head  is  distinct,  and  is  provided  with  a  pair  of  many- 
jointed  antenna-like  tentacula  and  two  simple  eyes.  The 
mouth,  situated  upon  the  und^  surface  of  the  head,  is  sur- 
rounded by  a  prominent  lip,  which  encloses  a  pair  of  jaws, 
each  of  which  is  terminated  by  two  curred  chitinous  claws, 
similar  to  those  of  the  feet.  On  each  side  of  the  mouth, 
the  head  supports  a  short  obscurely  jointed  '  oral  papiUa,' 
which  is  somewhat  like  one  of  the  feet,  but  is  devoid  of  claws 
and  perforated  at  its  extremity.  The  head  is  followed  by  an 
unsegmented  body  produced  laterally  into  paired  appen- 
dages, which  vary  in  number  from  fourteen  to  more  than 
thirty,  according  to  the  species ;  and  each  of  these  appen- 
dages is  indistinctly  articulated,  the  terminal  joint  being 
provided  with  two  small  curved  daws. 

The  anus  is  terminal  and  the  genital  aperture  is  situated 
on  a  papilla,  a  little  distance  in  front  of  the  anus,  on  the 
neural  or  ventral  face  of  the  body. 

The  alimentary  canal  commences  by  an  ovoid  muscular 
pharynx.  The  OBSophagus,  continued  from  this,  gradually 
dilates  into  a  wide  and  long  stomach,  from  which  a  very 
short  intestine  is  continued  to  the  anus,  situated  at  the 
posterior  end  of  the  body.  There  are  no  Malpighian  ceeca. 
Two  very  large  ramified  tubular  glands,  which  secrete  the 
viscid  matter  of  which  the  web  is  c<miposed,  lie  at  the 
sides  of  the  alimentary  canal,  and  open  outwards  by  the 
perforations  of  the  oral  papillsB.  A  vessel  occupies  the 
middle  line  of  the  dorsal  body- wall,  and  is  probably  a  heart. 

The  respiratory  organs  are  the  trachesB  discovered  by 
Mr.  Moseley.  The  numerous  pores,  or  HigrmUa,  from  which 
the  trachesB  take  their  origin,  are  scattered  all  over  the 
surface  of  the  body,  one  row  being  median  and  ventral 
Each  stigma  is  the  outward  termination  of  a  short  mvl^ 
tube,  which^  at  ite  opposite  end,  \>T«iic^e»  qtq^VdXx^  ^^^le&ss^ 


026      THB  AKATOICY  OF  nTfBBTBBBATKD  AJTIMAUB. 

of  fine  traches,  which  rarely  diiide,  and  are  distribnted  in 
great  abundance  to  the  viscera.  They  are  very  delicate 
tobes,  which  often  take  an  nndnlating  course,  and  are 
rarely  more  than  yi^th  of  an  inch  in  diameter.  In 
optical  section,  their  walls  have  a  finely  beaded  appearance, 
as  if  from  the  presence  of  transrerse  thickenings,  thongh 
distinct  transrerae  marking^  are  rarely  to  be  seen. 

The  nervous  system,  as  Milne-Edwards  discovered, 
consists  of  two  ganglia  in  the  head,  closely  united  above 
the  (Bsophagus.  From  each  of  these  a  relatively  stout 
longitudinal  cord  proceeds,  overlying  the  bases  of  the  feet 
(and  hence  widely  separated  from  its  fellow)  to  the 
posterior  extremity  of  the  body.  As  Ghnbe  has  stated,  there 
are  no  distinct  ganglia  on  this  cord.  On  the  contrary, 
ganglionic  cells  appear  to  be  pretty  evenly  distributed 
along  its  ventral  face,  throughout  its  length ;  and  nerves, 
which  pass  transversely  outwards  and  inwards,  are  given 
off  from  opposite  sides  of  it  at  short  intervals.  Grube  has 
shown  that  many  of  the  branches  that  take  the  latter 
direction  are  commissures  between  the  two  cords. 

The  muscles  of  Peripahu  are  not  striated,  which  is  a 
curious  exception  to  its  g^erally  well-marked  arthropod 
characteristics. 

Mr.  Moseley  has  proved  that  the  sexes  are  distinct.  The 
ovary  is  small,  divided  by  a  median  septum  into  two  lobes, 
and  lies  beneath  the  alimentary  canaL  The  oviduct,  at 
first  single,  divides  into  two  branches,  which  are  long,  and, 
posteriorly,  present  uterine  dilatations.  They  then  unite, 
and  terminate  by  a  short  vagina  on  the  ventral  aspect  of 
the  rectum.  The  testes  are  ovate  bodies,  each  with  a 
cflBcal  appendage.  The  long  and  coiled  vasa  defeientia 
unite  into  a  common  duct,  which  opens  in  the  same 
position  as  in  the  female.  The  ova  are  developed  within 
the  uterine  dilatations  of  the  oviducts.* 

*  One  of  the  fpeeimena  whieli  1  of  the  spirit  is  which  it  hsd  been 

aamined  wea  a  pregnant  female,  preserved,  in  such  a  manner,  that 

tetths  vteoeca  wex«  tAaed  to-  Uttleeoiild  be  made  of  their  strae- 

gttti0r,a(Vtnnid;f'V>l  m  aftXlin^  N3(n»«t^\haitorths«oibfyos. 


THS  XTZ08TOMATA.  627 

Mr.  Moseley  baa  made  out  the  chief  points  in  the  develop* 
mental  history  of  Peripatus. 

In  an  early  condition,  the  embryo  is  Teiy  like  that  of 
a  Scorpion,  but  is  folded  upon  itself,  so  ihai  the  yentral 
aspects  of  the  anterior  and  posterior  halyes  of  the  body 
are  turned  towards  one  another.  As  in  the  Scorpion, 
there  is  a  pair  of  large  procephalic  lobes,  succeeded  by  a 
series  of  segments,  from  the  sides  of  which,  processes — ^the 
rudiments  of  the  limbs — ^bud  out.  The  procephalic  lobes 
give  rise  to  a  kind  of  hood,  the  lateral  angles  of  which 
extend  over  the  bases  of  the  first  pair  of  limbs,  and  join 
with  those  of  the  second  pair,  which  are  the  oral  papillse 
of  the  adult.  The  first  pair  of  limbs  thus  become  enclosed 
within  the  hood  (the  margins  of  which  form  the  suctorial 
lip  of  the  adult),  and  developing  two  chitinous  daws  upon 
their  extremities,  like  those  of  the  other  limbs,  they  are 
converted  into  the  jaws  of  the  adult  animaL  It  is  remark- 
able that  the  antennsd  are  developed  from  the  anterior 
part  of  the  procephalic  lobes;  while  the  chelicersB  of 
the  Scorpion  appear  at  the  posterior  margin  of  these  lobes, 
in  a  position  corresponding  with  that  of  the  first  pair  of 
limbs,  or  jaws,  of  Peripatus. 

It  is  obvious  that  whether  we  consider  the  appendages, 
the  respiratoiy  and  reproductive  systems,  or  the  develop* 
ment  of  the  embryo,  Perip<xtu8  is  a  true  Arthropod*  ap* 
X>arently  nearly  allied  to  the  suctorial  Mkfriapoda, 

The  Mtzostohata. — ^The  genus  Myzostomwn^  compre- 
hends certain  small  animals,  the  largest  species  not  exceed* 
ing  ith  of  an  inch  in  length,  which  are  parasitic  upon 
the  Feather-stars.  The  body  has  the  form  of  a  flattened 
oval  disk,  the  surface  of  which  is  ciliated,  while  its  margins 
may  be  produced  into  as  many  as  twenty  short  filamen* 
tons  processes  or  cirri.  Within  the  margin  of  the  ventral 
face  are  eight  suckers,  four  on  each  side,  and,  internal 
to  these  again,  are  ten  short  conical  'feet,'  five  on  each 
side;  each  of   these  lodges  two  strong  setsa^  "whidL  <sksd^ 


i:  I 


tbe  middle  line  on  tbe  poeterior 
of  the  alimentary  cosal  long  ram 

No  Teseela  or  organs  of  circulai 
All  that  is  known  of  the  nervoi 
ganglionic  mass,  from  which  bran 
Bide,  ritnated  in  the  middle  line  of  i 

The  Bexea  are  combined  in  tl 
acini  of  the  generative  glands  i 
body.  IhoHe  of  the  testes  pour 
which  unite  together  and  open  hjr 
each  side  of  the  bodj,  about  the 
The  two  oriducta  conTej  tbe  ora 

The  derelopment  of  Xytotiomu 
Semper  and  bj  Metacbnikoff.* 
complete  diviBion,  and  tbe  embiyi 
morula,  covered  with  vibratile 
obwrved,  the  embiyo  ie  cjtindro 
a  month  at  one  end  and  an  anni 
mencement  of  the  etraigbt  and  m 
the  form  of  a  moacnlar  bulb  or  ] 
pairs  of  mdimentaij  appendag 
sete.  The  number  of  the  se 
oreaaea  np  to  five  pairs,  and  the 


THB  ENTSROPNSnSTA.  629 

The  presence  of  cilia  on  the  surface  of  the  body  and  of 
protractile  sets  in  the  parapodia  excludes  Mya>$to7n/um 
from  the  Atihropoda ;  while  Metschnikoff  has  justly  com- 
pared its  larval  state  with  that  of  SyUis.  Sufficient  doubt, 
however,  still  adheres  to  the  determination  of  the  true 
place  of  Myxoatomum,  to  lead  me  to  discuss  it  apart  from 
the  Annelids. 

The  Entbrophteusta. — The  Teiy  singular  animal  BaJanO" 
glo88U8f  which  is  the  only  known  example  of  this  group,  is 
an  elongated,  apodal,  soft-bodied  worm,  with  the  mouth  at 
one  end  of  the  body  and  the  anus  at  the  other  (Fig.  153,  III.) 
The  mouth  is  surrounded  by  a  sort  of  collar  or  prominent  lip, 
within  the  margin  of  which  springs  a  long  proboscidif  orm 
median  appendage,  which  is  hollow  within  and  has  a  terminal 
pore.  On  the  same  side  as  that  from  which  the  proboscis 
springs,  the  anterior  region  of  the  body  presents  an  elon- 
gated, somewhat  flattened  area,  bounded  by  raised  longi- 
tudinal folds.  On  each  side  of  this  area  is  a  longitudinal 
series  of  apertures — the  branchial  apertures.  The  latter 
communicate  with  saccular  dilatations  of  the  anterior  part 
of  the  alimentary  canal,  and  these  branehidl  aaca  are  sup- 
ported by  a  peculiar  skeleton. 

No  nervous  system,  nor  any  organs  of  sense,  have  yet 
been  certainly  made  out. 

According  to  Kowalewsky,*  who  was  the  first  to  elucidate 
the  true  nature  of  Balanogloeeue,  the  vascular  system 
consists  of  a  dorsal  and  a  ventral  Tessel.  At  the  posterior 
end  of  the  branchial  region,  the  former  divides  into  a 
superior  and  an  inferior  dorsal,  and  two  lateral,  trunks. 
The  superior  trunk  passes  forwards ;  and,  at  the  anterior 
end  of  the  body,  divides  into  two  descending  branches,  which 
unite  with  the  ventral  trunk.  The  inferior  dorsal  trunk 
supplies  the  branchisB,  of  which  the  lateral  trunks  are  the 
efferent  vessels. 

For  the  pharyngeal  branchiee  of  Bakmoglasiua,  the  only 

*  <  AnAtomie  dei  Balsnogossus.'  (*  Mem.  de  I'Acad.  Imp.  de  8t« 
P^tenboorg/  1866.) 


observers,  until  its  true  nature  waa 

derw-larva,  on  account  of  its  eitr 

the  larTiE  of  some  Star-fisliea  (Fig. 

It  is  an  elongated  ovoid  bodj,  p 

Fig.  la. 


,  .  view  (abont  - 
D,  YCHela  IcadiDB  to  tha  dorul  pore  (d) 
tuodIu  ■yitam ;  v'  prolongBtiDn  of  U 
>,  ttomach :  a,  teMidiairiii :  m.  mauth ; 


THS  DSYSLOPMBNT  OF  BAULHOOLOBSUS.  631 

extremitj,  while  posteriorly  it  occupies  nearly  the  middle  of 
the  body.  On  the  yentral  face,  a  deep  groove  separates  it 
from  the  prsB-oral  ciliated  band,  and  in  this  groove  the 
mouth  is  situated.  The  margins  of  the  prs-oral  and  post- 
oral  ciliated  bands  are  deeply  sinuated,  and  they  come  into 
contact  in  the  median  dorsal  line.  A  wide  gullet  leads  from 
the  mouth,  and  opens  into  the  gastro-intestinal  portion  of  the 
alimentary  canal,  which  passes  backwards  in  the  middle  line, 
to  terminate  in  the  anus,  at  the  hinder  end  of  the  body. 
About  the  middle  of  the  dorsal  face  of  the  body  there  is  a 
circular  pore  (Fig.  153, 1  d),  whence  a  canal  leads  to  a  rounded 
sac,  which  lies  on  the  junction  between  the  gullet  and  the 
stomach.  The  sac  g^ves  off  two  lateral  short  diverticula, 
which  embrace  the  oesophagus.  A  delicate  band,  apparently 
of  a  muscular  nature,  connects  the  summit  of  the  water-sac 
with  that  part  of  the  dorsal  aspect  of  the  body  at  which  the 
prsB-oral  and  post-oral  ciliated  bands  unite.  Here  two  eye* 
spots  are  developed.  A  constriction  separates  a  rounded 
gastric,  from  a  tubular  intestinal,  division  of  the  alimentary 
canal.  Diverticula  of  the  gastro-intestinal  part  of  the 
alimentary  canal  give  rise  to  two  pairs  of  discoidal  bodies, 
from  which,  apparently,  the  mesoblast  and  the  perivisceral 
cavity  of  the  Balanoglosaus  are  developed. 

From  the  sides  of  the  (esophagus,  a  series  of  diverticula 
are  given  off,  which  unite  with  the  ectoderm,  open  extern- 
ally, and  become  the  gill-pouches.  When  only  two  of  these 
branchial  apertures  are  formed,  they  are  said  by  Metschni- 
koff  to  have  a  striking  resemblance  to  those  of  Appendieu' 
laria.  A  pulsating  vesicle — ^the  so-called  '^  heart," — ^makes 
its  appearance  close  to  the  water-sac.  The  anterior  end  of 
the  body,  in  front  of  the  mouth,  now  elongates,  and  is  con- 
verted into  the  proboscis ;  while  the  poet-oral  region  loses 
its  ciliated  bands,  and  lengthening,  becomes  the  long  body 
of  the  adult  worm.*    (Fig.  153, 11.  III.) 

*  See  Asassiz,  **  The  History  gen  fiber  die  Metamorphoso  eini- 

of  Balanogtotsui  9Jid    TomariaJ*  ger  SeetUere."    (*  Zeitichrift  fBr 

O  Memoirs  of  the  American  Aca-  Wissensohaftliohe  Zooli^e,'  zz. 

demy  of  Arti  and  Sdenoea,'  1873) ;  1870.) 
and  Metsobnikofi^  **  Untennohon- 


settled.  Anatomically,  it  appmacl 
and  the  oligocba'toua  Annelids  Ie 
derelopracDt  presents  peculiaritiei 
known  among  these  animaU,  whi 
Braehiopoda  and  the  Eekinodermati 
The  hoAj  of  Sagiila  (Fig.  154)  r 
long,  ia  elongated,  anbcylindrical  ai 
Urged  at  one  end  into  a  ronnded  It 
tApen  to  a  point.  There  are  nopa 
the  chitinoaB  cuticle  ia  prodaoed  inl 
fin,  on  each  side  of  the  body  and  ta 
On  each  side  of  the  head  there  e 
cnrred,  claw-like  chitinons  procesi 
allj  diTaricat«d  and  approiimab 
Between  them  ia  the  moatii ;  and,  a 
are  four  Bets  of  abort  but  atrong  a] 
into  B  simple  and  straight  inteel 
anna  sitoated  on  the  ventral  face 
tapering  caudal  region  commences, 
meaenteno  band  connect  the  intest 
bodj,  and  divide  the  perivisceral  a 
Beneath  the  ectoderm  liee  a  layer  ( 
moBColar  fibres.  The  nervons  syH 
oval  ganglion,  which  lies  in  the  mi 
of  the  bod;,  and  aenda  off  ant^orl] 
which  nnite  with  a  ■ 


TBI  OUnOOHATHA. 


attached  to  the  pnietw  of  Uie  body.    Theii-  ciliated  dncta 
open  close  to  the  T«it  and  on  provided  with  dilatations 


Fig.  154. — Smitta  fty—rtirfa. — a,  the  bead  trlth   Iti  «Jt»  and  appan- 
dagei ;  b,  the  anui ;  c,  the  OTacj ;  f^  the  teatlcuUr  ehamban. 


634       THE  AKATOKT  OF  IHTXBTBB&^TBD  AKIMALS. 

which  divides  the  cavity  of  the  caudal  part  of  the  body  into 
two  chambers.  On  the  lateral  walls  of  these,  cellular  masses 
are  developed,  which  become  detached,  and,  floating  freely 
in  the  perivisceral  fluid,  are  developed  into  spermatozoa. 
The  latter  escape  by  spout-like  lateral  ducts,  the  dilated 
bases  of  which  may  be  r^^arded  as  vesiculsB  seminales. 

Thus  far,  although  the  organisation  of  Sagiita  is  very 
peculiar,  it  presents  analogies  both  with  the  NemcUaidea  and 
with  the  Annelida.  But  its  development,  as  described  by 
Kowalewsky,*  is,  in  some  respects,  unlike  anything  at 
present  known  in  either  of  these  groups.  Yelk-division 
takes  place,  as  usual,  and  converts  the  egg  into  a  vesicular 
morula,  with  a  large  cleavage  cavity,  or  blastocode.  One 
face  of  the  vesicle  thus  constituted  now  becomes  invagi- 
nated,  with  the  effect  of  gradually  obliterating  the  blasto- 
coele,  and  converting  the  spherical  single- walled  sac  into  a 
hemispherical,  double-walled,  cup-shaped  gastrula.  The 
cavity  of  the  cup  is  the  future  digestive  cavity ;  the  layer 
of  invaginated  blastodermic  cells  which  lines  this  cavity 
is  the  hypoblast,  which  will  become  the  endoderm;  and 
the  outer  layer  of  cells  is  the  epiblast,  and  will  become 
the  ectoderm.  In  this  condition,  the  embryo  resembles 
that  of  the  Leech  in  its  early  state.  The  embryo  elongates, 
and  the  aperture  of  invagination,  or  blastopore,  eventually 
ceases  to  be  discernible.  Whether  it  becomes  the  anus,  or 
whether  the  anal  aperture  is  formed  anew,  is  not  certain. 
The  nervous  ganglia  result  from  the  modification  of  cells 
of  the  ectoderm.  The  anterior  end  of  the  primitive 
alimentary  cavity,  or  archenteron,  is  at  first  closed.  It  soon 
sends  out  an  enlargement  on  each  side,  so  that  the  archen- 
teron is  divided  into  a  central  and  two  lateral  divisions. 
The  central  division  opens  externally  and  anteriorly  by 
the  development  of  the  oral  aperture;  and,  as  the  body 
elongates,  it  becomes  the  tubular  intestine.  The  lateral 
diverticula  at  first  communicate  with  it,  but  they  are 
eventually  shut  off,  and   constitute  the  right   and  left 

•  *  Mimo\i«  d«  Vlk»u^Toi<b  Ink^emla  dM  Setonoet  de  St 
bourgy'  18il« 


THS  DSYBLOPMSNT  OF  8AOITTA. 


635 


perivisceral  cavities,  their  walls  becoming  converted  into 
the  cellnlar  and  nrascolar  lining  of  those  cavities.  It 
results,  from  the  mode  of  development  of  the  perivisceral 
cavity  of  ScigUta,  that  this  cavity,  like  the  perivisceral 
cavity  of  the  Brachiopods  and  the  ''  peritoneal "  cavity  of 
the  Echinoderms,  is  an  enterocoele,  comparable  to  that  of 
the  Hydrozoa  and  Aetinoaoa ;  but  which,  instead  of  remain- 
ing in  communication  with  the  alimentary  cavity,  is  shut 
off  from  it,  its  wall  becoming  the  mesoderm,  and  its  cavity 
the  perivisceral  cavity.* 

Nothing  of  this  kind  is  known  to  occur  in  the  TwrheUariOt 
Annelida,  Nemaioidea,  or  BoHfera;  but  when  a  peri- 
visceral cavity  exists  in  these  animals,  it  appears  always  to 
result  from  the  excavation  of  the,  at  first,  solid  mesoblast. 
The  perivisceral  cavity  thus  developed  is  what  I  have 
termed  a  schizoccele.  But  whether  there  is  any  funda- 
mental difference  between  an  enteroecele  and  a  Mchiaoeceh  is 
a  matter  for  further  inquiry.  I  have  referred  above  (p. 
565)  to  the  case  of  an  Ophiurid,  in  which  the  hollow  diver- 
ticula of  the  archenteron,  characteristic  of  the  Echinoderms, 
are  represented  by  solid  outgrowths  of  the  hypoblast. 
From  this  condition  there  would  appear  to  be  an  easy 
ti*an8ition  to  that  presented  by  the  embryos  of  those 
Oligoehceia  and  Hirudinea,  in  which,  though  the  mesoblast 
is  a  product  of  the  hypoblast,  it  contains  no  continuation 
of  the  alimentary  cavity,  but  eventually  splits  into  a 
visceral  and  a  parietal  layer,  the  interval  between  which  is 
the  perivisceral  cavity ;  and  there  is  much  probability  in 
Kowalewsky's   suggestion   that   the    longitudinal   bands 


*  Kowalewslnr't  account  of  the 
development  ofSaffitta  has  been 
confirmed  by  Bittschli  i  who  has 
further  determined  the  ori^n  of 
the  reproductive  organs,  which 
arise  as  outgrowths  from  the 
hypoblast;  and  the  division  of 
each  primitive  enteroecele  into 
two  sacs,  one  for  the  head, ana 
another  for  the  body.    It  appears 

1  •«  Zar  Entwickelang^BBSchl<&te  der  fiaf^Wteu*    (; 
2873.) 


probable  that  the  latter  becomes 
subdivided  by  a  transverse  par- 
tition between  the  ovary  and 
testis.  Butschli  suggests  that 
the  segmentation  of  the  meso- 
blast, which  forms  the  walls  of 
the  enteroecele,  is  a  point  of  ap- 
proximation between  SagUta  and 
the  Annelids. 


ment  of  all  invertebrate  periviacoi 
otber  hand,  it  must  be  remember 
endoderm  and  the  ectoderm  in  the  d 
the  body  of  a  Ctenophoran  or  Ti 
gelatinouB  mesoderm  wbich  occnpit 
primitive  blaatocoele.  Now,  this  m 
probably  is,  a  prodact  of  the  endod 
which  appear  in  it,  anch,  for  example 
canala  of  the  TWrbellaria,  can  have  i 
enteroccele. 

Again,  in  the  Timicata,  aa  we  ha 
a  kind  of  "  periTiaceral  cavitj,"  whi< 
an  invagination  of  the  ect«derm,  in 
termed  an  cptaeJe,'  oreleeitisa  true 
the  former  altemstiTe,  for  the  moD 
onght  to  be  adopted,  what  is  called  a 
maj  be  one  of  foar  things  : — 

1.  A  cavity  within  the  meaobUa 
Renting  the  primitive  blaitoeadt. 

2.  A  diverticnlom  of  the  digeati 
become  ahnt  off  from  that  cavity  (en 

3.  A  solid  oatgrowth,  representing 
in  which  the  cavitj  appears  only  lai 


THE  KBMATOIDBA. 


637 


are  devoid  of  limbe,  thougli  they  may  occasionally  be  pro- 
vided with  setiform  spines  or  papillse.  In  Desmoacolex,  the 
papillte  and  setsB  acquire  an  almost  Annelidan  aspect,  and  the 
annulation  of  the  body  is  much  more  distinct  than  in  any 
other  Nematoid  Worm. 


Fig.  \h5.—AnffuiUuIa  brevitpinus  (after  Claus).* 

I,  initio :  II,  female ;  III,  female  genital  organs ;  IV,  teminal  oorpusclea 
in  different  stages  of  development. 

a,  opsophagus;  a',  chitinised  oral  capsule;  e,  gastric,  and  d,  rectal 
portion  of  the  alimentary  canal.  A,  anus ;  ^',  anterior  and  posterior 
thickenings  with  tiieir  commissures ;  6,  sexual  aperture  *,  JP,  fatty- 
looking  gland ;  r,  dilatation  of  the  uterus,  serving  as  a  recepta- 
culum  seminis.  D,  unicellular  cutaneous  glands  at  the  anal  ex- 
tremity; D',  glandular  mass  with  its  excretory  duct  above  the 
giszard ;  oo,  ovarium ;  T',  testis;  S,  seminal  corpuscles. 

The  outermost  layer  of  the  body  is  a  dense  chitinous 
cuticula,  usually  divisible  into  several  layers.    These  layers 

*  ''Uebereinige  in  Humus  leb<mda  Anguillulinen."    (<Zdtschrift 
fur  Wias.  Zoolo^e,'  xii.) 


638   THE  AKATOMT  OW   INYBBTBBSATBD  ANIMAL8. 

may  be  fibrillated,  the  direction  of  the  fibrillation  being  dif- 
ferent in  the  saccesBive  layers.  Cilia  are  found  neither  on 
the  surface,  nor  elsewhere,  at  any  period  of  life.  The  month 
is  situated  at  one  extremity  of  the  body,  the  anus  at,  or  near, 
the  other  end.  The  first  portion  of  the  alimentary  canal  is 
a  thick-walled  pharynx,  lined  by  a  continuation  of  the 
chitinous  layer  of  the  integument,  which  may  be  raised 
up  into  ridges  or  tooth-like  prominences.  Transrerse  fibres, 
apparently  of  a  muscular  nature,  radiate  from  the  lining 
of  the  pharynx  through  its  thick  wall,  and  probably  serve 
to  dilate  its  cavity.  A  straight  and  simple  tubular  ali- 
mentary canal,  witJiout  any  distinction  into  stomach  and 
intestine,  extends  through  the  axis  of  the  body,  a  narrow 
oesophageal  portion  usually  connecting  it  with  the  pharynx. 

The  endoderm,  or  wall  of  the  alimentaiy  canal,  consists 
of  a  single  layer  of  cells,  disposed  in  few  or  many  longitu- 
dinal series ;  and  lined,  both  internally  and  externally,  by  a 
cuticular  layer.  On  each  side,  the  intestine  is  fixed  through 
its  whole  length  to  the  "  lateral  area,"  to  be  described 
below.  The  cuticle,  which  lines  the  inner  faces  of  the 
endodermal  cells,  and  circumscribes  the  digestive  cavity, 
appears,  on  vertical  section,  to  be  divided  into  rods,  which 
are  possibly  merely  the  intervals  of  minute  vertical  pores. 
In  some  cases,  muscular  fibres  invest  the  posterior  portion 
of  the  intestine. 

Beneath  the  layers  of  the  chitiuous  cuticle  there  is  a 
proper  integument,  or  ectoderm,  internal  to  which  again  is 
a  single  layer  of  longitudinally-disposed  muscles,  which  may 
or  may  not  be  divided  into  distiuct  series  of  '*  muscle-cells." 
The  space  between  these  and  the  outer  face  of  the  intestine 
is  occupied  by  a  spongy  or  fibrous  substance,  which  must 
probably  be  regarded  as  a  kind  of  connective  tissue.  The 
muscles  and  tiiis  tissue,  taken  together,  constitute  the 
mesoderm. 

In  the  typical  NemaMdea,  the  muscular  layer  does  not 
form  a  complete  investment  of  the  body,  but  is  interrupted 
along  tour  eqxadiAtant  longitudinal  lines.  One  of  them  is 
termed  donid,  l^e  o^i^qaXa  ^«ii\x^  vsL^Xystli  these  are  veiy 


THS  KSMATOIDXA. 


639 


narrow.  The  other  two  are  much  broader,  and  are  termed 
the  lateral  areas.  They  often  (Fig.  156)  pre8en%two  or 
more  series  of  conspicuons  nuclei,  and  each  is  traversed 
by  a  canal  with  well-defined  contractile  walls  and  clear 
contents.  Opposite  the  junction  of  the  oesophageal  with 
the  gastric  portion  of  the  alimentary  canal,  each  of  these 
latend  canals  passes  inwards  and  towards  the  mid-yenti-al 
line,  and,  joining  with  its  fellow,  opens  by  a  pore  on  the 
exterior.  In  some  cases,  continuations  of  the  lateral  canals 
extend  forwards  into  the  head. 
A  ring  of  fibres  and  nerve-cells  surrounds  the  gullet, 

Fig.  156. 


Fig.  156. — Oxyuru. — a  Month.  6.  Pliurynx.  e.  Commeiicement  of  in- 
testine, and  dj  iti  termination.  The  intennediate  portion  it  not 
figured,  e.  Genital  aperture,  f.  Opening  of  vessels,  g.  Their  re- 
ceptacle. A.  One  of  the  vessels,  t.  Cellular  matter  enveloping 
them.  A  portion  of  one  of  the  oontraotile  vessels  is  represented 
more  highly  magnified  in  the  upper  figure. 

about  the  level  of  the  opening  of  the  water-yascnlar  system, 
and  gives  off  filaments  forwards  to  the  head,  and  backwards 
to  the  muscles  and  to  the  lateral  area ;  while  two  cords  pass 
back,  along  the  dorsal  and  ventral  median  lines,  to  the  hinder 
end  of  the  body.  In  the  males  of  some  species,  nervous 
ganglia  have  been  observed  in  the  neighbourhood  of  the 
sac  of  the  spicula.*     Organs  of  sense  are  not  certainly 

*  The  question  of  the  structure      system  in  the  JVcMatoMba  U^'^9tt> 
and  disposition  of  the  nervous      ha^it,  not  «v«ii  ^«fc  ^nsoK^fM^ 


v.\ 


The  female  apparatuB  (Fig.  155, 1] 
with  which  ie  connected  a  eingle, 
tubular,  organ,  which  tapers  to  a 
tremitj,  and  is  at  once  ovarium,  ovi 
cwcal  end  is  occupied  by  a  nuclea 
Further  on,  thia  maee  becomes  diffi 
cord  of  protopUfimic  aubBtance  — 
pheral  maaaee,  each  cont&iniiig  a  nn 
a  et&lk  with  the  rhaekit,  which  a 
Still  further  on,  in  the  oridncal  p 
ova  become  free;  while,  in  the  ut 
impregnated,  and  acqnire  a  hard,  ol 

The  teetJB  is,  generallj,  a  ein^e 
end  of  which  cells  are  developed, 
as  in  the  ovaiy :  they  become  frc 
tube  which  playe  ihe  part  of  a  vsi 
what  happena  in  most  aniTnnlii,  thei 
character  of  cells,  and  may  even  eihi 
The  deferential  end  of  the  teeticnl 
cloee  to  the  anoB,  from  the  dorsal  v 
carved  chitinoiiB  spicnla  are  deve! 
dnced  into  the  vnlva  of  the  femal< 
place,  and  appear  to  distend  it,  in  i 
passage  of  the  seminal  corposclet  ii 
into  the  ntems.    In  tbe  female  c 


THI  DBTBLOPMBNT  OF  THI  KBMATOIDBA. 


e4i 


becomes  indented  on  one  side,  and  the  embryo,  as  it  grows, 
folds  itself  in  accordance  with  this  indentation.  In  most, 
it  would  appear  that  the  central  cells  of  the  solid  momla 
are  differentiated  from  the  rest  to  form  the  endoderm, 
which  thus  arises  bj  delamination.  But  Btitschli*  has 
recently  shown  that  the  morula,  which  results  from  the 
division  of  the  yitelluB  of  Cucuilanu$  elegana,  has  the 
form  of  a  flattened  plate,  composed  of  two  layers  of 
blastomeres,  the  blastocoele  being  reduced  to  a  mere  fissure. 
The  lamellar  blastoderm  next  becomes  concaye  on  one 
side,  convex  on  the  other,  and  passes  into  the  gastrula 
form.  The  blastopore,  at  first  very  wide,  gradually  narrows 
and  appears  to  be  converted  into  the  oral  opening  of  the 
worm.  The  mesoblast  takes  its  origin  from  certain  cells 
of  the  hypoblast^  which  lie  dose  to  the  mouth,  and  grow 
thence  towards  the  caudal  extremity.  The  resemblance  of 
this  developmental  process  to  that  of  Lumbrieus  is  obvious. 

The  female  reproductive  apparatus  is,  at  first,  represented 
by  a  solid  cellular  body  which  lies  in  the  mesoderm ;  though 
whether  it  originally  belongs  to  this,  or  to  the  ectoderm,  or 
to  the  endoderm,  is  not  clear.  The  cellular  body  acquires  a 
tubular  form,  and  eventually  opens  externally  by  uniting 
with  an  inward  process  of  the  ectoderm,  which  gives  rise 
to  the  vagina. 

The  young  cast  their  cuticle  twice — ^first,  when  they  leave 
the  egg,  and,  again,  when  they  acquire  their  sexual  organs. 

The  Nemaioidea  have  been  divided  into  three  principal 
groups  t — Polymyaria,  Meromyaria,  and  JEToIomyaria^- cha- 
racterised by  the  nature  of  their  muscular  system. 


*  <*ZarEntwickelangsge8chieh- 
te  des  Cucuilanuselegan»7*  ('  Zeit- 
ichrifl  fur  Zoolog{e,^187ft.)  Halles 
(*  Revae  des  Sciences  Naturelles,' 
1877)  has  observed  a  similar  pro- 
cess in  Anguillula  aceti,  but  he 
denies  that  the  blastopore  becomet 
the  moQth. 

t  Schneider, '  Monographie  der 
Kematoden,'  1866.  See  alto 
Bastian,     'Monograph    of    the 


Angaillnlidse '  (Trans.  linnean 
Society^  1865) :  and  <  On  the  Ana- 
tomy and  Physiology  of  the  Nema- 
toids'  (PhU.  Trans.  1866);  and 
several  memoirs  by  Bntschli. 
The  latter  af&rms  that  the  mnseles 
are  as  much  made  up  of  mnsole 
cells  in  the  *  Hohmpria^  as  in  the 
rest.  ("QiebtesHolomyarier?" 
«Zeitsehxifl  fOr  Wlss.  Zoolog|i< 
1878.) 


642       THS  AKATOMY  OF  INVBBTBBSATBD  ANIMALS. 

In  the  Tolymyaria,  the  muBcles  of  the  parietes  of  the  body 
are  divided  into  many  series,  each  made  up  of  many  "  muscle 
cells."  In  the  Meromyaria  there  are  only  eight  longitudinal 
series  of  such  muscle  cells,  two  between  each  lateral  area  and 
the  dorsal  and  ventral  lines  respectively.  In  the  Holomyaria 
the  muscles  are  not  divided  into  series  of  muscle  cells. 

The  first  two  divisions  contain  only  such  genera  as  answer 
to  the  general  description  just  given ;  but,  in  the  Holomyaria, 
there  are  included  several  aberrant  forms.  Thus,  TrichO' 
eephalus  has  no  lateral  areas;  IcMhyonenui  has  no  anus; 
Mermis  has  no  anus  and  the  alimentary  canal  is  rudimentary ; 
though  it  possesses  the  lateral  areas,  and  the  males  have 
spicula.  Oordius  has  no  lateral  areas,  and  only  the  ventral 
line ;  the  alimentary  canal  is  reduced  to  a  rudiment,  with- 
out either  oral  or  anal  aperture,  and  the  male  has  no  spicula. 
In  both  these  genera,  the  anterior  ends  of  the  embryos  are 
provided  with  spines,  which  aid  them  to  bore  their  way  into 
the  bodies  of  the  insects  on  which  they  are  parasitic.  In 
Sphcertdaria  the  alimentary  canal  is  similarly  rudimentary, 
and  Sir  John  Lubbock  discovered  that  the  small  male 
becomes  permanently  adherent  to  the  female. 

Some  NemcUoidea  {e.g.  Lepiodera,  Felodera)  live  in  water 
or  damp  earth,  and  are  never  actually  parasitic ;  but  they 
require  abundant  nitrogenous  food  in  order  to  develope 
their  sexual  organs,  and  hence  they  are  found  in  the  sezuiEd 
state  only  among  putrefying  vegetable  or  animal  matters. 
The  sexless  worms,  which  live  in  moist  earth,  are  at  once 
attracted  by  nutriment,  such  as  a  few  drops  of  milk.* 
Here  they  multiply  with  great  rapidity  as  long  as  the  store 
of  food  lasts ;  but,  when  it  is  exhausted,  the  last  hatched 
young  wander  away.  In  the  course  of  their  wanderings, 
the  embryos  enter  into  the  larval  condition;  but,  beforo 
doing  so,  they  become  twice  as  large  as  those  which  attain 
the  larval  state  in  putrefying  substances.  The  embryonic 
cuticle  becomes  thickened,  and  its  oral  and  anal  apertures 
^oaed,  so  that  it  forms  a  cyst  for  the  larva.  The  larva, 
liow^Yer,  ift  not  T<£«^x«ASi»i  by  this  cyst  from  moving  about 


r'**j 


THB  NBMATOIDEA.  643 

and  oontintiing  its  wanderings,  though,  at  length,  it  passes 
into  a  quiescent  condition.  Its  inner  substance,  at  the 
same  time,  becomes  dark  by  transmitted  light,  in  consequence 
of  the  accumulation  of  small  f attj  granules ;  and,  if  this 
state  of  things  lasts  long,  the  liurva  dies.  If  the  larvae 
should  dry  up,  the  circumstance  tends  to  their  preservation. 
The  embryonic  cuticle  is  separated,  and  forms  a  protective 
cyst;  and,  when  moistened,  the  larvee  resume  their  vital 
activity. 

Nematoid  worms  belonging  to  naturally  free  and  non- 
parasitic genera  may  enter,  and  become  encysted  in,  worms 
and  slugs;  but  they  only  attain  their  sexual  state  when 
their  host  dies,  and  they  are  nourished  by  the  products 
of  its  putrefaction. 

Anguillula  scandens,  the  Nematoid  which  infests  and 
gives  rise  to  a  diseased  condition  of  the  ears  of  wheat,  is 
a  true  parasite.  The  young  are  hatched  from  the  eggs 
laid  by  the  parent  in  the  infected  ear,  and  there  become 
encysted.  When  the  wheat  dies  down,  the  larvsB  are  set 
free,  and  wander  on  the  moist  earth,  until  they  meet  with 
young  wheat  plants,  up  which  they  creep,  and  lodge  them- 
selves in  the  developing  ears.  Here  they  acquire  the 
seroal  condition,  nourishing  themselves  at  the  expense  of 
the  inflorescence,  which  becomes  modified  into  a  kind  of  gall. 

Most  Nematoids  found  in  the  alimentary  canal  of  «^TiiTnft.Ttt 
are  i>arasitic  in  the  sexual  state,  but  have  a  longer  or 
shorter  period  of  freedom  as  larvsB  or  aa  eggs.  But  some, 
as  Cucullanus  elegans,  are  parasitic  both  in  the  sexless  and 
the  sexual  condition;  inhabiting  Cyclops,  while  in  the 
former  state,  and  sundry  fresh-water  fishes,  particularfy 
the  Perch,  in  the  latter. 

Trichina  gpiralia^  acquires  its  sexual  state  in  the  ali- 
mentary canal  of  Man,  of  the  Pig,  and  other  Twi^TnTn^la ; 
but  the  young,  set  free  in  the  alimentary  canal,  bore  their 
way  through  its  walls,  and  enter  the  fibres  of  the  voluntary 
muscles,  in  which  they  become  encysted  in  the  sexless 
state.    If  the  flesh  thus  trichinised  be  eaten,  the  Triehimm, 


*  Leaekart,  ^Untexsttehimgeik  fAMt  TrkiiMML  ip^raUi^  \%Mk« 


j.ne  ineect  paraiBit«a,  Uordiui 
long  aa  they  are  parasitic ;  bu 
their  full  f^owth.  they  leave  th 
semal  orgajis,  copniate.  ajld  laj 
proceed,  which  bore  their  way  i 

It  has  been  stated  that  the  A 
part,  diiEcions.  Schneider  has, 
apeoiea  of  the  non-paiasitic  gen 
whicli  alwajra  have  the  external 
in  the  OTarian  tnbee  of  which 
and  impregnation  takes  place, 
donbt  bj  isolating  embiyoe  of  t1 
out  the  development  of  the  spei 
the  subdivision  of  the  first  cells 
After  a  time,  the  development 
the  cells  separated  from  the  i 
are  impregnated  by  the  aln 
These  Nematoidea  are  probabi 
necessary  hermaphrodites  know 

A»eari4  nigrovttutta  is  parasiti' 
Toads,  and  attains  a  length  of 
It  has  the  characters  of  a  femi 
been  met  with,  bnt  spermatozoa  i 
ia  the  same  manner  as  in  the  pi 

The  e^is  of  thia  Aacarit  are  d 
find  their  way  into  the  inteatines 


THX  PHT8BMABIA.  645 

The  free  embryos,  introduced  into  the  frog's  mouth,  pass 
into  the  lungs,  and  take  on  the  characters  of  the  large 
hermaphrodite  forms.  It  is  not  unHkely  that  the  Guinea 
worm  (FHaria  medinentia),  which  infests  the  integ^ument  of 
Man  in  hot  climates,  may  answer  to  the  hermaphrodite 
stage  of  a  similarly  dimorphous  Nematoid,  though  its  mul- 
tiplication has  hitherto  been  supposed  to  take  place 
agamOgenetically. 

The  many  points  of  resemblance  between  the  Nemaiaidea, 
the  OligochcBia,  and  the  PolyeJicBta  have  been  indicated  by 
Schneider.  They  differ,  however,  from  these,  no  less  than 
from  the  Turhellaria  and  BoHfera,  in  possessing  only 
longitudinal  parietal  muscles.  In  this  respect  they  agree 
with  Rhamphogordiua  and  Polygordiu8  (united  by  Schneider 
into  the  group  of  Oymnotoma),*  which  are  segmented  worms, 
devoid  of  setsB,  but  possessing  mesenteries,  segmental 
organs,  and  pseud-hsBmal  vessels.  Polygordius  has  a  telo- 
trochous  larva,  and  in  its  development,  as  in  other  respects, 
it  is  extraordinarily  like  a  polyduetous  Annelid. 

Butschli,t  on  the  other  hand,  dweUs  upon  the  connexion 
between  the  NemcUoidea  and  the  Ocuieroiricha  (see  Chap.  I Y. 
p.  192)  and  Atrieha  (Echinoderes)  which  he  includes  in  the 
group  of  NenuUorhyncha,  on  the  one  side,  and  the  lower 
Arthropods,  such  as  the  Tardigrada,  on  the  other. 

The  Physemabia. — Since  the  completion  of  the  third 
chapter  of  this  work,  Haeckel  %  1^^  published  an  account 
of  certain  low  Meiazoa,  constituting  the  two  genera,  HciU- 
phyaema  and  Oiutrophysema,  which  had  previously  been 
confounded,  partly,  with  the  Sponges  and,  partly,  with  the 
Protozoa. 

These  are  minute  marine  bodies,  having  the  form  of  cups 
with  longer  or  shorter  stalks,  by  which  they  are  attached. 
The  cavity  of  the  cup  into  which  the  wide  or  narrow  oral 

*  See  Mipra,  p.  186,  iMte.  Ludwig,    *<Ueber  die   Ordnang 

t  <*  Uatereuchungen  iiber  frei-  QMtrotricha  **  (tbid,), 

lebende     Nematoden    und    die  ^  *  BiologUche  Studien,' Heft  2, 

Gattang  Chatomohu^*  (*  Zeitschrift  1877. 

f.  Wise.  Zoologie,'  1876).  Seealao 


SW       THE  ANATOKY  QF  IKTIBTEBBATED  iMIMALS. 

up«nmg  lewis,  is  eithOT'  eimple  (HcUiphysema)  or  divided  by 
circalar  conatrictions  into  two  or  more  ogmmiioicatiiig 
chamberH  {Giutrophyimivi}.  Ttie  wbU  ia  composed  of  two 
latere,  aa  ectoderm  and  &ii  endodorm — the  latter  beting 
forme'l  b;  a  single  layer  of  tlagcUate  cells,  like  those  of 
apongea ;  and  a  series  of  larger  fl^?llat«  celle  aie  diapoaed 
in  a  apinU,  ua  the  inner  face  of  the  endoderm  near  tlie 
mouth.  The  ectoderm  ia  a  sjncf  tium,  vliich  attaches  foreign 
bodies,  sueh  as  sponge  Bpiculu  or  alieletone  at  Fbremtinifern. 
to  itself,  and  thus  becomes  provided  with  as  adventitioos 
skeleton,  tbe  nature  of  which  vaiies  in  different  speciea,  bat 
is  constant  for  each.  Reprodnctian  is  efiected  bjOTa.  which 
are  said  to  be  modified  cella  of  the  eododerm.  In  Oa»tro- 
phygema,  the  endoderm  of  the  ionei-moat  chamber  alone 
gives  rise  to  ova.  The  place  of  development  of  the  spar- 
matoKoii  has  not  been  made  out. 

Telk  diviaion  is  complete  and  re^ar,  and  gives  rise  1<> 
a  vesicular  morula  {OirchAliuittila  of  Haecbel)  eooh  oell  of 
which  is  provided  with  a  Ha^llate  cilinm.  A.  ga^trula 
arises  hy  invagination,  but  the  tiuiil  stages  of  developminit 
have  not  been  made  out. 

As  Hneckel  points  out,  the  PAi/mtnuiria  are  obvionslf 


THK  ACUTTBOCBPHAI^  647 

MntsatDTich  oonetricted  neck  (Fig.  157,/).  It  would  appear 
that,  eventnallj,  the  Eehinorhynehi  completely  pass  out  of 
the  inteatine,  as  thej  are  foond  enclosed  in  detached  cjeta 
Ijing  in  the  peritoneal  cavitj.  The  anterior  eztremilj'  of 
the  EehinorhyTuihuM  ia  produced  into  a  short  cylindrical 
proboscis,  covered  with  manj  rows  of  recurved  hooks,  and, 
behind  this,  it  forms  a  dilatation,  in  which  the  internment 
and  the  moscnlar  coat  are  separated  by  a  considerable  in> 

Fig.  157. 


of  the  body.  /.  N«ck  or  eouatricliou  belwesn  th 
lmr);eincnt  ind  the  rmt  of  the  body,  d.  e.  Poaterior  "  fuDoel."  p. 
Meniscus.  A.  Superior  olilique  InbnlBr  bandi.  i.  Inferior  muKln 
of  tha  pnboarfi.  /.  ■■.  Geniulik.  o.  Penis  or  vuIvk.  B.  Lower 
eilremity  of  the  >lem  of  the  prubotcii.  a.  GuigliDn.  b.  Vuculsr 
*pkce.  d.  Ou(er  coat.  t.  Inner  wall.  t.  Tubular  band,  with  the 
nerve.  A,/.  Muicular  bands,  g.  fiuapensDrluin  of  the  genitalia. 
C.  Part  of  the  female  genitalia,  a.  Ovary,  bh.  Ducta  leading 
from  ovar;  lo  nterui,  ■permiductj  (?).  c.  Open  mouth  of  ovidsot. 
d,  e,  ITtema  and  vagina. 

terval.      The  body,  behind  the  constricted   neck,  which 
separates  it  from  this  ant«rior  dilatation,  bu  &  ^^Jbas^V 


1 

w 

1 

1  • 

1 

- 

■ 

i 

r 

» 

I 

1 
1 
1        « 

f 

1 
i 

; 

.1 

1 

■ ' 

■ 

1 
1 

■k 

f 

1 

1 

.1 
1 

9 

« 

1 

\ 

•    1 

i 

t 

1 

1 

t 
1 

the  vosriels  lit'S  a  double*  layer 
fihrils,    tlie  externsil  of  which   a 
U'riial  are  lou^tudinaL*     The  »: 
with  a  fluid,  in  which  the  ova, 
at  it«  .anterior  extremity,  two  elo 
from  the  parietes,  and  han«;  fr 
lemni^ci ;  they  are   traversed  b} 
thoHe   of    the   parietes.      The   i 
continued  downwards    into    an 
stem,  rounded  below,  which  hang 
the  cavity  of  the  body.     The  exti 
nect'ed  by  broad  retractor  muacl 
^ives  attachment  to  the  suspenso 
ductive  apparatus  (Fig.  157,  B). 
attached  a  little  above  these,  an< 
to  the  parietes ;  they  are  not  mere 
norily  described,  but  contain  a  wit 
a  kirge  sinus,  which  sepanitcs  the 
of  the  proboscis  from  itB  investing 
-stem  of  the  proboscis  is  the  oval  ] 
some  small  branches  upwards,  and 
which  can  be  followed  into  the  vesi 
and,  in  other  species,  have  been  t 


TRX  AOAHTHOOBPHALA.  649 

the  animal  being  probably  nomiBhed  bj  imbibition  tbrongh 
the  walls  of  the  body.  The  reprodnctiye  organs  are,  both 
in  the  male  and  in  the  female,  attached  bj  a  snspensorj 
ligament  to  the  extremity  of  the  proboscis,  and  extend 
thence,  through  the  axis  of  the  body,  to  the  posterior  ex- 
tremity. Here  they  open  in  a  papilla  at  the  bottom  of  a 
funnel-shaped  terminal  dilatation  of  the  body,  which  exists 
both  in  the  nude  and  in  the  female,  though  it  is  much  more 
marked  and  separated  by  a  constricted  neck  from  the  body, 
in  the  former.  On  each  side  of  the  papilla  is  an  organ 
which  has  much  the  appearance  of  a  sucker,  but  which  is 
apparently  non-contractile,  while  the  funnel  itself  undergoes 
constant  and  rhythmical  contractions. 

In  the  male,  the  testes  are  two  oval  sacs,  one  behind  the 
other,  connected  by  vasa  deferentia,  often  provided  with 
peculiar  accessory  glands,  with  the  genital  outlet,  which 
is  provided  with  a  long  penis.  In  the  female,  the  ovary  is 
a  single,  long,  thin- walled,  cylindrical  tube,  the  anterior  end 
^  of  which  is  usually  empty  for  a  short  distance.  Further 
back,  clear,  pale,  rounded  masses  appear,  containing  cavities 
in  which  corpuscles,  like  the  germinal  spots  of  ova,  Ue. 
More  posteriorly  still,  these  masses  become  elliptical,  and 
are  surrounded  by  a  membranous  coat,  which  gradually 
thickens,  and  g^ves  rise  at  each  end  to  a  spiral  filament 
which  surrounds  the  enclosed  egg.  The  ova  thus  constituted 
then  pass  into  the  cavity  of  the  body,  where  they  accumulate 
in  great  numbers ;  but,  in  this  species,  I  have  not  found  the 
free  floating  ovarian  masses  described  in  other  Echino^ 
rhynchi.  From  the  lower  end  of  the  ovarium  two  short  ovi- 
ducts, or  rather  spermiducts,  arise,  and  almost  immediately 
unite  into  a  sort  of  uterus,  which  is  continued  into  the 
vagina  (Fig.  157,  G).  The  uterus  passes  above  into  a  short, 
open,  funnel-shaped  canal,  which  lies  between  the  two 
oviducts  (Fig.  157, 0  c),  and,  according  to  Von  Siebold,  takes 
in  the  ova  from  the  perivisceral  cavity  by  a  peculiar 
swallowing  action. 

The  embryos  of  the  different  species  of  Eckmorhynchi 
vary  somewhat  in  structure.    Von  Bi^\M\<l  \^3m^  ^^ssrsc^rj^. 


previously  been  Been  by  Leuckar 
water  containing  apeciniens  of 
E.  protein  were  tninsferreil.  A 
could  easilj  be  detected  in  tbe  i 
maru*,  whilst  numerous  embrj 
shell,  were  fonnd  within  the  app 

Each  ovum  has  two  coats ;  an 
inner,  chitinous.  The  first  ia 
through  the  alimentary  canal; 
ruptured  by  the  embryo,  which  b 
walla  into  the  cavity  of  the  body, 
the  sit«  proper  for  its  developmei 

The  body  of  the  embryo  is  soi 
and  consists  of  a  colourless,  tmn 
t«ct6d  by  a  cuticle.  The  parench 
an  onter,  homogeneooH,  contract] 
mednllary  substance.  Within  this 
mass,  made  up  of  large  highly-refi 
grannies  of  the  same  kind  maj 
tbronghont  the  soft  medullar;  anl 
end,  the  embryo  tapers  to  a  puint,  w 
is  obliquely  truncated  towards  the 
oblique  surface   may  be  observer 


THB  DBYBLOPMBNT  OV  BCHIKOBHTVCHUS;    651 

the  middle  line  to  form  an  arch,  the  central  and  largest 
spine  constituting  its  summit.  Two  short,  ridge-like  ele- 
vations  of  the  cuticle,  close  to  the  middle  line,  separate 
the  spines  on  either  side  from  one  another.  Behind^  the 
peripheral  layer  g^ves  rise  to  a  knob-like  process. 

At  the  end  of  fourteen  days,  the  embryo  is  found  to  have 
increased  much  in  size,  but  presents  few  changes  of  form. 
The  anterior  extremity  displays  two  rounded  elevations, 
the  spines  retaining  their  original  position.  The  peripheral 
layer  has  become  thicker  and  more  distinct ;  its  knob-like 
process  has  by  this  time  disappeared.  The  central  mass, 
now  much  larger,  has  assumed  a  spherical  figure.  No 
longer  granular,  it  is  seen  to  be  composed  of  numerous 
pale  cells,  which  continue  rapidly  to  increase. 

During  the  third  week,  ntmibers  of  large  yellow  granules 
begin  to  appear  within  the  outer  layer  of  the  embryo.  No 
other  changes,  save  those  of  growth,  take  place  in  its 
walls:  but  the  central  mass,  still  continuing  to  enlarge, 
gradually  puts  on  the  aspect  of  a  young  Echinorhynchus, 
This  mode  of  deyelopment  has  been  compared  by  Leuckart 
to  that  of  certain  Echinoderms,  or  to  the  production  of  the 
Nemertid  larva  within  its  pilidium. 

The  first  part  to  become  differentiated  is  the  oaviiy  of 
the  future  proboscis,  which  appears  as  a  transparent 
lenticular  vesicle  at  the  anterior  end  of  the  spherical  mass. 
Behind  this  are  soon  seen  rudiments  of  the  central  axis 
and  its  contained  ganglion ;  and  the  suspensorial  ligament, 
with  the  reproductive  organs,  are,  at  the  same  time,  marked 
out.  The  muscles  of  the  outer  wall  have  also  commenced 
their  development.  Next,  the  central  region  of  the  young 
Echinorhynchvs  rapidly  elongates ;  its  walls  become  thinner, 
and,  separating  from  the  included  structures,  show  the  first 
trace  of  the  visceral  cavity.  About  this  time  distinctions 
of  sex  first  make  themselves  evident.  The  posterior  end 
of  the  body  undergoes  a  disproportionate  increase  of  size, 
the  muscles  become  more  distinct,  and  the  rudimentary 
generative  organs  are  clearly  manifest.  At  length  the 
young  Echinorhynchus  occupies  almost  iJb!^  ^V<^^  \s^ii5c\ss<& 


652        THE    INATOMT   OF    INVBRTGBRATED    ANrHALS.  ^H 

of  t.Le  embrjo.  the  wallB  of  whicb  h&vc,  me&nwhile,  UOdav> 
gone  but  aliglit  histolo^coi  cban^.  The  epines,  bowever. 
have  disappeared,  together,  it  would  se«m.  with  the  cnliol* 
to  which  the/  were  attached.  No  niptiire  of  thu  other 
cinhr/onic  struetures  takea  place,  bat,  they  gmdunll;  nttiKih 
themaelvea  to  the  body  of  the  coat^aed  .SchiHorliynchmi. 
becomiiig  cloaety  fitted  to  its  eurfuce,  and  uppureDtij  per- 
sisting throughout  its  entire  life.  The  development  of  titt 
EohinorhTpich-iig  now  approaches  completion.  The  lemnimii 
appear.  Hooke  arise  on  the  surfaoe  of  the  proboaoia.  not, 
as  might  be  Bnppoeed,  from  it«  out«r  cntiub.  but  from 
Bpociolly  modified  cells  of  an  inner  membrane,  The  in- 
ternal organs  begin  to  a«siinie  their  final  napoct.  The 
external  form  of  theadiilt  organiemia  rather  slowly  reached, 
and  a  few  changes  which  take  place  a[l«r  tr>tiiBfi!rpn<>e  of 
the  Echiiiorkynekag  to  its  final  host  have  yet  to  be  obeerrcii. 
The  AeanthncepluUa  tindonbtedl;  present  certain  re«eai- 
hlanceB  to  the  NmnatoiiUa,  and  more  particularly  to  the 
Oordiaeea,  but  the  fundamental  differences  in  the  etmctnn) 
of  the  mnaciilar  and  nerrons  systems,  ajid  in  that  of  the 
reprodactive  organs,  are  so  great,  that  it  ia  impoaaibte  to 


THB  DICTXMIDA. 


053 


cjlindrical,  or  more  or  less  fusiform,  awial  eeU,  which 
extends  from  the  slightly  enlarged  head-end,  hj  which  the 
animal  is  attached,  to  its  posterior  eztremiiy,  and  is  in- 
yested  by  a  single  layer  of  relatiyely  small  flattened  cortical 

Fig.  158. 


Fig.  1&8.— DtcyenM.— I.  D.  typut.  The  large  papillsB  of  the  cortical 
layer  and  the  ^enoM  in  the  interior  of  the  axial  cell  are  noticeable. 

IT.  1>.  tvptu.    Different  stages  of  the  development  of  a  Yermifonn  germ. 

III.  Inmsoriform  embryo  found  tree  in  the  renal  organs  of  £iedone 
wtotehatOf  treated  with  osmic  acid :  /»,  the  urn  ;  oa«  its  capsule ;  «» 
its  lid ;  t,  multinucleate  cells  in  its  interior.  (After  Van  Beneden,  /.  e.) 


cells.  These  are  arranged,  like  a  payement  epithelimn, 
around  the  axial  cell,  their  edges  being  juxtaposed ;  they 
are  nucleated,  and  their  free  surfaces  are  ciliated.  There 
is  no  interspace  between  the  cortical  cells  and  the  axial 
cell,  and  the  organism  is  a  simple  cell-aggregate,  deyoid 
of  connectiye,  muscular,  or  nenrous  tissues. 

The  cortical  cells  which  inyest  the  anterior  or  head-end 
of  the  IHeyema,  haye  peculiar  characters,  and  are  dis- 
tinguished as  the  polar  cells.  They  are  arranged  in  such 
a  manner  that  the  head  ia  bilaterally  symmetricaL  Some- 
times the  polar  cells  constitute  the  whole  of  the  cephalic 
enlargement,  but,  in  others,  cells  of  the  adjacent  put  of 
the  body  {parapolar  eelU)  contribute  to  the  inyestn^siSQiJu  ^ 


654       THB  ▲HATOmr  OV  INYSBTBBRATED  ANIMALS. 

the  head.  Stronglj-refracting  globules  and  rods  aconmu- 
late  in  some  of  the  ectodermal  cells,  and  cause  them  to 
project  in  the  form  of  papUlse. 

The  axial  cell  is  a  mass  of  protoplasm.  Its  relatiyelj 
dense  outer  layer  passes  into  a  central  reticulation,  in  the 
midst  of  which  there  is  a  large  oval  nucleus. 

Reproduction  takes  place  by  the  formation  of  germs,  and 
the  development  of  embryos  from  them,  in  the  axial  cell. 
The  embryos  are  of  two  kinds,  the  one  vermiform,  the  other 
infusoriform,  and  are  not  met  with  in  the  same  Dieyema, 
but  in  individuals  of  somewhat  different  characters.  Those 
which  g^ve  rise  to  the  vermiform  embryos  are  termed 
Nematogena,  while  the  others  are  named  Bhomhogena. 

In  the  Nematogena,  the  germs  arise  in  the  protoplasmic 
reticulum  of  the  axial  cell,  and,  at  first,  are  minute  spherical 
bodies,  each  of  which  is  provided  with  a  nucleus.  This 
germ-cell  divides  into  two,  and  each  of  these  again  becom- 
ing bisected,  four  cells  are  produced,  of  which  one 
remains  undivided,  while  the  rest  go  on  dividing.  The 
former  enlarges,  and  gives  rise  to  an  axial  cell,  around 
which  the  other  cells  airange  themselves,  until  eventually 
they  enclose  it.  Before  they  meet,  they  surround  an  open- 
ing through  which  one  end  of  the  axial  cell  protrudes.  This 
corresponds  with  the  oral  pole. 

Before  the  young  Dieyema  thus  developed  leaves  the 
body,  which  it  generally  does  by  traversing  the  oral  pole, 
(though  it  may  make  its  way  out  through  the  parietes,)  two 
embryos  of  the  same  kind  appear  within  its  axial  celL 

Thus  the  nematogenous  Dieyema  gives  rise  by  an  agamo* 
genetic  process  to  new  Dieyemas. 

In  the  Ehombigena,  the  germs  are  developed  in  from  two 
to  five  special  nucleated  parent  cells,  the  origin  of  which  is 
not  known.  They  are  found  imbedded  in  the  protoplasm  of 
the  axial  cell,  and  the  germs  are  developed  endogenously 
from  the  protoplasm  of  the  parent  cell,  the  nucleus  of 
which  remains  unchanged.  The  germs  undergo  division, 
and  beoome  sp\iecQvdal  bodies  composed  of  two  kinds  of 


THB  DBYBLOPMBNT  OF  DICTXMA.  655 

cells,  small  and  large.  Each  of  these  bodies  is  converted 
into  an  inf  usorif  orm,  bilaterally  symmetrical  embryo,  which 
consists  of  an  urn,  a  ciliated  body,  and  two  refractive  bodies. 

The  nm,  situated  on  the  ventral  side  of  the  embryo, 
is  composed  of  a  capsule,  a  lid,  and  contents. 

The  latter  are  four  granular  masses,  each  of  which 
contains  many  nuclei,  and  eventually  becomes  covered 
with  cLLia.  The  refractive  bodies  take  their  origin  in  two 
adjacent  cells.  They  partially  cover  the  urn  in  front,  and 
form  the  largest  portion  of  the  dorsal  face  of  the  embryo. 
The  ciliated  body  consists  of  ciliated  cells,  and  forms  the 
caudal  poiidon  of  the  embryo. 

While  the  vermiform  embryo  becomes  a  Dicyema  in  the 
body  of  the  Cephalopod  on  which  its  parent  is  parasitic, 
the  infusorif orm  embryo  is  set  free,  and  probably  serves 
as  the  means  by  which  the  parasite  is  transmitted  from  one 
Cephalopod  to  another. 

Professor  E.  van  Beneden  compares  the  cortical  layer 
of  a  Dicyema  to  the  ectoderm,  and  the  axial  cell  to  the 
endoderm  of  a  Metazoon ;  and  the  mode  of  production  of 
the  embryo  to  the  process  of  epiboly  in  the  Metatoa.  But, 
from  the  complete  absence  of  any  mesoblastic  layer,  he 
proposes  to  establish  a  new  division  of  Mesosoa,  inter- 
mediate between  the  Protozoa  and  the  Metatoa,  for  the 
Dicyemida. 


THB   ASATOMY  0*    raVERTBBHATEl 


CKAPTEB  XU. 

IirVEBTEDKATBD 


I 


Thb  grouping  of  the  various  kinds  of  inTertobrUvil 
ftpim^lH  which  ba.s  been  adopted  in  the  preceding  pagu*  U 
to  be  regarded  merely  ha  a  temporarj  arrangeioent.  Ench 
chapter,  from  the  aecoud  to  the  tenUi,  ia  devoted  to  «  snnr> 
of  formH,  the  morphological  relationa  of  which  are  man 
or  leea  obvious,  nhile  Chapter  XI.  is  resei-ved  partlj  tut 
Buch  groups  BM  do  not  rcadilj  find  a  place  in  any  of  Ac 
Beriea  which  precede  them ;  and,  partly,  for  such  as  hxit 
been  establlBhed  since  this  work  was  commenced. 

Our  knowledge  of  the  anatomy,  and  espeaiully  <if  Um 
developmest,   of  the  Znvffriebrala   is  increneing  with   aucb 
prodigious   rapidity,   that   the  views    uf    Taxonomiat* 
regard  to  the  proper  majuier  of  expressing  tJ      ' 


ITATITSAL  OBDBBB  OV  AKOfALfl,  657 

It  is  x>068ible  to  divide  inyertebrated  aTiimalfl  into  a 
certain  nnmber  of  groups,  each  of  whicli  will  be  admitted 
bj  every  morphologist  to  be  in  itself  a  perfectly  natural 
assemblage.  That  is  to  say,  all  the  forms  thus  associated 
together  will  resemble  one  another,  and  will  differ  from  all 
other  animals,  in  certain  respects.  Each  such  assemblage 
is,  in  fact,  a  "  natural  order "  in  the  sense  in  which  that 
word  is  used  by  botanists ;  and,  although  the  number  of 
these  natural  orders  may  be  increased  by  the  discovery 
of  new  forms,  or  diminished  by  the  ascertainment  of  closer 
bonds  of  union  than  are  at  present  known  to  exist,  between 
the  orders  already  discriminated ;  yet,  the  morphological 
types  which  they  represent  will  always  remain ;  and  there- 
fore the  knowledge  of  their  characters,  once  acquired,  will 
be  a  permanent  possession. 

It  is  not  needful  that  these  natural  orders  should  be 
morphologically,  still  less  numerically,  equivalent ;  and,  in 
forming  them,  it  is  more  important  that  similarities  should 
not  be  neglected,  than  that  differences  should  be  overlooked. 
Those  which  have  been  recognized  in  the  preceding  pages 
are  enumerated  in  the  following  list,  arranged  in  sections 
corresponding  with  the  chapters  in  which  they  are  discussed. 
Under  the  head  of  each  section,  I  shall  proceed  to  make 
such  observations  as  have  been  suggested  to  me  by  new 
information  or  by  further  reflection,  during  the  progress  of 
this  work. 

Section  I. — Monera  [Foraminifera]  IHeliotoa],  Badio- 
laria,  Protoplada,  ChregarinidcB,  CaiaUacta,  InfiMoria 
[Opalinina,  CUiaia,  Flagellata,  Tentaculifera], 

Section  II. — ForiferajHydrozoa,  Coralligena  [Ctenophora]. 

Section  III. — Turbellaria,  Boiifera  [NefruUorhyncha], 
Trematoda,  Cestoidea, 

Section  IV. — Hirvdinea,  Oligochceta,  Folychceta,  Qephyrea. 

Section  V. — Crustacea,  Arachnida  \_Fycnog(mida,  Tardi- 
grada,  Fentagtomida],  Myriapoda,  Inseda. 

Section  YI. — Folyzoa,  Brachiopoda,  LameUibranehiaia, 
Odontophora, 


668     THX  ▲HATomr  or  nrmnriBBATKD  avukals. 

Beckon  YIL^EMmodermaitL 

Section  YUL—IHmteaick 

Section  IX — PeripaHdea,  Myaodomaia^  EnieropneudOj 
Ckadognaiha,  NemaMdea,  Phyaemaria,  AeafUkoc^phala, 
DieyemidcL 

SscnoH  L — ^In  the  commencement  of  Chapter  IL,  I 
hvre  expiesBed  a  doubt  as  to  the  yaliditj  of  the  distinction 
of  the  groups  contained  in  this  section  bj  the  presence  or 
absence  of  a  nucleus,  and  the  recent  inyestigations  of 
Schulze*  and  Hertwigf  haye  justified  mj  hesitation. 
These  obeerrers  haye,  in  ^t,  demonstrated  the  existence 
of  one  or  more  nuclei  in  many  Foramimfera  {EnlomUenia, 
PolysiomeUii^  Botalia,  TexMaria,  some  Miliolidce).  These 
nuidei  may  be  simple  or  multiple ;  in  the  latter  case,  thej 
haye  no  special  relation  to  the  cameration  of  the  skeleton, 
and  they  are  single  in  the  young. 

The  discoyery  of  the  nuclei  was  effected  by  treating  the 
Foraminifera  in  which  they  were  found  in  a  special  manner : 
and,  considering  the  negatiye  results  at  which  the  best 
obseryers  of  the  Foraminifera  haye  hitherto  arriyed,  and 
the  fact,  that  the  other  Monera  haye  not  been  inyestigated 
by  the  same  methods,  it  will  probably  be  wise  to  consider 
the  question  of  the  non-existence  of  a  nucleus  in  them  as 
an  open  one. 

Hertwig  proposes  to  include  all  the  Bhizopods  which  are 
inyested  by  a  coat  of  chitin,  or  by  silicious  or  arenaceous 
particles,  or  which  possess  a  skeleton,  under  the  head  of 
Tkalavwphora ;  but  the  name  of  Foramintfera  is  now  so 
widely  accepted  and  so  long  established  that  I  cannot  but 
think  that  the  better  course  is  to  retain  it. 

I  haye  included  the  AeHnophryida  and  the  similar  forms 
found  in  fresh  water,  and  proyided  with  Badiolarian  skele- 
tons, with  the  marine  Sadidaria, 

*  "  Rhisopoden-Stadien,    YI.'*  tion  imd  tjBtemstifehe  Stdlimg 

CArehiv  fur  ilikr.   AnAtomie,'  der  FonminifeKa."  OJeosuehe 

1876.)  ZeitMhrifl,'  1^6.) 

t  **BsB>eitoBiy!ikianOtfyBSaiap 


THX  HBUOaOA.  659 

Hertwig  and  Lesser,*  However,  in  their  important 
monograph  upon  the  Bhizopoda,  have  stated  reasons  for 
separating  the  former  as  a  distinct  gronp  (the  Helioeoa  of 
Haeckel),  though  their  conclusion  that  there  are,  at  present, 
no  grounds  for  assuming  even  a  remote  relation  between 
the  Heliozoa  and  the  Baddolaria  (L  c.  p.  159)  appears  to  me 
to  have  no  sufficient  warranty. 

The  Heliozoa  are  defined  bj  these  authors  to  be  uni- 
cellular organisms,  which  occasionallj  become  multicellular, 
or  at  any  rate  multinucleate,  by  the  multiplication  of  the 
nucleus.  They  are  usually  spheroidal  and  free,  but  some 
are  fixed  by  means  of  a  stalk.  In  most,  the  protoplasm  of 
which  they  consist  is  differentiated  into  a  cortical  and  a 
medullary  substance  (ectosarc  and  endosarc).  The  sharpness 
of  demarcation  of  the  ectosarc  from  the  endosaro  Taries. 
In  Aetinophrye  sol  the  two  pass,  imperceptibly,  one  into  the 
other ;  in  ActinosphcBrittm,  the  change  from  the  ectosarc  into 
the  endosarc  takes  place  within  a  narrow  zone,  eyerywhere 
equidistant  from  the  centre.  The  line  of  separation  between 
the  endosarc  and  the  ectosarc  is  best  defined  in  the  Aean- 
(hocyatidcB,  HeterophryidaB,  &a,  but  it  arises  only  from  a 
differentiation  of  the  protoplasm,  and  not  from  the  derelop- 
ment  of  a  definite  membranous  investment  around  the 
endosarc.  The  nuclei  lie  in  the  endosaro.  When  only  one 
exists  it  is  usually  eccentric,  and,  when  there  are  manj, 
they  are  scattered  irregularly.  The  ectosarc  contains  con- 
tractile, and  sometimes  non-contractile,  yacuoles,  which 
last  may  also  be  met  with  in  the  endosarc.  The  pseudo- 
podia  are  thin,  filiform,  and  radiate  from  the  body ;  some- 
times their  surface  presents  moving  granules.  They  rarely 
branch  or  anastomose.  In  many  cases  they  present  an 
axial  substance  which  may  be  traced  as  far  as  the  endosaro. 
The  silicious  skeleton  may  c<msist  of  separate  spicula  or 
form  a  continuous  shelL 

*  "UeberKhisopodeoiindden-  of  the  subjeet  will  be  found  Ib 
■elben  nahestehender  Organis-  this  memoir  and  in  I>r.  Car- 
men." (*  ArchivfarMikr.  Anat*  penter*8  •Introduction  to  the 
Bd.  X.  Supplement  heft,  1866.)  Study  of  the  Formminiferm,' 1682. 


full  references  to  the  literature 


^Ti^ 


(ito       THS  ▲HATOKT  OV  nTYBSTSIuiLATSD  UriMALS. 

The  JETeZiosoa  propagate  by  siinple  diyision  with  or  without 
preYioQB  enc jstation ;  and  the  products  of  diyision  may  or 
may  not  become  encysted.  They  may  either  pass  directly 
into  the  adult  state  or  become  monadif orm  actiye  larfie, 
provided  with  two  flagella,  a  nucleus  and  contractile  yesicle, 
which  in  course  of  time  develope  into  the  parent  form.* 

'  JL  completely  new  light  has  been  thrown  upon  the  vexed 
question  of  the  supposed  sexual  method  of  reproduction 
otinfusoria  by  the  inyestigations  of  Engelmann^f  Biitschli^ 
and  Hertwig,§  the  results  of  whose  observations  may  be 
■iunined  up  as  follows : — 

1.  The  so-called  acinetiform  embryos  are  parasites. 
'   2.  The  rod-like  bodies  occasionally  observed  in  the  endo- 
plast  are  also  parasites,  and  probably  BaeUria, 

3.  The  globular  so-called  g^erms  in  the  VoHieeUidcB  and 
the  bodies  termed  '  ovules '  by  Balbiani  have  nothing  to  do 
with  reproduction. 


*  As  this  chapter  was  passiiig 
through  the  press,  Hertwie*s 
monograph  '  Zur  Histologie  der 
Badiolarien'  has  come  into  my 
hands.  The  Radiolaria  are  de- 
fined as  Rhisopods  with  pointed, 
branched,  usoally  anastomosing 
and  granular  pseodopodia,  which 
proceed  from  a  protoplasmic 
body  enclosing  either  numerous 
•mall  heterogeneous  nuclei,  or  a 
single  larger  highlydifferentiated 
vesicular  nucleus.  The  protoplasm 
of  the  bod^  is  further  separated 
into  a  peripheral  non-nndeated 
and  a  cential  nucleated  portion, 
by  a  membranous  capsule  with 
porous  walls.  The  capanle  is  in- 
vested by  a  homogeneous  gelati- 
nous substance ;  the  extracapsular 
protoplasm  usually  contains  nu- 
merous yellow  cells. 

Propagation  is  effected  (pro- 
bably always)  by  the  breaking  up 
of  Um  body  into  unicellular 
IB0iiadif6im  tmYn^tA  ^ROtVied 
With  %  ibi^t  fiai^^aaD^    hA  % 


result  of  these  inyestigations, 
Hertwig  admiU  that  the  /lo^iio- 
laria  and  the  Heiiozoa  are 
closely  allied,  and  even  suggests 
that  the  name  of  RadiMorim 
should  apply  to  both  groups, 
which  would  then  form  the  sub- 
divisions of  Heiiozoa  and  Cfto- 
phora.  The RadiolariaCCgttjphon) 
are  distinguished  into  CoUozoa 
(with  numerous  small  nuclei) 
and  CoUida  with  a  single  highly 
differentiated  nucleus. 

t  *'Ueber  Entwickelnng  und 
Fortpflanzung  der  Infhsorien." 
(*  Morpbologlsches  Jahrboch,* 
1876.) 

X  *^Mittheilongen  uber  die 
Coijogation  der  Infiisorien  and 
die  ZeUtheUung."  (*  Zeitschrift 
fiir  Wiss.  Zoologie,'  1875.) 

§  **Ueber  Podophrya  gtmmi- 
parOy  nebst  Bemerkungen  sum 
Ban  und  snr  systematische  Stel- 
lung  der  Acineten."  (*Morph. 
Jahrboch,'  1876.) 


Iv     ^ 


THB  REPBODUCTION  09  THB  INFUSOfilA.  ^1 

•   ■       ■  '  •  .        .'  •  ■  I  ' 

4.  In  the  VarticeUicUBt  when  conjugation  takes  place,  the 
endqplasts  of  both  individuals  break  up  into  a  number  o£ 
fragments.  These  become  mixed  up  in  the  common  body 
which  results  from  conjugation.  The  endoplast  of  the 
latter  results  from  the  gradual  union  of  many  smaller 
particles  which  make  their  appearance  in  the  endosarc. 
Whether  they  are  identical  with  the  fragments  into  which 
the  endoplasts  of  the  conjugated  individuals  have  divided, 
is  not  certain. 

5.  When  Infusoria  which  possess  an  endoplastule,  as  well 
as  an  endoplast,  conjugate,  both  of  these  structures  undergo 
division ;  and  the  endoplastule,  before  division,  acquires  the 
striated  structure  and  spindle  shape,  which  has  obtain^ 
for  it  the  name  of '  seminal  capsule.* 

6.  The  final  result  of  coi^jugation  is  the  appearance  in 
each  of  the  individuals  which  have  undergone  conjugation 
of  the  endoplast  and  endoplastule  (either  single  or  multiple) 
which  characterise  the  species. 

It  does  not  appear  that  there  is  any  positive  proof  that 
the  striated  endoplastule,  or  endoplastules,  of  the  conjugated 
individuals  are  or  are  not  exchanged.  From  Biitschli's 
observations  on  Styhnichia  myiilua,  he  concludes  that  tiie 
endoplast  divides  into  four  fragments ;  that  these  round 
themselves  oS  into  the  so-called  '  ovules '  of  Balbiani,  and 
are  expelled  from  the  body;  while,  of  the  four  striated 
endoplastules  into  which  the  endoplastules  which  exist 
before  fecundation  divide,  one  is  converted  into  a  large 
transparent  body,  and,  dividing,  g^ves  rise  to  the  two  new 
endoplasts  which  appear  in  the  Stylonichica,  after  their 
separation.  Two  of  the  others  become  the  new  endo- 
plastules ;  while  one,  apparently  undergoing  retrogpressive 
metamorphosis,  is  cast  out  of  the  body. 

From  these  facts,  and  from  the  circumstance  that  the  en- 
doplastules of  Infusoria^  which  are  merely  dividing,  acquire 
the  striated  structure,  it  must  be  concluded  that  the  as- 
cription of  a  spermatozoal  nature  to  the  strise  of  the  modified 
endoplastules  is  not  warranted.    And  the  remarkable  ob- 


062       THE  UTATOKT  OV  UrTXBTBBJlATED  ▲HIMALS. 

•eryations  of  Butschli,  Strassburger,*  Van  Beneden  and 
Hertwig,t  on  the  changes  which  take  place  in  the  anclei 
of  both  animal  and  vegetable  cells,  which  are  undergoing 
division,  or  are  preparing  for  fecundation,  seem  to  leave  no 
doubt  as  to  the  justice  of  this  negative  conclusion.  In  such 
oeUs  the  nucleus  becomes  elongated  and  assumes  a  striated 
appearance,  so  as  to  resemble  in  a  very  striking  manner,  the 
so-called  '  seminal  capsule '  of  the  Infusoria.  Nevertheless, 
it  is  still  possible  that  the  conjugation  of  the  Infusajia  may 
be  a  true  sexual  process ;  and  that  a  portion  of  the  divided 
endoplastules  of  each  may  play  the  part  of  the  spermatic 
oorpuscle;  the  conjugation  of  which  with  the  nucleus  uf 
the  ovum,  appears,  from  recent  researches,  to  constitute 
the  essence  of  the  act  of  impregnation. 

With  the  proof  that  the  '  acinetif orm  embryos '  of  the 
Infusoria  eiliata  are  parasites,  the  view  of  the  relations  of 
the  TerUaculifera  with  the  CUieUa,  suggested  at  p.  109, 
oeases  to  be  exactly  tenable.  Nevertheless  the  resemblance  of 
the  ciliated  young  AeinetcB  to  the  simpler  forms  of  the 
CUicUa  is  so  close  that  they  may  still  be  said  to  be  modifica- 
tions of  a  common  type.  Hertwig  X  has  made  the  interest- 
ing observation  that,  in  some  AeinetoB,  the  tentacula  are  of 
two  kinds;  those  of  the  one  kind  are  the  characteristic 
suctorial  organs,  while  those  of  the  other  kind  are  simply 
prehensile,  and  have  a  structure  very  similar  to  that  of 
the  prehensile  pseudopodia  of  the  AeHnophryicUB.  The 
same  author  shows  that  the  ciliated  germs  do  not  arise 
from  the  endoplast  alone,  but  that  a  portion  of  the  proto- 
plasm of  the  body  invests  each  division  of  the  endoplast. 
In  fact  the  process  by  which  these  germs  are  developed  is 
altogether  similar  to  ordinary  cell-division. 

The  Opalinina  must  clearly  be    arranged  among  the 


t  <<  Ueber  PodophryapemmqHtra 
nebst  Bemerkangen  cum  Bau  und 


^  <  Ueber  Zellbildung  und  Zell- 
theilung,'  1876. 

f  "Beitragezor  Kenntnissnnd       cur   systeroatiscLe   Stellung  der 
Blldung,  B?t'nxcY^tan^  uml  Thei-      Aoinetea."      C  Morpbologfaches 
luns    Sea     l\\\etT\«ctxwi    "^x^^r       ^^Su&Wcbu,'  1876.) 
(« liorph.  Ja^Wcks'  \^^.^ 


THX  PBTSIiOPMBHT  OF  »PONOB8.  668 

Ii^iuoria.  Stein  regards  them  as  simplj  the  lowest  forms 
of  the  Holoirieha,  bat  it  will  probably  be  safer  to  consider 
them  as  a  distinct  gronp,  standing  in  somewhat  the  same 
relation  to  the  Ciliata  as  the  QregarinicUB  do  to  the  AmoebcB. 

Sectigit  IL — The  elncidation  of  the*  problem  of  the 
mode  of  development  of  the  Sponges  has  been  greatly 
advanced  by  the  investigations  of  Oscar  Schmidt,*  Schnlze,t 
and  especially  of  Barrois4  which  confirm  the  assertion  of 
Metschnikoff  that  the  vesicolar  morula  >vhich  constitntes 
the  early  condition  of  the  sponge-embryo  consists  of  blasto- 
meres  of  two  kinds ;  those  of  the  one  half  of  the  spheroidal 
or  flattened  embryo  being  elongated  and  flagellate ;  those  of 
the  other,  rounded,  granular  and  non-ciliated.  Schulze  and 
Barrois  have  independently  ascertained  that  the  latter 
region  sometimes  undergoes  partial  invagination ;  and  that 
a  cup-shaped  body  is  produced,  composed  of  an  epiblast 
formed  of  flagellate  cells  and  a  hypoblast  of  spheroidal, 
non-ciliated  c^ls.  Thus  the  '*  gastrula  "  stage  of  Haeckel 
may  exist,  though  it  is  not  formed  by  delami  nation,  as  he 
supposed,  but  by  invagination.  But  it  appears  that  this 
gastrula-stage  does  not  always  occur,  and  that  when  it 
does,  it  is  transitory,  in  so  far  as  the  hypoblaatio  cells 
subsequently  enlarge,  protrude  beyond  the  epiblaatio  cells, 
and  give  rise  to  the  free  ovate  embryo  formed  of  a  ciliated 
and  non-ciliated  half,  which  has  so  often  been  observed. 
According  to  Barrois'  observations,  this  free  swimming 
larva  fixes  itself  by  its  non-ciliated  hypoblastic  half,  and  the 
hypoblastic  cells  are  invested  by  those  of  the  epiblast^  which 
thus  constitute  the  whole  outer  covering  of  the  young 
sponge.  The  central  cavity  of  the  sponge,  which  represents 
the  archenteron,  arises  in  the  midst  of  the  included  hypo- 

*  *Zar  Orientirung  ilber  die  £ntwiokeliing       von     Sycandra 

Entwickelung    der     SpoDffien  "  raphanui  "   {'  Zcitschrift  f.  Wiss. 

("  Zeitschrift  fur  Wiss.  Zoologie,'  Zooloffie/  1875) ;  and  *«  Zur  Ent- 

1875) ;     and     **  Nochmals     die  wickelungsgescbichte  von  Sycao- 

Gastrula   der    Kalkschwamme"  dra"    (Ibid.  1876.) 

(•  Archiv  f.  Mikr.  Anat.,'  187d).  %  '  Annales  des  ^eiences  Natu- 

t  "•  Deber  den   iiau   und   die  reUea,'  1876. 


^6i      THX  AVATOKT  OT  nfYSSTBBlULTBD  awtmat^. 

blastic  oellB,  while  the  oscnlnm  is  a  seoondary  opening, 
formed  apparentlj  by  an  invagination  of  the  ectoderm,  and 
has  nothing  to  do  with  the  primitiTe  blastopore.  Thus 
even  the  simplest  sponge  has  passed  beyond  the  gastmla- 
stage. 

Schnlze  has  made  the  important  discovery  that,  in  Sy- 
eandra  raphanus,  there  is  a  layer  of  flattened  cells  external 
to  the  syncytinm ;  whence  the  latter  may  rather  be  regarded 
as  the  equivalent  of  the  mesoderm  than  of  the  ectoderm  of 
the  Ckdewterata,  And  the  observations  of  Barrois  on  other 
calcareous  sponges  tend  to  the  same  conclusion.  The  care- 
ful investigations  of  the  last-named  writer  have  not  enabled 
him  to  discover  spermatozoa  in  any  sponge,  and  he  finds 
that  the  ova,  when  they  are  first  disoemible,  are  situated  in 
the  syncytium  or  mesoderm,  and  not  in  the  endoderm.  In 
the  free  larv®  of  the  calcareous  sponges  an  equatorial  zone 
of  rounded  equal-sized  blastomeres  is  interposed  between  the 
ciliated,  or  epiblastic,  and  the  non-ciliated,  or  hypoblastic, 
hemisphere;  and  it  appears  probable  that  these  cells  re- 
present a  mesoblast  and  give  origin  to  the  mesoderm.  The 
embryo  in  this  condition  has  a  very  interesting  resemblance 
to  that  of  Clepsine,  in  the  stage  in  which  the  epiblast 
occupies  one  face  of  the  embryo,  and  the  hypoblast,  formed 
of  three  very  large  blastomeres,  the  opposite  face;  while  an 
incomplete  zone  of  six  or  eight  large  blastomeres,  which  are 
eventually  enclosed  by  the  epiblast,  surrounds  the  margins 
of  the  latter. 

At  p.  150, 1  have  quoted  Haeckel's  account  of  a  process 
of  Entogcuftrie  gemmation  in  Carmarina  hasicUa  of  an 
altogether  anomalous  character. 

F.  E.  Schulze*  has  lately  investigated  specimens  of 
Oeryonia  hexaphyUa  provided  with  entogastric  processes 
beset  with  budding  CwiiruB,  and  he  proves  that,  in  this 
case,  at  any  rate,  the  phenomenon  is  one  of  parasitism. 

*  ^'UeberdieCiminenKnotpeii-       sohafUichen    Yereines.'     Grax, 
aehren  im  Mtg<ni  t.  QcrfOTAea.."      1875.) 
(*  BiitthillimgMk4«i'&«toKm^n«Bk- 


CT7VINA  AND  aSBTONIA.  665 

The  stem  from  whicli  the  bads  proceed,  in  fact,  is  not  a 
process  of  the  bodj  of  the  C^eryonia,  bnt  is  simply  attached 
to  the  wall  of  the  gastric  chamber  of  the  latter.  It  is 
hollow,  and  its  cavity  is  lined  by  an  endodermal  epithelium. 
The  Cunina  bnds  are  not  developed  from  the  epithelinm 
which  covers  the  stem  and  represents  its  ectoderm,  but 
commence  in  the  ordinary  way,  as  csBcal  diverticula  of  the 
wall  of  the  stem,  the  apices  of  which  soon  open  to  form 
the  hydranth  of  a  medusoid,  the  disk  of  which  results  from 
the  outgrowth  of  the  base  of  the  hydranth.  In  all  pro- 
bability the  larva  of  the  Cwnina  enters  the  gastric  cavity  of 
the  Chryonia  as  a  planula;  and,  attaching  itself  to  the 
wall,  grows  out  into  a  stolon  whence  the  medusoids  bud. 

It  may  be  suspected  that  the  other  cases  of  supposed 
entogastric  proliferation  will  prove  to  be  susceptible  of  a 
similar  explanation. 

Although,  as  I  have  endeavoured  to  show,  the  Ctenophora 
are  readily  reducible  to  the  general  plan  of  the  Actinozoa, 
yet  considering  their  many  peculiar  characters,  I  think  it 
is  advisable  to  separate  them  from  the  Coralligena,  as  a 
distinct  natural  order. 

Moreover,  the  Physemaria  must  undoubtedly  be  placed  in 
this  section,  which  will  therefore  consist  of  the  following 
natural  orders :  Physemaria,  Porifera,  Hydrozoa,  Coralligena, 
Ctenophora, 

Section  III. — I  concur  in  the  proposal  of  Biitschli*  to 
establish  a  group,  Nematorhyncha,  for  the  genera  ChoetO' 
notus,  Echinoderes,  and  their  allies,  to  which  reference  is 
made  at  p.  192.  The  Nematorhyncha  are  divisible  into  the 
Gastrotrichaf  (Chcetonotua,  Chastura,  Cephalidiwn,  lehthy^ 
dium,  Turbanella,  Hemidasys  and  Dasyditee),  which  are 
ciliated  on  the  ventral  surface  of  the  body,  and  the  Atricha 
(Echinoderes),  which  possess  no  cilia.    Biitschli  finds  two 

♦  "  Untersuchungen  fiber  frei-  f  See  H.  Lndwig,  "  Ueber  die 

lebende  Nematodeu  and  die  Gat-  Ordnung  GaBtrotricha.'    (*  Zeit- 

tung   ChattoHOhur    CZeitBchrift  tchrift  mr  Wise.  Zoologie,' 1876.) 
fur  WiM.  Zoologie/  1876.), 


(W6       TUB   ANATOJffT  or   rNVKBTKBBATBD 

cDnvoli)t«cl  wat«r -vessels  aiiologous  to  thoee  of  tbo  £ol^«nt, 
bat  apparently  not  ciliated,  in  ChjeUmola*. 

Sectiok  LV. — Our  fenowledge  of  the  development  of  tW 
^t'rurfimia  has  received  an  impartimt  addition  in  Uw 
'  M^moire  sur  le  dereloppemcnt  embryogenique  dee  HinuU- 
sees,'  bj  M.  C.  Robia ;  irho,  amoiig  other  importiuii  ooB- 
tributiona  to  embryology,  bas  rectified  some  iinport«Bt 
errors  of  Rathke  reapocting  the  early  sta^^  of  the  devnlup- 
mcot  of  Chpgine.  1  hare  found  the  di^HoriptJoii  and  6i^ne* 
of  thii  various  stages  of  clcar^e.  and  of  the  >tepe  by  which 
the  blastoderm  ia  cuaTert«d  into  tlie  yoong  CUtptine,  given 
in  tbia  memoir,  to  be  exceeding'ly  acctimtc 

The  whole  process  in  Clepsine  ts  v«iy  eimilio'  to  thai 
whieh  hae  been  desdribed  in  Baaaei  by  Kowalewsky*  md 
sliarea  witb  it  the  remarkable  peculiarity  that  the  fini 
formed  portion  of  tfae  blajstodcrro  becumea  the  hnoial 
region  of  the  body.  Aa  tbta  blastodermic  disk  graws.  ib 
miLTgins  thiekeu  and  give  riee  to  tno  genn-hands  (Emb- 
streifen).  Thcee  gradually  approximate  and  eventually 
unit«  upon  the  opposite  face  of  the  ovom.     As  the  dwn 

of    m..n«lia    ia    thi-    n«i^,.^iL    nf   tbp    ^iff-wnHntinn    nl    tlM-> 


CKSTODBBMA,  KEOMSITIA  AND  CHITOK. 


667 


Manj  years  ago  *  I  directed  attention  to  the  fact  that 
"  the  development  of  a  Mollusk  commences  on  the  hsemal 
side  and  spreads  round  to  the  neural  side,  thus  reversing 
the  process  in  Articulata  and  Yertebrata ;"  and  it  is  very 
interesting,  considering  the  many  curious  points  of  ap- 
proximation between  the  Annelida  and  the  MoUusea  which 
are  now  coming  to  light,  to  observe  that  certain  Annelids 
present  this  especially  MoUuscan  peculiarity .f  As  Yon 
Baer  long  ago  pointed  out,  there  is  a  striking  likeness 
between  the  foot  of  a  Grasteropod  and  the  suctorial  disk  of 
one  of  the  Hirudinea,  The  so-called  jaws  of  the  Leeches 
(the '  teeth '  of  which,  I  may  observe  in  passing,  are  calcified) 
are  curiously  similar  to  an  odontophore  devoid  of  cartilages, 
the  representative  of  the  radola  being  supported  on  a 
muscular  cushion. 

The  statement  at  p.  245,  that  "  no  calcareous  skeleton  is 
found  in  any  of  the  Oephyrea  "  ceases  to  be  true  since  the 
discovery  of  L.  Graff,  J  that  the  minute  spines  of  Chcsto- 
derma  are  calcified.  It  is  a  further  peculiarity  of  this 
genus,  that  two  distinct  nerve  cords  proceed  from  the 
cerebral  ganglia,  parallel  with  one  another,  on  each  side  of 
the  body,  in  the  place  of  the  single  median  nerve  cord  of 
other  members  of  the  group. 

Dr.  Jhering  §  has  directed  attention  to  certain  points  of 


may  remark  that  the  evidence 
upon  which  the  identification  of 
the  stmctures  termed  **  Kiemen- 
gangwOlflte  *'  and  their  products 
with  the  branchial  apparatus  of 
vertebrate  animals  is  founded, 
appears  to  me  to  be  wholly  in- 
adequate to  bear  out  the  con- 
clusions deduced  from  it. 

^  '  On  the  Morphology  of  the 
Cephaious  MoUusca.'  (*  Phil. 
Trans.,'  1852,  p.  45  and  note.) 

t  The  mode  of  development  of 
the  central  nervous  svstem  in 
Ewxxe*  and  Clepsine  often  many 
points  of  interest  Not  the  least 
important  of  them  is  the  obvious 
similarity    (to   which  atteniion 


has  already  been  directed  by 
Semper)  between  the  germ 
bands  of  Clepnine  when  tiiey  have 
united  throughout  the  greater 
part  of  their  length,  but  surround 
the  blastopore  behind,  and  the 
Amphibian  embryo  with  its 
dorsal  ridges,  which  have  exactly 
similar  relations  (See  for  example 
Fig.  40,  in  Plate  III.  of  Gdtte's 
work  *■  Die  Entwickelungsge- 
schichte  der  Unke.*) 

X  *'Anatomie  des  Chtttodenna 
nkidulum:*  (*  Zeitschrift  f.  Wiss. 
Zoologie,*  1876.) 

§  *  Vergleiohende  Anatomic 
des  Nervensy stems  der  Mollua- 
k«i<  \«ll. 


668       THB  ANATOMT   OV   INTBBTEBRATBD  ASLKA_LS. 

resemblance  bctveen  durtodtinna,  Willi  tlio  allied  gmnt 
Neomenia.  imd  the  ChitouB,  cipeeinily  in  Uiu  nrrangiMnent 
of  the  tronkB  of  the  nervous  8/at«m  j  and  he  pt-->||>o«««  to 
unite  the  three  iDtoagruupof  Jifip^iw^tira — thus  (i<--p.-initiag 
the  Ohitona  from  tho  iSollutaa  oltogi^tlicr. 

Sbctiok  V. — I  regret  that  I  hnve  bpcn  unnble  \<t  main 
use  of  Claas'  recently  publiehod  iDi|iovt>iQt  contributionf 
to  the  history  of  the  develcipint-ut  of  thi-  CrualacBa.* 

Sbgtioh  YI.'-The  thorough eiaminationof  the  atmetan 
of  Pediaillitia  and  Loxoermia  by  Nitechet  has  ehowB  tk^l 
the  differences  between  the  ectopri>ctoiiB  and  the  endopmct- 
oue  Polyma  are  of  a  more  fundamental  character  than  had 
been  suspected.  In  the  Eetoprocla,  in  fact,  the  endoc^st 
coneisls  of  two  layers,  an  out^v  and  an  inner ;  of  which  the 
former  ia  the  representative  of  the  ectoderm  in  other  m 
The  latter  lines  the  wall  of  the  '  perivisceral  cavity,'  «; 
rehccted  thence,  like  a  peritoneal  tonic,  over  the  t 
eht^th  and  into  the  interior  of  the  teotacula.  wheuM  itH 
continued  ou  to  the  oliraeutAry  canal,  of  which  it  fonna  du 
external   investment.      The  endoderm.  which  Uties  the  all- 


THE  BOTOPBOCTA  AND  THB  BNDOPBOCTA. 


669 


Unfortiiiiatelj,  our  knowledge  of  the  embryome  de- 
Telopment  of  the  ectoproctons  Polyzoa  does  not  enable  ns 
to  determine,  with  certainty,  the  natnre  of  this  perivisceral 
cavity  and  of  the  layer  which  bounds  it.  Nitsche  shows 
that  the  saccular  cystid,  which  results  from  the  first  de- 
velopmental changes  of  the  embryo  in  the  FhylactoUBmata, 
is  composed  of  two  layers,  which  correspond  with  those  of 
the  endocyst  in  the  adult ;  and,  further,  that  the  polypide 
(alimentary  canal,  tentacula  and  ganglion)  results  from  an 
ingrowth  of  the  outer  layer  of  the  endocyst,  which  pushes 
before  it  an  involution  of  the  inner  layer.  The  latter  gives 
rise  to  the  reflected  *  peritoneum.' 

But  I  am  not  aware  that  there  is  any  evidence  which 
proves  conclusively  the  manner  in  which  these  two  layers  of 
the  embryonic  endocyst  take  their  origin,  or  with  what 
layers  of  the  ordinary  embryo  they  are  homologous.  If 
we  make  the  ordinary  assumption  that  the  inner  or  peri- 
toneal layer  of  the  endocyst  is  the  partial  or  complete 
homologue  of  the  hypoblast  in  other  animals,  it  foUows 
that  the  perivisceral  cavity  of  the  Ectoproda  is  really  an 
enterocoele,  as  it  is  in  the  Brachiopoda,  The  only  other 
alternative  appears  to  be  the  supposition  that  the  inner  layer 
of  the  endocyst  is  a  mesoblast,  differentiated  from  the  germ 
earlier  than  the  hypoblast ;  in  which  case  the  perivisceral 
cavity  will  be  a  schizocoele. 

Dr.  Jhering*s  work  on  the  nervous  system  of  the  MoUugca, 
to  which  I  have  already  referred,  contains  a  number  of 
valuable  anatomical  details,  and  especially  gives  a  better 
account  of  the  structure  of  the  nervous  system  of  Chiton, 
than  has  hitherto  existed.*^ 


*  In  addition  to  a  great  variety 
of  surprising  phylogenio  specu- 
lations, Dr.  Jhering  puts  forward 
the  novel  morphological  views, 
that  the  respiratory  sac  of  the 
Pulmonata  (Nephropneutta^  Jher- 
ing) is  morphologically  a  sort  of 
urinary  bladder,  and  that  the 
ganglia  whence  the  arm-nerves 
of    Uie    Cephalopoda    arise 


are 


cerebral  and  not  pedal.  The 
arms  are  thus  parts  of  the  head, 
and  only  the  funnel  represents 
the  foot  of  Gasteropoda. 

I  do  not  presume  to  rebel 
against  the  authoritative  censure 
of  my  memoir  on  the  'Mor- 
phology of  the  Mollosea,'  pub- 
lished now  five-and-twenty  yean 
ago,  which  ia  igEnfonraabSM^Xi^^V^* 


^^ r  KK\.  •«  . 


■  ■  1 
1 


I 


li! 


such  an  a.s8eDibl:i«^o,  tormcd  i\n 
t<*ri«t(l  by  the  sc'Ljniontatiou  ci 
cuticiila;  tbo  absence  of  cilia  i 
period  of  life ;  tbo  sc^niontiit 
system  and  its  perforatiou  by  t 
(with  tbc  possible  exception 
t    -  '  wbicb,  almost  always,  are  tbems 

.    !  The  reasons  for  includiog  the 

'  ,     .  have  been  given  in  Chap.  XI. ;  t 

I      j        j     *  must  be  regarded  as  hardly  wit 

i    '  \        I     1  tion,  1  think  that,  taking  into 

i      j  j  cations  which  are  undergone  bj 

Artxchnida,  it  is  not  needful  t 
I    }  i  f  practice  of  associating  them  wi 

The  Lamellihranchiata  and 

I  ;  another  very  well  marked   di 

t ' ,  characters  of  which  have  been 

I         I ;        ^  M  The  proposal  to  separate  tl 

J  I  •-  Mollusca,  to  which  I  have  aire 

I  :  V  to  be  devoid  of  any  justificatios 

certain  Ocphyrea,  such  as  Cha 
the  Polyplaeoj)Jiora,  are  accom 


:     !  ,i  .1 

;  li    . 

I  ; 

^ 


1  ' 


I  > 

i 


THS  HiaHSB  aBOUPS.  671 

and  even  if  these  resemblances  are  to  be  r^^arded  as  evidences 
of  affinity,  some  considerations,  such  as  the  restriction 
of  the  branchis  to  the  hinder  part  of  the  body,  and  the 
reduction  of  the  foot  in  ChiionelliiB,  rather  l^id  to  the 
suggestion,  that  Ouetoderma  and  Neomenia  may  be  ex- 
tremely modified  MoUusks,  allied  to  the  Polyphicophora. 

As  to  the  supposition  that  the  resemblances  between  the 
Nvdibranckiaia  and  the  TwrheUaria  indicate  a  direct  affinity 
between  these  groups,  it  seems  to  be  forgotten  that  the 
Nudibranchiata  are  all,  when  young,  unmistakeable  Guste- 
ropods  provided  with  mantle  and  shelL  Their  adult  struc- 
ture is  as  little  evidence  of  any  Turbellarian  affinities  as 
that  of  Lemcsa  is  proof  of  its  being  allied  to  the  worms, 
rather  than  to  the  Crustacea, 

The  Physemaria,  the  Porifera,  the  Hydrozoa,  the  CoraL 
Ugena  and  the  Ctenophora  are  obviously  modifications  of  the 
same  fundamental  plan.  I  think  it  is  convenient  to  retain 
the  well-established  name  of  Ccdenterata  for  the  last  three 
orders,  which  are  much  more  closely  related  to  one  another 
than  to  the  other  two.  Haeckel*s  proposal  to  apply 
the  old  name  of  Zoophyta  to  the  whole  division  appears 
to  me  to  be  well  worthy  of  adoption.  The  inconvenience 
of  using  a  term  the  connotations  of  which  have  varied 
somewhat  widely  since  it  was  first  invented,  is  probably 
less  than  that  which  would  attend  the  invention  of  a  new 
name. 

The  Monera,  Foraminifera,  Heliozaa,  Badiolaria,  Proto- 
plagta,  Qregarinida,  CataUada  and  Infiuoria,  (OpaUninat 
CUiaia,  Tentactdifera,  Flagellata),  again,  are  so  closely  united 
together  that  the  difficulty  is  to  distinguish  the  less  diffe- 
rentiated forms  of  each  from  one  another.  They  consti- 
tute the  division  of  the  Pbotozoa,  the  common  characters 
of  which  have  been  given  in  Chapter  11. 

If  there  were  no  invertebrated  animals  beside  those  in- 
cluded under  these  four  divisions  of  Abthbopoda,  Mol- 
LUSCA,  Zoophyta,  and  Pbotozoa,  the  task  of  claasificatioii 
would  be  very   easy,  and  each  of  the  higher  dSviiiiniM 


672       THB  ANATOMY  OF 

would  lie  ahfu-ply  defineii  from  the  othera.    But  a  raM*' 
mBiduum  remaiuB  to   be  countered:  luul  it  in  witb  Um 
att«mpt  to  arranife  these  ivaidiuU  urlI(^rB  into  bigbrr  ^>^ulM 
that  tbe  difficiiltieB  of  the  TaxonomUt  comuiMi«u. 

The  Polychala  and  the  Olu/neliiEta.  tlie  llimdinta  and  the 
Qephyrea,  rcflemble  one  another  gienerall;  in  the  Begmenta- 
tion  o!  the  body,  indicated  sit  temat  by  the  amoJly  mnlri- 
gtrngliiite  nervous  centres;*  in  the  presenile  of  cilia  luid  of 
Begmental  organa ;  and  in  the  nature  of  the  larrv  which 
are  set  free,  when  their  emhryoB  are  batched  in  an  early 
Btago  ot  development.  Aud  although  no  one  of  these  chu- 
ractere  is  of  universal  occurrenee  (cilia,  for  example.  lieiDj: 
absent  in  most  adult  mruditiea)^  yet  they  are  foand  in 
Buch  nEBociation,  that  the  accepted  ammgemcnt  of  thmi> 
four  groups  (to  tvhich,  though  not  without  some  faesitatioli. 
I  add  the  Myeoitomata).  into  the  division  of  the  Aunbioiia, 
is  undoubtedly  very  convenient. 

The  Tretnaloda,  the  Twbellaria,  and  the  Bot^ra,  tana 
another  very  natural  asicmbliige.  But  it  mn«t  be  admiUed 
that  the  highest  forma  of  this  division  are  seiianitcil  bjae 
very  sharp  line  of  demarcation  from  the  Annelida ;  wliileUw 
■im|ileat  TurbeHaria  are  almoat  on  a  level  with  ti 


THE  HIGHER  GSOUPS.  673 

form  between  the  TurheUaria  and  the  Polychcsta ;  while  the 
Botifera,  in  many  respects,  represent  larval  forms  of  the 
Polychceta  and  of  the  Oephyrea, 

The  Cestoidea  are  usually  regarded  as  anenterous  Trema- 
toda,  in  which  case,  of  course,  they  must  be  associated  with 
the  latter. 

I  propose  to  establish  a  division  of  Tbichoscolices 
for  the  natural  orders  now  enumerated,  in  order  to  dis- 
criminate the  morphological  type  which  they  exemplify 
from  that  of  the  Nematoscolices,  containing  the  Nema* 
toidea,  which  are  as  remarkable  for  the  univei'sal  absence 
of  cilia  as  the  former  are  for  their  presence ;  and  which  are 
further  so  cleai'ly  distinguished  by  the  arrangement  of  their 
nervous  and  muscular  systems  and  of  their  water- vessels ; 
and  by  their  ecdysis. 

The  connexion  between  the  two  divisions  by  way  of  the 
Nematorhyncha  and  the  Botifera  is  undoubtedly  very  in- 
timate, and  there  is  almost  as  much  reason  to  an*ange  the 
Nemaiorhyn^sha  with  the  Trichoscolices,  as  with  the  NemO' 
to8colic€8.  On  the  whole,  however,  I  think  that,  notwith- 
standing the  cilia  of  the  Oastrotricha,  the  closest  afi^ties 
of  the  Nematoi'hyncha  are  with  the  NerruUoidea,  and  I  there- 
fore place  them  among  the  Nematoscolices. 

But  I  may  remark,  once  for  all,  that  the  attempt  to 
establish  sharply  defined  large  divisions  of  the  animal 
kingdom  is  futile.  The  progress  of  knowledge  every  day 
rendei*s  it  more  and  more  clear,  that  morphological 
groups  are  comparable  to  distributional  provinces;  each, 
however  well  marked  may  be  its  characteristic  features, 
shades  off  at  its  margins  into  some  other  group ;  and  the 
object  of  classification  is  simply  to  bring  into  prominence 
the  morphological  types  which  embody  these  characteristic 
features. 

It  appears  to  me  impossible  to  compare  the  structure 
and  the  larval  conditions  of  a  Polyzoon  with  those  of  a 
Brachiopod,  without  arriving  at  the  conclusion  that  they 
are  more  closely  allied  with  one  another  thaxi.tii«3^Btfe^'«>i^ia^ 


674       THE  AHATOICY  OF  INYBBTBBBATED  ANIMALS. 

any  third  gronp.  Nereiihelefls,  the  Polytoa  approach  the 
Botifera,  and  the  Brachiqpadaj  the  Annelida,  on  the  one 
side;  while,  on  the  other,  thej  present  nnmistakeable 
affinities  with  the  lower  MoUtuea,  At  the  same  time,  the 
weight  of  the  resemblances  between  the  Fclytoa  and  the 
Tunicaia,  which  led  Milne-Edwards  to  the  establishment 
of  the  gronp  of  "  MoUusco'ides  "  (adopted  by  myself  under 
the  title  of  MoUuscoida)  has  been  much  lessened  by  the 
progress  of  investigation. 

I  conceive  that  we  may  best  keep  these  resemblances  and 
differences  in  view  by  associating  the  Polyzoa  and  the 
Brachiopoda  into  a  division  apart,  for  which  I  propose  the 
name  of  Malacoscolices  ;  in  order  to  indicate  its  rela- 
tions with  the  Worms  on  the  one  side,  and  with  the  Mollusea 
on  the  other. 

The  Tunicata  are  absolutely  distinguished  from  all  other 
invei'tebrated  animals  except  Balanoglosstu,  by  the  per- 
foration of  the  pharynx  and  its  conversion  into  a  respira- 
tory organ.* 

At  first  sight  there  appears  to  be  little  ground  for  the 
approximation  of  groups  apparently  so  widely  different  as 
the  Tunicata  and  the  Enteropneusta.  But  the  extraordinary 
similarity  in  the  structure  of  the  perforated  pharyngeal 
sac  in  the  larvee  of  Tunicates  and  of  BalanoglossuSf  is  a  fact 
of  great  morphological  weight.  An  ecaudate  Appendicu- 
laria  of  those  species  which  have  the  alimentary  canal 
nearly  straight,  would  be  marvellously  like  a  larval  BalanO' 
glosstu,  which  is  again  little  more  than  a  specially  modified 
Turbellarian.  I  think,  therefore,  that  the  Tunicaia  and 
the  Enteropneusta  may  proi)erly  constitute  a  division  of 
Phabtngopne  usta. 

The  Tunicate  PharyngopneuHa,  with  their  caudate  larvss 
may  be  supposed  to  stand  in  the  same  relation  to  the 

*  I  have  alluded  above  to  the  lead  ne  to   conclude    that   the 

structures  degcribed  by  Semper  structures  in  question  are  homo- 

in  some  Oligochaeta  and  in  Sabeila.  logons  with   either   Vertebrate, 

I  do  not  d«tuA)t  xYi«  ac^xunjc^  «»<(  Enteropneustal     or       Tunicate 

the  description  \  but  \\.  ^<>«»  imi\  XsnEM^ciMt, 


THE  AKEKTEBOUS  INYEBTEBBATA.        675 

Turbellariform  Pharyngopneusta,  as  the   Trematoda,  with 
their  oercarif  orm  larvs,  to  the  TtMrbeUaria, 

Another  very  well  marked  diyision  is  that  of  the  Echino- 
DEBMATA,  the  characteristics  and  relations  of  which  have 
been  folly  discussed  in  Chapter  IX. 

Although  the  structure  and  development  of  Sagitta  have 
now  been  as  thoroughly  elucidated  as  those  of  any  animal, 
the  proper  Taxonomic  place  of  the  Choetognatha  is  still  an 
unsolved  problem.  The  issues,  however,  appear  to  be 
narrowed  to  these :  either  they  belong  to  the  Annelida^  or  to 
the  Nematoscolices,  or  to  the  Trichoseoliees ;  or  the  Chceto- 
gnatha  are  to  be  regarded  as  an  independent  division,  allied 
to  all  these,  and  perhaps  to  the  lower  Arthropoda,  I  am 
disposed  to  adopt  the  last  view,  chiefly  on  the  ground  of 
the  mode  of  development  of  Sagitta,  which  is  unlike  any- 
thing at  present  known  to  occur  in  Annelida,  Trichoseoliees, 
Kematoseolices,  or  Arthropoda, 

The  Aeanihoeephala  are  hardly  less  anomalous  than  the 
Chceiognatha,  Taking  into  account  the  Oordiacea  and  the 
characters  of  the  proboscis  in  the  Nematorhyneha,  there  is 
undoubtedly  room  for  the  suggpestion  that  they  are  specially 
modified  anenterous  NemtUoseolices,  and  should  be  classed 
among  the  latter.  But  here,  as  in  the  case  of  the  Cestoidea, 
there  are  many  difficulties  in  the  way  of  accounting  for 
these  anenterous  forms  by  the  supposition  that  they  are 
the  results  of  a  retrogressive  metamorphosis  of  enterate 
animals. 

This  question  of  the  true  relations  of  the  anenterous 
invertebrates — ^by  which  I  mean  not  only  those  which,  like 
the  male  Rotifers,  have  no  functional  alimentary  canal  in 
the  adult  condition ;  but  those  which,  like  the  Cestoidea  and 
the  AcarUhoeephala,  never  exhibit  a  trace  of  an  alimentary 
canal,  even  in  the  embryo ;  which  is  usually  dealt  with  so 
summarily  by  the  assumption  of  retrogressive  metamor* 
phosis,  acquires  still  more  importance,  when  we  attem'Qt 
to  determine  the  Taxonomic  place  oi  \]b&  Dic^wwto» 


67(1       THE  ANATOMY  Olf   IKVEKTKBHATGD  ANIMALS. 

Pi-ofeaaor  E.  van  Beiieden  haa  proved  that  theec  panislUe 
cajinot  be  disniiBeed,  santfa^on,  as  rctrogreMJvel;  metajnor- 
pboEcd  '  worma ;'  and  ihougli  I  aiii  not  disposed  t«  attei^ 
iQucb  weiglit  to  the  ubeence  of  a  meH>dcrm,  on  wUieli  Tu 
Beoeden  maiBte  a«  a  distinctiolilwtw^en  tbo  Dicf/mtida  uid 
the  Metaxoa,  the  majULer  in  which  tliv  cuntenU  uf  the 
aiia]  cell  give  rise  to  genua  ia  so  completely  tuUiko  Bay- 
thing  which  ia  known  to  obtain  in  the  Melatoa,  aa,  to  mj 
mind,  to  justify  the  aeparation  of  the  IHeyemida  trata  the 
whole  of  tbia  division.  On  the  other  band,  the  similarity  td 
their  development  to  the  ftirmation  of  oaetosoic  embryua  hf 
epiboly,  aa  completely  divides  the  Di^e^nida  from  all  the 
Protozoa,  It  niuat  be  recollected  that  the  chiLDgea  which 
are  undergone  by  the  cili&t«d  emWyoe  aie  etiU  to  be  dis> 
covered;  but.  provisionally,  I  um  disposed  Ui  agree  tviib 
Van  Beneden,  that  the  Dieyrmido  should  be  regarded  M 
the  repreaentatives  ot  n  diHtinct  division,  th«  UssoxtU, 
intermediate  between  the  PTototoa  uid  the  Metatat.  Ami 
without  distinctly  pledging  myself  to  way  auch  view,  I  jk 
thinli  it  ia  worth  while  to  throw  out  the  suggeatiou  tluU 
the  Ceatoidfa,  if  not  the  Acanlhoevplutla,  may  be  modiSa- 


tm  MlOAL  ttlliAf  X6tf6  61"  iirtrifittfiAA^^.       6?7 


lin^,  none  of  wtdoli,  aa  f ar  as  ottf  pifdftent  knowledge 
enabled  us  to  jtidge,  can  be  traced,  withont  intermption, 
thronghOnt  the  whole  length  of  the  eetdei 

If  we  asenme,  in  the  absence  of  proof  to  the  contrary, 
that  the  Monera  have  the  simplicity  of  stmctnre  ascribed 
to  them  by  Haeckel ;  then^  on  comparing  the  BndoplatHca 
with  the  Monera,  the  different  gronps  of  the  former  appear 
to  be  related  to  those  of  the  latter  diyision,  as  if  thej  were 
similar  forms  complicated  by  the  addition  of  one  or  many 
nnclei.  Proiogenes  may  thns  be  considered  as  the  root  of 
the  Foraminiferal  series,  Pratama^a  of  the  Protoplasia, 
MytMghrum  of  the  Chregarinidct,  VampyreUa  of  the  Heliotoa, 
Prak/monaa  of  the  FiagelMa,  A  Moneran,  cUiated  over  liM 
whole  sorfaoe,  which  might  stand  in  the  same  relation  to 
the  OpaUrnna,  CcUaUcicta,  TentaoiUifera,  and  Ciliata,  is  at 
present  unknown.  The  Proiozoa  thus  fall  into  the  following 


series : — 


PnOTOZOA. 


I.  n. 

^  Prctog9M9,  Prokmaha, 

I  I 

FoTomiin^ferfu  Protoplcuta. 


III.  IV. 

MyxasirtMn.     VampyreUa, 

GregarimdcB,     HeUozoa, 

Badiolaria. 


V. 
7 

I 


? 


vn. 

Protomonas. 


TfffUaculifera,        Caia^ 


Uaeta,        PlagetuUa. 


Opalmvna, 
Ciliata. 


1  am  nnable  to  trace  any  one  of  these  series  of  modifies^ 
tions  further ;  that  is  to  say,  to  find  forms  which  actually 
bridge  over  the  interval  between  any  one  of  them  and  the 
Metazoa,  though  it  is  easy  enough  to  imagine  what  such 
forms  might  be.  The  spheroidal  free-swimming  ih.<^i&s^ 
aggregates,  such  as  Uvella  and  Polijionnva^  «aA  lAn^tMr^^xenw 


678       THE  ANATOMT  OT  IBTEl 

itself,  ore.  in  many  reepecta.  comparable  to  Phjaenuuian  or 
Poriforan  embryos ;  while  an  animal  Volvor.  wonld  be  »  aort 
ot  permanent  vesicular  mornliL  So,  one  of  the  hif^her 
In/iitoria,  if  it  became  multiniicWt«,  Uko  an  Opaliaa. 
would  approach  the  lowest  TttrbaUaria, 

The  axial  cell  of  a  Dw^«na.  from  tbo  protoplwiin  of 
-which  its  ciliated  and  noa-oiliat«d  genua  tire  produced,  i*. 
to  a  certain  extent,  comparable  to  the  capnnlu  of  a  BAdii»> 
larian ;  while,  on  the  other  hand,  n  Radiolarian  with  a 
multinucleate  cortical  layer  would  approach  the  etructmv 
of  Dieyema,  And  if  what  is  at  present  known  of  i)(«y«mit 
girea  a  just  couoeption  of  the  essentia!  points  tA  its  eatiTv 
hiBtory,  it  nndoubtedly,  as  E.  Tan  Beueden  has  sngge8t«iil. 
repi-escnts  a  type  intermediate  between  the  Proiotoa  aad 
the  Mdatoa.  though  it  can  hardly  be  said  to  fill  np  tiM  ( 
hialvi  between  them. 


ill  ip  th«_tj 

f  animA^B^I 


In  our  further  search  after  the  aei-ial  rolatiot 
we  must  therefore  start  nfresb  from  the  lowest  MetoMiM. 
Here  a  ZooPHTrro  Sekies  is  very  W'lU  marked;  com- 
menoing  with  the  Phy»nmtria.  and  thence  diverging,  on 
the  one  hand,  to  the  Porifera.  and,  on  the  other,  to  Uw 


9HB  BBBIAL  BBI.ATI0N8  OF  IKYEBTSBRATA.         679 

The  Nemaiorhyneha,  wHetHer  they  are  really  trandtional 
forms  between  the  Nemataidea  and  the  Arthropoda  or  not, 
at  any  rate,  indicate  the  road  by  which  the  tranfiition  may 
be  effected;  and  I  am  mnch  inclined  to  think  that  the 
ChcBtagncUha  may  occupy  a  place  in  this  seriee.  The  oral 
armature  of  Sagitta  may  be  regarded  as  a  modification  of 
the  oral  spines  of  Eehinoderes,  and  its  nervons  system  is 
as  mnch  .Ajrthropodal  as  is  that  of  the  PetUoHomida.  This 
may  be  called  the  Asthsozoic  Sekibs. 

A  fourth  series  is  that  which  I  shall  term  the  Mala- 
cozoio  Sebiss.  It  includes  the  Mdlaeogeoliees  and  the 
Molltuea,  The  entoproctous  Polyzoa  form  the  lowest  term 
of  this  series.  The  resemblances  of  the  Polyzoa  with  the 
Motifera  (e.  g.  with  St^hanoceros)  have  often  been  remarked, 
and,  indeed,  insisted  upon,  with  too  little  regard  to  the  differ- 
ences which  are  established  by  the  water-vessels  and  the 
peculiar  pharyngeal  armature  of  the  Rotifers.  Neverthe- 
less, these  resemblances  are  important  as  far  as  they  go, 
and  in  grade  of  organisation  the  two  groups  are  much 
upon  the  same  level.  On  the  other  hand,  the  comparison 
of  a  Polyzoon  with  a  larval  Lamellibranch  or  Gkuteropod,  or 
with  a  Pteropod,  leaves  no  doubt  in  my  mind  that  the 
Malacoscolices  have  the  same  relation  to  the  MoUusea,  as  the 
Triehoscoliees  to  the  Annelida. 

A  fifth  gradation  is  presented  by  the  TSmioata  and  the 
EfUeropneusta,  which  constitute  the  Phabtnoopnbu8TAI« 
Sebies.  I  do  not  regard  the  Enieropnetuia  as  of  distinctly 
lower  organisation  than  the  Tunieata,  but  rather  as  a 
collateral  group ;  and  I  conceive  it  to  be  probable  that  some 
lower  forms,  connecting  the  BinteropneuHa  and  the  Tunieata 
with  one  another  and  with  the  TrickoacoliceM,  will  yet  be 
found.  However  this  may  be,  Appendieularia  presents  a 
grade  of  organisation  but  little  higher  than  that  of  the 
Polyzoa. 

A  sixth  gradation  is  representedb^  V^afc'¥jCHX»^TS«wa>3*. 


t   ISTERTKBEATID   KVXXXIS.  1 

Sksies.  Liko  th«  fore^ing,  this  aeri««  at  preooat  etamda 
icolated.'no  uiDectent  forma  between  the  Eckinodorma  Bti4 
liigher  or  lower  ^Tcrnpn  1>eiiig  known.  On  the  ground  ot 
tlie  vntEormity  of  chaTiuTt«r  of  the  knw  of  tbe  £oluiu>- 
dermH.  honercr,  there  cut  be  little  doabt  llwt,  if  «ver  mch 
larniH  are  diacovercJ,  tbey  will  proTc  to  be  tUiod  to  the 
Qrphgrra,  the  TriehtiKoliwt  and  tbe  Bnterojiaaiuta. 

Thna  the  ntadj  of  the  frroduticinB  of  atractnre  Bmong  the 
Mi^tatoa  leade  to  the  conctnBiou  that  they  full  into  ax 
seriea,  which   may  be  anunged  in   the  tuUowing  tabular 

S&RtES. 


I. 


n. 


in. 


ZOOPHYTIC.          ECHINODEKMAL. 

Ccelentfral.!.         Echtnodennata.     E-it 
Parifn-a. 

pHABYSOOPSBUaTAt. 

IV. 
Malaoozoic, 

T. 

Asirntorv. 

TI.                   -. 
Arthiiosok:.          ^ 
Artliropoda.             i 

i 


THE  BBSULTS  OF  EMBBYOLOaT.  681 

form ;  and  that  common  form,  when  the  special  characters 
of  each  group  are  eliminated,  and  the  alimentary  canal  is 
reduced  to  its  primitive  aproctous  condition,  would  be 
exceedingly  similar  to  a  Physemarian. 

Hence  the  consideration  of  the  gradations  of  structure 
which  are  presented  by  the  various  series  of  Invertebrated 
animals,  irresistibly  leads  to  the  conclusion  that  the  whole 
of  the  Metazoa  may  be  conceived  as  diverse  modifications 
of  a  common  fundamental  plan. 

The  Sebial  Relations  of  the  Inyebtebbata  com- 
PABED  with  the  besults  OP  Embbyoloqy. — The  concep- 
tion of  the  unity  of  organisation  of  the  Invertebrata  thus 
reached,  so  far  as  it  is  based  upon  the  comparison  of  adult 
structures,  is  purely  ideal ;  and  the  study  of  the  development 
of  individual  animals  is  alone  competent  to  decide  the 
question  whether  this  ideal  unity  has  a  foundation  in  ob- 
jective fact.  But  the  history  of  the  development  of  animak 
appertaining  to  every  group  of  the  Invertebrata  which  has 
been  given,  bears  out  tiie  statement  which  is  made  in  the 
Introduction  that  the  ideal  unity  has  such  a  foundation 
in  fact ;  inasmuch  as  all  these  animals  commence  their 
existence  under  the  same  form ;  that  namely  of  a  simple 
protoplasmic  body,  the  ovum  or  germ. 

In  the  Introduction  I  have  said  that  "  among  the  lowest 
forms  of  animal  life,  the  protoplasmic  mass  which  represents 
the  morphological  unit  may  be,  as  in  the  lowest  plants, 
devoid  of  a  nucleus  "  (p.  12).  However,  as  I  have  remarked 
at  the  commencement  of  this  chapter,  until  the  seai*ch  for 
the  nucleus  has  been  instituted  afresh,  with  the  help  of 
such  methods  as  have  recently  proved  its  existence  in  the 
Foraminifera,  1  think  it  will  be  wise  to  entertain  a  doubt 
whether  any  of  the  Monera  are  really  devoid  of  this  amount 
of  structural  differentiation ;  and  the  tendency  of  recent  in- 
vestigations appears  to  render  it  very  questionable  whether 
the  nucleus  of  the  ovum  ever  really  disappears,  whatever 
may  be  the  modifications  undergone  by  the  germinal  vesicle 
and  its  contents.    I  shall,  therefore,  assume  provisioiiaUyy 


I 


of  the  euihryo  iroiu  mv  y,.. 

ovum,  in  iill  thn  Mrf.ivni.  i«  ita  di 

forui  -if  division  rortults  iu  the  fon 

diHcoidal  muss  of  eiiual.  or  Biib-oqii 

blastomerca.      Next,  tlie  nwruln. 

acquires  a  central  cavity,  the  hi 

hollow  vesicle,  the  blaatotphere,  tht 

of  a  ainfflc  layer  of  bloatonierce,  is 

I  '  The  bhistomercH  of  the  hUetod 

'  entiatiun  into  two  kinds,   diating 

activities,  if  not  by  their  outward 

>  set  constitute  the  cpiblatt.  the  O 

further  changes  of  the  cmliryo  ar 

tendencies  towards  further  rood 

I  epiblastic  uud  hypoblastic  blastoi 

;  '  of  these  is,  as  it  were,  a  ffcrm, 

I  ,       '  tho  adnlt  organism  will  be  evolTc 

1  i  Every  series  of  the  Invertebrata 

''(  of  examples  of  the  further  iiiodif 

\  by   the   process   of   iHvaifituition: 

■^  J  which  is  that  the  hypoblast  be 

) '  pletely  enclosed  within  the  epit 

;  j  accompanied  by  the  diminution 

' '  blastoccele,  and  the  formation  o 


THB  BBSXJLT8  OF  BMBBTOLOOT.  683 

It  very  oommonly  happens  that  the  process  of  deyelopment 
is  modified  by  an  inequality  in  the  size  of  the  blastomeres ; 
which  inequality  may  be  manifest  from  the  bisection  of 
the  OYum,  or  may  appear  later.  In  this  case,  it  usually 
happens  that  the  smaller  and  more  rapidly  dividing  blasto- 
meres belong  to  the  epiblast,  and  the  larger  and  more  slowly 
dividing  to  the  hypoblast.  Moreover,  no  blastoccele  may 
arise,  and  the  process  of  inclusion  of  the  hypoblast  within 
the  epiblast  may  have  the  appearance  of  the  growth  of  the 
latter  over  the  former,  or  what  is  termed  epiholy;  while 
the  archenteron  may  not  be  formed  within  the  hypoblast 
till  very  late. 

When,  in  cases  of  epiboly,  the  blastoderm  is  small  in 
relation  to  the  vitellus,  the  epiblast  and  hypoblast,  at  their 
first  appearance,  necessarily  adapt  themselves  to  the  surface 
of  the  yelk ;  and  thus  the  gastrula,  instead  of  having  the  form 
of  a  deep  cup,  becomes  more  or  less  flattened  and  discoidaL 
I  am  inclined  to  believe  that  all  the  various  processes  by 
which  the  gastrula  or  its  equivalent  are  produced,  are  re- 
ducible to  epiboly  and  emboly.  Even  when  the  epiblast 
and  the  hypoblast  appear  to  be  formed  by  delaminationt 
or  the  splitting  into  two  layers  of  cells  of  a  primitively 
single-layered  blastoderm,  there  seems  little  doubt  that 
what  happens  is,  either  the  very  early  inclusion  of  the 
hypobiastic  blastomeres  within  those  which  give  rise  to 
the  epiblast ;  or  a  very  late  and  inconspicuous  ingrowth,  or 
invagination,  of  the  hypobiastic  region  of  the  blastoderm. 

If  we  employ  the  term  gastrula  in  the  broad  sense 
defined  above,  it  may  be  truly  said  that  every  metazoon 
passes  through  the  gastrula  stage  in  the  course  of  its 
development.  The  question  whether  the  mode  of  develop- 
ment of  the  gastrula  by  emboly  is  primitive,  and  that  by 
epiboly  secondary;  or  whether  epiboly  is  primary  and 
emboly  secondary;  or  whether  the  two  processes  have 
originated  independently,  is  of  secondary  importance,  and 
belongs  to  the  debateable  ground  of  phylogeny.* 

*  Compare  Haerkel,  **Studien  zur  Gastrsea-theorie,"  in  hit  *Biolo- 
gische  Studien,'  1877. 


GS4       THE  ANATOMY  OF  INVBBTEBBATBD  ANIMALS. 

The  meauing  of  the  differeutiatioii  of  the  agg;regate  of 
cjtodes,  of  which  the  bod;  of  a  siaiple  metazoon  ia  com- 
poaed,  into  a  hypoblostic,  or  endodermal,  and  an  epi- 
blastic,  or  ectodermal  group  ia  to  be  sought  in  the 
pUyBiological  division  of  labour,  which  is  the  primarj 
source  of  morphological  changes.  It  is  a  separation  of  the 
aggregate  of  morphological  units  into  one  set  with  a 
specially  nutritive,  and  another  set,  with  a  specially  motor 
and  protective,  fnnction.  It  is  quite  possible  to  conceive 
of  an  adult  metazoon  having  the  structure  of  &  sponge 
embryo ;  moving  by  its  ectodermal  hemisphere,  and  feeding 
by  its  endodermal  hemisphere. 

The  next  advance  in  orgaaisatioii  of  such  a  metazoon 
would  doubtless  consist  in  the  more  complete  extension  of 
the  protective  layer  over  the  nntritive  layer,  with  due  pro- 
viEion  for  the  access  of  the  eurroimdiDg  medinm  to  the 
latter.  It  ia  obvious  that  this  advance  might  he  effected 
in  either  of  two  ways ;  the  one  by  emboly,  the  other  by 
L'lAljoly.  In  the  former,  the  lilastopore  w(mld  be  left  aa 
the  npiertttre  of  commiuiication  of  the  endoderm  with  the 
exterior;  and  the  result  would  be  the  formation  of  an 
iircIui:iiel<jiiiiiloiiegasiTaia,.»\n:h  aatbat  which  is  suppoaed  by 


r*-r 


THX  BBSXTLTS  OF  XMBBTOLOGT.  685 

ition  of  the  epiblaet  and  the  hypoblast,  or  it  may 
id  constitute  the  peri-enienm,  or  primitiye  peri- 
iTity. 

Miimalfl  which,  in  their  adult  condition,  most 
•resent  simple  gastmlsd  with  obliterated  blastocoele, 
^y§emaria  and  Hydra ;  cup«shaped  bodies  with  an 
ing  at  one  end,  the  walls  of  which  are  made  up 
an  ectoderm  and  an  endoderm.* 
preat  majority  of  the  Metatoa)  a  further  advance 
cation  is  effected  by  the  appearance,  between  the 
ad  the  hypoblast,  of  cytodes,  either  isolatedly  or 
QuouB  layer,  which  constitute  the  mesoblast,  and 
r  are  conyerted  into  mesodermal  structures.  The 
bheee  is  still  a  matter  of  doubt,  but  in  many  cases 
1  to  be  unquestionable  that  they  are  derived  from 
•last. 

rienteron,  more  or  less  interrupted  and  broken 
e  constituents  of  the  mesoblast,  may  give  rise 
o  the  perivisceral  space,  or  channels,  of  the 
lich  thus  constitute  a  aekizocmle.  It  is  hardly 
I  think,  that  the  perivisceral  cavity  takes  its 
this  manner  in  the  Botifera,  the  entoproctous 
he  Echinopsedia  of  the  Echinoderms,  the  Tuni- 
the  NemaJtoidea, 

other  hand,  in  many  Iwoertebraia,  one  or  more 
El  of  the  archenteron  extend  into  the  perienteron 
mtained  mesoblast.  Sometimes,  as  in  the  Coelen- 
»e  remain  connected  with  the  alimentary  cavity 
it  life,  and  are  termed  gastrovascular  canals.  In 
!8  {Eehinodermata,  Braohiopoda,  ChcstogncUha)  they 
ut  off;  their  cavities  constitute  a  variously  modi- 
^coele ;  and  their  walls  give  rise,  along  with  the 
mesoblastic  elements,  to  the  mesoderm. 
)h  of  these  two  possible  sources  of  the  mesoderm, 
ermal  structures  of  the  Annelida  and  the  Arthro- 
Lch  so  very  generally  take  on  the  form  of  two 

fcibink  that  KIeinenberg*s  fibres  in  Jlydra  strictly  represent 
I,  though  they  occupy  the  potiUon  oC  ou^ 


686       THE  ANATOMY  OF  INVSBTEBRATED  ANIMALS. 

longitudinal  germ-bands  in  the  embryo,  and  subsequently 
undergo  segmentation,  are  to  be  referred,  is  a  yery  interest- 
ing, but,  as  yet,  unsolved  problem.  It  is  possible  that  they 
are  solid  representatives  of  the  hoUow  diverticula  which,  in 
other  animals,  give  rise  to  the  enteroocele;  in  which  case,  the 
perivisceral  cavity  in  these  animals  will  be  a  virtual  entero* 
ooele.  On  the  other  hand,  they  may  merely  represent  the 
cells  of  the  mesoblast  of  the  entoproctous  Polyzoa  and  of  the 
Echinopsddia,  and  their  perivisceral  cavity  would  then  be  a 
schizocoele.  But  it  is  needless  to  pursue  this  topic  further ; 
enough  has  been  said  to  show  conclusively  that,  however 
different  one  invertebrated  animal  may  be  from  another, 
the  study  of  development  proves  that  each,  when  traced 
back  through  its  embryonic  states,  approaches  the  earlier 
stages  of  all  the  rest ;  er  in  other  words,  that  all  start  from 
a  common  morphological  type,  and  even  in  their  eztremest 
divergence  retain  traces  of  their  primitive  unity. 

It  is  very  important  to  remark  that  these  morphological 
generalisations,  so  far  as  they  are  correctly  made,  are 
simple  statements  of  fact,  and  have  nothing  to  do  with  any 
speculations  respecting  the  manner  in  which  the  inverte- 
brated animals  with  which  we  are  acquainted  have  come 
into  existence.  They  will  remain  true,  so  far  as  th^  are 
true  at  all,  even  if  it  should  be  proved  that  every  animal 
species  has  come  into  existence  by  itself  and  without 
reference  to  any  other.  On  the  other  hand,  if  there  are 
independent  gi'oundif  for  a  belief  in  evolution,  the  facts  of 
morphology  not  only  present  no  difficulty  in  the  way  of  the 
hypothesis  of  the  evolution  of  the  Itwertebrata  from  a 
common  origin,  but  readily  adapt  themsdvee  to  it. 

Hence  the  numerous  phylogenic  hypotheses  which  have  of 
late  come  into  existence,  and  of  which  it  may  be  said  that 
all  are  valuable,  so  far  as  they  suggest  new  lines  of  in- 
vestigation, and  that  few  have  any  other  significance, 
do  not  desire  to  add  to  the  number  of  these  hypotheses ; 
and  I  win  only  venture  to  xemark  that,  in  the  absence  of 
any  adequate  -j^aS^saisfi^uc^o^^^cA^iA^^     of  the  IfwerMnraiaf 


f~    «  1 


PALiBONTOLOOY  AND  PHYLOGBKY. 


687 


any  attempt  to  constmct  their  Phylogeny  most  be  mei*e 
Bpecolation. 

But  the  oldest  portion  of  the  geological  record  does  not 
furnish  a  single  example  of  a  fossil  which  we  have  any 
reasonable  grounds  for  supposing  to  be  the  representative 
of  the  earliest  form  of  any  one  of  the  series  of  invertebrated 
animals ;  nor  any  means  of  checking  our  imaginations  of 
what  may  have  been,  by  evidence  of  what  has  been,  the 
early  history  of  invertebrate  life  on  the  globe. 

Already,  indications  are  not  wanting  that  the  vast  multi- 
tude of  fossil  Arthropods,  Mollusks,  Echinoderms,  and 
Zoophytes  now  known  will  yield  satisfactory  evidence  of 
the  filiation  of  successive  forms,  when  the  investigations  of 
palaeontologists  are  not  merely  actuated  by  the  desire  to 
discover  geological  time-marks  and  to  multiply  species,  but 
are  guided  by  that  perception  of  the  importance  of  mor- 
phological facts  which  can  only  be  conferred  by  a  large  and 
thorough  acquaintance  with  anatomy  and  embryology. 
But,  under  this  aspect,  the  palaeontology  of  the  hwertehrata 
has  yet  to  be  created. 


^^'=L 


AbioEenesis,  35. 
AbioTagicBl  uiensu,  1. 
AcBiilliohdclU,  an. 
Acnnthocephala,  646,  B 


Aciuftjc,  95, 100,  101,  107-109. 
AcriJiilffi,  439. 
Aelinin,  53,  156,  173. 


ullferom,  G14. 


pjCDOgDDoidM 

AmuioQ,  69. 
AnKL'bB  indiogB.  91. 

AmiElni.  5,  91,  92,1... 
Amouroucium  prullferam, 
Amphibia.  59,  60,  es,  71,  i.^. 
AmpbldiiDiu.  117. 
AmpliiilotuB  cordatiu,  573 
Amphloxug,  b».  60. 
AmphlpodB,  36a. 
Amphiihttf,  3.'i<l, 
Ampul  laria,  61. 
Anitomy,  9, 10. 

Anenteroiu  lavettebrfttM,  6T5. 
Anguillula  brevlapiuoB,  637. 

scBndeDS,  6(3. 

Animals,  cbaroclen,  43  ;  moipho- 
phyiio" 


INDEX. 


689 


Aptychus,  536. 
Apus,  258,  27d-281. 

caneriformis,  279-281. 

gloclalii,  278. 

Arachnida,    59,    253,    256,    371, 

670. 
Araneina,  379. 
Area,  486. 
Arcella,  91. 
Arctisca,  387. 
Argonauta  argo,  538,  539. 
Argulufl,  276. 

**  AristoUe'B  lantern,"  575. 
Arthrogastra,  371. 
Arthropoda,  15, 29, 34,  52-57,  65- 

67,  218,  234,  250,  256,  371,  670, 

678,  685. 
Arthrozoic  series,  679. 
Articalata,  469. 
A  scans  nigrovenosa,  644. 
Aseetta  primordialis,  112. 
Aseidiaus,  44,  52. 
Ascidioida,  595. 
Ascones,  115, 116,  120. 
Ascala,  11.5. 
Asellus,  363,  367. 
Aspergillum,  472. 
Aspidobranchia,  517. 
Aspidogaster  conehlola,  194-201* 
Astacut,  68,  250»  303-^88. 

flaviatilis,  306. 

Asteridse,  543,  5.^. 
Astrsea  calycularis,  163. 
AtaxB<msi,383. 
Athorybia,  143. 

rosacea,  140-142. 

Atolls,  169. 
Atrocha,  243. 
Aurelia  aurita,  134. 
Avicolaria,  457. 


Bactzria,  4-7, 36. 
Balanidae,  299. 

BalanogkMBus,  52,  629,  674,  680. 
Balantidiom,  105,  106. 
Balanus,  291-299. 

balanoides,  296. 

Bees,  30,  31. 
Beetles,  424. 
Beleronitidffi,  541. 
Beryx,  38. 


Bicosoeca,  96. 

Bilbarzia,  202. 

Biogenesis,  38. 

Biology,  principles,  1 ;  diviaions, 

9. 
Bipinnaria,  561. 
Blastoderm,  444. 
Blastoidea,  594. 
Blastomere,  14»  16,  23^  29,  32,  47, 

367,484. 
Blastosphere,  484. 
Blastostyle,  131. 
Blatta,  351,  431,  433,  438,  442, 

444. 

orientalis,  401, 414,  417. 

Blood  and  circulatory  apparatus, 

57. 
Bojanus,   organs  of,  52,  58,  62, 

68,  478. 
Bombus,  429, 432. 
Bothriocephalus,  212. 

latus,  208. 

BotrylUd»,  600,  604,  609,  612- 

616. 
Botrytis  Bassiana,  43. 
Brachionus,  190. 
Brachiopoda,  452,  461, 486, 685. 
Brachvura,  324, 338^  340. 
Broncneliion,  214. 
Brancbise,  58. 
Branchiogasteropoda,   494,   505, 

506,509. 
Branchiopoda,  277. 
Branchipos,  283,  285. 
Brisinga,  560. 
Bryoxoa,  453. 
Buccinum,  506. 

undatum,  489. 

Bucepbalus  polymorphut,  205. 
Bugula  avicularia,  457. 
Butterflies,  425. 

O. 

CxiiCIBTOlfGIiB,  ll^iaO. 

Caligus,  276. 

CalycophoridsB,   38,    128,    141- 

145. 
Cambium  laver,  16. 
Campanulana,  130. 
Campanularida,  128, 129. 
Campodea  ntanbylinos,  420. 
CapiUlla,  227.' 


Cnprellft,  363. 

Clionid»,  119. 130. 

(.larclniii  raaTM,  341,  349  350. 
Cardium.  185,  4S6. 

CocC™«*,3M.      ' 

Cannikrina,  1^6,150. 

CaryaphyllKUs,  m. 

Codonellido,  106. 

CnUllarto,  34,  109,  671. 

Codwig*,  96. 

OiiilBrpB,  47. 

CMldomyis,  448. 

lis,  120,  12&,  671,  685. 

CpII»,  10.  15,  24,  a7-2U. 

CiEnanu,  209, 

Cell-Ull,  12, 

Cold,  aaUin  of,  on  living  matter. 

Ccntii)odM,  399. 

4. 

ColBUpIera,  424,  i%,  438. 

Cephf.  or-cllau,  laS-iaB. 

Collombola.  252,  420. 

I'ermritE,  53,  204,  406. 
CerennUiiii,  163. 

Colpod.,  6i,  103, 106. 

CstMulcB,  57,  176,  206,  673. 

ComatulB,  34. 

Ceiliacinn,  71. 

(AB;«>l«n),5=4. 

Cetiioeo,  72. 

Conjugation,  23,  77. 

Cliff  lodermn,  067, 

Contractiio  li.iue,  25. 

ChiElaKastcr,  219,  Q^. 

vacBole,  76, 

t.'hn;toBn.Iha,  612.  67S,  6BS. 

Conlligena,  153,671. 

94,  B6. 

CoralUue*,  453. 

ChBDfici,  cyoliul,  in  living  mkt- 

CoralliW,  155, 

ter,  3. 

Cora  Ilium  rubrum,  IM. 

Chora,  15. 

Coral.,  120. 

Chemical  compoiiUon  of  living 

Conlylophora,3i,M, 

C-^ryne,  129. 

rhirk,  13,^^^ 

Crayfish,  3I».  30^1,  328,  330. 

^M 

CjnthJ 


,8«. 


Crpraa  Europna,  409. 
Cjprii,  -iSS-iW. 
Cyatic  wotm,  an. 

CyitidcK,  MS. 
CjLhare,  'JSd,  389. 


DAUumm,  309. 
Dkpbnit,  383,  M*. 
Dceapodi,  540. 

Deep-iM  fiDnk,  3^  70,  HI,  85. 
I>«adroc<Ela,  ISO. 
DenUUdr,  Ml,  503. 

Detmli  (endaron),  5S, 
DsiailduE,  9i. 
DvvelopmenC,  10,  IS,  GS. 
Viatnmaecn,  a,  79, 84,  Si,  9&. 
Dibranchiala,  9U-M3. 
Dlcena,  173. 
DicoryDfl  con  Carta,  131. 
Diclyocyite,  81. 
Dietjocjstlda,  106. 
Diciema,6T8. 
Dinjemid*,  G5S,  873,  676. 
Dldemnum  styllferum,  6U 
Didiuium,  105. 

lerpulk,  S. 

DiO'eratitlMlon,  16. 

DimjarU,  480. 

DiphydK,  145. 

Dipbya*  ippcndlouUts,  138. 

UiphyllidM,  21  a. 

DiphruuHid,  139,  145. 

DiploiDon  parkdoxum,  30,  206. 

Dipnoi,  Bl. 

Diporpa,  30,  306. 

Diptars,  4:25,  4M,  443. 

Ditcophora,  139,  112,  146-149. 

niainlegrallop  of  liviog  nutler, ! 

Di.t..m»,  -iUl. 

Ri.iHbution,  9, 19-aa,  TO,  71. 

Dog-louie,  312. 

Dogi,  relrieviQK  of,  33. 

DuJlolum,  6i»,  605,  616. 

"  Donblo  oircDlfttiOD,"  61. 
Dngon-lllei,  3&3. 
DjaUriB,  103. 


Eaithwoih,  319. 
£ehenell>olhriuin,  313. 
EehiDidra,  S6,  543,  566. 
EcbiDococcua,  L-OJ. 

1,  210. 
Echinodareii,  Iu3. 
Eehiaodann4l  aerin,  6T9,  680. 
Eobinodermatn,  ii,  34,  53-56, 

543,  675,  635. 
EchinoidK,  570. 
EcblDOpedlum,  M,  544,  561,  590, 

680. 
Echlnarbrnchu*,  646. 
Echlnua,  h«7. 

spli^r*.  568,  563. 

Ecloderm,  56. 

Ecloprocbi,  458,  668,  669. 

Eetoi-arc,  78. 

Edrjmilsrida,  594. 

Edriopblhilmik,  368,  3.59. 

ElTtron,  3;ll. 

EmbryolDg]',  41,  49,  681. 

£mpuw,43. 

Eiiduparuites,  306. 

End.-plut,  46,  77. 

EDdoplutlc*,  76,  87. 

Enduprocca.  668. 

Eudoaarc,  78. 

Endoslyle,  597. 

EnteropDaasCs,     60,     629,    671, 

679. 


Entomoitnea,  356,  S66. 
EnloprocU,  458. 
Eoioon,  75. 

cuisdciue,  87. 

Epiblaat,  16,  50. 
Epidarmis  (mloderm),  56> 
Evigenaaia,  13. 
Epimerk,  3CK). 
EpiioL  373. 
EquidK,  31. 
EiKUllui,  376. 
Enaulia  floreui,  43S. 
Errantia,  235,  237. 


Ea^ariu,  335,  287. 
Euuiaa,  336,  6««. 
Euglaiu,  4,  5. 


EukIbtir  viridii  97, 
i:"i'liausin,  3sr.. 
Euplopielln,  IM), 
FurjpteriJ*.  isi,  SS8. 
Eii-jpiPrut  rmipw,  M7. 
tvLlmion,  38. 


Oaleodei,  STB. 

Ganoldi,  61.' 
Cuterot'O'}*-  *T(i,  5(H. 
Oulerowomuni.  206. 
Gaaleroiriclii,  19a, 

Giulropliv(em«,  116, 119 
'iMtrula,  lis. 


GetRT- 


7,  «13. 


Genu"l'7.""' 

Uephyrc*,  59,  314,  245,  667,  670, 

Geryonia,  665. 
GciyoaidiE,  138,  ISO 
Glimtcrabi,  SM. 

GloOi^feriM.  39,  1*4-67. 
GlouocodDii,  136. 
Gnalhiie*.  ITS.  270. 
GoiDphooema,  7S,  103. 

GraaQkn  jdlllole*,  68,  «43. 
Graptolltes,  ISl. 
Gregarina,  76,  92,  9S, 

gimintom,  9S,  94,  103. 

Gitgarinidir,  flS-M,  671. 


INDEX. 


693 


Heteromorphe,  72. 
Heteronereis,  245. 
Heteropoda,  494,  497,  512. 
Hetcrotricha,  102. 
Uexacoralla,  162,  164. 
liipparitidsB,  486. 
Hirudinea,    214.    218,  242,  243, 

666,  672. 
Hirado  medidnalis,  215, 216. 
Histoloffy,  9. 
Histriobtlella,  214-217. 
Holomyaria,  641. 
Holothuria,  171. 
Holothuridea,  59,  54S,  545. 
Holotricha,  102. 
Homarus,  68. 
Hamming  of  insects,  255. 
Hyalonema,  120. 
Hydatina  senta,  189. 
Hydra,  56,  63,  65.  126, 129,  6S5. 
Hydractina,  67, 126. 
Hydranth,  120. 
Hydrophilus  pioeos,  424. 
Hydrophora,  129,  130, 146. 
HydrophyUia,  128. 
Hydrosoma,  127, 128. 
Hy<irotheca,  128. 
Uydrozoa,  33,  34,  67,  116,  120, 

146-152,172,  173,671,672. 
Hymenoptera,  428. 
Hypoblast,  16,  50. 
Hypotricha,  102. 


ICBTHTOPSIDA,  58. 

Idoteidse,  364. 

Imperforata,  83. 

Impregnation,  28. 

Inarticulata,  469. 

Infusoria,  5, 14,  30,  43,  46,  77,  79, 

95-97,  101,  106-113,  176,  660, 

671. 

ciliata,  95. 

flagellata,  95, 96. 

—  tentaculifera,  9 a. 

Insecta,  15,  59,  69,  256,  366,  897, 

432-449,  670. 
Insectivorous  plants,  42. 
Integumentary  organs,  55. 
Invertebrata,  morphological  types 

among.  48. 
Isocardia,  473. 


Isopoda,  362. 
lulus,  396,  397. 
Ixodes  ricinus,  382. 

J. 

JAIIEU.IDJS,  514. 

Jaws,  56. 
Jelly-fishes,  120. 

I.. 

Labium,  in  insects,  230. 

Lacinularia,  190,  191, 193. 

Laeraodipoda,  362, 366. 

Lamellibranchiata,  470,  472, 670. 

Lampyris  splendidula,  440. 

Laomedea,  131. 

Larva?,  68,  69, 186,  191,  192,  203, 
243,  283,  296,  369,  385,  393, 424, 
430,  4.35,  436,  448-451,  467, 469, 
544,  643,  664,  680. 

Leeches,  214,  eS6. 

Lepadidee,  299. 

Lepas,  291-299. 

aufltralis,  296. 

Lepidoptera,  425,  436,  438,  443. 

Leptoplana,  182. 

Lemsea,  276. 

Lemseodiscus  porcellanie,  302. 

Leucifer,  346. 

Leucones,  115,  120. 

Lice,  421. 

Lieberkuhnia,  82. 

Ligula,  207. 

Lima,  475.  * 

Limaeidse,  514. 

Limax,  493,  498,  499. 

Limnetis,  283,  285. 

braehyurus,  286. 

Limpets,  511. 

Limulus,  259-269,  374. 

—  moiuccanus,  261. 

polyphemus,  264. 

Linens,  186. 

Linguatula,  371,  388. 

Lingula,  462.  466. 

Lithocysts,  126. 

LituiUds,  83. 

Living  matter,  propertieB  of,  1-41. 

Lobster,  303. 

LocustidsB,  440. 

Loxosoma,  459,  485,  668. 


694 

tucenmriB,  131,  l4T,  153. 

Liimbricui,  ai9>2al. 
Lung,,  60, 
I,yinnn!iii,49T,  500. 
paluslri*,  493. 


.MaoTurii,  3-M,  338-316. 
MndrDporei,  161. 
MaJropuHle,  670. 
Ktaeoiphcern,  \H,  95. 
MntacobdellB,  314-SI7,  666,  672. 
'■-'         colloes,  67*,  679. 


'  Mothi,  30. 
Mueor,  92. 
MUDDB,  3&8. 


MjB.1e  . 


itlallDpliiigiL,  420,  411. 
JUnubrium,  127. 
Mutieouods.  76. 
Mcanarina,  tei*. 
JiBduBo.-,  34,  120,  iaS-li9,  67i. 
McEBlopa,  31!(,  350. 
Merumy  Brill,  641. 
MtroiLomata.  256,  36S. 


MyrlBjn>ei«,  59,  256.  399, 670. 
My«U,a36,  346,  350,367. 
Mylilm,  476,  486. 
Myxulram,  79,  92. 
Hyxodictytim,  7tf.  79,81. 
SljiomycBlct,  5,  -U,  92. 
Jlyiopods,  7G,  7f,  87,  88. 
Myxospuugjs',  119. 
M>EOStuinBLB,  627,  672. 

K. 

Nlu,  219,  22U. 
Nnked-cyed  nieiiiia«,  129. 
NBUfHiu.  36».  271,  2S3,  290,  396- 
30),  317-H4S.  354,  337, 385,  3j7, 
NButitiu,  66,  71,  5ai-5ta. 
Kebalia,  177,283.  3B3. 
NimaloideB,  29,  636,  67d. 
Nematuphorea,  131. 
NoniBlQrhyncha,  66  j. 
NemBtoHolicci,  673,  678. 
Nemcnida.  186, 


Onchidmn,  61. 
.  Uniicidn,  366. 
Oniscua,  250, 361. 
Ophiodei,  131. 
Uphlolepii  oiliat^  565. 
(>|ihiurld«%  Mr%  S62. 
Opbnrdlda,  1(». 
UpiilhobrftDohlftU,  510. 
UpUtbomuiD,  179. 
OrbuUu,  $4. 
Olden,  IT. 

"  O^uiiMd,"  meaning  of,  8. 
OrgSDi,  S4  65,  67. 
Origin  of  liting  matter,  S3. 
"iriigiD  of  Siweiea,"  35. 
Orthido!,  471). 

Urthopwn,  422,  43G,  438,  *tS. 
(hiicula  audilui,  67. 
U*[ncuda,  S52,  287. 
Uitraa,  4T  5-486. 
UvipaTDUi  anlmata,  69. 
Ovovlvipaiuus  aaimali,  69, 
Uiidallon,  waala  of  living  matter 

by,  2. 
Oiyuria,  639. 
Oyiler,  475. 


Pxaimirn,  346. 

PalKucycluB,  171. 

PalteoDloloBy.  8m  Foul  li. 

Palinimu  vulgarii,  33SI. 

Paludina,  204,  4>*5,  4117- 

Pangeneili,  40. 

Paramceolum,  47, 104-109. 

Faraaite*.  43, 6%  193,  S05,  S06-207, 
212,  272,  276,  277,  291,301,  364, 
334,  388, 421,  450,  484,  513  634. 


646. 
Puleur'a  < 


an,  SI 


Fecten,  475-485. 
Feutoitraca,  290. 
Fedalion,  192,  193. 
Fedicellina,  668,  680. 
Pedietia,  53. 
Pedieulina,  420,  421. 
Pelagia,  146,  147. 
Fellogaater  pigurl,  302. 
Pennia,  3^)1,349. 
Penielliinm,  43. 
PeonataiidK,  161. 


PentAcrimu,  584. 
Paututomlda,  257,  368,  670. 
Pentaitaaium  tnuioide*,  388,  389. 
Pentremlte^  594. 
PerenolbnnchiatB,  59. 
Perfonta,  83,  163-167,  171,  ITi 
Peridlntn,  81, 99,10a 
PgripatiO*^  S57,  624,  670. 
Peritriehm,  102,  i03, 109. 
Perik  nigra,  422. 
pMonladw,  513. 
Peronia  vermoulata,  517. 
Peronnporai,  43, 44. 
Phaluiglde,  379. 
Fballuila,  601,  607. 
PhaijBgopDeoita,  674. 
PharyugopneiuUil  leiies,  679. 
Fliolaa,  472,  475,  4S5. 
PboTDDJg,  248. 
Pbrollna,  364. 
Ffaryoldie,  379. 
PbyUetoltttoaCa,  669. 
Pbyllndoce,  243. 

viridii,  240. 

Ptayilopoda,  277. 
PbylloMinula  355,  356. 
Phylogany,  41. 
Fhyialia,  125,  143, 143. 
FhyKmarla,  845,  671,  672,  685. 
Pbyiiology,  1,  9,  29. 
PhyaophoridB,  12S,  141-145. 
Filidiuro  gynui,  185,  186. 
Fiaidium,  483. 
Ptaceuta,  69, 109. 
Flagioatome  Bibea,  69. 
Flanaria,  180^218,672. 

dioica,  180. 

Plant!,  27,  29,  42,  71. 
Pleurobranchia,  173,  174, 
PleuTodiclyon,  172. 
Plumatellk  repeui,  453,  454. 
PlumularldK,  130. 
Foelllopara,  165. 


PoduridK,  444. 
Potcilopudk,  260. 
Foiiao  veaiolea,  546,  561. 
Palyarthra,  192. 
Pulycalia,  218. 

InvlgaU,  ISl. 

PolychKta,  68,  214,  226,  237,  673. 
Polyciilina,  88. 


'  -■'■ 

1=>      :         : 


I'orlio,  )(»■ 
Fnwn,  517. 

TriapnlM,  a«. 
Primordial  atricU,  12. 
ProEWch*.  177, 183. 
rroduoHiiB,  470. 
Proglc.ltl.,211. 

Proteoa,  G1. 

BoiraalcalW,  '.'2. 

P™t«occu.,5,ll.    .   ., 


ProuiiOT.  36,  4W7,  51,  62,  6.1, .«, 

110,111,117,671. 
Protoeoia  serlts,  677. 
ProtuK  233,  2-U. 

Dystari,  a3B. 

ProTinees  of  distribution,  lA 
Pseuri-hirmn!  syileni,  57. 


INBBX. 


697 


Scyllaros,  339. 

Sea  anemones,  120. 

Sensitive  plant,  42. 

Sensory  organs,  23. 

Sepiadae,  520,  528,  540,  542. 

Sepia  officinalis,  518-5*29. 

Serial  relations  of  invertebrata, 

676. 
Serpulidse,  235,  244. 
SertularidsB,  128,  129. 
Shrimp,  350. 

Siphonophora,  129,  140,  147-149. 
Sipunculos  nudus,  247-249. 
Snail,  515. 

Solenhofen  slates,  151. 
Somatopleure,  57. 
Somites,  227. 
Sounds  from  insects,  437. 
Spatangoida,  570. 
Spermatophores,  529. 
Spbsromidse,  3&4. 
Spbaerozoura  ovodimare,  89,  90. 
•~-—  punctatum,  89. 
Sphinx  ligustri,  426. 
Spiders,  379. 
Spiriferidae,  470. 
Spirillum  volutans,  4. 
Spirorbis,  235. 
Spirostomum,  105. 
Spirulid«e,  540. 
Splanchnopleure,  57. 
Spongida,  110,  663. 
Spongilla,  113-120. 

lluyiatilis,lll,  116. 

Sporocysts,  206. 

Springs,  hot,  living  things  in,  7. 

Squids,  540. 

Squilla,  361,  369. 

scabricauda,  368,  369. 

Star-fish,  553. 

Stentor,  108. 

Stephanoceros,  187,  191. 

Stemaspis,  245. 

Stigmata,  60,  377,  394,  413,  435. 

Stings  of  insects,  432. 

Stomatopoda,  272,  367. 

Stone  corals,  165. 

Strepsiptera,  431,  450. 

Strombidium,  104. 

**  Struggle  for  existence,"  26. 

Stylifer,  513. 

Srylonychia,  108. 

Stylops  aterrimus,  450. 


Son-animaloule,  87. 
Sundew,  42. 

"  Survival  of  the  fittest,"  40. 
Sycandra  raphanus,  664. 
Sycon,  120. 

dliatum,  115. 

SyUis,  244. 

vittata,  240. 

Synapta,  513,  545. 

digitata  and  inhaerens,  543. 

Syncytium,  113. 
Syrphus  ribesii,  427. 

T. 

Tabulata,  163, 165, 166, 167. 
Taenia,  207-213. 
Tape-worms,  206. 
Tardigrada,  257,  387,  670. 
Taxonomy,  10, 16,  656. 
Teeth,  56. 

Tegumentary  system,  55. 
Telotrocha,  186. 
Temperature  in  relation  to  living 

matter,  3,  37. 
Tentacula,  50. 
Tentaculifera,  100. 
Terebratula,  33. 

psittacea,  38. 

Terebratulidse,  470. 
Terebratulina       septentrionalis, 

465. 
Teredo,  472-486. 
Testacellidse.  514. 
Tetrabranchiata,  532. 
Tetraphyllidea,  212. 
Tetrarhynchus,  207,  212. 
Tetrastemma,  183,  18i. 
Teuthidee,  528,  540.  542. 
Thecosomata,  .',07.  503,  510. 
Thysanopoda,  346. 
Thysanura,  252,  420. 
Ticks,  382. 
Tissues,  10. 
Tomopteris,  235. 
Torquatella,  105. 
Torula,  36. 
Tracheae,  59. 
Tracheo-branchise,  2.'i2. 
Trachynemata,  149. 
Tradescantia  hair,  78. 
Trematoda,  53,  57,  176,  193,  207- 

213,  217,  672. 


'rrioiincjsts,  ins. 

TriFhodinB 'grnndlnelll,  103. 


Tubicola,  M5. 
Tubifoi.  21!',  226. 
Tiibipon.  163. 
TiibulariiJiE,  129,  146. 
I'unicalB,  52,  ib,  60,  69,  595,  671, 

fiT'J. 
TiirlwllBris,  43, 51, 66-fia,  67, 176, 


Vibraruli,  *Ti6. 
Vibrioniite,  95, 
Tilal  force.  9. 
TiFipsroui  anhnali,  63. 


WMte  of  living  ni«i 
Water  in  living  mi 
WilldK,  131. 
Wolffian  duet,  69. 


\ 


Pvhlished  ly  J,  dt  A.  ChurehiU, 


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