128  DE.  T,  WILLmiS’S  EESEAECHES  02^  THE  HOMOLOGY  AXD  STEUCTUEE 
respect  to  the  reproductive  organs  of  the  Annelids  in  general,  the  conclusion  may  safely 
be  drawn,  that  in  escaping  from  the  body  the  ova  take  the  coui’se  of  one  of  the  limbs  of 
the  ciliated  tube*. 
Cirrliatulus  Lamarckii  is  a common  worm  on  the  coast  of  the  Bristol  Channel.  It  may 
be  readily  found  in  every  stage  of  growth.  The  region  of  the  tail,  in  some  specimens, 
at  a certain  (young)  age  is  quite  transparent.  It  is  then  easy  to  obtain  a view  of  the  seg- 
mental organ  (fig.  22  a c h).  In  this  worm,  as  in  the  Nereids  generally,  the  ova  are  not 
retained  within  the  segmental  organ  as  in  the  Leech  tribe ; they  escape  into  a dependent 
tissue  which  fills  the  chamber  of  the  annulus  in  the  mature  indhidual.  It  is  provided 
with  its  own  specially  disposed  vascular  apparatus  {cl).  Its  position  in  the  chamber  of 
the  segment  is  vertical.  The  ends  of  the  loop  are  situated  closely  together.  In  gene- 
ral figure  the  organ  is  intermediate  between  that  of  Terebella  and  that  of  J^enne.  The 
sexes  in  Cirrliatulus  are  situated  on  separate  individuals. 
The  author  has  made  numerous  attempts  to  arrive  at  a correct  knowledge  of  the  seg- 
mental organ  in  Glycera  alba.,  an  Annelid  which  is  remarkable  for  the  entii’e  absence  of 
the  blood-vascular  system.  He  has  been  able  to  do  little  more,  in  consequence  of  the 
dense  character  of  the  tegumentary  structures,  than  to  prove  the  presence  of  the  organ. 
It  has  been  observed  by  He  Quateefages,  but  never  anatomically  defined.  It  is  an 
irregularly  looped  organ,  destitute  of  a vascular  tuft,  and  unciliatecl.  In  another  parti- 
cular it  is  remarkable : the  ova  in  the  female  are  retained  within  the  proper  limits  of 
the  membranous  walls  of  the  organ  itself,  after  the  type  of  the  ovarian  segmental  organs 
of  the  Hirudinei.  This  fact  the  author  has  proved  repeatedly  by  direct  obsen  ation ; 
but  it  may  also  be  established  negatively.  The  branchiae  are  capacious  hollow  processes, 
communicating  in  the  most  open  manner  with  the  perigastric  ca\ity.  The  fluid  of  the 
latter  circulates  freely  in  the  former.  In  this  branchial  fluid  the  ova  are  never  observed. 
In  looking  back  over  the  preceding  description  of  the  segmental  organs  of  the  Nereid 
group,  it  is  impossible  to  resist  the  belief  that,  notwithstanding  the  numerous  varieties 
of  size,  figure,  position,  structural  peculiarities,  mode  of  the  looping  of  the  ciliated  tube, 
the  place  and  method  by  which  it  is  connected  with  the  mass  of  the  generative  products, 
and  other  diversities,  in  one  and  all  the  genera,  it  is  beyond  all  doubt  the  same  organ. 
If  the  identity  of  the  organ  in  the  several  groups  of  this  family  be  admitted,  then  the 
homology  between  the  Nereid  type  of  the  segmental  organ  and  that  of  the  other  families 
of  Annelids  akeady  referred  to  in  this  memoir,  must  also  be  admitted.  This  conclusion 
is  one  of  great  importance  and  novel  interest.  It  simplifies  a question  which,  up  to  this 
moment,  has  proved  as  complex  and  perplexing  as  any  problem  in  comparative  anatomy. 
It  atiirms  that  hitherto,  and  in  the  typical  families  of  Annelids  examined,  the  anatomist 
has  discovered  only  one  essential  organ,  under  manifold  varieties  of  form,  upon  which  is 
ingrafted  the  reproductive  system. 
* By  reference  to  a paper  by  De  Quatreeages  in  the  Annales  des  Sciences  Nat.  ISo-i,  on  the  develop- 
ment of  the  spermatozoids  in  Torrea  vitrea,  it  wid  be  seen  that  in  no  single  particular  are  the  results  of  my 
researches  on  the  genus  Syllis  confirmatory  of  the  statements  which  he  has  made. 
