OF  THE  EEPEODUCTIVE  OEGANS  OF  THE  AENELIDS. 
127 
There  is  no  discoverable  difference  between  the  segmental  organ  of  Nerine  and  that  of 
Nereis.  The  ova  are  very  distinctive  and  characteristic,  however,  in  the  former. 
The  segmental  organs  are  very  largely  developed  in  the  genus  Eunice.  The  blood- 
vascular  system  is  here  highly  developed.  The  branchiae,  which  carry  the  blood-proper 
exclusively,  are  closely  connected  with  these  organs.  The  same  trunks  supply  the  caecal 
tufts  of  the  latter  and  the  straight  capillaries  of  the  former.  All  the  Euniceadae  are 
dioecious.  The  female  is  nearly  twice  as  large  as  the  male  during  the  height  of  the 
reproductive  season.  Although  they  appear  to  be  in  the  free  cavity  of  the  body,  it  is 
quite  certain  that  the  generative  products  do  not  move  to  and  fro  in  the  fluid  of  that 
cavity.  They  are  contained  in  a delicate  areolar  structure,  which  serves  to  limit  the  pro- 
ducts of  each  segment  to  its  own  proper  chamber.  The  ciliated  tube  and  its  appended 
vascular  tuft  (fig.  20  c)  can  only  be  demonstrated  by  transverse  vertical  sections  of  the 
body ; sometimes,  and  by  a pure  accident,  a most  complete  view  of  the  segmental  organ 
(a  e b)  may  be  obtained  by  this  method.  It  is  a far  more  saccular  and  prominent  organ 
in  Eunice  than  in  Nereis  and  Nerine.  The  fundus  [e)  shows  a union  of  the  two  limbs 
as  in  Terebella  and  Arenicola,  and  as  in  the  latter,  the  vascular,  ovarian  or  ingoing  leg 
is  of  a denser  structure  and  darker  colom'  than  the  outgoing  limb  (fig.  20  «),  which  is 
long  and  tubular*.  There  is  every  reason  to  beheve  that  in  the  allied  genera  oiLycidice., 
Aglaura  and  (Enone,  the  segmental  organs  coincide  in  structural  type  with  the  standard 
of  that  of  Eunice.  They  are,  however,  less  vascular  than  in  the  latter.  All  the  genera 
of  this  family  are  dioecious. 
In  the  genus  Syllis  the  segmental  organ,  which  cannot  by  any  manoeuvre  be  directly 
demonstrated,  is  most  probably  correctly  represented  in  its  minute  and  general  anatomy 
by  that  of  Psamathe  fusca,  a closely  allied  genus.  Once  recognized  in  this  Annelid, 
there  is  no  difficulty  in  readily  demonstrating  the  entire  characters  of  the  segmental 
organs.  The  integuments  covering  the  roots  of  the  feet  are  perfectly  transparent. 
Within  the  hollow  of  each  foot  a beautifully  looped,  extremely  delicate,  slender,  mem- 
branous, ciliated  tube  (fig.  21,  a be)  may  be  discerned,  corresponding  in  every  essential 
particular  with  the  looped  ciliated  tube  of  Nerine. 
But  what  is  of  special  interest  in  this  case  is,  that  the  appended  glandular  yellowish 
mass  {e  e)  in  the  female,  which  spreads  irregularly  into  the  hollow  bases  of  the  cirri  and 
setiferous  feet,  can  be  most  distinctly  traced  into  organic  connexion  with  the  ciliated 
tube,  and  ufith  that  limb  (a)  of  the  loop,  of  which  the  vessels  are  most  developed. 
During  the  constant  movement  of  the  little  worm  while  under  examination,  it  may  be 
distinctly  observed  that  the  ova-  or  sperm-bearing  mass  moves  in  constant  connexion  with 
the  ciliated  tube.  So  exquisitely  delicate  is  the  entire  apparatus,  and  so  minute  are  the 
ova,  that  it  is  quite  impracticable  to  trace  them  in  their  passage  from  the  “ mass  ” into 
the  tube.  Since  however  this  fact  has  been  observed,  beyond  doubt,  in  other  Annelids, 
and  since  it  is  supported  by  the  analogy  of  everything  that  is  now  clearly  known  with 
* The  dissections  upon  which  rest  the  statements  in  the  text,  were  made  upon  JEunice  gallica  (Milni:- 
EnwAEns),  E.  sanguinea,  and  E.  ELarrassii  (M.-E.),  which  are  common  on  the  shores  around  Swansea. 
