134  DE.  T.  WILLIAMS’S  EESEAECHES  ON  THE  STErCILTIE  AND  HOMOLOGY 
The  family  of  the  Aphroditadse  comprehends  the  genera  Aplirodita.  Polynoe,  Pholoe. 
Sigalion  and  Spinther  (Johnst.). 
They  are  all  more  or  less  common  on  the  coast  of  the  Bristol  Channel.  In  all.  the 
system  of  the  segmental  organs  is  reducible  to  one  typical  standard.  'The  sexes  are 
seated  on  separate  individuals. 
The  anatomical  position  of  the  segmental  organs  involves  questions,  the  morphological 
meaning  of  which  (as  will  subsequently  be  discussed)  extends  far  beyond  the  limits  of 
this  family  of  Annelids. 
Let  us  take  for  type  the  condition  of  these  organs  as  they  exist  in  Aphrodita  aculeata. 
In  order  to  arrive  at  a correct  estimate  of  the  reproductive  system  of  this  Annelid,  speci- 
mens of  both  sexes  should  be  examined  in  the  spring,  and  again  in  the  autumn.  A good 
example  of  a female  Aphrodita  being  obtained,  the  dissection  should  thus  be  proceeded 
with : — Pin  the  animal  down  to  the  trough  with  the  back  upwards.  Open  it  by  a longi- 
tudinal incision  extending  from  the  tail  to  the  head.  The  incision  should  cut  through 
the  scales,  felt  and  integuments,  in  order  to  lay  open  the  spacious  perigastiic  chamber. 
The  integuments  should  be  now  carefully  stretched  and  pinned  doAvn  to  the  sides.  The 
interior  is  now  exposed.  Let  the  dissection  be  then  gently  floated  in  salt  water.  The 
entire  alimentary  system  and  a considerable  portion  of  the  segmental  system  will  be 
now  rendered  perfectly  and  distinctly  recognizable.  At  this  stage  the  parts  will  present 
exactly  the  appearance  exhibited  in  fig.  26,  in  which  a network  of  minute  tubes  or 
threads  [d  d,  h 5,  c)  seem  to  twine  around  and  embrace  the  diverticula  (a,  a,  a)  of  the 
ahmentary  canal  *.  From  the  gastric  end  of  the  proboscidiform  oesophagus  (e,  fig.  26) 
to  the  tail,  the  digestive  caeca  (a,  a)  are  co-numerous  with  the  feet,  into  the  hollow  bases 
of  which  they  are  inserted. 
In  proceeding  to  the  second  stage  of  this  dissection,  the  entire  alimentary  system  must 
be  taken  away,  and  with  it,  necessarily,  a considerable  portion  of  the  reproductive  net- 
work. If  this  part  of  the  proceeding  be  delicately  and  successfully  performed,  a perfect 
view  will  have  been  obtained  of  the  attached  ends  (a,  b,  a,  b,  fig.  28)  or  roots  of  the 
branched  segmental  organs  (A,  B).  These  roots  will  be  found  to  equal  the  alimentarv 
C0eca  in  number,  and  therefore  that  of  the  feet  Avhich  are  situated  posteriorly  to  the 
proboscidiform  oesophagus.  They  appear  under  the  character  of  pyriform  tubuli  (a,  A. 
a,  B),  commencing  or  ending  in  a single  external  orifice  (a,  a).  Internally  they  are  lined 
by  a ciliated  epithelium,  the  cilia  being  large,  dense,  and  acting  with  great  force  and 
vigour.  'L'he  current  raised  by  these  cilia  sets  up  on  one  side  and  down  on  the  other 
(see  arrows).  The  ciliary  epithelium  ceases  at  the  point  where  the  primary  branches 
(b,  b)  divide.  All  the  rest  of  the  organ  (from  b to  c)  is  unciliated^  and  filled  with  the 
reproductive  products.  This  portion  is  elaborately  branched  (at  A d is  shown  a small 
portion,  magnified,  of  the  female  organ,  at  B d,  of  the  male), — the  branches,  as  for- 
merly stated,  twining  round  the  diverticula  of  the  stomach.  No  microscopic  object  can 
* Both  the  number  of  the  alimentary  diverticula  and  that  of  the  embracing  segmental  organs  have  been 
very  much  reduced,  for  the  sake  of  distinctness,  in  this  figure. 
