130  DE.  T.  WILLIAMS’S  EESEAECHES  ON  THE  STEECTEEE  AND  HOMOLOOT 
they  enter  into  this  chamber.  In  this  particular  the  Chlorsemea  fall  in  with  the  rule 
which  prevails  without  exception  throughout  the  great  group  of  the  Errant  Annelides. 
Eecognizing  the  parallel  tubes  (A  h and  ff,  and  B h)  as  the  true  segmental  organs,  and 
remembering  the  demonstrated  facts,  that  at  one  time  the  germinal  products  are  actually 
to  be  seen  within  these  tubes,  and  that  at  another  they  hang  in  masses  externally  around 
them,  the  truth  of  the  proposition  contended  for  in  this  memoir  is  established,  that  the 
segmental  organs  are  in  the  female  the  true  ovaria,  and  in  the  male  the  true  testes. 
But  careful  homological  study  is  required,  in  order  to  convince  one’s  seK  that  the  primary 
and  secondary  looped  tubes  of  the  Chlorsemea  are  in  truth  the  morphological  representa- 
tives of  the  ciliated  segmental  tubes  of  the  Nereid  families.  In  the  Chloreemea  these 
tubes  are  not  ciliated,  either  within  or  without.  This  is  a distinctive  peculiarity,  which 
allies  them  with  those  of  the  Hirudinei.  But  they  stand  alone  and  udthout  example 
amongst  the  other  Annelids  in  this  feature,  viz.  that  the  three  looped  organs  {ffc.  A) 
on  either  side  are  connected  together  by  means  of  intermediate  tubes.  The  anatomical 
conditions  in  the  male  (B)  and  the  female  (A)  are  precisely  the  same.  The  same 
description  applies  to  both. 
The  worm  being  properly  arranged  for  observation  under  the  microscope,  it  may  be 
seen  that  at  the  base  of  the  cephalic  tentacle,  on  either  side,  there  appear  the  ends  of 
two  independent  tubes  (fig.  23,  a,  1).  The  smaller  one  [a)  is  uivaginated  or  embraced 
by  the  larger  [h).  The  smaller  is  very  much  darker  (in  the  female)  in  colour’  than  the 
larger.  This  colour  is  due  to  the  vitellus  of  the  ova.  The  larger  one  is  pellucid  and 
colourless,  and  filled  (in  May  and  June)  with  ova  in  a very  immature  condition.  By  this 
distinction  of  colour  the  entire  organ  may  be  traced  backwards  in  the  direction  of  the 
tail  of  the  animal.  At  a short  distance  is  discernible  a second  bulge  (c)  in  the  trans- 
parent half  of  the  tube.  From  the  centre  of  this  bulge  or  dilated  portion  there  pro- 
ceeds a secondary  tube  (jf),  which,  forming  a short  loop  [j),  returns  upon  itself,  and  ends 
by  a similar  tube  in  the  longitudinal  tube  [a  a).  The  second  lateral  loop  is  formed  m 
the  same  manner.  The  third  and  the  last  (c  a)  is  formed  by  the  union  of  the  turn  long 
ducts  [h  c and  a a).  The  limbs  (/*,/*)  of  the  secondary  processes  have  at  the  points  of 
their  origin  (c,  c)  an  external  communication,  but  the  returning  or  dark-coloui’ed  limbs, 
Avhich  end  in  the  horizontal  duct  (^  a),  have  no  such  external  communication.  They 
open  outwardly  only  at  the  extreme  cephalic  termination  (a) ; all  the  loops,  hoAvever,  by 
some  means  or  other,  are  enabled  to  discharge  tlieii’  contents  into  the  appended  masses 
(e,  e,  e),  which  correspond  with  the  former  in  number  and  position. 
Now  if  the  connecting  tubes  (k,  k)  which  unite  the  secondary  loops  did  not 
exist,  the  analogy  between  the  latter  and  the  normal  or  standard  segmental  organ  of  the 
Nereid  group  would  be  at  once  admitted ; but  the  presence  of  intermediate  ducts,  AAliich 
unite  all  the  secondary  parts  into  one  system,  involves  apparently  the  morphology  of  the 
chlorsemacean  organ  in  ditficulty  and  doubt,  and  withdraAvs  it  from  the  chain  of  that 
series  which,  up  to  this  point  in  the  class,  has  been  found  to  consist  of  links  uninter- 
ruptedly connected  and  reciprocally  related. 
