124  DE.  T.  WILLIAMS’S  EESEAECHES  ON  THE  STEHCTUEE  AND  HOMOLOOT 
In  every  species  of  Sahella  and  Serpula  examined  by  the  author,  the  sexes  have  been 
seated  on  separate  individuals.  In  the  majority  of  species  the  ova  Qi)  have  a bright  pink 
colour.  The  female,  by  this  mark,  may  be  readily  distinguished  from  the  male,  the 
colour  of  which  is  brownish  or  greenish*.  From  these  statements  it  follows  that  the 
segmental  organ  in  Sahella  and  Serpula  are  permanent  viscera^  and  not  temporary  forma- 
tions, as  affirmed  by  De  Quateefages.  In  fact,  it  is  a mistake  to  suppose  that  the  pro- 
cess of  ova-  and  sperm-development,  in  any  Annelid,  is  limited  to  a month  or  two  in  the 
year.  Ova  in  an  immature  state  are  found  in  the  bodies  of  the  youngest  as  of  the 
oldest.  This  fact  proves  that  the  structures  by  which  the  ova  are  generated  must  be 
permanently  present. 
The  preceding  account  of  the  segmental  organs  of  the  Sabelhdse  and  Serpuhdse  has 
been  drawn  from  an  examination  of  the  following  species : — S.  alveolata,  8.  vesiculosa, 
Leucodore  dliatus  (very  favourable  for  this  purpose),  Amphitrite  auricoma,  Sahella  a 
sang  vert,  Sahella  hospita  (mihi).  Of  the  Serpulidee  the  author  has  only  studied  with 
care  the  following  species : — 8.  triguetra,  S.  contortuplicata,  S.  lactea.  In  all  the  Sabel- 
lidee  and  Serpulidse  the  segmental  organ  is  present  in  every  ring  of  the  body,  except  the 
thorax  and  the  caudal  appendage. 
The  Nereid  group. — Under  the  head  of  the  Nereid  group,  for  the  purposes  of  this 
memoir,  several  families  of  “ errant  Annelids  ” will  be  included.  Of  the  reproductive 
organs  of  this  group  nothing  whatever  is  known.  No  comparative  anatomist  has  even 
suspected  the  existence  of  the  “ segmental  organ  ” in  any  one  of  the  members.  Staa- 
Nius,  Kollikee  and  De  Quateefages,  and  probably  other  microscopic  obsen-ers,  have 
indeed  established  the  fact  that  the  ova  and  the  spermatozoa  are  found  on  separate 
individuals.  Hence  has  been  inferred  the  dioecious  character  of  this  group.  Not  one 
single  observation  has  ever  been  made  by  any  of  these  observers  as  to  the  character  of 
the  reproductive  organs  themselves.  The  author  begs  therefore  to  offer  the  succeeding 
description  as  drawn  exclusively  from  his  own  researches. 
In  every  Nereid,  the  ciliated,  looped,  horseshoe  organ  to  which  the  author  has  apphed 
the  name  of  the  “ segmental  organ,”  exists  without  a single  exception. 
The  demonstration  of  this  organ  in  Nereis  margaritacea  is  attended  by  great  difficulty. 
It  can  only  be  accomplished  either  by  the  tedious  process  of  placing  annular  sections  of 
the  body  under  the  microscope,  or  by  the  discovery  of  a young  specimen  at  that  age  at 
which  the  integuments  are  transparent ; and  then  it  is  only  in  the  region  of  the  tail  of 
the  worm  that  the  ciliated  organ  becomes  visible  to  the  eye.  In  N.  margantacea  it 
* Stannitjs  and  De  Quatbeeages  have  already  pointed  out  the  fact  that  the  sexes  were  seated  on  sepa- 
rate individuals  in  the  Sabellidw ; but  it  is  evident  from  the  following  passage,  that  De  Qttatbeeages  has 
altogether  overlooked  the  real  ovaria  and  testes  of  these  Annelids,  and  mistaken  for  them  the  masses, 
attached  to  them,  of  the  ova  and  sperm-cells.  He  says  in  his  essay,  “Sur  les  Hermelliens  ” (Ann.  d.  Sc. 
Nat.  1848,  1. 10.  p.  46)  ; “ Le  testicule  consiste  en  une  sorte  de  trame  areolaire  d’lme  tenuite  extreme,  qui 
part  de  I’aponevrose  mediane,”  &c. . . . “ L’ovaire  est  en  tout  semhlable  au  testicule.”  De  Quateefages 
then  states  that  these  organs  are  temporary,  and,  after  the  ova  and  the  sperm-cells  pass  into  the  general 
cavity,  they  disappear  through  atrophy.  It  will  be  seen  how  entirely  the  results  stated  in  the  text  difler 
from  those  published  by  the  French  naturalist. 
