OF  THE  EEPEODUCTIVE  OEGANS  OF  THE  ANNELIDS. 
139 
which  the  author  has  given  as  to  the  relation  in  which  the  great  ovarian  and  testicular 
masses  in  Nais  and  Lmibricus  stand  to  the  ciliated  tubes. 
If  the  author’s  interpretation  with  reference  to  the  reproductive  system  in  these  two 
genera  be  founded  in  truth,  then  it  must  follow,  of  absolute  necessity,  that  the  repro- 
ductive masses  in  the  Rotifera  bear  to  the  “ trumpet-ending  ciliated  tubes”  an  exactly 
similar  relation. 
This  inference  however,  thus  forcibly  pressed  upon  the  morphologist,  is  directly  con- 
tradicted by  one  of  the  most  recent  writers  on  natural  history,  who  declares  most  empha- 
tically that  the  ciliated  tubes  of  the  Rotifera,  which,  like  those  of  Lumhricus,  Nais  and 
the  Hirudinei,  open  by  trumpet-shaped  extremities  into  the  perigastric  chamber,  “ have 
nothing  whatever  to  do  with  the  generative  organs  * ! ” Leydig  has  already  suggested  a 
form-hkeness  between  the  “ arabeskenformige  Organ  der  Nephelis”  and  the  “rosetten- 
formige  Wimperorgan  der  Clepsine,”  and  the  “ Respirationsorgan  ” (as  called  by  him)  of 
the  Rotifera.  With  the  most  unfeigned  respect  for  this  sincere  and  straightforward 
naturahst,  the  author  is  compelled  to  observe  that  he  has  only  understood  one-half  of 
this  great  homological  question.  The  form-likeness  does  not  end  with  the  ciliated  tubes. 
It  extends  to  the  function^  to  the  associated  germinal  masses : though  in  both  the  tubes 
are  excretion  organs,  they  are  something  more  and  deeper. 
The  “ fiillhornformige  Wimperorgane  am  Gekrose  hangend”  (Mullee)  of  Synapta 
dirjitata,  have  already  been  compared  by  Leydig  to  the  “arabeskenformige  Organ”  of 
Nephelis,  and  to  the  “ rosettenformige  Wimperorgan”  of  Clepsina.  But  this  comparison 
involves  only  one-half  of  the  truth.  If  there  be  any  probability  in  the  view  maintained 
in  this  memoir,  the  ciliated  organs  of  Synapta  are  themselves  only  modifications  of  the 
cseca  or  tubules,  upon  which  the  office  of  reproduction  devolves,  being  ovaria  in  the 
female  and  testes  in  the  male. 
Both  are  equally  homologous  with  the  typical  organ. 
At  present  it  would  merit  the  censure  of  being  speculative,  if  an  attempt  were  made 
to  interpret  the  “respiratory  tree”  of  Holothuria  and  its  generative  system.  It  is  not 
improbable  that,  when  correctly  described,  they  will  legitimately  fall  within  the  definition 
of  the  segmental  system  as  propounded  in  this  memoir.  This  Echinoderm  is  so  rare 
however  in  the  British  seas,  that  conjecture  as  to  the  nature  and  character  of  its 
segmental  system  must  for  the  present  be  postponed. 
The  form  which  the  segmental  organ  exhibits  in  the  Terebellidee  and  Arenicolidte, 
meets  with  an  exact  counterpart  in  that  of  the  Sipunculidse  and  Echinidse.  In  the 
Sipunculan  Echinoderms  there  is  no  ciliated  organ.  Those  which  are  present  are 
engaged  in  the  generative  function.  They  are  simple  ceecal  pouches.  They  fail  in 
their  resemblance  to  their  homologues  in  the  Arenicolidae  in  this  respect,  that  at  their 
attached  extremities  they  are  not  divided  into  two  limbs  or  tubular  processes  as  in  the 
* This  is  all  that  I am  willing  to  say  in  this  place  ; but  I trust,  in  my  forthcoming  Eeport  on  the  Annelids, 
in  the  Transactions  of  the  Britisli  Association,  to  enter  at  much  greater  length  into  the  important  and 
interesting  history  of  the  “ segmental  organ.” 
