OF  THE  EEPEODUCTIYE  OEGANS  OF  THE  ANNELIDS. 
133 
the  universal  rule  which  requires  that  the  segmental  organs  should  observe  a bilateral 
and  symmetrical  arrangement  in  all  Annelids,  is  entirely  set  aside  in  this  case.  This 
anomaly  will  be  found,  however,  rather  to  corroborate  than  to  violate  this  morphological 
principle. 
The  male  system  (d)  is  in  truth  composed  of  two  distinct  segmental  organs,  fused  into 
one  sacculus  in  the  median  line.  The  female  system  (e)  is  also  composed  of  two  distinct 
segmental  organs,  blended  like  the  male  into  one  vagino-utricular  pouch  in  the  median 
line. 
This  simple  \iew  of  the  case  resolves  all  difficulties.  If  the  Jbur  constituent  organs 
stood  apart  from  each  other  and  in  their  normal  anatomical  positions,  they  would  at 
once  be  seen  in  their  true  morphological  relations.  But  these  relations  are  not  the  less 
real,  albeit  they  are  rendered  the  less  obvious  by  the  fusion  of  the  two  opposite  organs. 
The  testes  (e  e,  fig,  25)  are  two  long  unbranched  csecal  appendages ; the  ovaria  (d  d, 
ff)  constitute  a -widely-distributed  and  complexly-branched  system  of  csecally-ending 
canals,  all  meeting  at  the  utricular  centre  (c).  No  part,  either  of  the  male  or  female 
system,  is  ciliated.  The  ova  are  at  all  times  contained  within  the  limits  of  the  tubuli 
(B) ; they  never  fall  into  the  general  ca-vuty  of  the  body.  In  this  particular  the 
segmental  organs  of  the  Planariea  agree  Avith  those  of  the  Hirudinei  and  Aphroditacese. 
It  should  here  be  noted  as  remarkable,  that  this  is  the  first  occasion  on  which  the 
anatomist  has  observed  a branched  structure  in  the  segmental  organ.  It  foreshadoAvs 
that  formation  Avhich  Avill  be  immediately  described  in  the  corresponding  organs  of  the 
Aphroditaceee.  The  looped  or  horseshoe-like  character  is  noAV  surrendered.  But 
although  this  type  of  structure  is  lost,  the  homological  identity  of  the  organ  itself  is 
unquestionably  'preserved.  Thus  far,  then,  the  history  of  the  reproductive  system  of  the 
Annelida  has  proved  to  rest  on  a natural  and  consecutive  series  of  individual  demonstra- 
tions, folloAving  one  another  in  an  order  of  obvious  and  necessary  sequence. 
We  now  approach  the  last  hnk  in  the  Annelidan  chain.  It  surpasses  all  the  others 
in  interest ; it  enables  the  morphologist  to  state  that  the  exception  proves  the  rule ; it 
is  hoped  that  it  Avill  bring  within  known  analogies  systems  of  organs  which  hitherto 
have  been  regarded  as  irreconcilable  anomalies.  This  remark  could  scarcely  until  now 
have  been  made  with  reference  to  the  segmental  organs  of  that  class,  of  which,  indeed, 
nothing  'whatever  Avas  knoAvn. 
The  author  is  not  aAvare  that  any  light  whatever  has  been  thrown,  by  any  former 
anatomist,  upon  the  nature  and  structure  of  the  generative  and  segmental  system  of  the 
Aphroditaceae. 
When  he  commenced  his  researches  on  this  subject,  he  had  to  grope  through  perfect 
darkness.  He  could  draw  no  light  from  anterior  investigations ; no  anatomist  had  ever 
before  recognized  the  generathe  organs  of  this  family  under  any  shape.  The  problem 
to  be  solved,  therefore,  was  not  simply  to  discover  the  true  organs  upon  which  the 
function  of  reproduction  devoh^d,  but,  being  knoAvn,  to  bring  them  within  the  sphere 
of  established  homologies. 
MDCCC'LVIII. 
T 
