OF  THE  EEPEODUCTIVE  OEGANS  OF  THE  ANOTILIDS. 
105 
critical  study  of  their  structure  has  convinced  the  author  that  they  are  not  the  young  of 
the  Earth-worm,  but  individuals  belonging  to  the  genus  Filaria. 
This  dilated  muscular  portion  of  the  segmental  organ  is  not  ciliated  internally.  But 
its  walls  are  capable  of  contracting  vermicularly  or  peristaltically. 
The  vascular  system  connected  with  the  segmental  organ  receives  a special  develop- 
ment. In  Nais,  however,  this  is  not  the  case. 
During  the  past  summer,  1856,  the  author  was  so  fortunate  as  to  discover  five  or  six 
specimens  of  Earth-worm  very  large,  the  ordinary  segmental  organs  of  which  were  pre- 
cisely in  the  condition  illustrated  in  fig.  5,  in  which  the  vascular  system  had  acquired  an 
extraordinary  degree  of  development  {g  g and  h h).  The  vessels  connected  with  the  ciliated 
tubes  of  the  ordinaiy  as  well  as  with  those  of  the  generative  segments  were  on  these  occa- 
sions found  to  be  in  this  remarkable  state.  This  botryoidal  condition  of  the  vessels  has 
been  cursorily  alluded  to  by  Siebold  and  Gegenbauee.  It  is  not  present  in  every  indi- 
vidual and  on  all  occasions.  It  is  in  some  way  connected  with  the  condition  of  sexual 
maturity.  That  this  is  the  case  the  author  has  assured  himself  by  a great  number  of 
most  careful  dissections.  Sometimes  the  vascular  system  of  the  segmental  organ  is  in  a 
state  of  almost  entire  abeyance.  When  present  under  the  most  evident  circumstances 
(as  in  fig.  5),  it  may  be  described  as  consisting  of  three  parts.  First,  of  two  or  three 
large  trunks  [n^  g,  m),  which  curve  upwards  from  the  ventral  to  the  dorsal  trunks. 
These  vessels  form  thus  a frameivork  by  which  the  slender  ciliated  tube  (a,  a^)  is  held 
vertically  in  situ,  they  themselves  being  vertically  disposed. 
Between  the.  primary  vertical  trunks  extends  a vast  multitude  of  secondary  branches 
{I,  1),  which  further  subdiride  to  form  a dense  plexus  of  smaller  vessels  (omitted  in  the 
figure  for  clearness’  sake),  in  the  meshes  of  which  the  ciliated  tube  [a,  (F)  is  entangled. 
It  is  the  presence  of  this  mass  of  vessels  which  renders  it  so  extremely  difficult  to  trace 
the  coils  {d,  i,j)  of  the  tube.  This  reticular  plexus,  in  a more  or  less  pronounced  form, 
is  much  more  frequently  present  than  that  curious  portion  of  the  vascular  system  next 
to  be  examined. 
As  already  stated,  in  the  Earth-worm,  at  certain  seasons  and  conditions  of  growth,  a 
dense  mass  of  florid  blood  is  attracted  to,  and  held  in  the  region  of  the  segmental  organs. 
It  is  contained  at  these  times,  not  in  ordinary  cylindrical  vessels,  but  in  capacious  lateral 
csecal  branches,  terminating  in  large  bulbous  pear-shaped  extremities  [h,  h).  Now  this 
portion  of  the  vascular  apparatus  of  the  organ  evidently  constitutes  a special  provisio7i. 
What  is  its  purpose  1 It  is  not  fitted  in  any  way  or  in  any  sense  to  aerate  the  contained 
fluid. 
In  virtue  of  a contractile  power  with  which  the  bulbous  extremities  are  endowed,  not 
only  are  they  adapted  to  attract  towards,  and  detain  in  the  neighbourhood  of  the 
segmental  organ  a large  extra  supply  of  blood,  but  they  are  also  fitted  to  exercise  a 
supplementary  power  to  drive  into  the  plexus  of  capillaries  which  more  immediately 
embraces  the  coils  of  the  ciliated  tube  an  extraordinary  supply  of  blood.  Does  not 
this  definition  at  once  suggest  the  inference,  that  therefore  at  certain  seasons  and  under 
