104  DE.  T,  WILLIAMS’S  EESEAECHES  ON  THE  STEHCTHEE  AND  HOMOLOGY 
description  conveys  an  exact  and  faithful  account  of  the  anatomical  structure  and  dispo- 
sition of  this  marvellous  organ. 
In  Lumbricus  terrestris  the  divisions  or  segments  of  the  alimentary  canal  posteriorly 
to  the  gizzard  and  proventriculus  are  very  numerous  and  closely  packed.  Each  “ ring” 
of  the  body  is  divided  from  the  adjacent  ones  by  the  intervention  of  membranous  par- 
titions, which  either  completely  or  partially  isolate  the  fluid  contents  of  each  annular 
space.  It  is  probable,  however,  that  the  fluid  of  the  general  cavity  freely  oscillates 
from  one  extreme  of  the  body  to  the  other  through  perforations  in  the  septa. 
But  whether  the  segmental  spaces  be  isolated  or  not,  the  ciliated  organs  which  they 
circumscribe  are  individualized  and  independent,  the  adjoining  ones  having  no  connexion 
whatever  with  one  another.  The  following  account  is  descriptive  of  all  those  which  are 
situated  posteriorly  to  the  proventriculus  and  the  generative  region. 
This  organ  is  far  more  complicated  in  structure  in  the  Earth-worm  than  it  is  in  any 
other  species  of  Lumbricus.  The  tube  which  connects  the  free  extremity  (fig.  of)  with 
the  fixed  end  (pf)  is  extremely  convoluted,  lengthened  and  thickly  intermixed  with  vessels. 
This  intermediate  tube  is  divisible  into  three  distinct  portions.  First,  a smooth- 
walled,  minutely  diametered  membranous  part,  which  extends  (from  e,  to  d)  from  the 
umbrella-like  termination  {f)  to  the  camerated  or  cellular  portion  (at  d).  This  divi- 
sion of  the  tube  is  uniform  throughout  in  diameter.  It  is  the  smallest  and  most  con- 
tracted of  the  entire  tube.  It  is  vigorously  ciliated  in  its  interior  bore.  The  ciliaiy 
current  sets  from  the  free  end  (f)  in  the  direction  of  the  fixed  end  («^).  The  next  divi- 
sion of  the  tube  extends  from  the  termination  of  the  smooth  membranous  part  (at  d) 
to  the  commencement  of  the  third  stage  (at  ^).  This  portion  is  not  ciliated.  The  walls 
bulge  out  into  lateral  cells.  This  part  of  the  tube  appears  to  split  into  two,  which 
unite  again,  as  is  the  case  in  the  corresponding  organ  of  the  Eotifera.  Such  an  arrange- 
ment is  not,  however,  represented  in  the  accompanying  figure  (5) ; for  it  is  only  apparent 
{d,  i). 
The  segmental  organ  in  this  portion  is  inextricably  blended  and  matted  up  with 
blood-vessels  (although  in  the  figure,  for  the  sake  of  clearness  and  simplicity,  the  vessels 
are  omitted).  From  its  peculiar  structure  and  extreme  vascularity,  this  part  may  be 
regarded  as  typically  indicating  the  true  seat  of  the  process  of  ovogenesis,  as  it  occurs  in 
the  segmental  organs  of  other  Annelids. 
The  fourth  division  of  the  tube  stretches  from  the  end  of  the  celled  portion  (^)  to  the 
commencement  of  the  muscular  part  [j).  This  again  is  strongly  ciliated.  In  fimction 
it  is  evidently  exclusively  expulsatory.  Its  walls  are  thick  and  contractile.  The  last, 
outermost  or  dilated  portion  [b),  bounded  internally  by  the  smooth-walled  division  (j)  and 
externally  by  the  attached  end  (a^),  is  however  the  most  striking  and  remarkable  part  of 
the  whole  apparatus.  It  is  almost  invariably,  in  the  months  of  July,  August  and  Sep- 
tember, crowded  with  the  ova  and  the  young  of  a certain  species  of  Nematoid  Entozoon 
(5,  A:),  which  might  readily  be  mistaken  for  the  ova  and  the  young  of  the  Earth-worm 
itself.  Although  formerly  deceived  by  the  appearance  presented  by  these  Entozoa,  a 
