116  DE.  T.  WILLIAMS’S  EESEAECHES  ON  THE  STEUCTL’HE  AND  HOMOLOGY 
as  the  oviduct,  but  it  is  also  a mtellarium.  The  tubular  limb  {g  a)  is  entirely  devoid 
of  vessels.  No  part  whatever  of  the  segmental  organ  in  the  common  leech  is  ciliated. 
In  this  particular  it  strikingly  departs  from  that  of  Nais  and  lAimbricus.  This  observa- 
tion applies  also  to  the  segmental  organ  of  Alhione.  It  is  of  great  homological  import- 
ance to  note,  that  in  Hirudo  and  Alhione  (fig.  10),  probably  in  aU  the  genera  of  this 
family,  the  segmental  organ  is  made  the  uterine  receptacle  of  the  ova  as  they  are  being 
thrown  off  from  the  ovary.  This  is  not  the  case  in  any  other  family  of  Annelids  that  the 
author  is  acquainted  with,  except  the  Aphroditacece  and  Glycera  alba.  In  JAais  and  Lum- 
bricus  the  sperm-  and  germ-structures,  as  has  been  explained  (figs.  6,  7,  8),  are  accu- 
mulated by  the  side  of,  or  as  an  appendage  to,  this  organ.  In  other  Annelids,  as  will 
be  afterwards  explained,  other  deviations  from  this  mode  of  storing  the  generative  pro- 
ducts occur.  It  follows  therefore  that,  in  the  Leech  tribe,  the  ova  at  aU  events  at  no 
time  reach  the  cavity  of  the  body.  This  may  be  one  reason  why  m this  family  the 
perigastric  cavity  is  so  much  contracted,  and  the  contained  fluid  so  reduced  in  volume. 
In  Alhione  muricata,  several  specimens  of  which  the  author  has  examined  with  great 
care,  the  female  system  exhibits  precisely  the  same  characters  as  that  of  the  common 
leech.  In  Alhione  the  annuli  are  not  so  close  and  numerous ; consequently  the  ovaria, 
which  are  synonymous  with  the  segmental  organs,  are  not  so  close  and  numerous  as 
they  are  in  the  common  leech. 
They  are  much  larger,  broader,  and  more  evident  than  those  of  the  latter  Annelid. 
The  months  of  July,  August,  and  September  should  be  selected  for  the  exammation 
of  this  worm.  When  opened,  after  the  manner  already  explained  in  the  case  of  the 
common  leech,  the  whole  interior  of  the  body,  from  the  head  to  the  tail,  Avill  be  found 
to  be  lined  by  what  appears  to  the  naked  eye  to  consist  of  a bright  pink-coloured 
flocculent  lining  membrane.  But  when  detached  in  pieces  and  placed  under  the  micro- 
scrope,  its  real  composition  becomes  evident. 
The  pink  tint  is  due  to  the  colour  of  the  vitellus  of  the  ova,  and  the  membrane- 
like  appearance  of  the  whole  arises  from  the  union  and  apposition  of  the  individual 
ova-laden  segmental  organs.  Successfully  individualized,  these  organs  in  Alhione  (fig.  10) 
will  be  found  to  present  the  same  outline  as  those  of  the  Leech.  They  are  looped, 
horseshoe-like  tubes.  They  are  utero-ovarian  as  in  the  Leech.  Alhione  differs  from  the 
Leech  in  two  important  organic  facts.  In  Alhione  the  cavity  of  the  body  is  wide  and 
spacious ; in  the  Leech  it  is  contracted  and  numerously  bridled. 
In  Alhione  the  blood  vascular  system  is  in  a rudimentary  stage ; in  the  Leech  it  is 
highly  developed.  The  ovarian  limb,  therefore,  in  the  former  is  not  vascular  as  in  the 
latter. 
This  completes  an  outline  of  the  account  which  the  author  has  to  offer  of  the  female 
system  of  the  Hirudinei : — how  universal  in  extent  and  distribution,  compared  with  that 
which  has  hitherto  been  received  as  the  utero-ovarian  apparatus  in  these  Annelids!* 
* In  the  grand  edition  of  the  Regne  Animal,  the  female  system  in  Hirudo  vacca  (see  pi.  24,  fig.  1,  p.  213) 
is  figured  and  described  as  consisting  of  a single  pouch,  the  uterus  (with  its  appended  vagina)  and  two 
