1 42  DE.  T.  WILLIAMS’S  EESEAECHES  ON  THE  HOMOLOGY  AND  STEHCTTEE 
two  limbs  (^,  c)  of  the  loop  h.  In  a the  ova,  j,  are  large  and  matnre  ; in  the 
limb  which  is  the  true  ovary  and  ingoing  hmb,  they  are  small,  pellucid 
{k)  and  destitute  of  vitellus.  The  arrows  mdicate  the  ova  pursuing  their  path 
outwards ; dh\s,  the  duct  by  which  the  so-called  “ respiratory  sac  ” of  Duges, 
Im,  communicates  with  the  ingoing  hmb  of  the  segmental  organ;  i is  the 
orifice  by  which  the  sac  of  Duges  communicates  with  the  general  ca%ity  of  the 
body ; ef,  the  vascular  system  of  the  ovarian  hmb. 
Fig.  10.  The  ovarian  segmental  organ  of  Alhione  muricata,  differing  very  triflingly  from 
the  former: — d,  ovarian  hmb ; f,  immature  ova ; A,  loop  ; c,  duct  leading  from 
the  sac,  a ; b,  internal  opening ; e,  oviduct  or  outgoing  hmb ; g,  mature  ova 
contained  in  it. 
Fig.  11.  Segmental  organ  of  Arenicola piscatorum,  with  its  vascular  appendage : — A*,  ex- 
ternal orifice  or  commencement  of  ingoing  hmb,  A d,  which  opens  into  the 
fundus,  c m,  of  the  organ;  h,  B,  B*,  the  outgoing  hmb,  from  which,  at  n,  di- 
verges a process  by  which  the  ova  and  sperm-cells  are  conducted  into  the  gene- 
ral cavity  of  the  body ; I represents  a large  glandular  organ,  into  which,  about 
the  middle  of  its  course,  the  hmb  developes  itself ; i h and  g'^  (f^  great  vascu- 
lar trunks  of  the  organ ; e,  the  great  lateral  blood-pouches,  loop-shaped  ; 
k,  capillary  plexus,  by  which  the  body  of  the  organ  is  supphed  with  blood. 
Fig.  12.  Two  segmental  organs  (from  the  same  side)  of  Terehella  nehulosa.  B,  fuh-drawn ; 
A,  in  outline,  to  show  the  course  of  the  internal  cihary  currents.  Each  organ 
is  divided  into  two  weU-marked  halves.  B m m,  dark  glandular  and  iugouig 
half ; n n,  light-coloured,  membranous,  outgoing  half ; f,  true  seat  of  ovo- 
genesis with  its  complex  vascular  apparatus,  A ; at  e diverges  the  tube  along 
which  the  ova  and  spermatozoa  find  then*  way  into  the  general  ca^ity. 
Fig.  13.  Segmental  organ  of  Sabella  alveola,  viewed  as  a transparent  object,  differing  in 
several  respects  from  that  of  Terehella : — a,  ingoing  hmb ; f g e,  vascular  ap- 
pendage ; d,  fundus  of  the  loop ; d b,  outgoing  hmb  ; c,  point  at  wlhch  the 
ova  enter  the  reproductive  appendage ; h,  ova ; i,  spermatozoa. 
Fig.  14.  Two  segments  of  the  body  (near  the  tail)  of  a very  young  Nereis  margantacea. 
showing  the  relative  position  of  the  segmental  organs,  d,  d,  d,  d,  "siewed  as  a 
transparent  object,  under  strong  pressure : — c,  c,  sacculi  of  the  intestine ; d,  d, 
ingoing  limbs  of  the  segmental  organs ; a,  fundus ; e e,  vascular  appendage ; 
b,  long  tubular  outgoing  hmb. 
Fig.  15.  Vertical  section  of  one  half  (left)  of  a ring  or  segment  of  the  body  of  a fuU-sized 
female  Nereis  niargaritacea,  and  looked  at  from  the  side,  showing  the  relatiA  e 
places  of  the  appended  ovarian  mass,  g i e,  and  the  segmental  organ ; a b d. 
intestine. 
lig.  10.  The  cirrus  A of  the  former  figure  enlarged,  representing  the  intimate  blending 
of  the  ovarian  mass,  dec,  and  the  vessels,  b. 
