OF  THE  EEPEODUCTIVE  OEGAHS  OF  THE  ANNELIDS. 
125 
consists  of  a tube,  highly  ciliated,  both  ends  of  which  communicate  with  the  exterior. 
The  ingoing  limbs  (fig.  14,  cZ  tZ)  are  situated  in  the  immediate  neighbourhood  of  each 
dorsal  foot.  The  outgoing  limbs  {h  Z»),  considerably  longer  and  more  tubular  than  the 
former,  open  externally  to  the  median  side  of  the  root  of  each  ventral  foot.  The  cilia 
by  which  this  horseshoe  tube  is  lined  are  highly  vigorous,  capable  of  supporting  a 
powerful  current.  Thus  much  is  quite  certain*,  that  this  current  arises  externally  and 
terminates  externally.  It  can  consist,  therefore,  only  of  the  exterior  element.  The  cur- 
rent of  the  element  thus  excited  can  only  traverse  the  organ  itself.  It  cannot  enter  into 
the  perigastric  chamber.  But  it  can,  as  will  now  be  shown,  convey  outwards  the  gene- 
rative products  along  the  outgoing  limb.  And  this,  as  evidence  accumulates,  will  appear 
as  the  true  function  of  this  water-current. 
With  the  short,  broad,  ingoing  limb  is  intimately  connected  the  tuft  of  caecal  vessels 
{e  e,  fig.  14)  to  which,  in  other  Annelids,  reference  has  already  so  often  been  made. 
Now  if  the  demonstration  could  be  pushed  no  further  than  this  point,  it  would  con- 
fessedly be  difficult  to*  connect  this  horseshoe  ciliated  tube,  and  its  associated  tuft  of 
vessels,  with  the  true  reproductive  function.  But  it  is  capable  of  proof  that  the  ova  in 
the  female,  and  the  sperm-cells  in  the  male,  escape,  although  in  some  undetermined  mode 
and  by  some  undemonstrated  passage,  from  this  organ  into  the  complexly  areolated  tissue 
(shown  at  fig.  16  e i a g)  which  fills  the  chamber  of  the  pedal  appendages.  From 
various  observations  the  author  is  persuaded  that  this  tissue  is  a development  from  the 
segmental  mxgan  (at  fig.  16,  a single  cutus  filled  with  this  ovarian  tissue  {d)  and  its  blood- 
vessels is  figured),  and  that  in  size  and  vascularity  it  is  proportionate  to  the  stage  at 
which  the  contained  germinal  elements  have  arrived  j*. 
In  the  Nereid  group  generally  the  female  is  much  larger  than  the  male.  This  differ- 
ence is  very  striking  in  W.  lamelligera  and  N.  renalis.  The  cephalic  extremity  of  these 
worms  is  entirely  destitute  of  the  “ segmental  organ.”  This  is  also  remarkably  the  case 
in  Nephthys  Hombergii.  The  nervous  chord  in  this  oesophageal  region  is  highly  deve- 
loped in  all  the  Nereid  group. 
This  feature  of  structui’e  is  also  very  prominent  in  the  Ariciadse  J.  The  segmental 
organ  in  this  family  is  limited  in  its  distribution  to  the  two  posterior  thirds  of  the  body. 
The  ova-  and  sperm-bearing  masses  (fig.  VJ  ah  c and  a h c)  exhibit  the  same  relation 
* In  Sjpio  vulgaris  and  S.  coniocepliala  I have  enjoyed  the  advantage  of  demonstrating  this  fact  to  Mr.  Busk 
and  Dr.  Caepenteh. 
t Until  I came  to  study  the  generative  system  of  the  Annelids,  I always  looked  upon  the  florid  and 
brightly  vascular  elements  of  the  feet  as  specially  designed  to  fulfil  a respiratory  function.  I am  now  con- 
vinced that,  if  this  purpose  is  fulfilled  at  aU,  it  is  only  so  incidentally.  The  great  and  paramount  office  of 
these  specially  developed  parts  of  the  vascular  system  is  to  supply  the  means  of  growth  to  the  generative 
organ.  It  is  now  almost  certain  that  what  Milke-Edwaeds  has  called  the  “branchial  hearts,”  in  the 
Eunicidae,  are  sacculated  developments  of  the  vessels  designed  to  supply  the  reproductive  system. 
J The  drawings  which  accompanied  the  original  draught  of  the  present  paper  to  the  Eoyal  Society,  in- 
cluded carefully  executed  figures  of  four  species  of  Aricia,  viz.  A.  Cuvieri,  A.  Owenii  (mihi),  Janira  crini- 
gera  (liiihi),  and  Janira  illecta  (mihi). 
MDCCCLVIII. 
S 
