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VI.  Researches  on  the  Structure  and  Homology  of  the  Reproductive  Organs  of  the  Annelids. 
By  Thomas  Williams,  M.D.,  F.R.S.,  Physician  to  the  Swansea  Infirmary. 
Communicated  hy  Thomas  Bell,  Esq.,  F.R.S.,  President  of  the  Linnean  Society,  Ac. 
Eeceived  December  30,  1856, — Eead  February  12,  1857. 
Although  several  distinguished  comparative  anatomists  have  done  much  by  their  labours 
to  elucidate  the  general  organization  of  the  Annelids,  the  reproductive  system  of  organs 
in  this  class  has  been  little,  if  at  all,  investigated.  On  this  account  the  author  of  this 
memoir  is  tempted  to  lay  before  the  Eoyal  Society  the  results  of  a systematic  series  of 
researches  on  this  subject,  on  which  he  has  been,  for  some  years,  laboriously  occupied. 
These  researches  conveniently  arrange  themselves  under  two  leading  divisions. 
The  first  will  include  a merely  anatomical  description  of  the  chief  or  typical  varieties 
of  form  and  structui’e  which  these  organs  are  found  to  exhibit  in  the  leading  genera  of 
the  class ; while  the  second  will  embrace  a brief  statement  of  such  homological  views  as 
the  ascertained  facts  with  respect  to  their  structure,  form,  and  anatomical  relations  may 
appear  to  warrant. 
As  the  organ  upon  which  always,  in  some  part  or  other  of  the  body  of  the  Annelid, 
the  ofiice  of  reproduction  devolves,  is  frequently  in  other  parts  diverted  to  other  pur- 
poses, and  modified  in  outward  characters,  it  will  prevent  circuitousness  of  expression  if 
at  the  outset  a name  be  adopted,  under  which,  whatever  its  place,  size  or  form,  this 
organ  may  be  generically  distinguished. 
Under  the  appellation  of  the  “ segmental  organ*,”  accordingly,  it  is  proposed  to  de- 
scribe that  viscus  upon  the  basis  of  which,  under  several  striking  variations  of  place  and 
figure,  are  always  ingrafted  the  true  generative  structures.  By  way  of  a general  historical 
introduction,  the  author  will  content  himself  with  the  following  citation  from  the  recently 
published  lectures f of  Mr.  Huxley,  exhibiting  the  state  of  knowledge  on  this  subject 
at  the  date  of  its  publication,  July  23,  1856.  “The  genitalia  of  the  typical  Annelida 
are  excessively  simple  in  their  structure ; indeed,  special  reproductive  organs  can  hardly 
* This  is  an  unobjectionable  title  ; it  implies  no  theory,  it  simply  states  the  fact  that  the  organ  is  repeated 
more  or  less  regularly  in  the  segments  of  the  body.  No  other  organ  in  the  body  of  the  Annelid  is  “ seg- 
mental;” every  other  organ  is  continuous  throughout  the  body.  This  is  the  case  with  the  alimentary,  the 
nervous  and  the  vascular  systems.  The  feet  are  not  “ organs.”  Indeed,  so  intimate  in  an  anatomical  sense 
is  the  relation  between  the  segmental  organ  and  the  foot,  that  in  the  development  of  the  embryo  Annelid 
they  constitute  one  system.  The  hoUow  bases  of  the  feet  are  so  frequently  the  depositories  of  the  genera- 
tive products,  that  they  may  be  regarded  as  bearing  the  same  relation  to  the  segmental  organ  as  the  uterus 
does  to  the  ovaries  of  the  Mammal. 
t Medical  Times  and  Gazette,  1856-57. 
MDCCCLVIII. 
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