OF  THE  EEPEODUCTIVE  OEOANS  OF  THE  AJ^NELIDS. 
97 
It  is  by  far  the  most  important  bearing  of  this  subject.  It  has  not  been  hinted  at  by 
any  preceding  observer. 
In  Nais,  and,  as  will  be  afterwards  shown,  in  Jjiimbricus,  it  may  be  readily  demon- 
strated that  one,  two,  or  possibly  more  of  the  “ segmental  organs  ” on  either  side  of  the 
body  undergo  a remarkable  increase  of  size  and  variation  of  form. 
In  Nais  it  often  happens  that  only  one  of  these  organs  on  either  side  is  thus  involved 
(fig.  2 a,  •,  compare  a,  a?  with  g,  g,  f in  the  same  figure).  At  some  seasons,  however 
(especially  one  in  which  the  weather  has  continued  for  some  time  warm  and  dry),  indi- 
viduals of  Nais  Jiliformis,  N.  ^roboscidea  and  N serpentina  may  be  found  in  which  two 
organs  on  either  side  have  undergone  a marked  generative  development.  This  was 
remarkably  the  case  in  Nais  filiformis  in  the  summers  of  1850-61*.  Four  organs  (two 
on  either  side)  were  then  constantly  found  in  an  enlarged  and  modified  condition.  The 
two  anterior  were  developed  into  saccuh,  in  which  were  lodged  arrow-shaped  lemnisci  or 
intromittent  organs.  Dui’ing  the  present  year,  while  conducting  many  hundred  exami- 
nations, no  single  individual  of  the  same  species  could  be  discovered  in  this  condition. 
The  two  organs  in  the  ring  immediately  in  front  of  the  genital  segment  have  this  year 
exhibited  the  ordinary  or  undeveloped  state.  It  is  therefore  evident  that  only  two 
segmental  organs,  the  one  being  developed  into  the  male  and  the  other  into  the  female 
moiety  of  the  reproductive  system,  are  necessary  to  the  generative  maturity  of  the  indivi- 
dual. The  anterior  organs  may  or  may  not  experience  a special  growth.  When  this 
has  happened,  they  are  accessory,  not  essential  in  office. 
The  two  segmental  organs  (fig.  2 «,  k and  6)  which  form  the  basis  of  the  reproductive 
masses  (7,  o),  are  observed  even  on  first  view  to  be  similar  in  general  outline  to  those 
which  are  repeated  in  every  ring  of  the  body  (^,  g).  But  on  minute  comparison,  they 
will  be  foimd  in  reality  to  be  identical  with  the  latter,  difiering  only  in  size  and  in  the 
shape  of  some  of  their  parts.  The  dilated  portions  (a,  a^)  correspond  in  the  most 
obvious  manner  with  the  equivalent  parts  (h)  of  the  other  organs.  The  umbrella-hke 
extremities  (k,  e)  (which  are  the  same  in  form  on  the  ovarian  and  testicular  sides)  are 
seen  at  once  to  be  the  counterpart  of  the  free  ciliated  ends  {g,  g)  of  the  ordinary  organs. 
* This  condition  is  correctly  represented  in  pi.  viii.  fig.  72,  appended  to  my  Eeport  on  the  British  An- 
nelida*. I hope  I may  be  permitted  in  this  place  to  observe  that,  between  the  results  of  my  recent  and 
those  of  my  former  investigations  on  the  reproductive  system  of  the  Annelids,  there  is  no  essential  difference 
as  far  as  the  latter  were  carried.  The  following  passage  proves  that  I then  suspected  that  the  generative  seg- 
mental organs  were  only  modifications  of  the  non-geuerative “ A comparison  between  the  familiar  figures 
of  Duoes  and  those  which  ai’e  published  for  the  first  time  in  comiexion  with  this  memoir,  will  enable  the 
physiologist  at  once  to  perceive  that  the  whole  system  is  limited  by  Duges  to  the  glandular  mass  which  is  so 
readily  observed  about  the  anterior  third  of  the  body,  whereas  in  reality  this  only  constitutes  one  segmental  unit, 
more  developed  only  than  those  which  are  repeated  in  every  ring  of  the  hody'' — Loc.  cit.  p.  264.  The  results 
of  my  subsequent  inquiries,  which  it  is  the  purport  of  this  paper  to  state,  enable  me  now  to  contribute  very 
materially  to  a better  knowledge  of  the  anatomy  and  physiology  of  this  part  of  the  Annelidan  organization, 
Transactions  of  the  Britisli  Association,  1851. 
