96  DE.  T.  WILLIAMS’S  EESEAECHES  ON  THE  STEECTLTIE  AND  HOMOLOGY 
beyond  the  possibility  of  doubt  that  the  organ  in  this  ordinary  state  subserves  the  func- 
tion of  discharging  externally  the  fluid  contained  in  the  general  cavity  of  the  body. 
This  fluid  must  necessarily  escape  in  body  through  the  tube.  This  organ  does  not  appear 
to  be  endowed  with  any  selective  power  over  the  principles  or  elements  of  which  the 
fluid  is  composed.  It  conveys  externally  the  entire  body  of  the  nutritive  fluid,  leaving 
behind  only  the  corpuscles.  This  is  a fact  which  is  capable  of  being  brought  in  a direct 
manner  before  the  mind  and  under  the  eye  of  the  physiologist.  Around  it  there  crowd 
many  suggestions.  It  proves  that  in  this  comparatively  exalted  class  of  animals,  the 
process  of  secretion,  in  one  case  at  least,  is  accomplished  by  a mechanism  comparatively 
rude,  viz.  by  the  direct,  unchanged  siphonic  discharge  (outwardly)  of  the  body  of  the 
nutritional  fluid. 
The  segmental  organs  in  Nais  cannot  convey  externally  either  the  normal  corpuscles 
of  the  chylaqueous  fluid,  or  the  spermatic  products ; these  bodies  are  by  many  times  too 
large  to  traverse  the  bores  of  the  tubes.  [But  in  this  genus  neither  the  ova  nor  the  sper- 
matozoa are  at  any  time  found  in  the  general  cavity.]  They  cannot  convey  a cuiTent  of 
water  from  without  to  within,  from  the  exterior  into  the  perigastric  chamber.  This 
would  be  contrary,  directly  opposed,  to  the  ciliary  motion  vTithin  the  tube,  which  sets 
from  within  outwards. 
They  cannot  belong,  as  suggested  by  Leydig,  to  the  mechanism  of  the  respu'atory  act. 
It  is  contrary  to  all  analogy  to  suppose  with  him  that  they  are  the  agents  of  the  expira- 
tory act.  The  inference  that  they  are  simply  discharge-tubes  to  the  chylaqueous  fluid,  does 
not  necessarily  imply  that  they  are  renal  in  office,  as  suggested  by  several  authors.  The 
preceding  description  applies  only  to  the  segmental  organ  in  Nais  serpentina,  as  it  is 
distributed  throughout  that  part  of  the  body  of  the  worm  which  is  behind  the  repro- 
ductive mass. 
In  other  species  of  this  genus  the  same  organ  occurs  under  characters  more  or  less 
modified. 
In  Nais  filiformis  it  (fig.  2 g,  g)  is  not  so  tape-hke  or  flattened  as  in  N.  serpentina.  The 
trumpet-end  is  difierently  fixed  in  the  cavity.  The  tube  in  its  mid-portion  is  also  dis- 
similarly coiled.  The  attached  end  (A)  is  more  muscular ; the  free  enlarged  extremity  [g) 
is  more  elongated ; but  in  this  species,  as  in  N.  serpentina,  the  organ  consists  of  a single 
tube,  beginning  internally  in  an  expanded  ciliated  extremity,  floating  freely  m the 
general  cavity,  and  terminating  in  a thickened  dilated  portion,  m which  in  an  especial 
manner  is  seated  a strong  muscular  power.  In  N.  proboscidea  it  is  formed  after  the 
pattern  of  that  of  N.  serpentina.  It  is,  however,  more  bulbous  at  its  free  extremity,  and 
more  cord-like  in  figure.  A further  variety  occurs  in  N. parasita.  In  N.pusulosa  (mihi) 
(not  uncommonly  found,  at  certain  seasons,  in  the  finest  sand  of  the  sea-shore),  another 
modification  occurs  in  the  form  and  structm’e  of  this  organ. 
It  remains  now  to  investigate  the  claims  of  this  organ  in  a new  and  hitherto  unthought- 
of  relation,  namely,  in  that  bearing  in  which  it  connects  itself  with  the  generative  or 
reproductive  structures. 
