98  DE.  T.  WILLIAMS’S  EESEAECHES  ON  THE  STEUCTL’HE  AND  HOMOLOGY 
The  latter  are  more  pear-shaped  ; the  former  more  umbrella-  or  fan-like.  This  difference 
of  figure,  it  will  be  afterwards  proved,  does  not  involve  a difference  of  function. 
The  intermediate  cihated  tubes  {j,  d)  are  specially  distinguished  only  for  their  great 
length  and  thickness.  In  all,  the  ciha  at  the  free  fioating  extremity  of  the  organ  beat 
in  such  a manner  as  to  raise  a current  setting  strongly  into  the  organs,  and  out  of  the 
body  of  the  animal.  This  fact  is  worthy  of  note.  It  proves  that  neither  the  ova  nor 
the  sperm-cells  can  escape  through  or  along  these  ciliated  tubes  into  the  cavity  of  the 
body,  supposing  that  in  this  Annelid,  as  in  many  others,  they  were  destined  at  some 
time  to  find  their  way  into  this  chamber.  But  the  author  has  cominced  himself,  by 
recent  observations,  that  this  never  takes  place  in  this  genus.  The  general  ca\ity  is  not 
used  at  any  time,  or  under  any  circumstances,  for  the  purpose  of  incubation. 
The  ciliated  tubes  of  the  generative  organs,  it  must  therefore  be  inferred,  fulfil  the 
same  office  as  those  of  the  ordinary  segmental  organs ; that  office  is  imdoubtedly  to 
discharge  externally  the  ffuid  of  the  perigastric  cavity.  .The  cmnent  thus  raised,  in  the 
case  of  the  special  organs,  serves  also  subsidiarily  to  convey  outwards  the  generative  pro- 
ducts. The  wider  bore,  more  vigorous  cilia,  and  stronger  currents,  are  well  adapted  in 
them  for  this  purpose*. 
It  is  of  great  importance  to  place  beyond  dispute  the  mode  in  which  the  generative 
masses  (fig.  2 i,  b)  occupying  the  special  segments  are  related  to  the  ciliated  tubes  [j,  d). 
The  first  impression  is  that  there  must  be  some  connexion  between  them ; else  why  the 
enormous  growth  of  the  tubes  in  the  reproductive  ring,  as  compared  with  those  of  other 
parts  ] The  demonstration  of  this  point  is  attended  with  great  difficult)".  The  rolling  of 
the  animal  under  view,  and  the  density  of  the  integuments,  preclude  a clear  inspection ; 
but  it  may  be  constantly  seen  that  the  ovarian  mass  {c  b)  moves  to  and  fro  ivith  the  dilated 
portion  of  the  tube  [a?).  It  is  impossible  to  see  the  opening  by  which  the  ova  arrive 
in  the  interior  of  this  part  (J)  {utriculus)  of  the  tube ; that  they  do  get  there  is,  however, 
certain,  for  they  have  been  actually  seen  therein  on  several  occasions  by  the  author,  as 
shown  at  fig.  2 a^.  From  this  portion  of  the  tube  they  escape  by  the  external  orifice. 
It  was  the  discovery  and  the  clear  definition  of  this  important  anatomical  fact,  which 
first  convinced  the  author  that  he  was  justified  in  deducing  from  this  arrangement  the 
final  conclusion,  that  the  ovarian  and  testicular  masses  in  Nais  did  not  constitute  detached 
and  independent  viscera,  but  that  they  were  structures  which  were  evolved  from,  or  ingrafted 
upon,  a segmental  organ,  specially  modified  for  this  purpose. 
This  conclusion  has  been  since  arrived  at  by  several  different  modes  of  observation. 
The  testes  on  the  other  side  bear  the  same  relation  to  the  tube  as  the  ovary  on  the 
side  just  described.  The  utriculus  on  the  one  side  is  represented  by  the  ejaculatory 
pouch  on  the  other.  At  present  it  is  beyond  the  power  of  science  to  explain  why  these 
organs,  in  only  one  or  two  annuli  of  the  body,  should  be  implicated  in  the  sexual  deve- 
* The  corpuscles  of  the  chylaqueous  fluid  in  Nais  serpentina  are  very  large  and  granular  : they  may  easily 
be  mistaken  for  ova.  One  clear  view  of  the  true  ova  in  the  ovarian  mass  will  however  convince  the  observer 
that  these  corpuscles  are  not  ova,  hut  the  normal  form, — elements  of  the  chylaqixeous  fluid. 
