﻿SIMKOXH 
  : 
  ON 
  THE 
  ANATOMY 
  OF 
  NEEITIDJE. 
  

  

  29 
  

  

  A 
  little 
  chalk 
  is 
  still 
  secreted 
  in 
  the 
  common 
  form 
  of 
  calco-sphaerites, 
  

   but 
  no 
  dart 
  is 
  formed. 
  

  

  The 
  vagina 
  is 
  the 
  same 
  as 
  in 
  the 
  Pulmonata. 
  The 
  receptaculum 
  

   seminis 
  is 
  the 
  bursa 
  copulatrix, 
  which 
  is 
  also 
  named 
  receptaculum 
  

   by 
  many 
  authors. 
  The 
  sperm-sac 
  or 
  spermatophore-sac 
  of 
  Faranerita 
  

   and 
  Nerita 
  (Figs. 
  B 
  and 
  C, 
  Sp.s., 
  but 
  not 
  Fig. 
  C, 
  Sp.s'.) 
  is 
  a 
  secondary 
  

   dilatation 
  or 
  a 
  secondary 
  bursa 
  copulatrix. 
  It 
  is 
  smaller 
  in 
  the 
  true 
  

   freshwater 
  forms 
  Septaria 
  and 
  Neritma, 
  in 
  Neritina 
  being 
  the 
  smallest. 
  

  

  od/'^ 
  

  

  The 
  cause 
  of 
  the 
  dilatation 
  and 
  of 
  its 
  differences 
  seems 
  to 
  be 
  the 
  

   following. 
  In 
  the 
  terrestrial 
  ancestor 
  there 
  was 
  transferred 
  in 
  

   copulation 
  one 
  spermatophore, 
  as 
  in 
  nearly 
  all 
  Pulmonata. 
  The 
  first 
  

   tropical 
  forms 
  that 
  invaded 
  the 
  sea, 
  i.e. 
  Nerita, 
  and 
  in 
  a 
  second 
  

   degree 
  Faranerita 
  (for 
  this 
  see 
  below), 
  conserved 
  the 
  spermatophore, 
  

   but 
  transferred 
  in 
  one 
  copula 
  not 
  one 
  spermatophore 
  but 
  a 
  number 
  

   together 
  (Fig. 
  C). 
  Whilst 
  one 
  spermatophore 
  has 
  room 
  enough 
  in 
  

   the 
  bursa 
  or 
  receptaculum 
  {E.s.), 
  the 
  space 
  is 
  too 
  narrow 
  for 
  the 
  

   passing 
  of 
  several 
  together 
  ; 
  therefore 
  the 
  secondary 
  bursa 
  is 
  formed 
  

  

  