﻿SIMROTH 
  : 
  ON 
  THE 
  ANATOMY 
  OF 
  NERITID^. 
  31 
  

  

  of 
  the 
  coelomic 
  or 
  pericardial 
  ducts 
  as 
  nephridia 
  is 
  already 
  a 
  secondary 
  

   function. 
  Nierstrasz 
  ^ 
  has 
  lately 
  shown 
  that 
  the 
  Solenogastres 
  possess 
  

   these 
  ducts, 
  but 
  without 
  excretory 
  functions. 
  

  

  In 
  the 
  same 
  way 
  the 
  question 
  arises 
  whether 
  there 
  is 
  only 
  the 
  left 
  

   ctenidium 
  or 
  also 
  the 
  remains 
  of 
  a 
  right 
  one. 
  In 
  my 
  opinion 
  the 
  

   ctenidia 
  are 
  secondary 
  acquisitions 
  on 
  the 
  margin 
  of 
  the 
  mantle, 
  as 
  in 
  

   Valvata, 
  the 
  typical 
  hermaphrodite 
  freshwater 
  Prosobranch. 
  In 
  one 
  

   species 
  of 
  Pleurotomaria 
  Bouvier 
  found 
  in 
  the 
  hind 
  part 
  of 
  the 
  

   mantle-cavity 
  a 
  typical 
  network 
  of 
  blood-vessels 
  as 
  in 
  the 
  Pulmonate 
  

   lung, 
  the 
  ctenidia 
  being 
  restricted 
  to 
  the 
  outer 
  parts. 
  Valvata 
  shows 
  

   that 
  the 
  right 
  ctenidium 
  is 
  already 
  vanishing 
  before 
  it 
  enters 
  into 
  the 
  

   mantle-cavity 
  itself. 
  Therefore 
  I 
  think 
  it 
  uncertain 
  whether 
  the 
  

   right 
  ctenidium 
  in 
  Nerita 
  was 
  once 
  fully 
  developed 
  or 
  not. 
  Perhaps 
  

   the 
  rudimentary 
  right 
  ventricle 
  of 
  the 
  heart 
  is 
  a 
  proof 
  of 
  the 
  full 
  

   development 
  in 
  the 
  ancestors. 
  Professor 
  Bourne 
  has 
  given 
  a 
  valuable 
  

   description 
  of 
  the 
  nervous 
  sj'stem. 
  He 
  demonstrates 
  that 
  the 
  pedal 
  

   ganglia 
  are 
  rounded 
  organs, 
  and 
  that 
  there 
  are 
  no 
  transverse 
  com- 
  

   missures 
  between 
  the 
  pedal 
  nerves. 
  The 
  pleural 
  ganglia 
  are 
  joined 
  bj' 
  

   a 
  short 
  commissure 
  with 
  a 
  ganglion 
  therein, 
  as 
  in 
  many 
  Pulmonata. 
  

   And 
  even 
  the 
  absence 
  of 
  the 
  supra-intestinal 
  nerve 
  in 
  Neritina 
  connects 
  

   tlieir 
  form 
  more 
  closely 
  with 
  the 
  Pulmonata. 
  

  

  Other 
  organs, 
  e.g. 
  the 
  radula, 
  can 
  be 
  taken 
  in 
  the 
  same 
  sense. 
  The 
  

   rhipidoglossate 
  radula 
  is 
  a 
  highly 
  differentiated 
  one, 
  whereas 
  many 
  

   Pulmonata, 
  e.g. 
  Ostracolethe,- 
  possess 
  an 
  equally 
  large 
  number 
  of 
  

   denticles, 
  but 
  all 
  of 
  the 
  same 
  simple 
  form. 
  The 
  stomach 
  has 
  

   a 
  diverticulum, 
  homologous 
  to 
  the 
  spiral 
  caecum 
  of 
  many 
  Aspido- 
  

   branchs. 
  Its 
  absence 
  in 
  Neritina 
  is 
  in 
  accordance 
  with 
  its 
  higher 
  

   systematic 
  position 
  (see 
  above). 
  The 
  same 
  diverticulum 
  we 
  find 
  in 
  

   the 
  Cephalopoda, 
  but 
  not 
  less 
  in 
  the 
  Aplysiidae,^ 
  where 
  it 
  is 
  described 
  

   as 
  liver 
  caecum 
  ; 
  and 
  I 
  may 
  add 
  that 
  among 
  the 
  Pulmonata 
  one 
  

   species 
  of 
  Hyalimax 
  possesses 
  the 
  same 
  organ, 
  whereas 
  it 
  is 
  wanting 
  

   in 
  others, 
  agreeing 
  with 
  what 
  we 
  find 
  in 
  the 
  Neritidse. 
  The 
  caecum 
  

   is 
  the 
  sign 
  of 
  great 
  antiquity, 
  which 
  is 
  lost 
  in 
  the 
  progress 
  of 
  develop- 
  

   ment. 
  The 
  nephridium 
  of 
  the 
  Neritidae, 
  as 
  described 
  by 
  Professor 
  

   Bourne, 
  is 
  composed 
  of 
  an 
  excretory 
  part 
  and 
  of 
  a 
  non-excretory 
  part. 
  

   He 
  avoids 
  naming 
  the 
  latter 
  part 
  ureter, 
  because 
  it 
  is 
  not 
  a 
  straight 
  

   duct. 
  But 
  have 
  we 
  not 
  such 
  ureter 
  forms 
  in 
  many 
  Pulmonata, 
  

   e.g. 
  Limax 
  and 
  Arion? 
  

  

  The 
  Geographical 
  Distribution. 
  

  

  Given 
  the 
  similarity 
  of 
  most 
  of 
  the 
  organs 
  of 
  the 
  Neritidae 
  to 
  the 
  

   Pulmonata, 
  we 
  may 
  ask 
  whether 
  the 
  Pulmonata 
  are 
  derived 
  from 
  

   the 
  Neritidae 
  or 
  the 
  Neritidae 
  from 
  the 
  Pulmonata. 
  Perhaps 
  the 
  

  

  ' 
  H. 
  F. 
  Nierstrasz, 
  " 
  Die 
  Amphineuren 
  " 
  : 
  Ergebuisse 
  iiud 
  Fortschritte 
  der 
  Zoologie, 
  

  

  herausgeg. 
  von 
  Spengel, 
  Bd. 
  i. 
  Heft 
  ii. 
  

   ^ 
  Simroth, 
  Zool. 
  Anz., 
  vul. 
  xxv, 
  p. 
  62. 
  

   =* 
  F. 
  M. 
  MacFarland, 
  " 
  The 
  Opisthobranchiate 
  MoUusca 
  of 
  the 
  Branaer-Agassiz 
  

  

  Expedition 
  to 
  Brazil"; 
  Leland 
  Stanford, 
  jun., 
  Univ. 
  Publications, 
  Univ. 
  

  

  Series 
  II, 
  1909. 
  

  

  