﻿ANATOMY 
  AND 
  APFTNTTII'IS 
  OF 
  TFIE 
  TIJOOHID^E. 
  59 
  

  

  tliese 
  are 
  distributed 
  to 
  the 
  crop, 
  salivary 
  glands, 
  and 
  the 
  

   odontophore. 
  

  

  This 
  peculiar 
  method 
  of 
  origin 
  of 
  the 
  stomatogastric 
  nerves 
  

   in 
  Trochus, 
  in 
  arising 
  from 
  the 
  same 
  root 
  as 
  the 
  labial 
  

   commissure, 
  finds 
  its 
  parallel 
  not 
  only 
  in 
  Plenrotomaria 
  

   (Woodward, 
  45, 
  p. 
  242), 
  but 
  also 
  in 
  Patella 
  and 
  Chiton 
  

   (Pelseneer, 
  36, 
  p. 
  48). 
  The 
  extreme 
  fineness 
  of 
  the 
  connectives 
  

   uniting 
  the 
  buccal 
  ganglia 
  to 
  the 
  cerebrals, 
  and 
  the 
  fact 
  that 
  

   they 
  are 
  only 
  indirectly 
  connected 
  with 
  the 
  latter, 
  arising 
  in 
  

   reality 
  in 
  common 
  with 
  the 
  labial 
  commissure, 
  is 
  in 
  all 
  

   probability 
  the 
  reason 
  which 
  led 
  Bela 
  Haller 
  (19, 
  p. 
  26, 
  

   pi. 
  ii^ 
  fig. 
  3) 
  to 
  overlook 
  the 
  true 
  point 
  of 
  origin 
  of 
  these 
  

   nerves, 
  and 
  to 
  suppose 
  that 
  they 
  originated 
  from 
  the 
  sub- 
  

   oesophageal 
  mass. 
  

  

  From 
  the 
  posterior 
  border 
  of 
  each 
  cerebral 
  ganglion 
  two 
  

   long 
  connectives, 
  the 
  cerebro-pedal 
  {ch. 
  p.), 
  and 
  the 
  cerebro- 
  

   pleural 
  {ch. 
  pi-) 
  arise, 
  the 
  latter 
  being 
  the 
  larger 
  of 
  the 
  two. 
  

   Tliese 
  cords 
  pass 
  backwards 
  over 
  the 
  odontophore 
  and 
  

   penetrate 
  the 
  floor 
  of 
  the 
  body-cavity, 
  where 
  they 
  unite 
  with 
  

   the 
  large 
  ganglionic 
  mass, 
  repi-esenting 
  the 
  pleural 
  and 
  pedal 
  

   ganglia. 
  

  

  The 
  pleural 
  ganglia 
  (^j/. 
  g.) 
  in 
  Trochus 
  are 
  perfectly 
  distinct 
  

   structures, 
  and 
  are 
  situated 
  at 
  the 
  anterior 
  extremity 
  of 
  the 
  

   ventral 
  or 
  pedal 
  nerve-cords 
  (figs. 
  30, 
  40, 
  pi. 
  g.) 
  as 
  two 
  pro- 
  

   jecting 
  horns 
  immediately 
  in 
  front 
  of 
  the 
  anterior 
  commissure 
  

   which 
  unites 
  the 
  pedal 
  cords. 
  The 
  close 
  approximation 
  of 
  

   the 
  pleural 
  and 
  pedal 
  ganglia 
  is 
  undoubtedly 
  a 
  specialised 
  

   condition, 
  and 
  is 
  in 
  all 
  proliability 
  due 
  to 
  the 
  shortening 
  of 
  the 
  

   pleuro-pedal 
  connective, 
  which 
  in 
  Troch 
  u 
  s 
  has 
  become 
  almost 
  

   entirely 
  oblitei-ated. 
  the 
  basal 
  portion 
  of 
  the 
  pleural 
  being 
  

   fused 
  to 
  the 
  anterior 
  portion 
  of 
  the 
  large 
  ventral 
  pedal 
  nerve- 
  

   cords. 
  Such 
  a 
  condition, 
  though 
  unusual 
  in 
  Prosobranchiate 
  

   Gasteropods, 
  is 
  not 
  unique, 
  being 
  met 
  with 
  in 
  Cyclophorus 
  

   and 
  also 
  in 
  Am 
  pull 
  aria. 
  

  

  From 
  the 
  pleural 
  ganglia 
  are 
  given 
  off 
  right 
  and 
  left 
  pallial 
  

   nerves 
  (figs. 
  30, 
  39, 
  pa. 
  n., 
  pa. 
  n'.). 
  These 
  branch 
  shortly 
  

   after 
  entei'ing 
  the 
  mantle, 
  the 
  anterior 
  nerves 
  being 
  distributed 
  

  

  