﻿54 
  W. 
  B. 
  RANDLES. 
  

  

  closing 
  between 
  tliem 
  a 
  caecal 
  groove 
  [cse.g). 
  Within 
  this 
  

   groove, 
  and 
  situated 
  in 
  close 
  proximity 
  to 
  the 
  aperture 
  of 
  the 
  

   oesophagus, 
  the 
  larger 
  of 
  the 
  two 
  bile-ducts 
  opens 
  {h. 
  d). 
  It 
  

   may 
  be 
  regarded 
  as 
  a 
  point 
  of 
  considerable 
  interest 
  that 
  in 
  all 
  

   Gasteropods 
  in 
  which 
  a 
  spiral 
  caecum 
  is 
  present, 
  and 
  also 
  in 
  

   many 
  of 
  the 
  Cephalopoda 
  in 
  which 
  a 
  cfceal 
  diverticulum 
  

   of 
  the 
  stomach 
  exists, 
  whether 
  spiral 
  or 
  otherwise, 
  there 
  is 
  

   always 
  this 
  relationship 
  between 
  the 
  aperture 
  of 
  the 
  bile-duct 
  

   and 
  the 
  folds, 
  or 
  rather, 
  the 
  coecal 
  groove 
  bounded 
  by 
  the 
  

   folds 
  leading 
  into 
  the 
  spiral 
  ca9cum 
  or 
  stomachic 
  diverti- 
  

   culum. 
  This 
  correlation 
  of 
  structure 
  exists 
  in 
  such 
  archaic 
  

   forms 
  as 
  Pleurotomaria, 
  Nautilus, 
  and 
  Spirula 
  (Mooi*e, 
  

   30), 
  and 
  is 
  uudonbtedly 
  indicative 
  of 
  the 
  homology 
  of 
  the 
  

   spiral 
  c£ecum 
  of 
  the 
  Gasteropods 
  and 
  the 
  cfBcal 
  diverticulum 
  

   of 
  the 
  Cephalopod 
  stomach. 
  

  

  The 
  stomach 
  of 
  Trochus 
  is 
  lined 
  with 
  a 
  thin 
  membrane 
  of 
  

   a 
  chitinous 
  nature 
  (fig. 
  46, 
  cut.). 
  This 
  cuticle 
  is 
  a 
  product 
  of 
  

   secretion 
  of 
  the 
  epithelium 
  {g. 
  ep.) 
  of 
  which 
  the 
  Avail 
  of 
  the 
  

   stomach 
  is 
  mainly 
  constituted; 
  this 
  epithelial 
  layer 
  is 
  com- 
  

   posed 
  of 
  very 
  elongate 
  columnar 
  cells 
  with 
  large 
  nuclei. 
  The 
  

   upper 
  portion 
  of 
  these 
  cells, 
  viz. 
  that 
  part 
  immediately 
  

   underlying 
  the 
  cuticle, 
  presents 
  a 
  finely 
  sti'iated 
  appearance. 
  

   Between 
  this 
  striated 
  border 
  and 
  the 
  nucleus 
  the 
  protoplasm 
  

   of 
  the 
  cells 
  is 
  very 
  granular, 
  owing 
  to 
  the 
  presence 
  of 
  numer- 
  

   ous 
  small 
  bodies 
  of 
  a 
  greenish 
  colour; 
  these 
  are 
  probably 
  of 
  

   the 
  nature 
  of 
  enterochlorophyll, 
  and 
  comparable 
  to 
  the 
  

   granules 
  of 
  enterochlorophyll 
  described 
  by 
  McMunn 
  as 
  

   present 
  in 
  the 
  epithelial 
  cells 
  lining 
  the 
  stomach 
  of 
  

   Patella.i 
  

  

  Subjacent 
  to 
  the 
  gastric 
  epithelium 
  is 
  a 
  thin 
  layer 
  of 
  

   muscle-fibres 
  with 
  elongate 
  nuclei, 
  and 
  this 
  layer 
  is 
  further 
  

   surrounded 
  by 
  a 
  loose 
  connective 
  tissue, 
  many 
  of 
  the 
  cells 
  of 
  

   which 
  contain 
  large 
  granules 
  analogous 
  to 
  those 
  found 
  in 
  the 
  

   excretory 
  cells 
  of 
  the 
  right 
  kidney. 
  These 
  (fig. 
  46) 
  are 
  the 
  

  

  ' 
  C. 
  A. 
  MacMunn, 
  " 
  On 
  the 
  Gastric 
  Gland 
  of 
  MoUusca 
  and 
  Decapod 
  

   Crustacea; 
  its 
  Structure 
  and 
  Function" 
  ('Phil. 
  Trans. 
  Roy. 
  Sec. 
  Lond.,' 
  

   vol.cxciii, 
  B. 
  11, 
  1900). 
  

  

  