﻿ANATOMY 
  AND 
  AFFINITIES 
  OF 
  THE 
  TKOCHIDiE. 
  49 
  

  

  correctly 
  described 
  by 
  Pelseneer 
  (36, 
  p. 
  54), 
  who 
  found 
  that 
  

   it 
  opened 
  into 
  the 
  right 
  reno-pericardial 
  canal. 
  The 
  genital 
  

   duct, 
  or 
  rather 
  tliat 
  portion 
  which 
  is 
  common 
  to 
  the 
  right 
  

   reno-pericardial 
  canal 
  and 
  the 
  genital 
  duct, 
  opens 
  into 
  the 
  

   right 
  kidney 
  on 
  a 
  small 
  papilla 
  (fig. 
  30, 
  g. 
  d.). 
  From 
  the 
  

   cavity 
  of 
  the 
  right 
  kidney 
  the 
  genital 
  products 
  are 
  discharged 
  

   into 
  the 
  mantle-cavity 
  through 
  the 
  ureter. 
  In 
  the 
  male 
  the 
  

   ureter 
  is 
  quite 
  unmodified, 
  but 
  in 
  the 
  female 
  the 
  terminal 
  

   portion 
  is 
  enlarged, 
  either 
  as 
  a 
  tiiick-walled 
  ampulla, 
  as 
  in 
  

   members 
  of 
  the 
  sub-genus 
  Calliostoma 
  (figs. 
  43, 
  49, 
  amp.), 
  

   or 
  as 
  a 
  rosette-shaped 
  enlargement 
  in 
  the 
  members 
  of 
  the 
  

   sub-genus 
  Clibbula 
  (figs. 
  39 
  — 
  42). 
  

  

  The 
  Alimentary 
  Canal. 
  — 
  The 
  mouth, 
  situated 
  on 
  the 
  

   ventral 
  surface 
  of 
  the 
  snout, 
  leads 
  into 
  a 
  thick-walled, 
  

   muscular, 
  buccal 
  cavity, 
  on 
  the 
  antero-lateral 
  walls 
  of 
  which 
  

   are 
  placed 
  two 
  chitinous 
  jaws 
  (figs. 
  12, 
  13). 
  These 
  jaAvs 
  are 
  

   moderately 
  well 
  developed 
  in 
  both 
  T. 
  zizyj^hinus 
  (fig. 
  12) 
  

   and 
  T. 
  granulatus; 
  each 
  jaw 
  being 
  made 
  up 
  of 
  two 
  

   portions- 
  — 
  a 
  large 
  outer 
  plate-like 
  part 
  and 
  an 
  inner 
  smaller 
  

   structure, 
  the 
  free 
  margin 
  of 
  which 
  is 
  irregular, 
  and 
  fringed 
  

   with 
  chitinous 
  projections. 
  In 
  T. 
  magus 
  (fig. 
  13) 
  and 
  the 
  re- 
  

   maining 
  species 
  of 
  Trochus 
  examined 
  the 
  jaAvs 
  are 
  com- 
  

   paratively 
  small 
  and 
  insignificant, 
  consisting 
  of 
  very 
  thin 
  

   membranous 
  structures 
  composed 
  of 
  chitinous 
  tesseree, 
  which 
  

   are 
  more 
  or 
  less 
  restricted 
  to 
  the 
  free 
  margins; 
  there 
  is 
  no 
  

   indication 
  of 
  the 
  small 
  inner 
  plate 
  that 
  occurs 
  in 
  T. 
  zizy- 
  

   phinus. 
  

  

  A 
  section 
  through 
  the 
  jaw 
  and 
  its 
  associated 
  parts 
  reveals 
  

   the 
  fact 
  that 
  each 
  rod-like 
  chitinous 
  tessera 
  is 
  secreted 
  by 
  a 
  

   single 
  cell 
  (fig. 
  14). 
  On 
  the 
  outer 
  margin 
  of 
  the 
  jaw 
  there 
  is 
  

   a 
  thin 
  limiting 
  membrane 
  (o. 
  m.) 
  covering 
  the 
  exposed 
  

   faces 
  of 
  the 
  tesserae 
  (f. 
  -s-.) 
  ; 
  the 
  tessera) 
  are 
  long 
  rod-like 
  

   bodies 
  closely 
  applied 
  to 
  each 
  other; 
  they 
  present 
  a 
  finely 
  

   striated 
  appearance, 
  the 
  sfrias 
  being 
  arranged 
  in 
  a 
  longi- 
  

   tudinal 
  direction. 
  Immediately 
  underlying 
  these 
  and 
  attached 
  

   to 
  their 
  basal 
  ends 
  are 
  the 
  formative 
  cells 
  (/. 
  c), 
  each 
  

   tessera 
  beinff 
  connected 
  to 
  an 
  individual 
  cell. 
  I^hese 
  cells 
  are 
  

  

  