﻿BLOOMEK 
  : 
  ON 
  TUE 
  ANATOMY 
  OF 
  PSAJOIOSIA. 
  236 
  

  

  and 
  in 
  the 
  centre 
  the 
  matrix 
  has, 
  under 
  high 
  magnification, 
  a 
  mottled 
  

   appearance. 
  

  

  Eig. 
  7 
  is 
  a 
  transverse 
  section 
  of 
  the 
  caecum 
  of 
  the 
  crystalline 
  style 
  

   and 
  intestine, 
  and 
  shows 
  the 
  epithelium 
  of 
  the 
  former 
  to 
  contain 
  long 
  

   columnar 
  cells 
  with 
  the 
  nuclei 
  near 
  the 
  centre, 
  and 
  the 
  free 
  ends 
  

   carrying 
  a 
  mass 
  of 
  long 
  cilia. 
  The 
  cells 
  increase 
  in 
  length 
  as 
  they 
  

   approach 
  the 
  passage 
  leading 
  to 
  the 
  intestine. 
  This 
  passage 
  apparently 
  

   can 
  be 
  closed 
  by 
  a 
  prolongation 
  of 
  the 
  divisional 
  wall 
  which 
  projects 
  

   into 
  the 
  lumen 
  of 
  the 
  intestine. 
  In 
  the 
  same 
  figure 
  can 
  be 
  seen 
  the 
  

   typhlosole 
  in 
  the 
  ascending 
  intestine. 
  

  

  As 
  the 
  caecum 
  of 
  the 
  crystalline 
  style 
  and 
  the 
  fore-part 
  of 
  the 
  

   intestine 
  are 
  in 
  one 
  piece, 
  the 
  latter 
  has 
  the 
  appearance 
  of 
  being 
  

   a 
  somewhat 
  constricted 
  groove 
  on 
  the 
  left 
  side, 
  and 
  the 
  intestinal 
  wall 
  

   only 
  becomes 
  complete 
  at 
  the 
  distal 
  end 
  of 
  the 
  caecum. 
  The 
  intestine 
  

   turns 
  dorsally, 
  its 
  wall 
  is 
  invaginated, 
  forming 
  the 
  typhlosole, 
  and 
  

   near 
  the 
  posterior 
  part 
  of 
  the 
  stomach 
  makes 
  a 
  number 
  of 
  folds 
  ; 
  

   afterwards, 
  turning 
  posteriorly, 
  it 
  proceeds 
  as 
  the 
  rectum, 
  and 
  is 
  

   shortly 
  encircled 
  by 
  the 
  ventricle. 
  It 
  then 
  passes 
  over 
  and 
  partly 
  

   round 
  the 
  posterior 
  adductor 
  muscle, 
  enters 
  the 
  pallial 
  chambei-, 
  

   and 
  terminates 
  with 
  a 
  small 
  anus. 
  

  

  The 
  digestive 
  gland 
  surrounds 
  the 
  stomach, 
  but 
  the 
  greater 
  portion 
  

   lies 
  ventrally 
  to 
  it. 
  The 
  large 
  duct 
  enters 
  the 
  central 
  division 
  from 
  

   the 
  right 
  and 
  larger 
  lobe, 
  and 
  the 
  other 
  duct 
  from 
  the 
  left 
  and 
  

   smaller 
  lobe 
  enters 
  the 
  anterior 
  end 
  of 
  the 
  pyloric 
  division 
  on 
  the 
  

   left 
  side. 
  

  

  The 
  renal 
  organs, 
  which 
  are 
  of 
  an 
  orange-red 
  colour, 
  are 
  situated 
  

   on 
  the 
  outside 
  and 
  over 
  the 
  pedis 
  retractor 
  posterior 
  muscle, 
  and 
  

   adjoining 
  the 
  pericardium. 
  

  

  The 
  animals 
  examined 
  are 
  unisexual, 
  the 
  organ 
  being 
  situated 
  

   around 
  the 
  digestive 
  gland, 
  

  

  liegarding 
  the 
  branchia 
  Dr. 
  Ridewood^ 
  states 
  that 
  the 
  inner 
  denii- 
  

   branch 
  hangs 
  much 
  lower 
  than 
  the 
  outer, 
  and 
  the 
  ascending 
  lamella 
  

   of 
  the 
  latter 
  rises 
  considerably 
  above 
  the 
  level 
  of 
  the 
  gill-axis, 
  forming 
  

   a 
  supra-axial 
  extension. 
  The 
  gill 
  lamellae 
  have 
  enlarged 
  principal 
  

   filaments 
  with 
  a 
  grooved 
  frontal 
  border. 
  

  

  The 
  number 
  of 
  filaments 
  in 
  a 
  plica 
  varies 
  from 
  twenty-four 
  to 
  thirty, 
  

   and 
  are 
  the 
  same 
  in 
  both 
  deniibranchs. 
  There 
  is 
  a 
  fairly 
  large 
  

   blood-tube 
  in 
  the 
  sub-filamentar 
  tissue 
  in 
  the 
  apex 
  of 
  the 
  plica, 
  and 
  all 
  

   the 
  interlamellar 
  septa, 
  and 
  not 
  the 
  alternate 
  ones 
  only, 
  extend 
  high 
  

   up 
  the 
  demibranch. 
  The 
  ordinary 
  filaments 
  present 
  no 
  exceptional 
  

   features. 
  There 
  is 
  a 
  fair 
  amount 
  of 
  muscle-fibre 
  around 
  the 
  inter- 
  

   lamellar 
  spaces 
  and 
  in 
  the 
  interlamellar 
  septa. 
  

  

  Nervous 
  System. 
  — 
  The 
  cerebro-pleural 
  ganglia 
  (Fig. 
  2, 
  C.P.G.) 
  are 
  

   far 
  apart, 
  and 
  situated 
  between 
  the 
  adductor 
  and 
  the 
  anterior 
  retractor 
  

   muscles, 
  and 
  close 
  to 
  the 
  ventral 
  surface. 
  They 
  are 
  joined 
  by 
  a 
  

   commissure 
  passing 
  close 
  to 
  the 
  adductor 
  muscle 
  and 
  in 
  front 
  of 
  the 
  

   oesophagus. 
  Each 
  ganglion 
  sends 
  out 
  anteriorly 
  a 
  nerve 
  which 
  

  

  ^ 
  " 
  On 
  the 
  Structure 
  of 
  the 
  Gills 
  of 
  Lamellibranchia 
  " 
  : 
  Phil. 
  Trans., 
  B. 
  cxcv, 
  

   p. 
  248, 
  1903. 
  

  

  