﻿ANATOMY 
  AND 
  AFFINITIlilS 
  OF 
  THE 
  TUOOHID.E. 
  45 
  

  

  adequately 
  described 
  by 
  Perrier 
  (37, 
  pp. 
  118 
  — 
  131) 
  iu 
  his 
  

   admirable 
  memoir 
  on 
  tlie 
  kidneys 
  of 
  Prosobrancbs. 
  There 
  

   are 
  two 
  kidneys 
  present 
  in 
  this 
  genus, 
  though 
  one 
  only, 
  the 
  

   right, 
  functions 
  as 
  a 
  true 
  depuratory 
  organ. 
  The 
  left 
  

   kidney, 
  or 
  papillary 
  sac 
  (figs. 
  39, 
  43 
  and 
  49), 
  is 
  an 
  oval 
  

   body 
  situated 
  on 
  the 
  left 
  side 
  of 
  the 
  rectum 
  at 
  the 
  posterior 
  

   end 
  of 
  the 
  mantle-cavity, 
  where 
  it 
  abuts 
  on 
  tlie 
  pericardium. 
  

   It 
  communicates 
  with 
  the 
  exterior 
  by 
  a 
  slit-like 
  aperture 
  

   [l. 
  h. 
  a.) 
  at 
  its 
  anterior 
  end. 
  The 
  walls 
  of 
  the 
  papillary 
  sac 
  are 
  

   thick, 
  and 
  when 
  opened 
  are 
  seen 
  to 
  be 
  covered 
  with 
  numerous 
  

   filiform 
  papiilfe, 
  which 
  in 
  section 
  are 
  found 
  to 
  be 
  made 
  up 
  of 
  

   a 
  thick 
  layer 
  of 
  connective 
  tissue 
  traversed 
  by 
  a 
  central 
  or 
  

   axial 
  cavity 
  which 
  functions 
  as 
  a 
  blood-space. 
  The 
  con- 
  

   nective 
  tissue 
  is 
  covered 
  externally 
  by 
  a 
  layer 
  of 
  small, 
  

   ciliated, 
  epithelial 
  cells. 
  This 
  kidney 
  is 
  placed 
  in 
  communi- 
  

   cation 
  with 
  the 
  pericardium 
  by 
  means 
  of 
  a 
  long 
  reno-peri- 
  

   cardial 
  canal 
  (figs. 
  34, 
  48, 
  r.' 
  p. 
  c.) 
  which 
  runs 
  longitudinally 
  

   but 
  somewhat 
  obliquely 
  from 
  the 
  anterior 
  angle 
  of 
  the 
  

   pericardium 
  along 
  the 
  floor 
  of 
  the 
  papillary 
  sac. 
  The 
  aper- 
  

   ture 
  in 
  the 
  pericardium 
  is 
  large 
  and 
  vei-y 
  easily 
  discernible, 
  

   and 
  is 
  situated 
  on 
  the 
  left 
  side 
  of 
  the 
  rectum. 
  

  

  The 
  aperture 
  leading 
  into 
  the 
  kidney 
  is 
  much 
  smaller 
  and 
  

   is 
  ciliated 
  (fig. 
  34, 
  7-.' 
  p. 
  c). 
  This 
  figure, 
  which 
  represents 
  a 
  

   longitudinal 
  section 
  through 
  the 
  left 
  reno-pericardial 
  canal 
  

   of 
  T. 
  magus, 
  is 
  somewhat 
  diagrammatic, 
  and 
  has 
  been 
  re- 
  

   constructed 
  from 
  serial 
  sections, 
  the 
  entire 
  passage 
  of 
  the 
  

   canal 
  from 
  the 
  pericardium 
  to 
  the 
  kidney 
  occupying 
  some 
  

   fifteen 
  sections, 
  each 
  having 
  a 
  thickness 
  of 
  10/^. 
  

  

  The 
  right 
  kidney 
  (figs, 
  o^, 
  40, 
  etc., 
  r. 
  A-.) 
  is 
  seen 
  without 
  

   dissection 
  as 
  a 
  narrow 
  band 
  of 
  tissue 
  extending 
  between 
  the 
  

   pericardium 
  and 
  the 
  stomach 
  and 
  liver. 
  It 
  is 
  differently 
  

   coloured 
  in 
  the 
  various 
  species, 
  being 
  most 
  generally 
  of 
  a 
  

   yellowish-green 
  colour, 
  though 
  in 
  T. 
  zizyphinus 
  it 
  cissumes 
  

   a 
  rose-pink 
  tint; 
  and 
  in 
  this 
  case 
  the 
  excretory 
  granules 
  

   present 
  in 
  the 
  constituent 
  cells 
  have 
  the 
  same 
  colour 
  when 
  

   living 
  tissue 
  is 
  examined, 
  though 
  in 
  material 
  which 
  has 
  been 
  

   preserved 
  in 
  alcohol 
  they 
  always 
  present 
  a 
  greenish 
  appearance. 
  

  

  