﻿72 
  W. 
  B. 
  KANDLKS. 
  

  

  the 
  pericardium^ 
  though 
  the 
  pericardium 
  at 
  the 
  point 
  where 
  

   a 
  canal 
  might 
  possibly 
  have 
  existed 
  was 
  torn, 
  rendering- 
  

   accurate 
  observation 
  impossible. 
  

  

  We 
  see, 
  therefore, 
  that 
  in 
  the 
  majority, 
  if 
  not 
  all, 
  of 
  the 
  

   Diotocardia 
  a 
  communication 
  exists 
  not 
  only 
  between 
  the 
  

   left 
  kidney 
  and 
  the 
  pericardium, 
  but 
  also 
  between 
  the 
  right 
  

   kidney 
  and 
  that 
  structure, 
  while 
  in 
  some 
  cases 
  only 
  the 
  right 
  

   canal 
  persists. 
  This 
  is 
  undoubtedly 
  a 
  point 
  very 
  much 
  in 
  

   favour 
  of 
  regarding 
  the 
  right 
  kidney 
  of 
  the 
  Diotocardia 
  as 
  

   giving 
  rise 
  in 
  part, 
  if 
  not 
  wholly, 
  to 
  the 
  single 
  kidney 
  of 
  the 
  

   Monotocardia. 
  

  

  When 
  we 
  come 
  to 
  consider 
  the 
  total 
  difference 
  in 
  function 
  

   between 
  the 
  right 
  kidney 
  and 
  the 
  left 
  or 
  papillary 
  sac 
  of 
  such 
  

   forms 
  as 
  Trochus, 
  Haliotis, 
  and 
  Pleurotomaria, 
  it 
  

   seems 
  much 
  more 
  rational 
  to 
  suppose 
  the 
  kidney 
  of 
  the 
  

   Monotocardia 
  to 
  have 
  been 
  derived 
  principally 
  from 
  the 
  right 
  

   kidney 
  of 
  the 
  Diotocardia, 
  for 
  the 
  function 
  of 
  these 
  organs 
  is 
  

   the 
  same 
  in 
  the 
  two 
  groups 
  — 
  since 
  they 
  are 
  the 
  true 
  excretory 
  

   organs, 
  whereas 
  the 
  left 
  kidney 
  or 
  papillary 
  sac 
  of 
  Trochus 
  

   and 
  its 
  allies 
  has 
  an 
  entirely 
  different 
  function. 
  It 
  is 
  more 
  of 
  

   the 
  nature 
  of 
  a 
  lymphatic 
  gland, 
  waste 
  products 
  being 
  

   removed 
  from 
  the 
  blood 
  traversing 
  it 
  by 
  a 
  process 
  of 
  phago- 
  

   cytosis 
  (Pelseneer, 
  35). 
  

  

  The 
  nephridial 
  gland 
  of 
  the 
  Monotocardia 
  possesses 
  similar 
  

   functions, 
  and 
  so, 
  from 
  a 
  physiological 
  point 
  of 
  view, 
  can 
  

   more 
  easily 
  be 
  homologised 
  with 
  the 
  papillary 
  sac 
  of 
  

   Trochus. 
  

  

  Von 
  Erlanger 
  (14), 
  in 
  maintaining 
  the 
  homology 
  of 
  the 
  

   Monotocardian 
  kidney 
  to 
  the 
  left 
  kidney 
  of 
  the 
  Diotocardia, 
  

   seeks 
  to 
  homologise 
  the 
  nephridial 
  gland 
  of 
  the 
  former 
  Avith 
  

   the 
  right 
  kidney 
  of 
  the 
  latter, 
  but 
  as 
  this 
  necessitates 
  a 
  com- 
  

   plete 
  inversion 
  of 
  the 
  functions 
  of 
  these 
  organs, 
  it 
  to 
  my 
  

   mind 
  seems 
  much 
  more 
  difficult 
  of 
  conception 
  than 
  to 
  accept 
  

   Perrier's 
  view. 
  

  

  