﻿44 
  W. 
  B. 
  HANDLES. 
  

  

  verse 
  pallial 
  vein 
  (t. 
  'p. 
  v.), 
  extending 
  up 
  to^ 
  and 
  a 
  little 
  way 
  

   beyond 
  tlie 
  orifice 
  of 
  tlie 
  left 
  kidney 
  ; 
  a 
  moderately 
  sized, 
  

   mucous 
  gland 
  is 
  present 
  in 
  T. 
  (Monodonta) 
  mono 
  don 
  

   (Bernard, 
  2, 
  p. 
  324). 
  In 
  T. 
  zizypliiuus 
  (fig. 
  43) 
  the 
  hypo- 
  

   brancliial 
  gland 
  is 
  lozenge 
  shaped, 
  and 
  the 
  mucus-secreting 
  

   cells 
  are 
  thickly 
  distributed 
  over 
  the 
  transverse 
  pallial 
  vein 
  

   and 
  the 
  vessels 
  uniting 
  with 
  it. 
  Out 
  of 
  the 
  species 
  examined 
  

   the 
  hypobranchial 
  gland 
  is 
  largest 
  in 
  T. 
  li 
  neat 
  us, 
  where 
  it 
  

   extends 
  from 
  the 
  transverse 
  pallial 
  vein 
  to 
  within 
  a 
  short 
  

   distance 
  of 
  the 
  thickened 
  edge 
  of 
  the 
  mantle. 
  

  

  In 
  all 
  the 
  species 
  the 
  main 
  portion 
  of 
  the 
  mucous 
  gland 
  is 
  

   situated 
  on 
  the 
  left 
  side 
  of 
  the 
  rectum, 
  but 
  there 
  is 
  present 
  a 
  

   small 
  lobe 
  on 
  the 
  right 
  side. 
  This 
  right 
  lobe 
  is 
  also 
  larger 
  in 
  

   T. 
  lineatus 
  than 
  others 
  of 
  the 
  species 
  examined. 
  

  

  The 
  presence 
  of 
  a 
  right 
  lobe 
  is 
  of 
  great 
  interest 
  when 
  con- 
  

   sidering 
  the 
  asymmetrical 
  condition 
  of 
  the 
  pallial 
  complex 
  of 
  

   Trochus. 
  We 
  have, 
  again, 
  the 
  case 
  of 
  an 
  organ 
  situated 
  on 
  

   the 
  right 
  side 
  of 
  the 
  body, 
  which 
  has, 
  owing 
  to 
  the 
  effects 
  

   of 
  dextral 
  torsion, 
  become 
  very 
  much 
  reduced, 
  and 
  following 
  

   in 
  the 
  wake 
  of 
  the 
  right 
  gill, 
  which 
  in 
  Trochus 
  has 
  been 
  

   completely 
  suppressed. 
  That 
  this 
  is 
  so 
  is 
  evidenced 
  by 
  com- 
  

   paring 
  it 
  with 
  Pleurotomaria 
  (45, 
  p. 
  228), 
  in 
  which 
  a 
  large 
  

   hypobranchial 
  gland 
  consisting 
  of 
  both 
  right 
  and 
  left 
  lobes 
  

   situated 
  on 
  either 
  side 
  of 
  the 
  rectum 
  is 
  present. 
  Here 
  the 
  

   right 
  lobe, 
  like 
  the 
  right 
  gill, 
  is 
  smaller 
  than 
  the 
  correspond- 
  

   ing 
  structure 
  on 
  the 
  left 
  side, 
  thus 
  foreshadowing 
  the 
  ultimate 
  

   reduction 
  and 
  suppression 
  which 
  occurs 
  in 
  the 
  Azygo- 
  

   branchiate 
  Diotocardia. 
  

  

  Bela 
  Haller 
  (19, 
  p. 
  28, 
  note) 
  regards 
  the 
  reduced 
  right 
  lobe 
  

   of 
  the 
  mucous 
  gland 
  of 
  Trochus 
  as 
  the 
  remains 
  of 
  the 
  right 
  

   gill 
  which 
  has 
  atrophied 
  ; 
  but 
  when 
  we 
  consider 
  that 
  in 
  

   Pleurotomaria 
  there 
  is 
  present, 
  co-existing 
  with 
  a 
  func- 
  

   tional 
  right 
  gill, 
  a 
  well-developed 
  right 
  lobe 
  of 
  the 
  mucous 
  

   gland 
  to 
  which 
  the 
  reduced 
  right 
  lobe 
  in 
  Trochus 
  is 
  un- 
  

   doubtedly 
  homologous, 
  the 
  fallacy 
  of 
  Haller's 
  supposition 
  

   becomes 
  apparent. 
  

  

  The 
  excretory 
  organs 
  of 
  Trochus 
  have 
  been 
  very 
  

  

  