﻿was 
  not 
  possible 
  to 
  determine 
  tlie 
  age 
  of 
  marketable 
  oys- 
  

   ters 
  from 
  what 
  appeared 
  to 
  be 
  annual 
  arrests 
  of 
  growth, 
  

   indicated 
  on 
  the 
  outside 
  of 
  the 
  shell 
  by 
  deeply 
  im]u-essHd 
  

   lines 
  or 
  projecting 
  laminae 
  placed 
  at 
  nearly 
  equal 
  dis- 
  

   tances 
  apart, 
  but 
  I 
  failed, 
  after 
  examining 
  a 
  great 
  num- 
  

   ber 
  of 
  living 
  and 
  dead 
  sliells, 
  tn 
  an-ive 
  at 
  any 
  satistactory 
  

   conclusicm. 
  

  

  THF, 
  ANIMAL. 
  

  

  In 
  Fig. 
  I 
  the 
  head- 
  of 
  the 
  animal 
  lies 
  directed 
  towards 
  

   H; 
  the 
  tail 
  end, 
  on 
  the 
  other 
  hand, 
  lies 
  towai'ds 
  A: 
  the 
  

   ba(^k 
  or 
  upper 
  side 
  of 
  the 
  animal 
  extends 
  from 
  h 
  to 
  c,-the 
  

   ventral 
  or 
  lower 
  side 
  reaches 
  from 
  c 
  to 
  a 
  up 
  to 
  the 
  mouth 
  

   M. 
  The 
  right 
  and 
  left 
  sides 
  of 
  the 
  animal 
  are 
  covered 
  

   by 
  an 
  organ 
  called 
  the 
  mantle 
  Mt. 
  Ml.: 
  it 
  is 
  not 
  attached 
  

   to 
  the 
  shell 
  anywhere 
  except 
  around 
  the 
  points 
  where 
  

   the 
  ends 
  of 
  the 
  adductor 
  muscle, 
  Miis, 
  are 
  fixed 
  to 
  the 
  

   valves 
  of 
  either 
  side. 
  This 
  organ 
  encloses, 
  like 
  a 
  curtain, 
  

   the 
  internal 
  organs 
  of 
  the 
  creature 
  on 
  either 
  side, 
  and 
  

   lies 
  next 
  to 
  the 
  shell, 
  and 
  secretes 
  and 
  deposits 
  the 
  

   layers 
  of 
  carl>onate 
  of 
  lime 
  composing 
  the 
  latter. 
  The 
  

   free 
  edges 
  of 
  the 
  mantle, 
  which 
  are 
  purplish, 
  are 
  gar- 
  

   nished 
  with 
  small, 
  highly 
  sensitive 
  tentacles 
  toit. 
  of 
  the 
  

   same 
  color, 
  and 
  which 
  serve 
  the 
  purpose 
  of 
  organs 
  of 
  

   touch 
  and 
  are 
  perhaps 
  also 
  to 
  some 
  extent 
  sensitive 
  to 
  

   light. 
  The 
  borders 
  of 
  the 
  right 
  and 
  left 
  folds 
  of 
  the 
  

   mantle 
  are 
  free 
  from 
  h 
  to 
  c, 
  where 
  they 
  unite, 
  and 
  fi'om 
  

   c 
  to 
  rt, 
  but 
  from 
  a 
  to 
  b 
  they 
  are 
  joined 
  t(jgether. 
  In 
  the 
  

   space 
  between 
  the 
  right 
  and 
  left 
  folds 
  of 
  the 
  mantle 
  from 
  

   6, 
  a 
  to 
  fZ, 
  the 
  palps 
  P, 
  or 
  lips 
  of 
  the 
  oyster, 
  are 
  included 
  ; 
  

   this 
  cavity 
  may 
  be 
  called 
  the 
  palpal 
  space 
  P. 
  .v>- 
  'I'he 
  

   palpal 
  space 
  is 
  continuous 
  with 
  the 
  inferior 
  gill 
  cavity 
  /. 
  

   cav., 
  from 
  d 
  to 
  c 
  ; 
  in 
  this 
  space, 
  bounded 
  like 
  tlie 
  latter 
  

   on 
  each 
  side 
  by 
  the 
  mantle, 
  the 
  four 
  leaf-like 
  branchiae 
  

   or 
  gills 
  (r 
  hang 
  suspended 
  by 
  a 
  meuibrane, 
  which 
  unites 
  

   with 
  the 
  mantle 
  on 
  either 
  side 
  along 
  the 
  line 
  e; 
  this 
  

   membrane, 
  together 
  with 
  the 
  bases 
  of 
  the 
  gills, 
  forms 
  a 
  

   cavity 
  limited 
  below 
  by 
  the 
  upi)er 
  edges 
  of 
  the 
  gills 
  at 
  g 
  

  

  