﻿64 
  

  

  tionary 
  basis 
  Zi, 
  sliows 
  that 
  the 
  ri<i;hr 
  valves 
  Its. 
  is 
  

   concave 
  within 
  and 
  convex 
  without, 
  while 
  the 
  attached 
  

   left 
  valve 
  Ls. 
  is 
  Mat 
  conformably 
  to 
  the 
  character 
  of 
  the 
  

   basis 
  of 
  fixation, 
  which 
  is 
  most 
  often 
  of 
  this 
  nature. 
  

   Contrary 
  to 
  what 
  is 
  noted 
  in 
  regard 
  to 
  the 
  shape 
  of 
  the 
  

   valves 
  in 
  the 
  "spat," 
  the 
  right 
  valve 
  of 
  the 
  adult 
  Rv. 
  is 
  

   nearly 
  flat, 
  while 
  the 
  left 
  one 
  Ld. 
  is 
  most 
  decidedly 
  con: 
  

   cave 
  Avithin 
  and 
  convex 
  without. 
  Other 
  changes 
  in 
  the 
  

   more 
  important 
  parts 
  during 
  growth 
  are 
  manifested 
  

   mainly 
  by 
  the 
  muscle 
  ATxs., 
  which 
  moves 
  the 
  position 
  of 
  

   the 
  insertions 
  more 
  tovrards 
  the 
  free 
  edges 
  of 
  the 
  valves, 
  

   while 
  the 
  ligament 
  Jir/. 
  is 
  moved 
  in 
  the 
  same 
  direction. 
  

   Other 
  differences 
  in 
  the 
  forms 
  of 
  the 
  valves 
  at 
  the 
  differ- 
  

   ent 
  stages 
  may 
  be 
  noticed 
  ; 
  for 
  instance, 
  the 
  shells 
  .of 
  the 
  

   "fry" 
  are 
  deeply 
  concave 
  and 
  very 
  thin, 
  the 
  valves 
  of 
  

   the 
  "spat" 
  are 
  still 
  also 
  relatively 
  thin, 
  while 
  it 
  is 
  only 
  

   the 
  adult 
  which 
  ha^ 
  a 
  very 
  thick, 
  stout 
  shell, 
  though 
  the 
  

   thickness 
  is 
  said 
  to 
  vary 
  with 
  the 
  depth 
  of 
  the 
  water, 
  the 
  

   thinnest 
  shelled 
  oysters 
  being 
  found 
  in 
  the 
  deepest 
  water. 
  

   These 
  deep-water 
  oysters 
  are 
  known 
  as 
  "paper-shells" 
  

   and 
  are 
  not 
  liked 
  by 
  oyster 
  packers 
  and 
  dealers, 
  because 
  

   the 
  valves 
  bi'eak 
  very 
  easily 
  in 
  oj^ening 
  them, 
  causing 
  

   additional 
  labor 
  in 
  their 
  removal. 
  This 
  last 
  fact 
  is 
  evi- 
  

   dence 
  in 
  favoi' 
  of 
  shallow-water 
  culture. 
  

  

  There 
  are 
  good 
  grounds 
  for 
  dividing 
  the 
  growth 
  of 
  the 
  

   oyster 
  into 
  the 
  three 
  stages 
  already 
  alluded 
  to 
  : 
  the 
  flrst 
  

   we 
  may 
  consider 
  as 
  answering 
  deflnitely 
  to 
  the 
  free 
  

   swimming 
  condition 
  or 
  that 
  of 
  the 
  "fry 
  ;" 
  the 
  second 
  the 
  

   thin-shelled 
  primary 
  flxed 
  condition 
  or 
  that 
  of 
  the 
  

   "sx)at 
  ;" 
  the 
  third, 
  that 
  of 
  the 
  adult, 
  which 
  already 
  has 
  

   a 
  pretty 
  thick 
  shell 
  when 
  a 
  year 
  old, 
  when 
  the 
  generative 
  

   orsans 
  too 
  are 
  in 
  active 
  functional 
  use, 
  a 
  circumstance 
  

   which 
  has 
  also 
  been 
  noticed 
  by 
  writers 
  on 
  the 
  life-history 
  

   of 
  the 
  oyster 
  of 
  Europe. 
  

  

  