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  shells 
  of 
  the 
  adults 
  by 
  hundreds, 
  the 
  number 
  of 
  half-grownv 
  

   oysters 
  is 
  alwa3's 
  less 
  than 
  one-half 
  the 
  number 
  of 
  adults. 
  

   The 
  great 
  mortality 
  of 
  the 
  young, 
  after 
  they 
  have 
  fastened 
  

   themselves 
  to 
  the 
  shells 
  of 
  the 
  adults, 
  is 
  due 
  in 
  part 
  to 
  want 
  

   of 
  room, 
  in 
  part 
  to 
  the 
  attacks 
  of 
  enemies, 
  in 
  part 
  to 
  acci- 
  

   dents, 
  such 
  as 
  the 
  shifting 
  of 
  the 
  bottom, 
  and 
  in 
  part, 
  no 
  

   doubt, 
  to 
  lack 
  of 
  food. 
  While 
  the 
  supply 
  of 
  organic 
  matter 
  

   which 
  is 
  carried 
  to 
  them 
  by 
  the 
  water 
  is 
  very 
  great, 
  it 
  is 
  not 
  

   unlimited, 
  and 
  the 
  amount 
  which 
  each 
  oyster 
  can 
  obtain 
  at 
  

   any 
  one 
  time 
  is 
  quite 
  small, 
  and 
  if 
  the 
  oysters 
  covered 
  the 
  

   bottom 
  in 
  sufficient 
  abundance, 
  some 
  of 
  them 
  might 
  fail 
  to 
  

   obtain 
  a 
  sufficient 
  supply. 
  I 
  do 
  not 
  believe, 
  however, 
  that 
  

   this 
  ever 
  occurs, 
  for 
  long 
  before 
  the 
  oysters 
  are 
  sufficiently 
  

   abundant 
  to 
  exhaust 
  the 
  supply 
  of 
  organic 
  matter, 
  their 
  num- 
  

   bers 
  are 
  limited 
  by 
  other 
  conditions. 
  The 
  growth 
  of 
  an 
  ani- 
  

   mal 
  does 
  not 
  depend 
  upon 
  the 
  supply 
  of 
  food 
  in 
  general, 
  

   but 
  upon 
  the 
  supply 
  of 
  the 
  least 
  abundant 
  of 
  the 
  ne- 
  

   cessary 
  ingredients 
  of 
  the 
  food. 
  It 
  is 
  well 
  known 
  that 
  

   a 
  field 
  that 
  is 
  very 
  fertile 
  will 
  fail 
  to 
  produce 
  a 
  satisfactory 
  

   crop 
  of 
  a 
  plant 
  which 
  needs 
  some 
  particular 
  food-ingredient 
  

   which 
  the 
  soil 
  contains 
  in 
  too 
  small 
  quantity. 
  Although 
  food 
  

   in 
  general 
  is 
  very 
  abundant, 
  the 
  growth 
  of 
  this 
  particular 
  

   crop 
  depends 
  upon 
  the 
  amount 
  of 
  this 
  ingredient, 
  and 
  while 
  

   the 
  seed 
  which 
  has 
  been 
  planted 
  yields 
  an 
  abundant 
  crop 
  of 
  

   young 
  plants, 
  only 
  a 
  few 
  are 
  able 
  to 
  grow 
  up, 
  and 
  these 
  can 
  

   grow 
  no 
  faster 
  than 
  they 
  can 
  extract 
  this 
  particular 
  ingredi- 
  

   ent 
  from 
  the 
  soil. 
  

  

  In 
  addition 
  to 
  organic 
  food, 
  the 
  oyster 
  needs 
  a 
  supply 
  of 
  

   carbonate 
  of 
  lime 
  to 
  make 
  its 
  shell, 
  and 
  this 
  is 
  supplied 
  to 
  it, 
  

   in 
  solution, 
  in 
  sea-water. 
  If 
  the 
  shell 
  is 
  thin, 
  or 
  if 
  it 
  is 
  formed 
  

   very 
  slowly, 
  the 
  danger 
  from 
  enemies 
  and 
  accidents 
  is 
  greatly 
  

   increased 
  ; 
  and 
  those 
  oysters 
  which 
  are 
  able 
  to 
  construct 
  their 
  

   shells 
  with 
  the 
  greatest 
  rapidity 
  are 
  the 
  ones 
  which 
  survive 
  

   and 
  grow 
  up. 
  The 
  amount 
  of 
  dissolved 
  carbonate 
  of 
  lime 
  

   which 
  the 
  ocean 
  contains 
  is 
  unlimited, 
  but 
  the 
  amount 
  which 
  

   can 
  reach 
  each 
  oyster 
  is 
  not 
  very 
  great 
  ; 
  and 
  if 
  all 
  the 
  oysters, 
  

   which 
  attach 
  theinselves 
  were 
  to 
  survive 
  there 
  can 
  be 
  no 
  doubt, 
  

   that 
  they 
  would 
  exhaust 
  the 
  available 
  supply 
  of 
  lime 
  before 
  

   they 
  failed 
  to 
  obtain 
  enough 
  organic 
  food. 
  

  

  