﻿been 
  ascertained 
  and 
  recorded, 
  at 
  intervals 
  of 
  a 
  few 
  years, 
  for 
  

   more 
  than 
  a 
  century, 
  by 
  a 
  systematic 
  method 
  of 
  counting 
  the 
  

   contents 
  of 
  a 
  certain 
  number 
  of 
  sample 
  dredgings. 
  From 
  a 
  

   Danish 
  book 
  on 
  the 
  subject 
  (Der 
  Danske 
  Osterbanker, 
  by 
  H. 
  

   Kroyer, 
  Kjobenhaven, 
  1839), 
  and 
  from 
  other 
  sources, 
  he 
  ob- 
  

   "tains 
  the 
  following 
  series 
  of 
  ratios 
  : 
  

  

  ere 
  were 
  486 
  half-grown 
  oysters 
  to 
  every 
  1,000 
  full-grown 
  ones. 
  

  

  " 
  310 
  " 
  " 
  " 
  1,000 
  

  

  " 
  418 
  " 
  " 
  " 
  1,000 
  

  

  " 
  490 
  " 
  " 
  " 
  1,000 
  

  

  " 
  484 
  " 
  " 
  " 
  1,000 
  

  

  " 
  307 
  " 
  " 
  " 
  1,000 
  

  

  " 
  388 
  " 
  " 
  " 
  1,000 
  

  

  a 
  417 
  u 
  .< 
  u 
  iQOQ 
  

  

  " 
  440 
  " 
  " 
  " 
  1,000 
  

  

  " 
  473 
  " 
  " 
  ,' 
  1,000 
  

  

  ■or 
  an 
  average 
  of 
  421.2 
  to 
  1,000, 
  or 
  42.13 
  per 
  cent, 
  of 
  young. 
  

   The 
  uniformity 
  of 
  the 
  ratio 
  between 
  the 
  half-grown 
  and 
  the 
  

   adult 
  oysters, 
  through 
  a 
  period 
  of 
  more 
  than 
  one 
  hundred 
  

  

  _years, 
  is 
  very 
  remarkable. 
  In 
  no 
  case 
  was 
  there 
  less 
  than 
  

   30 
  per 
  cent, 
  of 
  young 
  or 
  more 
  than 
  50 
  per 
  cent., 
  and 
  the 
  

   average 
  of 
  42 
  per 
  cent, 
  is 
  very 
  closely 
  followed 
  After 
  an 
  oys- 
  

   ter 
  has 
  become 
  half-grown 
  its 
  dangers 
  are 
  very 
  few, 
  and 
  this 
  

  

  "number 
  — 
  42 
  — 
  probably 
  gives 
  with 
  sufficient 
  accuracy 
  the 
  num- 
  

   ber 
  of 
  oysters 
  which 
  grow 
  up 
  each 
  year 
  for 
  each 
  100 
  adults. 
  

   Although 
  the 
  number 
  of 
  young 
  which 
  are 
  born 
  each 
  year 
  is 
  

  

  .^reat 
  beyond 
  computation, 
  those 
  which 
  survive 
  are 
  less 
  than 
  

   half 
  as 
  numerous 
  as 
  the 
  adults. 
  

  

  Mobius 
  has 
  estimated 
  the 
  number 
  of 
  adults 
  which 
  spawn 
  

  

  -each 
  year, 
  and 
  multiplying 
  this 
  number 
  by 
  the 
  average 
  num- 
  

   ber 
  of 
  eggs 
  laid 
  by 
  each, 
  and 
  dividing 
  by 
  the 
  number 
  which 
  

   grow 
  up, 
  he 
  reaches 
  the 
  conclusion 
  that 
  each 
  oyster 
  which 
  is 
  

   born 
  has 
  17^^57000 
  of 
  a 
  chance 
  of 
  reaching 
  maturity. 
  In 
  the 
  case 
  

  

  •of 
  the 
  American 
  oyster, 
  the 
  number 
  of 
  eggs 
  is 
  very 
  much 
  

   greater, 
  and 
  each 
  one's 
  chance 
  of 
  survival 
  is 
  accordingly 
  very 
  

   much 
  less, 
  and 
  it 
  is 
  evident 
  that 
  the 
  great 
  fertility 
  of 
  

   the 
  oyster 
  will 
  not 
  protect 
  a 
  bed 
  from 
  destruction 
  by 
  exces- 
  

  

  -eive 
  dredging, 
  for 
  while 
  the 
  young 
  spat 
  frequently 
  cover 
  the 
  

  

  