﻿142 
  

  

  inated 
  "marketable,"' 
  "medium" 
  and 
  "young 
  growth." 
  The 
  

   "marketable" 
  oysters 
  were 
  full 
  grown 
  and 
  mature, 
  from 
  

   seven 
  to 
  nine 
  centimeters 
  in 
  length 
  and 
  breadth, 
  and 
  eighteen 
  

   millimeters 
  thick. 
  The 
  " 
  medium 
  " 
  were 
  half 
  grown 
  oysters, 
  

   from 
  sixteen 
  to 
  eighteen 
  millimeters 
  thick, 
  and 
  of 
  less 
  than 
  

   nine 
  centimeters 
  in 
  breadth. 
  The 
  " 
  young 
  growth 
  " 
  were 
  those 
  

   one 
  or 
  two 
  years 
  old. 
  From 
  these 
  observations 
  Prof. 
  Mobius 
  

   discovers 
  that 
  there 
  was 
  an 
  average 
  of 
  421 
  medium 
  oys- 
  

   ters 
  to 
  one 
  thousand 
  full 
  grown 
  ones; 
  that 
  is, 
  out 
  of 
  every 
  

   1421 
  oysters 
  there 
  would 
  be 
  only 
  one 
  thousand 
  full 
  grown 
  

   ones. 
  (?) 
  The 
  average 
  of 
  all 
  observations 
  differ 
  very 
  little 
  

   from 
  the 
  number 
  given 
  by 
  each, 
  and 
  consequently 
  shows 
  that 
  

   there 
  was 
  but 
  slight 
  fluctuation 
  in 
  the 
  proportion 
  in 
  122 
  years. 
  

   The 
  medium 
  oysters 
  are 
  considered 
  by 
  Prof. 
  Mobius 
  to 
  be 
  

   those 
  descendants 
  of 
  the 
  marketable 
  ones 
  that 
  have 
  survived 
  

   their 
  most 
  precarious 
  years 
  of 
  existence, 
  and 
  escaped 
  their 
  

   principal 
  enemies, 
  and 
  are 
  consequently 
  likely 
  to 
  reach 
  their 
  

   full 
  growth. 
  They 
  thus 
  represent 
  the 
  total 
  number 
  of 
  em- 
  

   bryos 
  spawned 
  which 
  have 
  survived 
  in 
  the 
  struggle 
  for 
  ex- 
  

   istence. 
  From 
  his 
  (Mobius') 
  experiments, 
  he 
  decides 
  that 
  an 
  

   oyster 
  spawns 
  about 
  one 
  million 
  embryos 
  in 
  a 
  season, 
  and 
  that 
  

   forty-four 
  per 
  cent, 
  of 
  the 
  mature 
  oysters 
  give 
  forth 
  "spat." 
  

   [Other 
  authorities 
  are 
  of 
  the 
  opinion 
  that 
  only 
  about 
  ten 
  per 
  

   cent, 
  spawn 
  ; 
  Prof. 
  Mobius' 
  data 
  appears 
  hardly 
  sufficient 
  to 
  

   justify 
  his 
  conclusion.] 
  

  

  From 
  the 
  above 
  it 
  is 
  evident 
  that 
  in 
  an 
  assemblage 
  of 
  a 
  

   thousand 
  oysters, 
  440,000,000 
  embryos 
  can 
  be 
  voided 
  every 
  

   season, 
  and 
  of 
  them 
  421 
  would 
  survive, 
  or 
  1,045,000 
  embryos 
  

   would 
  be 
  destroyed 
  where 
  one 
  was 
  preserved. 
  But 
  the 
  me- 
  

   dium 
  sized 
  oysters 
  also 
  spawn, 
  though 
  they 
  send 
  forth 
  a 
  much 
  

   smaller 
  number 
  of 
  embryos. 
  Mobius 
  estimates 
  that 
  the 
  421 
  

   in 
  the 
  community 
  would 
  produce 
  about 
  60,000,000 
  of 
  "spat." 
  

   It 
  would 
  therefore 
  require 
  about 
  500,000,000 
  embryos 
  to 
  pro- 
  

   duce 
  421 
  medium 
  oysters, 
  or 
  1,185,000 
  to 
  produce 
  one. 
  From 
  

   the 
  above 
  it 
  is 
  evident 
  that 
  it 
  would 
  be 
  necessary 
  to 
  have 
  4.2 
  

   oysters 
  assembled 
  to 
  produce 
  one, 
  though 
  the 
  proportion 
  would 
  

   only 
  hold 
  where 
  there 
  are 
  much 
  larger 
  assemblages. 
  Regard- 
  

   ing 
  these 
  results, 
  Prof. 
  Mobius 
  is 
  of 
  the 
  opinion 
  that 
  no 
  more 
  

  

  