﻿25 
  

  

  upon 
  the 
  ventral 
  surface, 
  and 
  almost 
  directly 
  opposite 
  the 
  

   point 
  where 
  the 
  primitive 
  month 
  was 
  situated 
  at 
  an 
  earlier 
  

   stage. 
  The 
  digestive 
  cavity 
  now 
  becomes 
  greatly 
  enlarged, 
  

   and 
  cilia 
  make 
  their 
  appearance 
  upon 
  its 
  walls, 
  the 
  mouth 
  

   becomes 
  connected 
  with 
  the 
  chamber 
  which 
  is 
  thus 
  formed, 
  

   and 
  which 
  becomes 
  the 
  stomach, 
  and 
  minute 
  particles 
  of 
  

   food 
  are 
  drawn 
  in 
  by 
  the 
  cilia, 
  and 
  can 
  now 
  be 
  seen 
  inside 
  the 
  

   stomach, 
  where 
  the 
  vibration 
  of 
  the 
  cilia 
  keep 
  them 
  in 
  con- 
  

   stant 
  motion. 
  Up 
  to 
  this 
  time 
  the 
  animal 
  has 
  developed 
  

   without 
  growing, 
  and 
  at 
  the 
  stage 
  shown 
  in 
  Figure 
  36 
  

   it 
  is 
  scarcely 
  larger 
  than 
  the 
  unfertilized 
  egg, 
  but 
  it 
  now 
  

   begins 
  to 
  increase 
  in 
  size. 
  The 
  stages 
  shown 
  in 
  Figures 
  44 
  

   and 
  45 
  agree 
  pretty 
  closely 
  with 
  the 
  figures 
  which 
  European 
  

   embryologists 
  give 
  of 
  the 
  oyster 
  embryo 
  at 
  the 
  time 
  when 
  it 
  

   escapes 
  from 
  the 
  mantle 
  chamber 
  of 
  its 
  parent. 
  The 
  Ameri- 
  

   can 
  oyster 
  reaches 
  this 
  stage 
  in 
  from 
  twenty-four 
  hours 
  to 
  six 
  

   days 
  after 
  the 
  egg 
  is 
  fertilized 
  ; 
  the 
  rate 
  of 
  development 
  be- 
  

   ing 
  determined 
  mainly 
  by 
  the 
  temperature 
  of 
  the 
  water. 
  

  

  Soon 
  after 
  the 
  mantle 
  has 
  become 
  connected 
  with 
  the 
  stom- 
  

   ach, 
  this 
  becomes 
  united 
  to 
  the 
  body 
  wall 
  at 
  another 
  point 
  a 
  

   little 
  behind 
  the 
  mantle, 
  and 
  a 
  second 
  opening, 
  the 
  anus, 
  

   is 
  formed. 
  The 
  tract 
  which 
  connects 
  the 
  anus 
  with 
  the 
  stom- 
  

   ach 
  lengthens 
  and 
  forms 
  the 
  intestine, 
  and, 
  soon 
  after, 
  the 
  

   sides 
  of 
  the 
  stomach 
  become 
  folded 
  off 
  to 
  form 
  the 
  two 
  halves 
  

   of 
  the 
  liver, 
  as 
  shown 
  in 
  Figure 
  44. 
  

  

  Various 
  muscular 
  fibres 
  now 
  make 
  their 
  appearance 
  within 
  

   the 
  body, 
  and 
  the 
  animal 
  assumes 
  the 
  form 
  shown 
  in 
  Figures 
  

   44 
  and 
  45. 
  

  

  A.11 
  my 
  attempts 
  to 
  get 
  later 
  stages 
  than 
  these 
  failed, 
  through 
  

   my 
  inability 
  to 
  find 
  any 
  way 
  to 
  change 
  the 
  water 
  without 
  

   losing 
  the 
  young 
  oyster, 
  and 
  I 
  am 
  therefore 
  unable 
  to 
  describe 
  

   the 
  manner 
  in 
  which 
  the 
  swimming 
  embryo 
  becomes 
  con- 
  

   verted 
  into 
  the 
  adult, 
  but 
  I 
  hope 
  that 
  this 
  gap 
  will 
  be 
  filled, 
  

   either 
  by 
  future 
  observations 
  of 
  my 
  own 
  or 
  by 
  those 
  of 
  some 
  

   other 
  embryologist. 
  

  

  In 
  my 
  attempt 
  to 
  raise 
  the 
  oyster 
  embryo 
  from 
  the 
  egg, 
  I 
  

   found 
  that 
  continuous 
  warm 
  weather 
  was 
  essential 
  to 
  success. 
  

  

  