﻿THE 
  DEVELOPMENT 
  OF 
  THE 
  OYSTER. 
  

   BY 
  W. 
  K. 
  BROOKS. 
  

  

  EXPLANATION 
  OF 
  THE 
  PLATES. 
  

  

  Unless 
  tlie 
  contrary 
  is 
  stated 
  the 
  figures 
  are 
  drawn 
  with 
  a 
  

   magnifying 
  power 
  of 
  250 
  diameters 
  ; 
  Zeiss. 
  F, 
  2, 
  but 
  it 
  was 
  

   necessary 
  to 
  amplify 
  the 
  sketches 
  considerably 
  in 
  order 
  to 
  re- 
  

   produce, 
  by 
  the 
  process 
  of 
  photo-engraving, 
  the 
  features 
  

   which 
  this 
  magnifying 
  power 
  rendered 
  visible, 
  and 
  the 
  figures 
  

   as 
  they 
  are 
  reproduced 
  are 
  of 
  about 
  twice 
  the 
  diameter 
  of 
  

   camera 
  sketches 
  made 
  with 
  the 
  same 
  magnifying 
  power. 
  

  

  The 
  first 
  thirty-two 
  figures 
  show 
  the 
  process 
  of 
  segmenta- 
  

   tion. 
  Figure 
  1 
  is 
  an 
  egg 
  at 
  the 
  end 
  of 
  the 
  first 
  period 
  of 
  rest 
  ; 
  

   Figures 
  2, 
  3, 
  4, 
  5, 
  6 
  and 
  7, 
  the 
  changes 
  during 
  the 
  first 
  period 
  

   of 
  activity; 
  Figures 
  8, 
  9, 
  10, 
  11, 
  12 
  and 
  13, 
  the 
  changes 
  dur- 
  

   ing 
  the 
  second 
  period 
  of 
  rest; 
  Figures 
  14, 
  15 
  and 
  16, 
  those 
  

   which 
  take 
  place 
  during 
  the 
  second 
  period 
  of 
  activity; 
  17, 
  18 
  

   and 
  19, 
  those 
  which 
  take 
  place 
  during 
  the 
  third 
  period 
  of 
  rest 
  ; 
  

   20 
  and 
  21, 
  during 
  the 
  third 
  period 
  of 
  activity 
  ; 
  22, 
  during 
  the 
  

   fourth 
  period 
  of 
  activity 
  ; 
  23, 
  during 
  the 
  fifth 
  period 
  of 
  ac- 
  

   tivity, 
  and 
  the 
  remaining 
  figures 
  show 
  more 
  widely 
  separated 
  

   stages. 
  In 
  all 
  the 
  figures 
  of 
  segmentation, 
  except 
  29, 
  30 
  and 
  

   31, 
  the 
  formative 
  pole 
  is 
  above 
  and 
  the 
  nutritive 
  pole 
  below. 
  

  

  