﻿Rep-' 
  U 
  S 
  '^ 
  C 
  '903 
  

  

  Fig. 
  1. 
  Unfertilized 
  egg 
  shortly 
  

  

  after 
  mixture 
  of 
  spawn 
  and 
  milt 
  ; 
  

  

  spermatozoa 
  are 
  adlieriug 
  to 
  the 
  

  

  surface. 
  

   Fig. 
  2. 
  Egg 
  after 
  fertilization. 
  

   Fig. 
  3. 
  Same 
  egg 
  --^ 
  minutes 
  later. 
  

  

  Polar 
  body 
  at 
  broad 
  end. 
  

   Fig. 
  4. 
  Same 
  egg 
  6 
  minutes 
  later. 
  

   Fig. 
  5. 
  About 
  6i 
  hours 
  later. 
  

   Fig. 
  6. 
  Another 
  egg 
  at 
  about 
  the 
  

  

  same 
  stage. 
  Mass 
  < 
  >f 
  small 
  cells 
  

  

  growing 
  over 
  large 
  cell 
  or 
  mac- 
  

  

  romere 
  a. 
  

   Fig. 
  7. 
  Egg 
  .55 
  minutes 
  later. 
  Mac- 
  

  

  romere 
  almost 
  covered 
  by 
  small 
  

  

  cells 
  of 
  ectoderm. 
  

  

  Fig 
  S 
  Optical 
  section 
  of 
  egg 
  27 
  

   houi 
  ^ 
  .ittt 
  1 
  iiiipK 
  ^nation, 
  show- 
  

   ing 
  two 
  lu^( 
  ((IN 
  derived 
  from 
  

   (I 
  in 
  h.: 
  I 
  ( 
  \( 
  It 
  (1 
  liy 
  a 
  layer 
  of 
  

   small 
  ecto(l( 
  iiiuiKt 
  lis. 
  

  

  Fig 
  9 
  Fggatev\ 
  hours 
  older,show- 
  

   ing 
  large 
  cells 
  viewed 
  from 
  below. 
  

  

  Fig. 
  10. 
  An 
  egg 
  somewhat 
  older 
  

   viewed 
  from 
  above, 
  showing 
  fur- 
  

   ther 
  subdivision 
  of 
  large 
  cells 
  as 
  

   seen 
  through 
  cells 
  of 
  upper 
  layer. 
  

  

  Fig. 
  11. 
  An 
  older 
  egg, 
  now 
  become 
  

   flattened 
  from 
  above 
  downward. 
  

   Viewed 
  in 
  oi)tical 
  section. 
  

  

  Fio 
  12. 
  Surface 
  view 
  of 
  an 
  embryo 
  

   just 
  beginning 
  to 
  swim. 
  

  

  After 
  W. 
  K. 
  Brooks. 
  

  

  Fig. 
  13. 
  Optical 
  section 
  of 
  same. 
  

  

  Fig. 
  14. 
  Surface 
  view 
  of 
  same 
  from 
  

   another 
  position. 
  

  

  Fig. 
  15. 
  Surface 
  view 
  of 
  same 
  from 
  

   another 
  position. 
  

  

  Fig. 
  16. 
  An 
  older 
  embryo 
  in 
  same 
  

   position 
  as 
  in 
  (ig 
  12 
  

  

  Fig. 
  17. 
  A 
  still 
  dlder 
  embryo 
  show- 
  

   ing 
  spherical 
  ciliated 
  tligestive 
  

   cavity 
  opening 
  by 
  mouth, 
  m. 
  

  

  Fig. 
  18. 
  An 
  embryo 
  with 
  well-de- 
  

   veloped 
  larval 
  shells, 
  older 
  than 
  

   flg. 
  1, 
  Plate 
  VIII. 
  rs, 
  right 
  shell; 
  

   ?.s, 
  left 
  shell; 
  vl, 
  velum; 
  m, 
  

   mouth. 
  

  

  