﻿Report 
  U. 
  S. 
  F. 
  C. 
  1897. 
  (To 
  face 
  page 
  340.) 
  

  

  Plate 
  VII. 
  

  

  Fig. 
  1. 
  Unfertilized 
  egg 
  shortly 
  

  

  after 
  mixture 
  of 
  spawn 
  and 
  milt; 
  

  

  spermatozoa 
  are 
  adhering 
  to 
  the 
  

  

  surface. 
  

   Fig. 
  2. 
  Egg 
  after 
  fertilization. 
  

   Fig. 
  3. 
  Same 
  egg 
  2 
  minutes 
  later. 
  

  

  Polar 
  body 
  at 
  broad 
  end. 
  

   Fig. 
  4. 
  Same 
  egg 
  6 
  minutes 
  later. 
  

   Fig. 
  ,'5. 
  About 
  6f 
  hours 
  later. 
  

   Fig. 
  G. 
  Another 
  egg 
  at 
  about 
  the 
  

  

  same 
  stage. 
  Mass 
  of 
  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. 
  8. 
  Optical 
  section 
  of 
  egg 
  27 
  

   hours 
  after 
  impregnation, 
  show- 
  

   ing 
  two 
  large 
  cells, 
  derived 
  from 
  

   a 
  in 
  fig 
  ti, 
  covered 
  by 
  a 
  layer 
  of 
  

   small 
  ectodermal 
  cells. 
  

  

  Fig. 
  9. 
  Egg 
  a 
  few 
  hours 
  older,show- 
  

   ing 
  large 
  cells 
  viewed 
  from 
  below. 
  

  

  Fig. 
  10. 
  An 
  egg 
  somewhat 
  older 
  

   viewed 
  fmiu 
  above, 
  showing 
  fur 
  

   ther 
  subdivision 
  of 
  large 
  cells 
  as 
  

   seen 
  through 
  cells 
  of 
  upper 
  laj'er. 
  

  

  Fig. 
  11. 
  An 
  older 
  egg, 
  now 
  become 
  

   flattened 
  from 
  above 
  downward. 
  

   Viewed 
  in 
  optical 
  section. 
  

  

  Fig. 
  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 
  

   anothei- 
  iiosition. 
  

  

  Fig. 
  1.">. 
  Surface 
  view 
  of 
  same 
  from 
  

   another 
  jxisition. 
  

  

  Fig. 
  10. 
  An 
  older 
  embryo 
  in 
  same 
  

   position 
  as 
  in 
  fig 
  12 
  

  

  Fig. 
  17. 
  A 
  still 
  older 
  embryo 
  show- 
  

   ing 
  spherical 
  ciliated 
  digestive 
  

   cavity 
  opening 
  by 
  mouth, 
  m. 
  

  

  Fig. 
  18. 
  An 
  embryo 
  with 
  well-de- 
  

   veloped 
  larval 
  shells, 
  olrler 
  than 
  

   fig. 
  1, 
  Plate 
  VIII. 
  (>•, 
  right 
  shell; 
  

   Is, 
  left 
  shell; 
  vl, 
  velum; 
  m, 
  

   mouth. 
  

  

  