﻿-180 
  J. 
  W. 
  JlWKtNSON. 
  

  

  not 
  tlierefore 
  been 
  sliown). 
  Centrosome 
  about 
  to 
  divide. 
  Note 
  the 
  cloud 
  of 
  

   pigment, 
  Tlie 
  sperm-patii 
  is 
  on 
  the 
  left 
  side. 
  

  

  Tig. 
  21. 
  — 
  Centrosome 
  elongated. 
  The 
  rest 
  as 
  in 
  Fig. 
  19. 
  

  

  Fig. 
  22. 
  — 
  The 
  daughter 
  centrosomes 
  have 
  moved 
  apart. 
  The 
  (accessory) 
  

   sperm-nucleus 
  is 
  coarsely 
  reticular, 
  and 
  the 
  nuclear 
  membrane 
  is 
  hard 
  to 
  see 
  

   on 
  the 
  right-hand 
  side. 
  The 
  large 
  size 
  of 
  the 
  yolk-granules 
  is 
  due 
  to 
  the 
  

   sperm 
  having 
  entered 
  below 
  ihc 
  equator. 
  Depigmented 
  preparation; 
  originally 
  

   like 
  Fig. 
  23. 
  

  

  Fig. 
  23. 
  — 
  In 
  the 
  (accessoiy) 
  sperm-nucleus 
  the 
  chromatic 
  portion 
  is 
  

   crowded 
  into 
  the 
  centre. 
  Towards 
  the 
  cloud 
  of 
  pigment 
  which 
  obscures 
  the 
  

   centrosomes 
  the 
  nuclear 
  membrane 
  is 
  very 
  much 
  weakened. 
  This 
  sperm 
  

   also 
  has 
  entered 
  below 
  the 
  equator. 
  

  

  Fig. 
  24. 
  — 
  Origin 
  of 
  the 
  centrosome 
  from 
  the 
  (accessory) 
  si)erm-nucleus. 
  

   Note 
  the 
  closeness 
  of 
  the 
  centrosome 
  to 
  the 
  nucleus, 
  Ihe 
  absence 
  of 
  a 
  mem- 
  

   brane 
  here, 
  and 
  the 
  pigmented 
  processes 
  running 
  up 
  into 
  the 
  nuclear 
  cavity. 
  

  

  Fig. 
  25. 
  — 
  Exactly 
  as 
  the 
  last, 
  but 
  nucleus 
  and 
  centrosomes 
  are 
  cut 
  con- 
  

   secutively. 
  Fcur 
  consecutive 
  sections; 
  a 
  is 
  the 
  topmost, 
  «? 
  at 
  the 
  bottom 
  of 
  

   the 
  series, 
  and 
  the 
  pigment 
  in 
  f/ 
  is 
  over 
  the 
  centrosome. 
  In 
  the 
  nucleus 
  the 
  

   chromatin 
  is 
  crowded 
  together 
  ceiitrally. 
  

  

  Fig. 
  2G. 
  — 
  Sperm-nucleus 
  and 
  centrosome. 
  a. 
  Tiic 
  centrosome, 
  granular. 
  

   b. 
  The 
  nucleus, 
  very 
  coarsely 
  reticular, 
  and 
  consequently 
  in 
  an 
  earlier 
  stage 
  

   than 
  in 
  Figs. 
  19 
  — 
  25. 
  

  

  Fig. 
  27. 
  — 
  Annular 
  dividing 
  centrosome. 
  Division 
  later 
  than 
  usual, 
  ihe 
  

   pronuclei 
  having 
  met. 
  

  

  Fig. 
  28. 
  — 
  Formation 
  of 
  the 
  female 
  pronucleus. 
  a. 
  Membrane 
  formed, 
  

   but 
  chromosomes 
  still 
  distinct, 
  b. 
  Chromosomes 
  breaking 
  up. 
  c. 
  Chromatin 
  

   coarsely 
  granular; 
  a 
  chromatic 
  reticulum 
  clearly 
  visible, 
  d, 
  e. 
  Chromntin 
  

   minutely 
  subdivided, 
  pronucleus 
  enlarged 
  and 
  lobed. 
  In 
  d 
  a 
  few 
  vacuoles 
  

   between 
  the 
  pronucleus 
  and 
  the 
  yolk-granules. 
  

  

  Fig. 
  29. 
  — 
  The 
  pronuclei 
  have 
  met. 
  Tiie 
  male 
  pronucleus 
  is 
  on 
  the 
  left; 
  

   in 
  it 
  the 
  chromatin 
  is 
  aggregated 
  centrally. 
  The 
  centrosomes 
  have 
  moved 
  

   apart, 
  in 
  a 
  direction 
  at 
  right 
  angles 
  to 
  the 
  line 
  joining 
  the 
  pronuclei. 
  Note 
  

   the 
  pigment, 
  and 
  the 
  vacuoles 
  of 
  the 
  sperm-aster. 
  

  

  Fig. 
  30. 
  — 
  The 
  same 
  as 
  the 
  last, 
  but 
  only 
  one 
  pronucleus 
  is 
  shown. 
  Note 
  

   the 
  fine 
  parallel 
  " 
  spindle 
  " 
  fibres 
  between 
  ir, 
  and 
  the 
  centrosomes. 
  Note 
  also 
  

   the 
  enormous 
  central 
  vacuoles 
  of 
  the 
  sperm-aster 
  with 
  the 
  remains 
  of 
  the 
  

   separating 
  lamellae, 
  and 
  the 
  astral 
  rays 
  passing 
  out 
  between 
  the 
  yolk-granules. 
  

  

  Fig. 
  31. 
  — 
  Early 
  stage 
  in 
  the 
  formation 
  of 
  the 
  fertilisation 
  spindle. 
  Notice 
  

   the 
  fine 
  parallel 
  spindle-fibres 
  between 
  the 
  centrosomes 
  and 
  the 
  pronuclei; 
  

   and 
  the 
  large 
  terminal 
  vacuoles 
  of 
  the 
  elongated 
  sperm-sphere. 
  The 
  plasmo- 
  

   somes 
  are 
  stained 
  black 
  with 
  iron-lisematoxylin. 
  

  

  