﻿426 
  J. 
  W. 
  JENKINSON. 
  

  

  tliis 
  process 
  sometimes 
  occurs 
  (figs. 
  28, 
  29, 
  36). 
  The 
  chro- 
  

   matin 
  may 
  become 
  crowded 
  together 
  in 
  the 
  centre 
  of 
  the 
  

   nucleus, 
  and 
  here 
  form 
  a 
  compact, 
  coarse, 
  deeply 
  staining 
  

   reticulum, 
  the 
  surrounding 
  intra-nuclear 
  space 
  beiiig 
  occupied 
  

   by 
  an 
  achromatic 
  substance 
  which 
  is 
  sometimes 
  homogeneous, 
  

   sometimes 
  reticular. 
  The 
  male 
  pronucleus 
  may 
  be 
  observed 
  

   in 
  this 
  condition 
  even 
  in 
  the 
  fertilisation 
  spindle, 
  in 
  Avhich 
  

   case 
  the 
  chromosomes 
  seem 
  to 
  be 
  formed 
  directly 
  from 
  this 
  

   chromatic 
  network 
  without 
  the 
  intervention 
  of 
  a 
  typical 
  resting 
  

   stage. 
  

  

  (c) 
  Appearance 
  of 
  the 
  definitive 
  centrosome. 
  — 
  In 
  the 
  

   previous 
  stage 
  the 
  centre 
  of 
  the 
  sperm-aster 
  was 
  occupied 
  

   by 
  a 
  vacuolated 
  mass. 
  These 
  vacuoles 
  now 
  swell 
  up 
  

   enormously 
  and 
  assume 
  a 
  radiate 
  arrangement 
  about 
  the 
  

   centre 
  of 
  the 
  aster 
  (figs. 
  19, 
  21, 
  24). 
  The 
  separating 
  lamellae 
  

   between 
  them 
  become 
  so 
  extremely 
  thin 
  and 
  delicate 
  as 
  to 
  be 
  

   almost 
  invariably 
  ruptured 
  during 
  the 
  process 
  of 
  fixation 
  or 
  

   subsequent 
  passage 
  through 
  the 
  alcohols. 
  Consequently 
  the 
  

   centre 
  of 
  the 
  aster 
  seems 
  to 
  be 
  occupied 
  by 
  one 
  great 
  vacuole, 
  

   the 
  cavity 
  of 
  which 
  is 
  traversed 
  by 
  irregular 
  broken 
  strands, 
  

   the 
  remains 
  of 
  the 
  thin 
  inter-vacuolar 
  lamella 
  (fig. 
  30). 
  A 
  

   few 
  pigment 
  granules 
  may 
  be 
  seen 
  dotted 
  along 
  these 
  strands, 
  

   but 
  they 
  are 
  much 
  more 
  numerous 
  around 
  the 
  periphery 
  of 
  

   the 
  large 
  vacuole. 
  They 
  are 
  also 
  to 
  be 
  seen 
  in 
  the 
  outer 
  zone 
  

   of 
  the 
  aster. 
  

  

  This 
  latter 
  has 
  still 
  the 
  same 
  structure 
  as 
  before, 
  that 
  is 
  to 
  

   say 
  it 
  consists 
  of 
  a 
  system 
  of 
  radiating 
  fibres 
  connected 
  by 
  

   numerous 
  anastomoses 
  and 
  continued 
  outwards 
  for 
  some 
  

   distance 
  between 
  the 
  yolk-granules. 
  As 
  before 
  the 
  spaces 
  

   between 
  these 
  fibres 
  or 
  lamellte 
  — 
  whichever 
  they 
  may 
  be 
  — 
  are 
  

   occupied 
  by 
  a 
  faintly-staining 
  coagulum; 
  the 
  large 
  central 
  

   vacuole, 
  or 
  vacuoles, 
  is 
  occupied 
  by 
  a 
  coagulum 
  of 
  precisely 
  

   the 
  same 
  nature. 
  

  

  This 
  substance 
  would 
  appear 
  to 
  be 
  of 
  more 
  watery 
  con- 
  

   sistency 
  than 
  the 
  rest 
  of 
  the 
  cytoplasm. 
  The 
  formation 
  of 
  the 
  

   large 
  vacuoles 
  is 
  in 
  that 
  case 
  to 
  be 
  looked 
  on 
  as 
  a 
  concen- 
  

   tration 
  in 
  the 
  centre 
  of 
  the 
  sperm-aster 
  of 
  water 
  withdrawn 
  

  

  