﻿574 
  J. 
  E. 
  S. 
  MOORE 
  AND 
  L. 
  E. 
  ROBINSON. 
  

  

  nucleolus 
  now 
  undergoes 
  fragmentation; 
  the 
  fragments 
  being 
  

   rapidly 
  passed 
  out 
  towards 
  the 
  cytoplasm 
  (fig. 
  5,/. 
  nc.'). 
  

  

  The 
  somatic 
  spindle 
  develops 
  rapidly, 
  and 
  during 
  the 
  

   separation 
  of 
  the 
  chromosomes 
  on 
  the 
  equator 
  of 
  the 
  spindle 
  

   (fig. 
  6), 
  the 
  fragments 
  of 
  the 
  nucleolus 
  are 
  seen 
  to 
  be 
  under- 
  

   going 
  rapid 
  degeneration 
  in 
  the 
  cytoplasm. 
  

  

  At 
  the 
  time 
  of 
  the 
  appearance 
  of 
  a 
  membrane 
  between 
  the 
  

   two 
  daughter 
  cells, 
  these 
  fragments 
  have, 
  as 
  a 
  general 
  rule, 
  

   become 
  indistinguishable. 
  

  

  The 
  Second 
  Maiotic 
  (Heterotype) 
  Divisions. 
  — 
  The 
  

   nucleolus 
  present 
  in 
  the 
  nucleus 
  of 
  the 
  spermatocyte 
  is 
  

   differentiated 
  very 
  soon 
  after 
  the 
  immediately 
  preceding- 
  

   somatic 
  division, 
  probably 
  at 
  the 
  time 
  of 
  the 
  reconstruction 
  

   of 
  the 
  nucleus. 
  It 
  arises 
  de 
  novo, 
  and 
  not 
  from 
  the 
  remains 
  

   of 
  the 
  nucleolus 
  present 
  in 
  the 
  previous 
  generation 
  of 
  cells. 
  

  

  The 
  resting 
  condition 
  of 
  the 
  nucleus 
  preceding 
  the 
  hetero- 
  

   type 
  division 
  differs 
  markedly 
  from 
  the 
  corresponding 
  stage 
  

   in 
  the 
  spermatogonium. 
  This 
  nucleus 
  (fig. 
  7) 
  is 
  larger 
  and 
  

   usually 
  spherical. 
  The 
  karyoplasm 
  is 
  more 
  regular, 
  consisting 
  

   of 
  a 
  rather 
  fine 
  reticulum 
  of 
  linin, 
  in 
  which 
  numerous 
  small 
  

   karyosomes 
  (k/) 
  appear. 
  

  

  The 
  nucleolus, 
  a 
  prominent, 
  highly 
  chromatic 
  body 
  {nc"), 
  

   lies 
  in 
  contact 
  with 
  the 
  nuclear 
  membrane, 
  and 
  usually 
  

   exhibits 
  a 
  bifid 
  condition, 
  Avhicli 
  gradually 
  disappears. 
  

  

  A 
  large 
  mass 
  of 
  dense 
  cytoplasm, 
  the 
  archoplasm 
  (a.), 
  

   becomes 
  visible, 
  lying 
  close 
  to 
  the 
  nucleus, 
  and 
  the 
  appear- 
  

   ance 
  of 
  this 
  structure 
  is 
  the 
  signal 
  for 
  the 
  commencement 
  of 
  

   the 
  i"emarkable 
  series 
  of 
  changes 
  about 
  to 
  take 
  place 
  in 
  the 
  

   arrangement 
  of 
  the 
  nuclear 
  contents, 
  in 
  connection 
  with 
  the 
  

   phenomenon 
  of 
  reduction. 
  

  

  The 
  whole 
  nucleus 
  becomes 
  more 
  chromatic, 
  the 
  increased 
  

   deposition 
  of 
  chromatin 
  granules 
  rendering 
  the 
  linin 
  reti- 
  

   culum 
  sharp 
  and 
  distinct 
  (fig. 
  8). 
  Almost 
  immediately 
  the 
  

   nuclear 
  contents 
  become 
  polarised 
  in 
  the 
  direction 
  of 
  an 
  

   axis, 
  passing 
  through 
  the 
  archoplasm 
  and 
  the 
  centre 
  of 
  the 
  

   nucleus. 
  The 
  linin 
  threads 
  lying 
  in 
  the 
  direction 
  perpen- 
  

   dicular 
  to 
  this 
  axis 
  rapidly 
  break 
  down, 
  leaving 
  a 
  number 
  of 
  

  

  