﻿THE 
  MAIOTIC 
  PHASE 
  IN 
  ANIMALS 
  AND 
  PLANTS. 
  ' 
  523 
  

  

  bivalent 
  chromosomes 
  become 
  almost 
  or 
  quite 
  detached 
  

   from 
  eacli 
  other 
  about 
  this 
  stage. 
  But 
  they 
  seem 
  always 
  to 
  

   unite 
  again 
  before 
  the 
  completion 
  of 
  the 
  spindle 
  formation. 
  

   The 
  fact, 
  however, 
  is 
  of 
  interest, 
  seeing 
  that 
  Korschelt 
  has 
  

   described, 
  in 
  the 
  case 
  of 
  Opliryotroclia, 
  an 
  example 
  in 
  

   which 
  the 
  somatic 
  number 
  of 
  chromosomes 
  appears 
  at 
  tlie 
  

   hetei'otype 
  prophase 
  ; 
  these 
  then 
  unite 
  in 
  pairs 
  before 
  they 
  

   become 
  finally 
  arranged 
  on 
  the 
  spindle.^ 
  The 
  appearances 
  

   here 
  described 
  for 
  Osmunda 
  are 
  very 
  plainly 
  visible 
  in 
  

   many 
  pleridophytes. 
  Figures 
  29 
  and 
  '30 
  illustrate 
  corre- 
  

   sponding 
  phases 
  in 
  Psilotum 
  triquetrum, 
  a 
  lycopodineous 
  

   plant. 
  When 
  the 
  chromosomes 
  of 
  Osmunda 
  congregate 
  on 
  

   the 
  equatorial 
  plane 
  of 
  the 
  spindle 
  their 
  differences 
  of 
  form 
  

   become 
  less 
  marked; 
  as 
  they 
  begin 
  to 
  separate 
  on 
  the 
  com- 
  

   mencement 
  of 
  the 
  diaster, 
  it 
  is 
  clearly 
  seen 
  that 
  the 
  division 
  

   is 
  a 
  transverse 
  one. 
  Most 
  oE 
  the 
  chromosomes 
  are 
  more 
  or 
  

   less 
  oval 
  or 
  diamond-shaped, 
  but 
  some 
  retain 
  the 
  form 
  of 
  long 
  

   rods 
  that 
  divide 
  transversely 
  across 
  the 
  middle. 
  

  

  The 
  longitudinal 
  fission 
  so 
  often 
  recognisable 
  in 
  other 
  

   plants 
  at 
  this 
  stage 
  is 
  often 
  difficult 
  or 
  impossible 
  to 
  distin- 
  

   guish, 
  though 
  it 
  may 
  be 
  seen 
  with 
  certainty 
  in 
  some 
  cases. 
  

   The 
  diaster 
  is, 
  as 
  a 
  whole, 
  rather 
  irregular. 
  The 
  daughter 
  

   chromosomes 
  cling 
  together 
  by 
  one 
  end 
  eqnatorially, 
  in 
  a 
  

   manner 
  recalling 
  that 
  so 
  often 
  met 
  with 
  at 
  the 
  corresponding 
  

   stage 
  in 
  Tradescantia. 
  The 
  way 
  in 
  which 
  these 
  rod-like 
  

   chromosomes 
  ultimately 
  break 
  asunder 
  suggests 
  a 
  pull 
  rather 
  

   than 
  a 
  repulsion 
  as 
  the 
  cause 
  of 
  their 
  final 
  separation, 
  

   although 
  the 
  fact 
  that 
  the 
  chromatin 
  leaves 
  the 
  central 
  zone 
  

   when 
  the 
  final 
  breaking 
  occurs 
  might 
  perhaps 
  be 
  utilised 
  as 
  

   an 
  argument 
  to 
  support 
  the 
  hypothesis 
  of 
  mutual 
  repulsion. 
  

  

  At 
  the 
  close 
  of 
  the 
  diaster 
  the 
  chromosomes 
  can 
  still 
  be 
  

   recognised 
  as 
  bands 
  within 
  the 
  nuclear-wall 
  which 
  is 
  formed 
  

   before 
  the 
  onset 
  of 
  the 
  next 
  (homotype) 
  mitosis. 
  

  

  The 
  chromosomes 
  as 
  they 
  become 
  isolated 
  and 
  distinct 
  at 
  the 
  

  

  ' 
  Strasburger 
  in 
  his 
  recent, 
  paper 
  (" 
  Uber 
  llediictioiisteilung," 
  'Sitzher. 
  d. 
  

   11. 
  Pr. 
  Akad. 
  d. 
  Wiss.,' 
  March 
  24t,h, 
  lOOi) 
  has 
  described 
  a 
  similar 
  condition 
  

   or 
  Gait 
  ouia 
  can 
  di 
  cans. 
  

  

  