﻿THE 
  MAIOTIO 
  PHASE 
  IN 
  ANIMALS 
  AND 
  PLANTS. 
  527 
  

  

  prophase 
  is 
  placed 
  beyond 
  a 
  doubt. 
  It 
  does 
  not 
  seem 
  to 
  be 
  a 
  

   matter 
  of 
  any 
  consequence 
  how 
  the 
  bivalent 
  arrangement 
  is 
  

   produced^ 
  since 
  there 
  is 
  so 
  much 
  variability 
  in 
  the 
  process, 
  

   but 
  the 
  temporary 
  union 
  in 
  pairs 
  of 
  somatic 
  chromosomes 
  is 
  

   the 
  really 
  important 
  feature. 
  

  

  The 
  further 
  history 
  of 
  the 
  chromosomes 
  is 
  less 
  easily 
  

   followed 
  than 
  in 
  Osmunda, 
  but 
  the 
  same 
  types 
  are 
  repro- 
  

   duced 
  here 
  in 
  almost 
  every 
  detail, 
  and 
  they 
  pass 
  on 
  to 
  the 
  

   spindle 
  in 
  a 
  precisely 
  similar 
  manner; 
  perhaps, 
  however, 
  the 
  

   ring-like 
  figures 
  are 
  rather 
  more 
  frequent 
  in 
  Aneura 
  than 
  

   in 
  Osmunda. 
  

  

  The 
  spindle 
  in 
  its 
  earlier 
  stages 
  has 
  already 
  been 
  described, 
  

   as 
  a 
  quadfipolar 
  structure. 
  The 
  individual 
  kinoplasmic 
  

   threads 
  can 
  easily 
  be 
  distinguished 
  in 
  good 
  preparations 
  ; 
  but 
  

   as 
  the 
  chromosomes 
  begin 
  to 
  assume 
  their 
  definite 
  form, 
  

   and 
  before 
  they 
  pass 
  on 
  to 
  the 
  spindle, 
  the 
  quadripolar 
  

   arrangement 
  becomes 
  obscured, 
  and 
  usually 
  obliterated. 
  The 
  

   sheaves 
  of 
  fibres 
  become 
  shortened, 
  and 
  hence 
  project 
  less 
  

   into 
  the 
  lobes, 
  and 
  then 
  the 
  ends 
  fuse 
  in 
  pairs, 
  so 
  that 
  a 
  

   bipolar 
  arrangement 
  supervenes. 
  But 
  it 
  sometimes 
  happens 
  

   that 
  a 
  sharp 
  bipolar 
  form 
  is 
  not 
  attained, 
  and 
  then 
  at 
  one 
  or 
  

   the 
  other 
  end 
  the 
  pole 
  is 
  seen 
  to 
  bifurcate 
  somewhat, 
  in 
  

   correspondence 
  with 
  its 
  mode 
  of 
  origin. 
  

  

  When 
  they 
  come 
  to 
  lie 
  on 
  the 
  spindle 
  the 
  chromosomes 
  

   are 
  often 
  difficult 
  to 
  analyse. 
  They 
  may 
  form 
  the 
  twisted 
  

   figures 
  so 
  frequent 
  in 
  the 
  corresponding 
  stage 
  of 
  a 
  lily, 
  or 
  

   they 
  may 
  exhibit 
  the 
  form 
  of 
  closed 
  rings 
  with 
  equatorial 
  

   thickenings, 
  or 
  finally 
  they 
  may 
  form 
  X-like 
  structures 
  (figs. 
  

   35, 
  36). 
  And 
  as 
  the 
  period 
  of 
  the 
  di 
  aster 
  approaches 
  they 
  

   present 
  the 
  highly 
  characteristic 
  form 
  and 
  arrangement 
  that 
  is 
  

   met 
  with 
  in 
  the 
  heterotype 
  mitoses 
  of 
  both 
  plants 
  and 
  animals. 
  

  

  When 
  the 
  diaster 
  is 
  formed 
  it 
  is 
  seen 
  that 
  each 
  bivalent 
  

   chromosome 
  is 
  so 
  divided 
  (fig. 
  36) 
  that 
  transverse 
  halves 
  (i. 
  e. 
  

   its 
  monovalent 
  constituents) 
  are 
  distributed 
  to 
  the 
  two 
  

   daughter 
  nuclei. 
  Sometimes 
  this 
  can 
  be 
  made 
  out 
  very 
  

   clearly 
  when 
  the 
  ring-like 
  forms 
  break 
  asunder 
  at 
  first 
  at 
  one 
  

   side. 
  The 
  Avhole 
  is 
  then 
  straightened 
  out 
  in 
  the 
  direction 
  of 
  

  

  