﻿THE 
  MAIOTIC 
  PHASE 
  IN 
  ANIMALS 
  AND 
  PLANTS. 
  499 
  

  

  Thus 
  much 
  of 
  the 
  existing 
  divergence 
  of 
  opinion 
  relates 
  to 
  

   the 
  interpretation 
  to 
  be 
  placed 
  on 
  these 
  later 
  stages, 
  although 
  

   these 
  cannot 
  really 
  be 
  understood 
  save 
  by 
  the 
  study 
  of 
  an 
  

   unbroken 
  series. 
  Naturally 
  the 
  omission 
  was 
  not 
  intentional. 
  

   But 
  the 
  later 
  stages 
  seemed 
  to 
  fit 
  so 
  well 
  on 
  to 
  the 
  earlier, 
  

   that 
  the 
  necessity 
  for 
  special 
  caution 
  as 
  regards 
  the 
  inter- 
  

   vening 
  ones 
  was 
  not 
  apparent. 
  

  

  Speaking 
  broadly, 
  the 
  longitudinal 
  fission 
  of 
  the 
  spireme 
  (or 
  

   its 
  representative) 
  has 
  been 
  very 
  generally 
  recognised, 
  but 
  the 
  

   phase 
  which 
  has 
  next 
  attracted 
  the 
  largest 
  share 
  of 
  attention 
  

   has 
  been 
  that 
  in 
  which 
  the 
  chromosomes 
  are 
  becoming 
  

   definitely 
  segregated 
  previously 
  to 
  the 
  assumption 
  by 
  them 
  

   of 
  their 
  mature 
  form 
  and 
  their 
  final 
  congregation 
  on 
  the 
  

   spindle. 
  

  

  With 
  the 
  hiatus 
  that 
  intervenes 
  between 
  these 
  two 
  phases 
  

   we 
  are 
  not 
  now 
  concerned, 
  as 
  it 
  forms 
  the 
  main 
  part 
  of 
  the 
  

   observations 
  recorded 
  in 
  the 
  body 
  of 
  this 
  memoir, 
  but 
  we 
  may 
  

   briefly 
  glance 
  at 
  some 
  of 
  the 
  interpretations 
  that 
  have 
  been 
  

   put 
  on 
  the 
  structure 
  of 
  the 
  heterotype 
  chromosomes 
  themselves. 
  

  

  In 
  the 
  case 
  of 
  salamander 
  and 
  lily, 
  as 
  examples 
  of 
  an 
  

   animal 
  and 
  plant 
  respectively, 
  the 
  definite 
  heterotype 
  chromo- 
  

   somes 
  exhibit 
  the 
  forms 
  of 
  rings, 
  loops 
  open 
  at 
  one 
  end 
  with 
  

   the 
  sides 
  more 
  or 
  less 
  twisted 
  round 
  each 
  other, 
  and 
  finally, 
  

   especially 
  in 
  the 
  lily, 
  of 
  rods, 
  lying 
  either 
  parallel 
  or 
  twisted 
  

   round 
  each 
  other. 
  These 
  figures 
  were 
  easily 
  referable 
  to, 
  and 
  

   were 
  supposed 
  to 
  be 
  derived 
  from, 
  the 
  split 
  spireme 
  thread 
  

   by 
  its 
  transverse 
  segmentation, 
  and 
  the 
  more 
  or 
  less 
  intimate 
  

   union 
  of 
  the 
  ends 
  of 
  the 
  parallel 
  halves 
  of 
  the 
  transversely 
  

   isolated 
  segments 
  with 
  each 
  other. 
  Within 
  the 
  last 
  ten 
  years 
  

   an 
  increasingly 
  large 
  number 
  of 
  examples 
  have 
  been 
  dis- 
  

   covered 
  in 
  which 
  the 
  two 
  "longitudinal 
  halves'^ 
  of 
  each 
  

   heterotype 
  chromosome 
  were 
  observed 
  to 
  show 
  signs 
  of 
  a 
  

   fission, 
  and 
  this 
  has 
  been 
  commonly 
  interpreted 
  as 
  the 
  second 
  

   longitudinal 
  fission 
  preparatory 
  to 
  the 
  further 
  division 
  of 
  the 
  

   chromosomes 
  in 
  the 
  next 
  succeeding 
  (homotype) 
  mitosis. 
  

  

  In 
  another 
  series 
  of 
  examples, 
  of 
  which 
  Arthropoda 
  

   (Riickert, 
  Hacker, 
  and 
  others) 
  and 
  ferns 
  (Calkins) 
  may 
  be 
  

  

  