﻿THE 
  MAIOTIC 
  PHASE 
  IN 
  ANIMALS 
  AND 
  PLANTS. 
  493 
  

  

  cliromosomes 
  of 
  tlie 
  lieterotype 
  and 
  homotype 
  mitoses 
  respec- 
  

   tively 
  are 
  provided 
  for. 
  

  

  Hacker 
  considered 
  that 
  during 
  the 
  heterotype 
  division 
  the 
  

   longitudinal 
  halves 
  of 
  each 
  bivalent 
  chromosome 
  were 
  

   separated, 
  exactly 
  as 
  happens 
  during 
  an 
  ordinary 
  mitosis. 
  At 
  

   the 
  second 
  (homotype) 
  division, 
  however, 
  each 
  chromosome 
  

   (which 
  is 
  still 
  bivalent) 
  splits 
  transversely 
  into 
  its 
  mono- 
  

   valent 
  individuals, 
  and 
  in 
  this 
  way 
  is 
  provided 
  the 
  mechanism 
  

   of 
  reduction 
  postulated 
  by 
  Weismann. 
  Rtickert 
  and 
  others 
  

   have 
  sounded 
  a 
  less 
  certain 
  note 
  as 
  to 
  the 
  particular 
  mitosis 
  

   during 
  which 
  reduction 
  is 
  effected. 
  They 
  admit 
  that 
  it 
  may 
  

   occur 
  in 
  the 
  heterotype 
  mitosis. 
  Now, 
  if 
  either 
  of 
  these 
  two 
  

   slightly 
  differing 
  views 
  as 
  to 
  the 
  general 
  significance 
  of 
  the 
  

   heterotype 
  and 
  homotype 
  mitoses 
  prove 
  to 
  be 
  generally 
  true, 
  

   it 
  is 
  clear, 
  in 
  the 
  first 
  place, 
  that 
  the 
  opinion 
  of 
  those 
  who 
  

   hold 
  that 
  the 
  chromosomes 
  are 
  to 
  be 
  regarded 
  as 
  permanent 
  

   and 
  persistent 
  entities 
  gains 
  a 
  strong, 
  if 
  somewhat 
  indirect, 
  

   support. 
  For 
  the 
  significance 
  of 
  the 
  numerical 
  reduction 
  is 
  

   clearly 
  related 
  to 
  the 
  restoration 
  of 
  the 
  full 
  number 
  of 
  chromo- 
  

   somes 
  at 
  the 
  next 
  succeeding 
  fertilisation. 
  And 
  on 
  the 
  view 
  just 
  

   outlined 
  above, 
  reduction 
  involves 
  no 
  loss 
  of 
  individuality, 
  for 
  

   it 
  is 
  effected 
  by 
  the 
  migration 
  of 
  half 
  the 
  entire 
  number 
  of 
  

   somatic 
  (or 
  pre-maiotic) 
  chromosomes 
  to 
  each 
  of 
  the 
  two 
  

   daughter 
  nuclei 
  respectively. 
  

  

  The 
  second 
  view, 
  Avhich 
  has 
  been 
  largely 
  entertained 
  by 
  

   botanists 
  and 
  by 
  some 
  zoologists, 
  explained 
  the 
  processes 
  

   differently. 
  During 
  the 
  later 
  stages 
  of 
  prophase 
  of 
  the 
  

   heterotype 
  mitosis, 
  an 
  appearance 
  strongly 
  suggestive 
  of 
  a 
  

   second 
  longitudinal 
  fission 
  of 
  the 
  chromosomes 
  may 
  often 
  be 
  

   observed. 
  This 
  was 
  believed 
  to 
  provide 
  for 
  the 
  division 
  of 
  

   these 
  bodies 
  in 
  both 
  the 
  heterotype 
  and 
  homotype 
  mitosis. 
  

   In 
  each 
  of 
  these, 
  then, 
  the 
  mode 
  of 
  chromosome 
  distribution 
  

   would 
  be 
  similar, 
  and 
  it 
  Avould 
  resemble 
  in 
  all 
  essential 
  

   respects 
  the 
  process 
  as 
  it 
  occurs 
  in 
  an 
  ordinary 
  somatic 
  

   division. 
  And 
  furthermore 
  every 
  precaution 
  would 
  seem 
  to 
  

   have 
  been 
  taken, 
  during 
  the 
  prophase 
  of 
  the 
  heterotype 
  

   mitosis, 
  to 
  secure 
  the 
  utmost 
  degree 
  of 
  similarity 
  between 
  the 
  

  

  