﻿492 
  J. 
  BRETLAND 
  FARMER 
  AND 
  J. 
  E. 
  S. 
  MOORE. 
  

  

  structui'al 
  features 
  that 
  reappear 
  at 
  each 
  division 
  oE 
  the 
  

   nucleus. 
  

  

  Agaiuj 
  the 
  regular 
  recurrence 
  of 
  a 
  numerical 
  reduction 
  of 
  

   the 
  chromosomes 
  in 
  the 
  maiotic 
  phase, 
  which 
  is 
  intercalated 
  

   once 
  in 
  every 
  normal 
  life 
  cycle, 
  emphasises 
  the 
  importance 
  of 
  

   these 
  bodies 
  in 
  a 
  still 
  higher 
  degree. 
  But 
  although 
  it 
  

   becomes 
  obvious 
  that 
  in 
  the 
  details 
  of 
  maiosis 
  we 
  may 
  reason- 
  

   ably 
  expect 
  to 
  find 
  an 
  important 
  clue 
  as 
  to 
  the 
  nature 
  of 
  that 
  

   relation 
  which 
  must 
  exist 
  between 
  the 
  chromosomes 
  and 
  the 
  

   essential 
  features 
  of 
  ontogeny, 
  opinions 
  are 
  still 
  much 
  divided 
  

   on 
  matters 
  of 
  cardinal 
  importance 
  connected 
  with 
  the 
  

   process. 
  

  

  As 
  is 
  well 
  known, 
  two 
  conflicting 
  classes 
  of 
  interpretation 
  

   have 
  been 
  advanced 
  to 
  account 
  for 
  the 
  phenomena 
  witnessed 
  

   during 
  the 
  maiotic 
  divisions. 
  The 
  divergence 
  of 
  opinion 
  is 
  

   largely 
  due 
  to 
  the 
  extreme 
  difficulty 
  of 
  disentangling 
  the 
  true 
  

   sequence 
  of 
  the 
  events 
  that 
  are 
  proceeding 
  in 
  the 
  intricate 
  

   series 
  of 
  changes 
  that 
  constitute 
  the 
  mitoses 
  in 
  question. 
  

  

  The 
  view 
  that 
  may 
  first 
  be 
  briefly 
  summarised 
  is 
  one 
  

   which 
  has 
  found 
  much 
  favour, 
  and 
  especially 
  with 
  zoologists. 
  

   Weismann 
  long 
  ago 
  insisted 
  on 
  the 
  theoretical 
  necessity 
  of 
  a 
  

   reduction 
  division 
  in 
  connection 
  with 
  his 
  views 
  as 
  to 
  the 
  re- 
  

   lation 
  of 
  ancestral 
  characters 
  with 
  material 
  primordia. 
  The 
  

   investigations 
  of 
  Hacker, 
  Riickert, 
  and 
  others 
  gave 
  a 
  welcome 
  

   support 
  to 
  Weismann's 
  views, 
  and 
  seemed 
  to 
  prove 
  that 
  they 
  

   accorded 
  with 
  actual 
  facts. 
  They 
  showed, 
  in 
  the 
  animals 
  in- 
  

   vestigated 
  by 
  them, 
  that 
  during 
  the 
  prophase 
  of 
  the 
  hetero- 
  

   type 
  mitosis 
  the 
  spireme 
  thread, 
  instead 
  of 
  giving 
  rise 
  to 
  the 
  

   full 
  number 
  of 
  chromosomes 
  characteristic 
  of 
  the 
  preceding 
  

   cell-nuclei, 
  only 
  formed 
  one 
  half 
  the 
  number 
  of 
  these 
  bodies. 
  

   Each 
  chromosome 
  was 
  therefore 
  regarded 
  as 
  bivalent, 
  and 
  as 
  

   consisting 
  of 
  two 
  monovalent 
  chromosomes 
  of 
  pi-ecediugnuclear 
  

   generations. 
  The 
  two 
  individuals 
  constituting 
  a 
  bivalent 
  

   chromosome 
  were 
  considered 
  as 
  being 
  attached 
  end 
  to 
  end. 
  

   Furthermore, 
  the 
  entire 
  bivalent 
  chromosome 
  suffered 
  longi- 
  

   tudinal 
  fission, 
  and 
  the 
  question 
  to 
  be 
  decided 
  lies 
  in 
  the 
  

   exact 
  determination 
  of 
  the 
  method 
  by 
  which 
  the 
  daughter 
  

  

  