﻿546 
  J. 
  BRETLAND 
  FARMER 
  AND 
  J. 
  E. 
  S. 
  MOORE. 
  

  

  more 
  chromatic, 
  and 
  often 
  polarised, 
  arrangement 
  of 
  their 
  

   nuclear 
  reticulum. 
  In 
  the 
  more 
  readily 
  elucidated 
  examples, 
  

   such 
  as 
  Blatta 
  or 
  Osmunda, 
  this 
  polarisation 
  increases 
  and 
  

   the 
  chromatin 
  becomes 
  finally 
  arranged 
  in 
  a 
  number 
  of 
  

   definite 
  loops. 
  In 
  a 
  large 
  number 
  of 
  instances 
  these 
  loops 
  can 
  

   readily 
  be 
  counted, 
  and 
  when 
  this 
  is 
  the 
  case, 
  there 
  are 
  

   always 
  found 
  to 
  be 
  half 
  as 
  many 
  loops 
  as 
  there 
  were 
  somatic 
  

   chromosomes 
  in 
  the 
  preceding 
  pre-maiotic 
  divisions. 
  

  

  At 
  thesame 
  time, 
  the 
  whole 
  chromatic 
  network 
  contractsaway 
  

   from 
  the 
  nuclear 
  membrane, 
  this 
  change 
  producing 
  the 
  First 
  

   Contraction 
  figure. 
  As 
  time 
  goes 
  on 
  the 
  loops 
  become 
  not 
  

   ouly 
  iucreasingly 
  chromatic 
  but 
  also 
  opened 
  out 
  again, 
  until 
  

   the 
  apparent 
  polarisation 
  is 
  more 
  or 
  less 
  completely 
  lost 
  and 
  

   the 
  nuclei 
  present 
  the 
  well-known 
  coarse 
  spirem 
  figure 
  

   withiu 
  the 
  strands 
  of 
  which 
  double 
  beading 
  or 
  actual 
  longi- 
  

   tudinal 
  fission 
  is 
  nearly 
  always 
  more 
  or 
  less 
  apparent. 
  The 
  

   coarse 
  spirem 
  figure 
  often 
  constitutes 
  a 
  prolonged 
  phase, 
  but 
  

   it 
  is 
  in 
  all 
  cases 
  ultimately 
  succeeded 
  by 
  a 
  short-lived 
  and 
  

   easily 
  missed 
  resumption 
  on 
  the 
  part 
  of 
  the 
  split 
  chromatic 
  

   thread-work 
  of 
  its 
  earlier 
  polarised 
  arrangement; 
  and 
  this 
  is 
  

   followed 
  by 
  a 
  strong 
  Second 
  Contraction 
  and 
  thickening 
  

   of 
  tlie 
  individual 
  loops. 
  Even 
  before 
  the 
  second 
  contraction 
  

   has 
  fully 
  supervened, 
  the 
  longitudinal 
  fission 
  of 
  the 
  thread- 
  

   work 
  has 
  in 
  the 
  great 
  majority 
  of 
  cases 
  almost 
  closed 
  up 
  and 
  

   disappeared 
  ; 
  and 
  although 
  the 
  exact 
  details 
  of 
  the 
  subse- 
  

   quent 
  evolution 
  may, 
  and 
  to 
  some 
  extent 
  do, 
  vary 
  in 
  the 
  

   different 
  types, 
  the 
  general 
  statement 
  that 
  each 
  of 
  the 
  indi- 
  

   vidual 
  loops 
  in 
  this 
  second 
  contraction 
  figure 
  becomes 
  

   directly 
  converted 
  into 
  one 
  of 
  the 
  heterotype 
  chromosomes 
  

   sufficiently 
  expresses 
  the 
  really 
  essential 
  parts 
  of 
  the 
  process. 
  

  

  In 
  some 
  cases, 
  as 
  in 
  the 
  cocki'oach 
  and 
  Osra 
  u 
  nda, 
  the 
  loops, 
  

   throughout 
  the 
  whole 
  series 
  of 
  events, 
  remain 
  distinct 
  from 
  

   one 
  another, 
  with 
  their 
  free 
  ends 
  open 
  in 
  the 
  region 
  of 
  the 
  

   pole 
  field; 
  but 
  during 
  the 
  later 
  stages 
  of 
  their 
  formation 
  

   they 
  often 
  break 
  transversely 
  in 
  the 
  curve 
  of 
  the 
  loop 
  as 
  well. 
  

   Consequently 
  since 
  the 
  number 
  of 
  unbroken 
  loops 
  is 
  half 
  the 
  

   number 
  of 
  pre-maiotic 
  chromosomes, 
  in 
  this 
  stage 
  as 
  well 
  

  

  