﻿530 
  J. 
  BRETLAND 
  FAKMER 
  AND 
  J. 
  E. 
  S. 
  MOORE. 
  

  

  proceeds, 
  moreover, 
  in 
  such 
  a 
  manner 
  tliat 
  the 
  chromatic 
  

   granules 
  become 
  arranged 
  or 
  grouped 
  in 
  two 
  distinct 
  rows, 
  

   or 
  tracts. 
  So 
  that 
  by 
  the 
  time 
  the 
  individual 
  chromosomes 
  have 
  

   attained 
  to 
  some 
  sharpness 
  of 
  definition 
  they 
  appear 
  also 
  as 
  

   if 
  they 
  had 
  been 
  split 
  longitudinally 
  from 
  end 
  to 
  end. 
  In 
  the 
  

   cockroach, 
  however, 
  it 
  is 
  obvious 
  that 
  this 
  split 
  has 
  not 
  arisen 
  

   from 
  the 
  sundering 
  of 
  a 
  pre-forraed 
  riband, 
  but 
  by 
  the 
  

   gradual 
  grouping 
  of 
  the 
  chromatin 
  granules 
  into 
  the 
  form 
  of 
  

   a 
  short 
  double 
  rod 
  (figs. 
  46-48) 
  .^ 
  

  

  It 
  will 
  have 
  been 
  seen 
  that 
  the 
  method 
  of 
  chromosome 
  

   formation 
  here 
  depicted 
  presents 
  nothing 
  exactly 
  comparable 
  

   to 
  the 
  long 
  spirem 
  thread 
  which 
  is 
  figured 
  in 
  so 
  many 
  of 
  the 
  

   existing 
  accounts 
  of 
  pre-maiotic 
  division 
  which 
  have 
  hitherto 
  

   appeared. 
  

  

  In 
  all 
  cases 
  Avhich 
  we 
  have 
  examined 
  the 
  number 
  of 
  the 
  rod- 
  

   like 
  chromosomes 
  which 
  are 
  eventually 
  produced 
  appears 
  to 
  

   be 
  generally 
  thirty-two 
  ; 
  that 
  is, 
  by 
  counting 
  the 
  chromosomes 
  

   in 
  a 
  large 
  number 
  of 
  cells, 
  and 
  then 
  taking 
  the 
  average 
  of 
  such 
  

   counts, 
  the 
  number 
  thirty-two 
  has 
  always 
  been 
  attained. 
  But 
  

   it 
  is 
  not 
  intended, 
  nor 
  should 
  it 
  be 
  assumed 
  that 
  there 
  is 
  an 
  

   absolute 
  numerical 
  rigidity 
  in 
  all 
  the 
  individual 
  cells; 
  for 
  

   many 
  figures 
  have 
  been 
  encountered 
  in 
  which 
  the 
  number 
  

   appeared 
  to 
  be 
  more 
  or 
  less 
  than 
  this, 
  by 
  one, 
  two, 
  or 
  even 
  

   more, 
  yet 
  in 
  these 
  cases 
  there 
  was 
  no 
  reason 
  to 
  suppose 
  that 
  

   the 
  cells 
  under 
  examination 
  had 
  in 
  any 
  way 
  been 
  altered 
  by 
  

   manipulation. 
  

  

  When 
  the 
  pre-maiotic 
  mitosis 
  has 
  reached 
  the 
  above 
  stage 
  

   the 
  cells 
  which 
  present 
  themselves 
  in 
  groups 
  with 
  the 
  short 
  

   double 
  chromosomes 
  just 
  described 
  possess 
  the 
  characteristic 
  

   appearance 
  represented 
  in 
  fig. 
  47; 
  while 
  about 
  the 
  same 
  

   time 
  the 
  parts 
  of 
  the 
  karyokinetic 
  figure 
  related 
  to 
  the 
  

   centrosomes, 
  as 
  well 
  as 
  these 
  bodies 
  themselves, 
  emerge 
  once 
  

   more 
  into 
  prominence. 
  

  

  All 
  the 
  ensuing 
  stages 
  of 
  the 
  pre-maiotic 
  divisions 
  are 
  in 
  

  

  ' 
  Cf. 
  Parmer 
  and 
  Shore, 
  "On 
  the 
  Structure 
  and 
  Development 
  of 
  tlie 
  

   Somatic 
  and 
  Heterotype 
  Chromosomes 
  of 
  Tradescantia 
  Virginica," 
  

   Quart. 
  Journ. 
  Micr. 
  Soc,' 
  1904. 
  

  

  