﻿520 
  J. 
  J5RETLAND 
  FARMER 
  AND 
  J. 
  E. 
  S. 
  MOORE. 
  

  

  clear 
  (Fig. 
  23). 
  The 
  sides 
  of 
  the 
  loops 
  become 
  di^awn 
  into 
  

   parallel 
  positions 
  as 
  the 
  tangle 
  increases, 
  and 
  at 
  the 
  same 
  

   time 
  the 
  nucleolus 
  suffers 
  a 
  considerable 
  loss 
  of 
  substance, 
  as 
  

   is 
  evidenced 
  by 
  its 
  vacuolation 
  at 
  this 
  stage. 
  

  

  The 
  sides 
  of 
  the 
  loops 
  just 
  described 
  continue 
  to 
  approxi- 
  

   mate 
  more 
  closely 
  together, 
  and 
  thus 
  simulate 
  an 
  appearance 
  

   of 
  a 
  longitudinal 
  fission. 
  It 
  is 
  quite 
  clear, 
  however, 
  that 
  this 
  

   appearance 
  is 
  illusory, 
  for 
  the 
  real 
  fission 
  can 
  often 
  be 
  traced 
  

   in 
  their 
  parallel 
  sides 
  (Fig. 
  24) 
  even 
  at 
  a 
  much 
  later 
  stage. 
  

  

  Gradually 
  the 
  tangle 
  around 
  the 
  nucleus 
  vanishes, 
  and 
  the 
  

   chromatic 
  filament 
  is 
  then 
  observed 
  to 
  have 
  segmented 
  trans- 
  

   versely 
  so 
  as 
  to 
  form 
  the 
  definitive 
  chromosomes. 
  The 
  actual 
  

   process 
  of 
  transverse 
  separation 
  is 
  somewhat 
  slow^ 
  for 
  all 
  

   stages 
  can 
  be 
  followed 
  in 
  suitable 
  preparations. 
  The 
  stainable 
  

   substance 
  (chromatin) 
  seems 
  gi'adually 
  to 
  become 
  attenuated 
  

   so 
  as 
  to 
  give 
  the 
  impression 
  of 
  a 
  viscous 
  body 
  being 
  pulled 
  

   asunder. 
  

  

  It 
  is 
  very 
  clear 
  that 
  much 
  nuclein 
  or 
  chromatin 
  has 
  been 
  

   withdrawn 
  fi'om 
  areas 
  of 
  the 
  original 
  filament, 
  for 
  consider- 
  

   able 
  tracts 
  of 
  the 
  linin 
  thread 
  can 
  be 
  seen 
  to 
  evince 
  no 
  

   affinity 
  for 
  basic 
  aniline 
  dyes, 
  and 
  it 
  often 
  happens 
  that 
  these 
  

   unstained 
  lengths 
  can 
  be 
  traced 
  as 
  being 
  in 
  direct 
  continuity 
  

   with 
  others 
  in 
  which 
  chromatin 
  is 
  abundantly 
  embedded. 
  

  

  Although 
  the 
  parallel 
  arrangement 
  of 
  the 
  chromosome 
  con- 
  

   stituents 
  may 
  be 
  provided 
  for 
  in 
  the 
  way 
  just 
  described, 
  

   namely, 
  by 
  the 
  approximation 
  of 
  the 
  sides 
  of 
  an 
  originally 
  

   looped 
  structure, 
  this 
  by 
  no 
  means 
  exhausts 
  the 
  variations 
  by 
  

   which 
  the 
  same 
  appearance 
  can 
  be 
  produced. 
  Sometimes 
  

   long, 
  rod-like 
  forms 
  with 
  a 
  slight 
  bend 
  in 
  the 
  middle 
  are 
  

   met 
  with, 
  and 
  at 
  others 
  it 
  seems 
  as 
  if 
  the 
  parallel 
  arrange- 
  

   ment 
  of 
  the 
  sides 
  is 
  certainly 
  affected 
  by 
  the 
  approximation 
  

   of 
  two 
  portions 
  of 
  the 
  thread 
  (Fig. 
  25) 
  that 
  have 
  broken 
  

   apart 
  from 
  each 
  other. 
  In 
  fact, 
  many 
  different 
  forms 
  are 
  to 
  

   be 
  seen, 
  often 
  in 
  the 
  same 
  nucleus. 
  The 
  U-shaped 
  loop 
  is 
  

   perhaps 
  the 
  most 
  common, 
  and 
  a 
  simple 
  variation 
  of 
  this 
  is 
  

   produced 
  when 
  the 
  sides 
  or 
  limbs 
  of 
  the 
  loop 
  are 
  twisted 
  

   round 
  each 
  other 
  ; 
  at 
  other 
  times 
  rings 
  or 
  elHpses 
  are 
  en- 
  

  

  