﻿MATURATION, 
  ETC., 
  OF 
  THE 
  EGG 
  OF 
  THE 
  AXOLOTL. 
  469 
  

  

  I 
  have 
  also 
  a 
  word 
  to 
  say 
  on 
  tlie 
  so-called 
  contractile 
  fibres 
  

   or 
  " 
  Zugf 
  asern 
  " 
  attached 
  to 
  the 
  chromosomes. 
  

  

  In 
  the 
  Axolotl 
  I 
  have 
  seen 
  such 
  fibres, 
  or 
  rather 
  fibre- 
  

   bundles, 
  passing 
  to 
  but 
  not 
  beyond 
  the 
  chromosomes 
  ; 
  as 
  the 
  

   latter 
  diverge 
  the 
  fibre-bundles 
  shorten, 
  though 
  they 
  cannot 
  

   be 
  said 
  to 
  thicken. 
  Usually 
  the 
  fibre-bundle 
  is 
  attached 
  to 
  

   the 
  end 
  of 
  a 
  chromosome 
  but 
  sometimes 
  at 
  a 
  short 
  distance 
  

   from 
  the 
  end. 
  In 
  this 
  case 
  the 
  point 
  of 
  attachment 
  is 
  during 
  

   the 
  anaphase 
  invariably 
  nearest 
  the 
  spindle-pole, 
  the 
  chromo- 
  

   some 
  thus 
  assuming 
  a 
  hooked 
  form. 
  This 
  all 
  seems 
  to 
  me 
  to 
  

   be 
  strongly 
  in 
  favour 
  of 
  the 
  belief 
  that 
  these 
  fibre-bundles 
  

   do 
  actually 
  pull 
  the 
  chromosomes 
  apart. 
  There 
  is 
  of 
  course 
  

   a 
  large 
  amount 
  of 
  evidence 
  to 
  the 
  same 
  extent 
  from 
  many 
  

   other 
  sources. 
  At 
  the 
  same 
  time 
  I 
  believe 
  it 
  to 
  be 
  a 
  wholly 
  

   gratuitous 
  error 
  to 
  attribute 
  to 
  such 
  fibres 
  the 
  properties 
  of 
  

   pieces 
  of 
  elastic, 
  as 
  so 
  many 
  authors 
  have 
  done, 
  or 
  to 
  assume 
  

   with 
  Boveri 
  (1888) 
  that 
  all 
  the 
  laws 
  that 
  hold 
  good 
  for 
  

   muscles 
  can 
  also 
  be 
  applied 
  to 
  these. 
  

  

  On 
  the 
  view 
  I 
  have 
  put 
  forward 
  these 
  fibres, 
  produced 
  

   by 
  the 
  precipitation 
  of 
  a 
  proteid, 
  are 
  probably 
  in 
  the 
  con- 
  

   dition 
  of 
  a 
  highly 
  viscous 
  fluid. 
  When 
  a 
  drop 
  of 
  egg-yolk 
  

   falls 
  from 
  a 
  glass 
  rod 
  it 
  di-aws 
  out 
  a 
  long 
  thread 
  behind 
  it 
  ; 
  

   when 
  the 
  drop 
  is 
  detached 
  the 
  thread 
  flows 
  back 
  on 
  to 
  the 
  

   rod. 
  And 
  so 
  in 
  the 
  spindle. 
  As 
  the 
  tubes 
  grow 
  out 
  some 
  

   of 
  the 
  lamella^, 
  or 
  fibres, 
  become 
  attached 
  to 
  the 
  chromosomes 
  ; 
  

   when 
  the 
  chromosomes 
  split 
  the 
  fibres 
  retreat 
  into 
  the 
  

   substance 
  of 
  the 
  centrosome, 
  carrying 
  the 
  halves 
  of 
  the 
  

   chromosomes 
  with 
  them. 
  The 
  astral 
  rays 
  on 
  the 
  other 
  hand 
  

   do 
  not 
  behave 
  in 
  this 
  way, 
  probably 
  because 
  their 
  outer 
  ends 
  

   never 
  become 
  severed 
  from 
  the 
  surrounding 
  cytoplasm. 
  

  

  Cases 
  have 
  been 
  described 
  (lijima, 
  Mark) 
  in 
  which 
  the 
  

   astral 
  rays 
  are 
  curved, 
  apparently 
  by 
  streaming 
  movements 
  

   in 
  the 
  cell. 
  Such 
  a 
  curvature 
  may 
  easily 
  be 
  imparted 
  to 
  

   the 
  artificial 
  radiations 
  by 
  simply 
  tilting 
  the 
  slide. 
  It 
  is 
  

   very 
  difficult 
  to 
  believe 
  that 
  these 
  rays 
  are 
  any 
  more 
  elastic 
  

   than 
  the 
  spindle-fibres. 
  

  

  Lastly, 
  the 
  living 
  aster 
  and 
  spindle 
  dissolve 
  and 
  disappear 
  

  

  