﻿MATURATION, 
  ETC., 
  OF 
  THE 
  EGG 
  OK 
  THE 
  AXOLOTL. 
  451 
  

  

  physiologically 
  a 
  centrosome, 
  even 
  though 
  it 
  refuses 
  to 
  stain 
  

   with 
  iron-ha3n]otoxylin. 
  With 
  respect 
  to 
  its 
  alleged 
  absence 
  

   from 
  certain 
  polar 
  spindles, 
  it 
  may 
  be 
  pointed 
  out 
  that 
  in 
  

   Ascaris 
  it 
  has 
  been 
  seen 
  by 
  several 
  investigators 
  (Carnoy, 
  

   Sala, 
  and 
  Fiirst), 
  and 
  that 
  in 
  any 
  case 
  the 
  broad 
  plate 
  Avhich 
  

   liei'e 
  occupies 
  the 
  pole 
  of 
  the 
  intra-nuclear 
  spindle 
  has 
  just 
  

   as 
  much 
  title 
  to 
  be 
  regarded 
  as 
  active 
  in 
  the 
  pi'oduction 
  of 
  

   the 
  spindle 
  fibres 
  as 
  has 
  the 
  quite 
  similar 
  pole-plate 
  in 
  the 
  

   spindles 
  of 
  Infusoria, 
  Actinospha3rium, 
  and 
  other 
  Protozoa. 
  

  

  That 
  the 
  centrosome 
  is 
  not 
  merely 
  passive 
  I 
  hold 
  to 
  be 
  

   proved, 
  first, 
  by 
  its 
  division 
  antecedently 
  to 
  the 
  formation 
  of 
  

   those 
  structures 
  on 
  which 
  the 
  division 
  of 
  the 
  nucleus 
  and 
  cell 
  

   obviously 
  depends; 
  and 
  secondly, 
  by 
  the 
  fact 
  that 
  these 
  

   structures 
  (astral 
  rays 
  and 
  spindle 
  fibres) 
  clearly 
  grow 
  out 
  

   from 
  the 
  centrosome. 
  Further, 
  I 
  think 
  it 
  possible 
  that 
  the 
  

   activity 
  depends, 
  as 
  Biitschli 
  (1894) 
  first 
  suggested, 
  on 
  its 
  

   faculty 
  of 
  absorbing 
  the 
  watery 
  substances 
  of 
  the 
  cytoplasm. 
  

   Such 
  absorption 
  will 
  readily 
  account 
  for 
  its 
  growth, 
  and 
  per- 
  

   haps 
  also 
  for 
  the 
  remarkable 
  series 
  of 
  periodically 
  recurrent 
  

   changes 
  which 
  it 
  passes 
  through. 
  

  

  These 
  changes 
  have 
  been 
  noticed 
  and 
  figured 
  by 
  many 
  

   cytologists 
  (Coe, 
  Lillie, 
  Veidovskj"-, 
  MacFarland, 
  Sobotta 
  

   [Amphioxus], 
  Conklin, 
  van 
  der 
  Stricht 
  [1898], 
  Lin 
  ville, 
  Gar- 
  

   diner, 
  Griffin, 
  and 
  myself) 
  ; 
  but 
  it 
  is 
  to 
  Boveri 
  (1901) 
  that 
  we 
  

   owe 
  the 
  clearest 
  description 
  of 
  the 
  details 
  of 
  the 
  process. 
  

  

  In 
  spite 
  of 
  much 
  disagreement, 
  especially 
  with 
  regard 
  to 
  the 
  

   nomenclature 
  of 
  the 
  different 
  parts 
  of 
  the 
  structure, 
  all 
  are 
  at 
  

   one 
  in 
  regarding 
  as 
  the 
  essential 
  feature 
  of 
  the 
  metamor- 
  

   phosis 
  (a) 
  the 
  enlargement 
  of 
  the 
  centrosome 
  at 
  a 
  certain 
  stage 
  

   in 
  mitosis, 
  (b) 
  the 
  gradual 
  fusion 
  of 
  the 
  centrosome 
  with 
  the 
  

   aster, 
  from 
  which 
  it 
  now 
  becomes 
  indistinguishable, 
  and 
  

   together 
  with 
  which 
  it 
  ultimately 
  degenerates, 
  (c) 
  the 
  for- 
  

   mation 
  of 
  a 
  new 
  centrosome 
  inside 
  the 
  old; 
  this 
  new 
  centro- 
  

   some 
  divides 
  preparatory 
  to 
  the 
  next 
  mitosis, 
  while 
  around 
  its 
  

   halves 
  the 
  new 
  asters 
  are 
  formed. 
  

  

  This 
  is 
  essentially 
  Boveri's 
  account 
  of 
  this 
  cycle 
  of 
  changes 
  

   in 
  the 
  fertilization 
  spindle 
  of 
  Echinus. 
  The 
  centrosome, 
  by 
  

  

  