﻿MATURATION, 
  ETC., 
  OF 
  THE 
  EGG 
  OF 
  THE 
  AXOLOTL. 
  441 
  

  

  tion 
  spindle. 
  The 
  cleavage 
  ceiitrosomes, 
  therefore, 
  are 
  

   derived 
  from 
  the 
  middle-piece 
  Avhich 
  is, 
  as 
  Fick 
  surmised 
  and 
  

   as 
  we 
  now 
  know, 
  the 
  enlarged 
  centrosome 
  of 
  the 
  spermatid. 
  

  

  As 
  I 
  have 
  tried 
  to 
  show, 
  such 
  a 
  view 
  is 
  untenable 
  ; 
  for 
  not 
  

   only 
  is 
  there 
  a 
  stage 
  in 
  which 
  the 
  middle-piece 
  has 
  clearly 
  

   disappeared, 
  but 
  also 
  wo 
  have 
  direct 
  evidence 
  for 
  the 
  

   formation 
  of 
  the 
  definitive 
  centrosome 
  de 
  novo 
  from 
  the 
  

   sperm-nucleus. 
  

  

  The 
  point 
  is 
  one 
  of 
  considerable 
  theoretical 
  importance. 
  

   Up 
  till 
  now 
  the 
  Axolotl 
  has 
  been 
  the 
  only 
  form 
  in 
  which 
  the 
  

   persistence 
  of 
  the 
  centrosome 
  from 
  the 
  spermatid 
  to 
  the 
  

   fertilisation 
  spindle 
  could 
  be 
  positively 
  asserted 
  ; 
  for 
  though 
  

   on 
  the 
  one 
  hand 
  the 
  origin 
  of 
  the 
  middle-piece 
  from 
  the 
  

   previous 
  centrosome 
  has 
  been 
  traced 
  in 
  many 
  cases, 
  while 
  on 
  

   the 
  other 
  there 
  are 
  numerous 
  observations 
  of 
  the 
  formation 
  of 
  

   the 
  fertilisation 
  spindle 
  by 
  division 
  of 
  the 
  sperm-aster, 
  both 
  

   processes 
  had 
  been 
  seen 
  in 
  no 
  animal 
  but 
  this. 
  

  

  In 
  several 
  other 
  respects 
  I 
  have 
  been 
  able 
  to 
  go 
  into 
  

   greater 
  detail 
  than 
  Fick 
  ; 
  the 
  polar 
  spindles, 
  the 
  structure 
  of 
  

   the 
  sperm-aster, 
  and 
  notably 
  the 
  formation 
  of 
  the 
  fertilisation 
  

   spindle. 
  Fick's 
  description 
  of 
  the 
  last 
  is 
  indeed 
  very 
  

   deficient. 
  

  

  On 
  the 
  other 
  hand 
  he 
  has 
  described 
  the 
  mode 
  of 
  entry 
  of 
  

   the 
  spermatozoon 
  and 
  the 
  entrance-cone 
  and 
  funnel. 
  The 
  

   entrance-cone 
  is, 
  according 
  to 
  him, 
  an 
  aggregation 
  of 
  

   " 
  Eiplasma," 
  and 
  is 
  produced 
  by 
  something 
  in 
  the 
  nature 
  of 
  a 
  

   ferment 
  provided 
  by 
  the 
  spermatozoon. 
  It 
  has 
  a 
  dense, 
  

   radially 
  striated 
  border. 
  

  

  More 
  recently 
  Michaelis 
  has 
  published 
  a 
  short 
  paper 
  on 
  the 
  

   fertilisation 
  of 
  a 
  closely-allied 
  form 
  — 
  the 
  newt. 
  

  

  His 
  observations 
  on 
  the 
  fate 
  of 
  the 
  middle-piece 
  agree 
  

   closely 
  with 
  my 
  own. 
  Radiations 
  appear 
  at 
  an 
  early 
  stage, 
  

   but 
  " 
  dass 
  dei 
  genannten 
  Strahlungen 
  in 
  irgend 
  einem 
  

   Zusammenhang 
  mit 
  der 
  spateren 
  Attraktions-sphare 
  stiinden 
  

   ist 
  kaum 
  anzunehmen." 
  Later 
  there 
  comes 
  a 
  stage 
  in 
  which 
  

   " 
  vom 
  Mittelstuck 
  ist 
  nichts 
  mehr 
  zu 
  sehen." 
  

  

  He 
  has 
  failed 
  to 
  find 
  any 
  cleavage 
  centrosome, 
  though 
  it 
  

  

  