﻿MATUKATION, 
  ETC., 
  OF 
  THE 
  EGG 
  OF 
  THE 
  AXOLOTL. 
  457 
  

  

  centre 
  is 
  first 
  seen 
  in 
  the 
  majority 
  of 
  cases 
  on 
  the 
  inside 
  

   of 
  the 
  sperm-nucleus. 
  In 
  this 
  case^ 
  its 
  origin 
  from 
  the 
  

   middle-piece 
  cannot 
  be 
  said 
  to 
  have 
  been 
  demonstrated. 
  

  

  The 
  rotation 
  of 
  the 
  sperm-head 
  has, 
  however, 
  been 
  observed 
  

   in 
  Toxopneustes, 
  the 
  Trout 
  (Behrens), 
  Petromyzon 
  (Herfort), 
  

   Sponges 
  (Maas), 
  Ophrytrocha^Branchipus; 
  while 
  the 
  formation 
  

   of 
  an 
  aster 
  round 
  the 
  middle-piece 
  is 
  recorded 
  for 
  Polyclada 
  

   (Francotte 
  and 
  von 
  Klinckowstr5ra), 
  AUolobophora, 
  Pliysa, 
  

   Crepidula, 
  Petromyzon, 
  Rhynchelmis, 
  Toxopneustes, 
  Ascaris, 
  

   the 
  Axolotl, 
  and 
  the 
  Newt. 
  Miss 
  Foot 
  and 
  Wilson, 
  hoAvever, 
  

   assert 
  that 
  in 
  Allolobophora 
  and 
  Toxopneustes 
  the 
  middle- 
  

   piece 
  disappears 
  and 
  stands 
  in 
  no 
  obvious 
  genetic 
  relation 
  

   to 
  the 
  cleavage 
  centrosomes. 
  

  

  It 
  is, 
  perhaps, 
  a 
  matter 
  of 
  little 
  moment 
  that 
  the 
  middle- 
  

   piece 
  should 
  have 
  been 
  traced 
  to 
  the 
  previous 
  centrosome 
  in 
  

   none 
  of 
  these 
  cases 
  except 
  the 
  Axolotl 
  ; 
  what 
  is 
  of 
  importance 
  

   is 
  that 
  the 
  formation 
  of 
  an 
  aster 
  about 
  this 
  structure 
  is 
  no 
  

   indication 
  whatever 
  of 
  its 
  survival 
  as 
  the 
  cleavage 
  centrosome, 
  

   as 
  its 
  fate 
  in 
  the 
  Axolotl 
  and 
  Newt, 
  in 
  Allolobophora 
  and 
  

   Toxopneustes 
  clearly 
  shows. 
  

  

  The 
  difficulty 
  of 
  drawing 
  any 
  positive 
  conclusion 
  from 
  this 
  

   conflicting 
  mass 
  of 
  testimony 
  is 
  obviously 
  very 
  great 
  ; 
  for 
  as 
  

   Wilson 
  has 
  pointed 
  out, 
  if 
  the 
  sperm-centres 
  disappear 
  there 
  

   is 
  no 
  more 
  reason 
  for 
  deriving 
  the 
  cleavage 
  centres 
  from 
  

   them 
  than 
  from 
  the 
  egg-centres. 
  The 
  possibility 
  of 
  the 
  

   formation 
  of 
  centrosomes 
  afresh 
  in 
  the 
  cytoplasm 
  has 
  also 
  to 
  

   bo 
  reckoned 
  with 
  (Mead, 
  centrosomes 
  in 
  the 
  oocyte 
  of 
  

   Chastopterus 
  ; 
  Wilson 
  [1901] 
  and 
  Morgan, 
  centrosomes 
  in 
  

   the 
  parthenogenetic 
  ova 
  of 
  Echinoderms) 
  . 
  

  

  It 
  would 
  be 
  unwise 
  to 
  prophesy 
  too 
  dogmatically 
  until 
  

   we 
  have 
  a 
  much 
  fuller 
  knowledge 
  of 
  the 
  exact 
  mode 
  of 
  

   formation 
  of 
  the 
  cleavage 
  centres 
  ; 
  but 
  it 
  does 
  not 
  seem 
  

   impossible 
  that 
  they 
  may 
  arise 
  in 
  other 
  forms, 
  as 
  they 
  do 
  in 
  

   the 
  Axolotl, 
  from 
  the 
  sperm-nucleus 
  ; 
  and 
  that 
  those 
  sperm- 
  

   asters 
  which 
  have 
  so 
  often 
  been 
  observed, 
  and 
  so 
  often 
  

   disappear, 
  are 
  the 
  transitory 
  primary 
  radiations 
  which 
  arise 
  

   around 
  the 
  middle-piece. 
  By 
  giving 
  up 
  therefore 
  the 
  doctrine 
  

  

  