﻿MATUllATION, 
  ETC., 
  OF 
  THE 
  EGG 
  OF 
  THE 
  AXOLOTL. 
  449 
  

  

  We 
  have 
  seen 
  that 
  in 
  the 
  Axolotl 
  soon 
  after 
  the 
  entrance 
  

   o£ 
  the 
  spermatozoon^ 
  the 
  head 
  and 
  middle-piece 
  become 
  sur- 
  

   rounded 
  by 
  a 
  clear 
  area 
  devoid 
  of 
  yolk-granules. 
  Such 
  a 
  

   sperm-sphere 
  is 
  of 
  wide-spread 
  if 
  not 
  of 
  universal 
  occurrence. 
  

   Without 
  stopping 
  now 
  to 
  inquire 
  into 
  its 
  physical 
  significance 
  

   I 
  may 
  quote 
  a 
  few 
  of 
  the 
  cases 
  in 
  which 
  it 
  has 
  been 
  seen. 
  

  

  It 
  has 
  been 
  described 
  by 
  Griffin 
  in 
  Thalassema, 
  by 
  Lillie 
  in 
  

   Unio, 
  by 
  Castle 
  in 
  Ciona, 
  by 
  Gardiner 
  in 
  Polychoerus, 
  by 
  

   Henking 
  in 
  Insects, 
  by 
  both 
  Coe 
  and 
  von 
  Kostanecki 
  in 
  

   Cerebratulus, 
  and 
  by 
  Vejdovskj' 
  in 
  Rhynchelmis. 
  

  

  Both 
  Coe 
  and 
  von 
  Kostanecki 
  express 
  the 
  opinion 
  that 
  the 
  

   yolk-granules 
  are 
  driven 
  away 
  by 
  the 
  formation 
  of 
  the 
  sphere, 
  

   while 
  Castle 
  and 
  Vejdovsky 
  hazard 
  the 
  conjecture 
  that 
  the 
  

   sphere 
  grows 
  by 
  the 
  addition 
  of 
  material 
  brought 
  to 
  it 
  by 
  

   streams 
  of 
  protoplasm 
  moving 
  along 
  the 
  surrounding 
  astral 
  

   rays. 
  

  

  In 
  the 
  Axolotl 
  the 
  sperm-sphere 
  becomes 
  subsequently 
  

   vacuolated. 
  Such 
  vacuoles 
  have 
  been 
  observed 
  by 
  Vejdovsky 
  

   in 
  Rhynchelmis, 
  by 
  Herfort 
  in 
  Petromyzon, 
  and 
  by 
  Oppel 
  and 
  

   Nicolas 
  in 
  Reptilia. 
  

  

  2. 
  The 
  centrosome 
  in 
  fertilisation. 
  

  

  (a) 
  The 
  centrosome 
  as 
  an 
  organ 
  of 
  the 
  cell. 
  

  

  (i) 
  Intra-nuclear 
  origin 
  of 
  the 
  centrosome. 
  

  

  In 
  the 
  Axolotl 
  the 
  definitive 
  centrosome 
  is 
  derived 
  from 
  the 
  

   male 
  pronucleus, 
  through 
  what 
  I 
  must 
  regard 
  as 
  a 
  precipita- 
  

   tion 
  of 
  the 
  egg-cytoplasm 
  by 
  the 
  nucleins 
  of 
  the 
  sperm. 
  

   Although 
  no 
  such 
  mode 
  of 
  formation 
  of 
  the 
  cleavage 
  centro- 
  

   some 
  has 
  up 
  to 
  the 
  present 
  been 
  described 
  by 
  any 
  author 
  

   (except 
  by 
  Carnoy 
  in 
  Ascaris), 
  there 
  are 
  yet 
  several 
  instances 
  

   on 
  record 
  of 
  the 
  intra-nuclear 
  origin 
  of 
  this 
  body 
  in 
  germ-cells. 
  

  

  The 
  case 
  which 
  stands 
  nearest 
  to 
  my 
  own 
  observation, 
  is 
  

   that 
  of 
  Styelopsis, 
  where 
  Julin 
  has 
  described 
  the 
  emergence 
  

   of 
  the 
  centrosome 
  from 
  the 
  nucleus 
  of 
  the 
  spermatid, 
  without, 
  

   however, 
  being 
  able 
  to 
  trace 
  it 
  into 
  the 
  fertilisation 
  spindle. 
  

  

  