﻿456 
  J. 
  W. 
  JRNKINSON. 
  

  

  seen 
  at 
  the 
  poles 
  of 
  the 
  united 
  pronuclei, 
  and 
  Lillie 
  surmises 
  

   that 
  one 
  is 
  derived 
  from 
  each. 
  Others 
  (Coe, 
  MacFarland) 
  

   conjecture 
  that 
  they 
  must, 
  nevertheless, 
  be 
  considered 
  to 
  

   come 
  from 
  the 
  sperm. 
  

  

  (iii) 
  Origin 
  of 
  the 
  cleavage-, 
  from 
  the 
  sperm-centres. 
  

  

  The 
  remaining 
  authors 
  express 
  themselves 
  more 
  posi- 
  

   tively, 
  and 
  in 
  some 
  cases 
  the 
  evidence 
  is 
  perfectly 
  

   good. 
  It 
  is 
  so, 
  for 
  example, 
  in 
  the 
  Axolotl, 
  in 
  Cyclops 
  

   (Riickert 
  [1895]), 
  Diaptomus 
  (Ishikawa), 
  Branchipus 
  (Brauer 
  

   [1892]), 
  Rhynchelmis 
  (Veidovsk)"'), 
  OiDhryotrocha 
  (Kors- 
  

   chelt), 
  Toxopneustes 
  (Wilson), 
  Ciona 
  (both 
  Castle 
  and 
  

   Boveri) 
  , 
  

  

  In 
  Cheetopterus 
  and 
  Thalassema, 
  again, 
  Mead 
  and 
  Griffin 
  

   assert 
  most 
  categorically 
  the 
  continued 
  existence 
  of 
  the 
  

   sperm-centrosomes, 
  but 
  in 
  Cerebratulus 
  and 
  Physa 
  and 
  in 
  

   the 
  Mouse 
  the 
  sperm-centres 
  disappear, 
  and 
  von 
  Kostanecki 
  

   and 
  Sobotta 
  are 
  constrained 
  to 
  fall 
  back 
  on 
  a 
  priori 
  con- 
  

   siderations 
  in 
  order 
  to 
  establish 
  their 
  identity 
  with 
  the 
  definitive 
  

   centrosomes. 
  

  

  In 
  other 
  cases 
  there 
  is 
  less 
  certainty 
  (Polyclada 
  [Francotte] 
  , 
  

   Petromyzon 
  [Bohm], 
  Amphioxus 
  [Sobotta]), 
  and 
  even 
  in 
  

   Ascaris 
  Boveri 
  (1888) 
  was 
  unable 
  to 
  do 
  more 
  than 
  state 
  what 
  

   was 
  in 
  his 
  opinion 
  the 
  very 
  great 
  probability 
  of 
  the 
  intro- 
  

   duction 
  of 
  the 
  cleavage 
  centres 
  by 
  the 
  spermatozoon. 
  Von 
  

   Erlanger 
  has, 
  however, 
  since 
  shown 
  that 
  this 
  was 
  justified 
  

   by 
  demonstrating 
  the 
  presence 
  of 
  a 
  centrosome 
  in 
  the 
  

   spermatozoon, 
  and 
  its 
  division 
  to 
  form 
  the 
  centres 
  of 
  the 
  

   fertilisation 
  spindle. 
  

  

  (iv) 
  The 
  persistence 
  of 
  the 
  centrosome 
  of 
  the 
  spermatid 
  

   as 
  tlie 
  sperm- 
  and 
  cleavage-centre. 
  

  

  It 
  is 
  true 
  that 
  the 
  most 
  recent 
  investigations 
  agree 
  in 
  

   tracing 
  the 
  centrosome 
  of 
  the 
  spermatid 
  into 
  the 
  middle- 
  

   piece 
  of 
  the 
  spermatozoon. 
  At 
  the 
  same 
  time 
  the 
  sperm- 
  

  

  