﻿454 
  J. 
  W. 
  JENKINSON. 
  

  

  I 
  cannot 
  help 
  thinking 
  that 
  a 
  media 
  via 
  may 
  be 
  found 
  

   between 
  these 
  two 
  opposite 
  views; 
  for 
  if, 
  as 
  I 
  have 
  suggested 
  

   above, 
  the 
  ceutrosome 
  is 
  capable 
  of 
  sending 
  out 
  radial 
  pro- 
  

   cesses 
  which 
  precipitate 
  the 
  cytoplasm, 
  it 
  is 
  quite 
  clear 
  that 
  

   the 
  centrosphere 
  must 
  be 
  derived 
  from 
  one 
  as 
  much 
  as 
  from 
  

   the 
  other. 
  

  

  (b) 
  The 
  origin 
  of 
  the 
  cleavage 
  centres 
  omes. 
  

  

  The 
  dominant 
  theory 
  of 
  the 
  origin 
  of 
  the 
  cleavage 
  centro- 
  

   somes 
  is 
  undoubtedly 
  that 
  propounded 
  by 
  Boveri 
  on 
  the 
  basis 
  

   of 
  observations 
  on 
  the 
  egg 
  of 
  Ascaris. 
  It 
  is 
  this 
  : 
  the 
  egg 
  

   lacks 
  the 
  organ 
  of 
  cell 
  division, 
  the 
  centrosome 
  ; 
  this 
  is 
  

   supplied 
  in 
  the 
  act 
  of 
  fertilisation 
  by 
  the 
  spermatozoon. 
  

  

  How 
  powerful 
  the 
  influence 
  of 
  this 
  conception 
  has 
  been 
  on 
  

   the 
  interpretations 
  which 
  subsequent 
  investigators 
  have 
  put 
  

   upon 
  their 
  work 
  s 
  patent 
  to 
  anyone 
  who 
  is 
  acquainted 
  with 
  

   the 
  literature 
  of 
  the 
  subject, 
  and 
  is 
  seen 
  in 
  the 
  frequency 
  with 
  

   which 
  the 
  identity 
  of 
  the 
  cleavage 
  with 
  the 
  spei-m-centro- 
  

   somes 
  is 
  asserted 
  on 
  purely 
  a 
  priori 
  grounds 
  when 
  positive 
  

   evidence 
  is 
  wanting. 
  

  

  On 
  the 
  other 
  hand, 
  there 
  have 
  been 
  a 
  few 
  who 
  have 
  been 
  

   content 
  to 
  leave 
  the 
  origin 
  of 
  these 
  organs 
  undetermined, 
  

   while 
  a 
  very 
  few 
  either 
  deny 
  the 
  participation 
  of 
  the 
  sperm- 
  

   centres 
  in 
  the 
  formation 
  of 
  the 
  fertilisation 
  spindle 
  altogether, 
  

   or 
  at 
  least 
  assert 
  that 
  the 
  egg 
  centres 
  also 
  play 
  a 
  part 
  in 
  the 
  

   process. 
  

  

  liastly, 
  an 
  attempt 
  has 
  been 
  made, 
  in 
  extension 
  of 
  Boveri's 
  

   original 
  hypothesis, 
  to 
  prove 
  the 
  persistence 
  of 
  the 
  centrosome 
  

   of 
  the 
  spermatid 
  as 
  the 
  sperm- 
  and 
  consequently 
  as 
  the 
  

   cleavage-centre. 
  

  

  These 
  various 
  hypotheses 
  I 
  propose 
  to 
  examine 
  separately. 
  

  

  (i) 
  The 
  participation 
  of 
  the 
  egg 
  centres 
  in 
  the 
  formation 
  

   of 
  the 
  cleavage 
  spindle. 
  

  

  While 
  the 
  majority 
  of 
  investigators 
  agree 
  in 
  asserting 
  the 
  

   disappearance 
  of 
  the 
  egg 
  centrosomes 
  and 
  asters 
  after 
  the 
  

  

  