﻿446 
  J. 
  W. 
  .TENKINSON. 
  

  

  B. 
  Fertilisation. 
  

  

  In 
  the 
  act 
  of 
  fertilisation 
  two 
  distinct 
  processes 
  are 
  involved. 
  

   The 
  first 
  is 
  the 
  union 
  of 
  two 
  cells, 
  the 
  bearers 
  of 
  those 
  

   hereditary 
  characters 
  which 
  reappear 
  in 
  the 
  offspring 
  sprung- 
  

   from 
  the 
  union. 
  The 
  second 
  is 
  the 
  restoration 
  to 
  the 
  germ- 
  

   cells 
  of 
  their 
  lost 
  power 
  of 
  reproduction 
  by 
  division. 
  That 
  

   this 
  is 
  true 
  of 
  the 
  egg-cell 
  is 
  obvious, 
  and 
  is 
  proved 
  to 
  be 
  so 
  

   in 
  the 
  case 
  of 
  the 
  spermatozoon, 
  or 
  at 
  least 
  of 
  its 
  nucleus, 
  by 
  

   the 
  experimental 
  production 
  of 
  a 
  larva 
  from 
  the 
  fertilisation 
  

   of 
  an 
  enucleated 
  fragment 
  of 
  an 
  egg. 
  

  

  It 
  is 
  with 
  the 
  second 
  only 
  of 
  these 
  two 
  processes 
  that 
  I 
  am 
  

   here 
  concerned. 
  In 
  it 
  a 
  stimulus 
  is 
  conveyed 
  to 
  the 
  ovum 
  by 
  

   the 
  spermatozoon, 
  under 
  the 
  influence 
  of 
  which 
  it 
  divides 
  and 
  

   gives 
  rise 
  to 
  a 
  new 
  multicellular 
  organism. 
  

  

  All 
  the 
  recent 
  work 
  on 
  the 
  subject 
  has 
  been 
  devoted 
  to 
  the 
  

   discovery 
  of 
  the 
  mechanism 
  by 
  which 
  this 
  is 
  effected. 
  On 
  

   the 
  one 
  hand 
  we 
  see 
  in 
  the 
  purely 
  descriptive 
  treatises 
  of 
  the 
  

   past 
  few 
  years, 
  a 
  constant 
  effort 
  to 
  ascertain 
  the 
  part 
  played 
  

   by 
  the 
  sperm-centrosome 
  in 
  the 
  process, 
  in 
  short 
  to 
  test 
  the 
  

   hypothesis, 
  first 
  put 
  forward 
  by 
  Boveri, 
  that 
  the 
  sperm- 
  

   centrosome 
  is 
  the 
  active 
  agent 
  in 
  the 
  act 
  of 
  fertilisation. 
  Nor 
  

   has 
  experimental 
  proof 
  of 
  the 
  theory 
  been 
  lacking. 
  Boveri 
  

   himself 
  showed 
  that 
  a 
  sporm-centi-osome 
  will 
  divide 
  in 
  an 
  

   enucleated 
  blastomere, 
  Avhicli, 
  as 
  Ziegler 
  was 
  able 
  to 
  demon- 
  

   strate, 
  may 
  itself 
  divide 
  too. 
  On 
  the 
  other 
  hand 
  the 
  work 
  on 
  

   artificial 
  parthenogenesis 
  initiated 
  by 
  Loeb 
  has 
  suggested 
  

   that 
  the 
  stimulus 
  so 
  given 
  to 
  the 
  egg 
  may 
  be 
  described 
  in 
  

   physical 
  or 
  chemical 
  terms. 
  

  

  It 
  is 
  this 
  theory 
  of 
  Boveri's 
  that 
  I 
  propose 
  in 
  particular 
  to 
  

   discuss. 
  In 
  doing 
  so 
  it 
  will 
  be 
  convenient 
  to 
  consider 
  separately 
  

   the 
  phenomena 
  accompanying 
  the 
  entrance 
  of 
  the 
  spermato- 
  

   zoon, 
  and 
  the 
  formation 
  of 
  the 
  cleavage 
  — 
  ^or 
  fertilisation 
  — 
  

   spindle, 
  

  

  1. 
  The 
  entry 
  of 
  the 
  spermatozoon. 
  

  

  The 
  time 
  at 
  which 
  the 
  sperm 
  itozoon 
  enters 
  the 
  ovnm 
  varies 
  

   in 
  different 
  forms. 
  

  

  