﻿548 
  J. 
  BRRTI,AND 
  FARMEK' 
  AND 
  .1. 
  E. 
  S. 
  M(30RE. 
  

  

  tion 
  dui'ing 
  the 
  course 
  of 
  what 
  otherwise 
  would 
  not 
  

   differ 
  materially 
  from 
  an 
  ordinary 
  pre-maiotic 
  

   mitosis. 
  In 
  the 
  first 
  of 
  the 
  two 
  divisions, 
  a 
  dis- 
  

   tribution 
  of 
  entire 
  pre-maiotic 
  chromosomes 
  is 
  

   secured, 
  and 
  thus 
  the 
  number 
  of 
  these 
  bodies 
  is 
  

   really 
  halved. 
  In 
  the 
  second 
  division, 
  the 
  longi- 
  

   tudinal 
  fission 
  begun, 
  but 
  temporarily 
  arrested, 
  in 
  

   the 
  preceding 
  prophase 
  takes 
  effect. 
  Consequently 
  

   this 
  mitosis 
  as 
  a 
  whole 
  resembles 
  the 
  later 
  stages 
  of 
  an 
  

   ordinary 
  one 
  save 
  in 
  the 
  reduced 
  number 
  of 
  the 
  chromosomes. 
  

  

  It 
  is, 
  of 
  course, 
  possible 
  that 
  the 
  succession 
  of 
  these 
  two 
  

   series 
  of 
  events 
  might 
  become 
  inverted, 
  and 
  cases 
  have 
  been 
  

   described 
  in 
  which 
  the 
  first 
  (heterotype) 
  maiotic 
  division 
  is 
  

   said 
  to 
  be 
  anaschistic, 
  while 
  the 
  second 
  one 
  is 
  diaschistic; 
  

   but 
  if 
  fresh 
  investigations 
  should 
  confirm 
  this, 
  it 
  would 
  in 
  no 
  

   wav 
  detract 
  from 
  the 
  utility 
  of 
  regarding 
  the 
  collection 
  of 
  

   events 
  in 
  question 
  as 
  constituting 
  a 
  definite 
  and 
  essential 
  

   phase 
  (maiosis) 
  in 
  the 
  cellular 
  life 
  history 
  of 
  an 
  organism. 
  

  

  It 
  is 
  obvious 
  from 
  the 
  foregoing 
  description 
  of 
  the 
  events 
  

   characteristic 
  of 
  maiosis 
  that 
  in 
  any 
  succeeding 
  cell-genera- 
  

   tions 
  we 
  shall 
  encounter 
  only 
  half 
  the 
  number 
  of 
  chromo- 
  

   somes 
  that 
  were 
  present 
  before 
  that 
  phase 
  supervened 
  ; 
  and 
  it 
  

   can 
  only 
  be 
  after 
  fertilisation, 
  or 
  some 
  other 
  process 
  analogous 
  

   to 
  that 
  described 
  by 
  us 
  for 
  the 
  case 
  of 
  apogamous 
  ferns, 
  that 
  

   the 
  reduced 
  (post-maiotic) 
  number 
  can 
  again 
  be 
  brought 
  back 
  

   to 
  the 
  full 
  pre-maiotic 
  complement. 
  The 
  number 
  of 
  post- 
  

   maiotic 
  cell-generations 
  varies. 
  There 
  may 
  be 
  none, 
  as 
  

   in 
  the 
  normal 
  cellular 
  cycle 
  of 
  an 
  animal, 
  in 
  which 
  the 
  

   differentiation 
  of 
  sexual 
  cells 
  follows 
  immediately 
  upon 
  the 
  

   second 
  maiotic 
  (homotype) 
  division. 
  On 
  the 
  other 
  hand, 
  there 
  

   may 
  be 
  a 
  considerable 
  number, 
  as 
  for 
  example 
  in 
  ferns, 
  in 
  

   which 
  the 
  whole 
  prothallial 
  individual 
  consists 
  of 
  post- 
  

   maiotic 
  cells. 
  In 
  animals 
  it 
  is 
  only 
  in 
  certain 
  pathological 
  

   o-rowths 
  that 
  an 
  analogous 
  condition 
  appears 
  to 
  obtain. 
  

  

  In 
  plants, 
  however, 
  there 
  is 
  no 
  case 
  known 
  at 
  present 
  in 
  

   which 
  the 
  maiotic 
  phase 
  leads 
  directly 
  to 
  the 
  production 
  of 
  

   sexual 
  cells, 
  although 
  in 
  Fucus, 
  and 
  also 
  in 
  some 
  of 
  the 
  

  

  