﻿490 
  J. 
  BREFLAND 
  FARMER 
  AND 
  J. 
  E. 
  S. 
  MOORE. 
  

  

  only 
  the 
  essential 
  details 
  within 
  the 
  phase 
  itself 
  that 
  admit 
  of 
  

   complete 
  comparison 
  in 
  the 
  case 
  of 
  some 
  of 
  the 
  more 
  widely 
  

   sundered 
  groups 
  — 
  such, 
  for 
  example, 
  as 
  animals 
  and 
  plants 
  

   respectively. 
  

  

  On 
  the 
  one 
  hand, 
  in 
  the 
  metazoa 
  the 
  divisions 
  included 
  in 
  

   the 
  maiotic 
  phase 
  invariably 
  lead 
  directly 
  to 
  the 
  formation 
  of 
  

   the 
  sexual 
  cells. 
  In 
  plants^ 
  on 
  the 
  other 
  hand, 
  not 
  only 
  is 
  

   the 
  position 
  of 
  the 
  phase 
  far 
  more 
  variable, 
  but 
  it 
  never 
  

   culminates, 
  so 
  far 
  as 
  is 
  known, 
  directly 
  in 
  the 
  production 
  of 
  

   sexual 
  cells. 
  The 
  latter 
  are 
  only 
  formed 
  after 
  a 
  greater 
  or 
  

   less 
  number 
  of 
  intervening 
  (post-maiotic) 
  divisions 
  have 
  been 
  

   passed 
  through. 
  

  

  It 
  is 
  evident, 
  then, 
  that 
  we 
  may 
  group 
  the 
  cells 
  that 
  are 
  

   produced 
  in 
  the 
  life 
  cycle 
  of 
  ^n 
  animal 
  or 
  plant 
  into 
  three 
  

   categories, 
  viz. 
  Premaiotic, 
  Maiotic, 
  and 
  Post-Maiotic 
  re- 
  

   spectively. 
  The 
  convenience 
  of 
  this 
  classification 
  will 
  at 
  once 
  

   be 
  obvious. 
  Thus 
  in 
  animals 
  there 
  are 
  (noi-mally) 
  no 
  post- 
  

   maiotic 
  divisions, 
  whereas 
  in 
  plants 
  there 
  may 
  be, 
  and 
  often 
  

   are, 
  a 
  large 
  number. 
  In 
  a 
  fern, 
  for 
  example, 
  the 
  whole 
  

   prothallial 
  generation 
  consists 
  of 
  post-maiotic 
  cells, 
  and 
  it 
  

   thus 
  becomes 
  clear 
  that 
  there 
  exists 
  no 
  necessarily 
  direct 
  

   relation 
  between 
  the 
  maiotic 
  divisions 
  and 
  the 
  differentiation 
  

   of 
  the 
  sexual 
  cells 
  or 
  gametes. 
  

  

  Referring 
  to 
  the 
  terms 
  in 
  common 
  use, 
  viz. 
  "heterotype," 
  

   "homotype," 
  and 
  ''synapsis," 
  we 
  employ 
  these 
  as 
  descriptive 
  of 
  

   incidents 
  that 
  invariably 
  are 
  present 
  in 
  the 
  maiotic 
  phase. 
  

   The 
  word 
  ''heterotype 
  " 
  is 
  applied 
  to 
  the 
  first 
  mitosis 
  as 
  it 
  was 
  

   originally 
  used 
  by 
  Flemming, 
  and 
  the 
  synapsis 
  represents 
  

   that 
  series 
  of 
  events 
  which 
  are 
  concerned 
  in 
  causing 
  the 
  tem- 
  

   porary 
  union 
  in 
  pairs 
  of 
  pre-maiotic 
  chromosomes, 
  previously 
  

   to 
  their 
  transverse 
  separation 
  and 
  distribution, 
  in 
  their 
  

   entirety, 
  between 
  two 
  daughter 
  nuclei. 
  We 
  restrict 
  the 
  term 
  

   "homotype" 
  to 
  signify 
  the 
  second 
  division 
  in 
  the 
  maiotic 
  phase, 
  

   instead 
  of 
  extending 
  it, 
  as 
  some 
  writers 
  have 
  done 
  in 
  the 
  case 
  

   of 
  plants, 
  to 
  include 
  all 
  post-maiotic 
  mitoses. 
  

  

  Thus 
  the 
  scheme 
  of 
  the 
  cellular 
  life 
  cycle 
  in 
  any 
  animal 
  or 
  

   plant 
  may 
  be 
  represented 
  as 
  follows 
  : 
  

  

  