﻿500 
  J. 
  BRETLAND 
  FARMER 
  AND 
  J. 
  E. 
  S. 
  MOORE. 
  

  

  cited 
  as 
  examples^ 
  the 
  processes 
  seemed 
  easier 
  to 
  interpret 
  

   in 
  another 
  sense. 
  The 
  chromosomes 
  appear 
  as 
  tetrad-like 
  

   bodies^ 
  which 
  separate 
  as 
  pairs 
  of 
  dyads 
  in 
  the 
  heterotype, 
  

   whilst 
  in 
  the 
  homotype 
  mitosis 
  each 
  dyad 
  further 
  divides 
  into 
  

   monads^ 
  which 
  are 
  thus 
  distributed 
  between 
  the 
  daughter 
  

   nuclei 
  at 
  this 
  (second) 
  division. 
  

  

  It 
  has 
  been 
  often 
  maintained 
  that 
  these 
  appearances 
  

   indicate 
  a 
  true 
  sorting 
  of 
  somatic 
  chromosomes, 
  i. 
  e. 
  is 
  a 
  

   qualitative 
  reduction 
  in 
  Weismann's 
  sense. 
  The 
  tetrads 
  are 
  

   admitted 
  to 
  have 
  arisen 
  as 
  the 
  result 
  of 
  a 
  longitudinal, 
  asso- 
  

   ciated 
  with 
  a 
  transverse, 
  fission 
  of 
  the 
  substance 
  of 
  the 
  

   chromosome, 
  each 
  of 
  the 
  latter 
  thus 
  being 
  a 
  bivalent 
  (Hacker) 
  

   structure, 
  and 
  representing 
  a 
  pair 
  of 
  adherent 
  longitudinally 
  

   split 
  somatic 
  chromosomes. 
  

  

  One 
  of 
  the 
  most 
  important 
  memoirs 
  on 
  this 
  subject 
  of 
  

   reduction 
  is 
  that 
  by 
  Korschelt 
  ^ 
  on 
  Ophryotrocha. 
  He 
  

   maintained 
  that 
  in 
  the 
  heterotype 
  prophase 
  the 
  full 
  somatic 
  

   number 
  of 
  chromosomes 
  appeared, 
  and 
  that 
  these 
  sub- 
  

   sequently 
  fused 
  in 
  pairs 
  to 
  form 
  the 
  reduced 
  number. 
  During 
  

   the 
  metaphase 
  they 
  again 
  became 
  separated 
  from 
  each 
  other 
  

   and 
  distributed 
  to 
  the 
  daughter 
  nuclei, 
  and 
  thus 
  the 
  first 
  

   (heterotype) 
  mitosis 
  was 
  clearly 
  a 
  qualitative 
  one. 
  Korschelt's 
  

   observations 
  did 
  not 
  fall 
  very 
  well 
  into 
  line 
  with 
  the 
  process 
  

   as 
  described 
  for 
  other 
  forms 
  by 
  other 
  investigators, 
  and 
  

   Wilson, 
  in 
  his 
  work 
  on 
  the 
  cell, 
  comments 
  on 
  the 
  isolated 
  

   nature 
  of 
  the 
  results. 
  But 
  our 
  own 
  observations, 
  extending 
  

   over 
  a 
  wide 
  range 
  of 
  forms, 
  of 
  whicli 
  a 
  brief 
  abstract 
  has 
  

   already 
  appeared 
  (1903), 
  as 
  well 
  as 
  the 
  more 
  recent 
  results 
  

   obtained 
  by 
  Strasburger 
  (1904), 
  show 
  that 
  Korschelt's 
  results, 
  

   obtained 
  in 
  Ophryotrocha, 
  are 
  susceptible 
  of 
  a 
  much 
  Avider 
  

   application. 
  

  

  In 
  1895 
  a 
  paper 
  was 
  published 
  by 
  H. 
  H. 
  Dixon,^ 
  in 
  which 
  

   he 
  suggested 
  the 
  existence 
  of 
  a 
  reduction 
  division 
  arising 
  by 
  

   the 
  distribution 
  of 
  the 
  equivalents 
  of 
  entire 
  chromosomes, 
  but 
  

  

  ' 
  Korsclielt, 
  "Ueber 
  Kerntbeilung, 
  Eireifung, 
  uiid 
  Befruchtung 
  bei 
  

   Opbryotrocha 
  puerilis," 
  * 
  Zeitschr. 
  fiir 
  Wiss. 
  Zool.,' 
  Ix. 
  

   ' 
  'Proc. 
  Roy. 
  Ir. 
  Acad.,' 
  iii. 
  

  

  