﻿542 
  J. 
  BRETLAND 
  FARMER 
  AND 
  J. 
  E. 
  S. 
  MOORE. 
  

  

  namely, 
  that 
  the 
  loops 
  and 
  rings 
  arise 
  through 
  the 
  opening 
  

   out 
  of 
  the 
  longitudinal 
  split 
  in 
  the 
  segments 
  of 
  the 
  spirem 
  

   thread. 
  A 
  careful 
  re 
  examination 
  of 
  our 
  own 
  amphibian 
  

   material 
  has, 
  however, 
  convinced 
  us 
  that 
  the 
  older 
  interpre- 
  

   tation 
  of 
  the 
  origin 
  of 
  the 
  diaschistic 
  (lieterotype) 
  chromo- 
  

   somes 
  is, 
  in 
  this 
  respect, 
  incorrect. 
  It 
  would 
  seem, 
  indeed, 
  

   that 
  amphibia, 
  although 
  possessing 
  gigantic 
  cells, 
  are 
  

   peculiarly 
  unfavourable 
  objects 
  for 
  the 
  elucidation 
  of 
  the 
  

   prophases 
  of 
  the 
  first 
  maiotic 
  division. 
  But 
  when 
  re-exam- 
  

   ined 
  after 
  a 
  knowledge 
  of 
  what 
  occurs 
  in 
  the 
  corresponding 
  

   stages 
  among 
  the 
  more 
  favourable 
  materials 
  presented 
  by 
  

   many 
  plant 
  and 
  some 
  animal 
  forms, 
  we 
  have 
  been 
  irresistibly 
  

   driven 
  to 
  the 
  conclusion 
  that 
  the 
  rings 
  in 
  the 
  amphibia, 
  like 
  

   those 
  of 
  the 
  cockroach, 
  are 
  produced 
  by 
  a 
  folding 
  or 
  some 
  

   other 
  form 
  of 
  association 
  between 
  two 
  portions 
  of 
  the 
  split 
  

   chromatin 
  riband. 
  It 
  is 
  quite 
  easy 
  in 
  the 
  case 
  of 
  axolotl 
  

   and 
  triton 
  to 
  discern 
  the 
  longitudinal 
  split 
  in 
  many 
  fully 
  

   formed 
  diaschistic 
  (heterotype) 
  loops, 
  and 
  in 
  these 
  forms 
  we 
  

   find 
  no 
  essential 
  difference 
  between 
  the 
  particular 
  phases 
  of 
  

   the 
  first 
  maiotic 
  division 
  and 
  what 
  occurs 
  in 
  a 
  more 
  obvious 
  

   manner 
  among 
  the 
  types 
  we 
  have 
  previously 
  described. 
  

  

  It 
  remains, 
  then, 
  merely 
  to 
  refer 
  briefly 
  to 
  what 
  is 
  known 
  

   with 
  respect 
  to 
  this 
  process 
  in 
  the 
  higher 
  vertebrates, 
  such 
  

   as 
  the 
  birds, 
  reptiles, 
  and 
  mammals. 
  Of 
  the 
  first 
  two 
  we 
  

   have 
  at 
  present 
  little 
  to 
  say 
  ; 
  but 
  with 
  respect 
  to 
  mammals, 
  

   we 
  have 
  examined 
  the 
  prophases 
  of 
  the 
  first 
  maiotic 
  division 
  in 
  

   the 
  testis 
  both 
  of 
  the 
  mouse 
  and 
  the 
  rat,^ 
  with 
  the 
  result 
  that 
  

   we 
  have 
  become 
  assured 
  that 
  the 
  evolution 
  of 
  the 
  diaschistic 
  

   (heterotype) 
  chromosqmes 
  is 
  here 
  the 
  same 
  as 
  in 
  the 
  lower 
  

   forms. 
  Quite 
  recently 
  we 
  had 
  the 
  opportunity 
  of 
  examining 
  

   the 
  same 
  stages 
  in 
  man; 
  and 
  altliough 
  it 
  is 
  necessary 
  that 
  tlie 
  

   full 
  results 
  of 
  this 
  investigation 
  shall 
  be 
  published 
  iu 
  a 
  

   separate 
  memoir, 
  it 
  may 
  be 
  stated 
  that 
  with 
  respect 
  to 
  the 
  

   prophases 
  of 
  the 
  first 
  maiotic 
  (heterotype) 
  division, 
  and 
  the 
  

   manner 
  in 
  which 
  the 
  diaschistic 
  chromosomes 
  are 
  evolved, 
  

  

  ' 
  Moore, 
  J. 
  E. 
  S., 
  " 
  Some 
  Points 
  in 
  the 
  Spermatogenesis 
  of 
  Mammalia," 
  

   ' 
  Int. 
  Mouat. 
  f. 
  Anat. 
  u. 
  PLys.,' 
  1894. 
  

  

  