﻿324 
  

  

  Mr. 
  L. 
  T. 
  Hogben. 
  

  

  the 
  sixteen 
  bivalents 
  are 
  rod-shaped 
  or 
  arc- 
  like, 
  the 
  remaining 
  two 
  being 
  

   much 
  more 
  attenuated 
  and 
  still 
  retaining 
  the 
  looped 
  condition 
  in 
  which 
  the 
  

   diplotene 
  threads 
  emerge 
  from 
  the 
  bouquet 
  stage. 
  These 
  latter 
  will 
  be 
  called 
  

   the 
  a 
  and 
  a' 
  chromosomes, 
  and 
  it 
  will 
  be 
  remembered 
  that 
  there 
  is 
  a 
  similar 
  

   lagging 
  behind 
  of 
  two 
  of 
  the 
  heterotype 
  elements 
  in 
  the 
  oocyte 
  descr 
  bed 
  

   earlier 
  in 
  this 
  paper. 
  The 
  order 
  and 
  method 
  of 
  division 
  of 
  the 
  bivalents 
  is 
  as 
  

   follows 
  : 
  (1) 
  the 
  first 
  seven 
  divide 
  longitudinally 
  by 
  median 
  fibre 
  attachment 
  

   being 
  drawn 
  out 
  into 
  elongated 
  rings 
  which 
  are 
  segmented 
  transversely 
  \ 
  

   (2) 
  of 
  the 
  next 
  seven, 
  the 
  first 
  three 
  divide 
  with 
  subterminal 
  attachment, 
  

  

  II 
  

  

  in 
  a 
  

  

  w 
  a 
  1 
  

  

  Four 
  types 
  of 
  division 
  exhibited 
  by 
  the 
  heterotype 
  chromosomes 
  in 
  metaphase. 
  

  

  I. 
  Median 
  fibre 
  attachment 
  — 
  the 
  first 
  seven 
  chromosomes 
  divide 
  in 
  this 
  manner. 
  

   II. 
  Subterminal 
  fibre 
  attachment 
  — 
  four 
  of 
  the 
  later 
  bivalents 
  to 
  divide 
  are 
  of 
  this 
  type. 
  

   Ill 
  and 
  IV. 
  The 
  a 
  and 
  a' 
  chromosomes 
  which 
  retain 
  the 
  looped 
  condition 
  of 
  the 
  bouquet 
  

   threads 
  till 
  the 
  other 
  fourteen 
  are 
  already 
  in 
  telophase. 
  

  

  while 
  of 
  the 
  remaining 
  four, 
  it 
  appears 
  that 
  three 
  probably 
  show 
  median 
  fibre 
  

   attachment 
  : 
  Morse's 
  belief 
  that 
  these 
  chromosomes 
  which 
  are 
  attached 
  to 
  

   the 
  spindle 
  subterminally 
  are 
  drawn 
  out 
  into 
  bracket-like 
  figures 
  was 
  not 
  

   confirmed 
  : 
  the 
  best 
  preparations 
  show 
  that 
  these 
  too 
  give 
  rise 
  to 
  stretched 
  

   rings 
  of 
  the 
  usual 
  type 
  ; 
  (3) 
  the 
  a 
  and 
  a' 
  chromosomes 
  retain 
  their 
  looped 
  

   forms 
  until 
  the 
  other 
  chromosomes 
  have 
  completely 
  segmented, 
  so 
  that 
  they 
  

   evidently 
  represent 
  the 
  open-ring 
  type 
  described 
  by 
  Farmer 
  and 
  Moore. 
  

   Actually 
  they 
  become 
  abbreviated, 
  last 
  of 
  all 
  being 
  drawn 
  out 
  into 
  rings 
  

   by 
  the 
  method 
  of 
  longitudinal 
  division 
  described 
  for 
  their 
  fellows. 
  Thus 
  

  

  