﻿310 
  

  

  Mr. 
  L. 
  T. 
  Hogben. 
  

  

  stage 
  of 
  the 
  nuclear 
  history 
  of 
  the 
  oogonia 
  in 
  a 
  manner 
  distinguishable 
  from 
  

   the 
  autosomes. 
  

  

  By 
  the 
  examination 
  of 
  sufficiently 
  thin 
  sections 
  it 
  is 
  possible 
  to 
  trace 
  the 
  

   behaviour 
  of 
  chromosomes 
  in 
  their 
  passage 
  to 
  the 
  polar 
  end 
  of 
  the 
  spindle 
  

   with 
  accuracy 
  and 
  assurance 
  (cf. 
  figs. 
  4 
  and 
  20) 
  ; 
  and 
  it 
  is 
  clear 
  that 
  in 
  the 
  

   later 
  oogonial 
  divisions, 
  at 
  least, 
  the 
  telophasic 
  chromosomes 
  undergo 
  no 
  

   cleavage. 
  This 
  conclusion 
  is 
  fully 
  consonant 
  with 
  succeeding 
  events. 
  It 
  

   is 
  possible 
  that 
  the 
  telophase 
  chromosomes, 
  in 
  some 
  cases, 
  pass 
  over 
  

   directly 
  to 
  prophase 
  prochromosomes 
  without 
  the 
  intervention 
  of 
  a 
  reticulum 
  : 
  

   all 
  that 
  can 
  be 
  legitimately 
  inferred 
  from 
  the 
  extraordinary 
  rarity 
  of 
  typical 
  

   resting 
  nuclei 
  is 
  that 
  the 
  reticulate 
  condition 
  must 
  occupy 
  a 
  very 
  brief 
  portion 
  

   of 
  the 
  nuclear 
  cycle. 
  In 
  the 
  prophase 
  the 
  reticulum 
  condenses 
  into 
  cloudy 
  

   areas 
  that 
  indicate 
  the 
  future 
  chromatic 
  elements 
  ; 
  and 
  in 
  elucidating 
  the 
  

   genesis 
  of 
  the 
  latter, 
  comparison 
  with 
  the 
  nuclei 
  of 
  the 
  incipient 
  follicle 
  cells 
  

   is 
  valuable 
  in 
  view 
  of 
  the 
  closer 
  resemblance 
  of 
  the 
  chromosomes 
  of 
  the 
  latter 
  

   to 
  the 
  curved 
  units 
  of 
  the 
  male 
  complex. 
  There 
  is 
  in 
  neither 
  case 
  any 
  sign 
  

   of 
  an 
  " 
  increasingly 
  intimate 
  " 
  reassociation 
  of 
  telophasic 
  half-chromosomes 
  

   for 
  the 
  " 
  organisation 
  of 
  a 
  completed 
  univalent 
  " 
  as 
  described 
  in 
  the 
  arche- 
  

   sporial 
  nuclei 
  of 
  Osmunda. 
  On 
  the 
  contrary, 
  the 
  cloudy 
  area 
  which 
  is, 
  in 
  the 
  

   first 
  place, 
  without 
  any 
  sign 
  of 
  division, 
  gives 
  place 
  to 
  a 
  more 
  definitive 
  

   chromatin 
  mass, 
  which 
  does 
  not 
  display 
  cleavage 
  until 
  the 
  characteristic 
  form 
  

   of 
  the 
  metaphase 
  unit 
  is 
  already 
  recognisable. 
  Stages 
  in 
  the 
  transformation 
  

   are 
  represented 
  in 
  Plate 
  10, 
  figs. 
  1-3 
  and 
  5-7. 
  A 
  comparison 
  with 
  corre- 
  

   sponding 
  events 
  in 
  the 
  male 
  germ 
  cells 
  will 
  be 
  made 
  later 
  when 
  further 
  

   details 
  have 
  been 
  supplied 
  under 
  that 
  heading. 
  

  

  Tlie 
  Meiotic 
  Phase 
  in 
  the 
  Oocyte. 
  

   According 
  to 
  the 
  account 
  already 
  quoted, 
  the 
  earlier 
  events 
  of 
  the 
  hetero- 
  

   type 
  prophase 
  of 
  Osmunda, 
  involved 
  in 
  the 
  first 
  contraction, 
  are 
  primarily 
  

   concerned 
  with 
  the 
  reassociation 
  of 
  the 
  telophasic 
  threads 
  (half 
  chromosomes) 
  

   as 
  in 
  a 
  normal 
  prophase 
  ; 
  in 
  fact, 
  they 
  are 
  equivalent 
  to 
  an 
  arrested 
  but 
  

   in 
  other 
  respects 
  normal 
  prophase. 
  It 
  is 
  clear, 
  then, 
  that 
  Gregoire's 
  attempt 
  

   to 
  compare 
  the 
  first 
  contraction 
  of 
  plants 
  with 
  the 
  parasyndetic 
  bouquet 
  is 
  

   rendered 
  invalid 
  : 
  indeed, 
  the 
  question 
  of 
  the 
  parasyndetic 
  interpretation 
  of 
  

   the 
  zygotene 
  stage 
  in 
  animals 
  itself 
  assumes 
  a 
  more 
  problematical 
  aspect. 
  

   To 
  ascertain 
  whether 
  in 
  the 
  light 
  of 
  what 
  occurs 
  in 
  Osmunda, 
  the 
  bouquet 
  

   stage 
  of 
  animals 
  like 
  the 
  first 
  contraction 
  figure 
  in 
  plants 
  is 
  amenable 
  to 
  

   interpretation 
  in 
  terms 
  of 
  the 
  normal 
  somatic 
  prophase, 
  " 
  it 
  is 
  evident," 
  as 
  

   Wilson 
  pertinently 
  observes, 
  " 
  how 
  essential 
  it 
  is 
  to 
  determine 
  the 
  number 
  

   of 
  presynaptic 
  threads, 
  for 
  if 
  they 
  have 
  such 
  an 
  origin 
  as 
  has 
  just 
  been 
  

  

  