﻿270 
  

  

  Mr. 
  L. 
  T. 
  Hogben. 
  

  

  the 
  ovaries 
  reach 
  this 
  stage 
  of 
  development 
  at 
  an 
  early 
  date 
  in 
  the 
  life 
  of 
  

   the 
  larva, 
  remaining 
  in 
  this 
  condition 
  until 
  pupation. 
  All 
  three 
  types 
  of 
  

   cells 
  in 
  the 
  ovariole 
  of 
  the 
  mature 
  ovary 
  of 
  Cynips 
  — 
  follicles, 
  nurse 
  cells, 
  and 
  

   oocytes 
  — 
  originate 
  from 
  germ 
  cells. 
  Certain 
  of 
  the 
  primary 
  oogonia 
  by 
  a 
  

   series 
  of 
  divisions 
  (probably 
  synchronous) 
  give 
  rise 
  to 
  groups 
  of 
  cells, 
  which 
  

   correspond 
  to 
  the 
  " 
  rosettes 
  " 
  described 
  in 
  other 
  insects." 
  The 
  rosettes 
  con- 
  

   sisting 
  of 
  16-32 
  cells, 
  when 
  division 
  has 
  ceased, 
  give 
  rise 
  both 
  to 
  the 
  oocytes 
  

   and 
  nurse 
  cells 
  which 
  are 
  not 
  distinguishable 
  until 
  the 
  nuclei 
  have 
  been 
  

   through 
  the 
  initial 
  stages 
  of 
  synapsis. 
  

  

  Differentiation 
  of 
  oocytes 
  and 
  nurse 
  cells 
  takes 
  place 
  in 
  the 
  young 
  pupa 
  

   before 
  the 
  ovaries 
  are 
  clearly 
  separated 
  into 
  strands 
  ; 
  and 
  no 
  synapsis 
  nuclei 
  

   are 
  found 
  in 
  the 
  terminal 
  portions 
  of 
  the 
  egg 
  tubes 
  except 
  in 
  very 
  young 
  

   pupa?. 
  The 
  cells 
  of 
  a 
  fully 
  formed 
  rosette 
  at 
  first 
  possess 
  nuclei 
  the 
  chromatin 
  

   of 
  which 
  is 
  present 
  in 
  masses 
  of 
  probably 
  inconstant 
  numbers 
  (fig. 
  4). 
  

  

  The 
  changes 
  which 
  ensue 
  preparatory 
  to 
  differentiation 
  are 
  : 
  (1) 
  Leptonema, 
  

   (2) 
  Synizesis, 
  (3) 
  Break 
  up 
  of 
  the 
  post 
  synaptic 
  spireme. 
  

  

  (1) 
  The 
  Leptotene 
  stage 
  is 
  characterised 
  by 
  the 
  appearance 
  of 
  a 
  dense 
  tangle 
  

   of 
  pale 
  and 
  very 
  much 
  convoluted 
  threads 
  (tig. 
  5). 
  

  

  (2) 
  Synizesis 
  follows 
  immediately 
  upon 
  the 
  Leptotene 
  stage 
  (fig. 
  6 
  a,b,c,d). 
  

  

  (3) 
  Post 
  Synaptic 
  spireme. 
  — 
  The 
  chromatin 
  emerges 
  from 
  the 
  synaptic 
  knot 
  

   at 
  first 
  as 
  an 
  apparently 
  continuous 
  spireme. 
  This, 
  however, 
  is 
  soon 
  seen 
  to 
  

   segment 
  into 
  separate 
  filaments 
  (fig. 
  8). 
  From 
  a 
  careful 
  examination 
  of 
  a 
  

   large 
  number 
  of 
  nuclei 
  seen 
  immediately 
  after 
  the 
  break 
  up 
  of 
  synizesis, 
  it 
  is 
  

   almost 
  certain 
  that 
  the 
  haploid 
  number, 
  i.e., 
  about 
  ten 
  threads, 
  make 
  their 
  

   appearance. 
  Immediately 
  after 
  this, 
  two 
  sorts 
  of 
  nuclei 
  can 
  be 
  distinguished 
  : 
  

   (a) 
  those 
  in 
  which 
  the 
  chromatic 
  elements 
  loose 
  their 
  visible 
  individuality 
  

   (fig. 
  9a) 
  ; 
  (b) 
  others 
  in 
  which 
  the 
  chromatin 
  threads 
  undergo 
  fragmentation 
  

   into 
  innumerable 
  minute 
  granules 
  (fig. 
  7c). 
  The 
  former 
  develop 
  into 
  

   functional 
  oocytes, 
  the 
  latter 
  become 
  nurse 
  cells. 
  A 
  large 
  number 
  of 
  cells 
  

   were 
  observed 
  which 
  indicate 
  (fig. 
  7 
  a, 
  b) 
  the 
  possible 
  intercalation 
  of 
  a 
  

   diplotene 
  stage 
  in 
  the 
  differentiation 
  of 
  the 
  nurse 
  cells 
  ; 
  at 
  the 
  time 
  when 
  the 
  

   latter 
  can 
  be 
  first 
  distinguished 
  from 
  oocytes 
  by 
  their 
  nuclear 
  behaviour, 
  

   there 
  are 
  no 
  recognisable 
  differences 
  in 
  the 
  size 
  of 
  the 
  cell 
  itself 
  or 
  the 
  

   appearance 
  of 
  the 
  cytoplasm. 
  

  

  The 
  nucleus 
  of 
  the 
  oocyte 
  remains 
  in 
  the 
  " 
  diffuse 
  " 
  stage 
  during 
  the 
  entire 
  

   growth 
  period, 
  until 
  the 
  end 
  of 
  pupal 
  life. 
  

  

  The 
  Growth 
  Period. 
  General 
  Characteristics 
  of 
  the 
  Egg. 
  

   The 
  young 
  egg 
  during 
  the 
  period 
  of 
  growth 
  is 
  oval 
  ; 
  it 
  is 
  not 
  completely 
  

   surrounded 
  by 
  follicular 
  cells 
  at 
  the 
  extremities 
  where 
  the 
  cytoplasm 
  projects 
  

  

  