﻿288 
  

  

  Mr. 
  L. 
  T. 
  Hogben. 
  

  

  Synopsis. 
  

  

  (1) 
  The 
  chromosome 
  cycle 
  has 
  been 
  investigated 
  in 
  relation 
  to 
  the 
  produc- 
  

   tion 
  of 
  females 
  from 
  virgin 
  eggs 
  in 
  the 
  Hyinenoptera 
  ; 
  the 
  process 
  of 
  

   synapsis 
  and 
  the 
  maturation 
  of 
  prophases 
  of 
  certain 
  parasitic 
  Hymenoptera 
  

   have 
  been 
  studied 
  and 
  contrasted 
  with 
  similar 
  stages 
  in 
  the 
  Aculeata; 
  the 
  

   origin 
  and 
  fate 
  of 
  secondary 
  nuclei 
  has 
  also 
  been 
  considered. 
  

  

  (2) 
  With 
  respect 
  to 
  three 
  genera 
  of 
  parasitic 
  Hymenoptera, 
  the 
  origin, 
  

   differentiation, 
  and 
  nuclear 
  history 
  of 
  the 
  oocytes 
  have 
  been 
  investigated, 
  

   viz., 
  Cynips 
  and 
  Rhodites 
  (Cynipidse) 
  and 
  Orthopelma 
  (Ichneumonidee). 
  The 
  

   results 
  confirm 
  the 
  existence 
  of 
  a 
  somewhat 
  unique 
  type 
  of 
  oogenesis, 
  m 
  

   suggested 
  by 
  available 
  particulars 
  relating 
  to 
  Braconid, 
  Chalcid, 
  and 
  Cynipid 
  

   genera 
  described 
  by 
  Hegner 
  and 
  other 
  authors. 
  The 
  more 
  salient 
  points 
  

   are 
  : 
  — 
  

  

  (a) 
  Origin 
  of 
  the 
  Oocytes. 
  — 
  All 
  three 
  types 
  of 
  cells 
  (oocytes, 
  follicle, 
  and 
  

   nurse 
  cells) 
  in 
  the 
  ovary 
  originate 
  from 
  germ 
  cells. 
  The 
  divisions 
  of 
  the 
  

   oogonia 
  are 
  apparently 
  equipotential, 
  and 
  no 
  distinction 
  exists 
  between 
  nurse 
  

   cells 
  and 
  oocytes 
  until 
  after 
  synapsis. 
  

  

  (b) 
  Synapsis 
  — 
  After 
  synizesis 
  the 
  haploid 
  number 
  of 
  pachytene 
  threads 
  

   appear, 
  and 
  in 
  Rhodites 
  split 
  lengthwise. 
  

  

  (c) 
  The 
  " 
  Diffuse 
  " 
  Stage. 
  — 
  During 
  the 
  growth 
  period 
  there 
  is 
  a 
  diffuse 
  or 
  

   confused 
  stage. 
  

  

  (d) 
  The 
  Double 
  Conjugation 
  of 
  the 
  Chromosomes. 
  — 
  At 
  the 
  termination 
  of 
  the 
  

   growth 
  period 
  the 
  diploid 
  number 
  of 
  chromosomes 
  reappears, 
  and 
  they 
  pair 
  

   end 
  to 
  end, 
  as 
  already 
  described 
  by 
  Hegner 
  in 
  the 
  Chalcid 
  Copidosoma, 
  so 
  

   that, 
  as 
  in 
  Lepidosiren, 
  a 
  temporary 
  separation 
  of 
  the 
  diplotene 
  threads 
  is 
  

   intercalated 
  between 
  synapsis 
  and 
  the 
  first 
  polar 
  mitosis. 
  This 
  is 
  the 
  first 
  

   confirmation 
  of 
  Agar's 
  account 
  of 
  a 
  double 
  syndesis 
  yet 
  published. 
  The 
  restora- 
  

   tion- 
  of 
  the 
  diploid 
  number 
  by 
  the 
  lengthwise 
  splitting 
  of 
  the 
  haploid 
  pachytene 
  

   threads 
  permits 
  the 
  inference 
  that 
  the 
  first 
  conjugation 
  is 
  of 
  the 
  type 
  described 
  as 
  

   " 
  parasyndesis." 
  

  

  (e) 
  The 
  Abortive 
  Maturation 
  Spindle. 
  — 
  Immediately 
  after 
  this 
  the 
  

   maturation 
  spindle 
  appears 
  precociously 
  in 
  the 
  late 
  ovarian 
  oocyte 
  ; 
  it 
  

   shows 
  no 
  asters 
  or 
  centrosomes. 
  The 
  chromosomes 
  on 
  the 
  equatorial 
  plate 
  

   condense 
  to 
  form 
  a 
  solid 
  " 
  chromatin 
  nucleus 
  " 
  without 
  proceeding 
  to 
  the 
  

   poles 
  of 
  the 
  spindJe, 
  which 
  eventually 
  disappear. 
  Such 
  behaviour 
  is 
  without 
  

   a 
  parallel 
  in 
  the 
  ookinesis 
  of 
  other 
  forms 
  previously 
  investigated. 
  In 
  all 
  

   genera 
  where 
  such 
  abortive 
  spindles 
  have 
  been 
  shown 
  to 
  occur, 
  the 
  

   separation 
  of 
  the 
  first 
  group 
  of 
  polar 
  chromosomes 
  is 
  atypical. 
  There 
  can 
  be 
  

   little 
  doubt 
  that 
  we 
  have 
  here 
  an 
  interrupted 
  mitotic 
  process. 
  

  

  