﻿Studies 
  on 
  Synapsis. 
  

  

  309 
  

  

  granular 
  ovoid 
  nuclei. 
  Neither 
  in 
  imagines 
  nor 
  in 
  early 
  instars 
  could 
  any 
  

   evidence 
  of 
  transition 
  between 
  cells 
  of 
  the 
  terminal 
  filament 
  and 
  the 
  large 
  

   oogonia 
  of 
  the 
  synaptic 
  zone 
  be 
  established, 
  though 
  the 
  relation 
  of 
  the 
  

   terminal 
  filament 
  and 
  chamber 
  in 
  the 
  Hymenoptera 
  and 
  some 
  other 
  insects 
  

   is 
  manifest 
  ; 
  from 
  a 
  comparison 
  of 
  the 
  number 
  of 
  eggs 
  in 
  the 
  remainder 
  of 
  

   the 
  ovariole 
  and 
  the 
  number 
  of 
  mitoses 
  observed 
  in 
  the 
  synaptic 
  zone, 
  and 
  

   also, 
  after 
  consideration 
  of 
  the 
  number 
  of 
  eggs 
  normally 
  laid 
  during 
  the 
  

   period 
  of 
  sexual 
  activity, 
  ifc 
  would 
  appear 
  that 
  the 
  terminal 
  filament 
  in 
  the 
  

   Blattidse 
  does 
  not 
  contribute 
  to 
  the 
  formation 
  of 
  new 
  oogonia. 
  The 
  origin 
  of 
  

   follicle 
  cells 
  in 
  P. 
  americana 
  is 
  particularly 
  easy 
  to 
  recognise, 
  owing 
  to 
  

   the 
  fact 
  that 
  the 
  follicular 
  chromosomes 
  assume 
  in 
  the 
  prophase 
  the 
  

   atelomitic 
  (U-shaped) 
  form 
  which 
  they 
  display 
  on 
  the 
  equatorial 
  plate, 
  

   thus 
  contrasting 
  sharply 
  with 
  the 
  short 
  stout 
  elements 
  of 
  the 
  oogonial 
  

   complex 
  ; 
  they 
  arise 
  from 
  the 
  oogonia 
  themselves. 
  This 
  has 
  also 
  been 
  

   shown 
  to 
  be 
  the 
  case 
  in 
  the 
  Hymenoptera 
  by 
  Paulcke 
  (10) 
  and 
  the 
  

   author 
  (11), 
  both 
  nurse 
  and 
  follicle 
  cells 
  being 
  of 
  germinal 
  origin 
  ; 
  whereas, 
  

   in 
  some 
  Diptera, 
  e.g., 
  the 
  Cecidomyid 
  Miastor, 
  the 
  oocytes 
  alone 
  are 
  derived 
  

   from 
  the 
  primordial 
  germ 
  cells. 
  

  

  In 
  view 
  of 
  recent 
  work 
  on 
  the 
  meiotic 
  phase 
  in 
  plants, 
  a 
  critical 
  survey 
  of 
  

   the 
  synaptic 
  events 
  necessitates 
  a 
  thorough 
  appreciation 
  of 
  the 
  character 
  of 
  

   the 
  premeiotic 
  mitoses. 
  A 
  very 
  full 
  description 
  of 
  the 
  process 
  as 
  it 
  occurs 
  in 
  

   the 
  archesporial 
  divisions 
  of 
  Osmunda 
  is 
  thus 
  epitomised 
  by 
  Miss 
  Digby 
  : 
  

   " 
  In 
  late 
  anaphase 
  the 
  substance 
  of 
  each 
  chromosome 
  is 
  seen 
  to 
  be 
  divided 
  

   already 
  into 
  longitudinal 
  halves. 
  As 
  the 
  newly 
  formed 
  nucleus 
  proceeds 
  to 
  

   rest 
  the 
  chromosome 
  halves 
  become 
  beaded. 
  The 
  threads 
  gradually 
  separate 
  

   widely, 
  and 
  the 
  beads 
  become 
  resolved 
  into 
  liner 
  and 
  finer 
  granules 
  until 
  a 
  

   fine 
  reticulate 
  edge 
  is 
  reached 
  — 
  the 
  so-called 
  resting 
  stage. 
  During 
  prophase 
  

   the 
  series 
  of 
  events 
  is 
  reversed 
  and 
  the 
  chromosome 
  halves 
  or 
  threads 
  

   reassociate 
  .... 
  The 
  association 
  of 
  the 
  two 
  halves 
  becomes 
  increasingly 
  

   intimate 
  until 
  it 
  results 
  in 
  the 
  organisation 
  of 
  the 
  completed 
  univalent 
  

   chromosome. 
  . 
  . 
  ." 
  It 
  is 
  a 
  singular 
  fact 
  that 
  in 
  Periplaneta 
  the 
  overwhelm- 
  

   ing 
  majority 
  of 
  oogonia, 
  either 
  in 
  adult 
  or 
  pre-adult 
  ovarioles, 
  are 
  always 
  seeri 
  

   to 
  be 
  in 
  the 
  prophase, 
  when 
  the 
  chromatin 
  elements 
  are 
  represented 
  by 
  

   prochromosomes 
  in 
  various 
  stages 
  of 
  development. 
  In 
  the 
  metaphase 
  of 
  the 
  

   oogonial 
  divisions 
  the 
  number 
  of 
  chromosomes 
  is 
  clearly 
  thirty-four 
  ; 
  they 
  are 
  

   stouter 
  than 
  those 
  in 
  the 
  male 
  germ 
  cells, 
  and 
  uncurved. 
  It 
  is 
  evident 
  that 
  

   the 
  representative 
  of 
  the 
  accessory 
  chromosome 
  described 
  in 
  the 
  male 
  of 
  the 
  

   species 
  by 
  Morse 
  (12) 
  is 
  accompanied 
  in 
  the 
  division 
  of 
  the 
  female 
  germ 
  cells 
  

   by 
  a 
  homologous 
  partner. 
  For 
  the 
  sake 
  of 
  brevity 
  it 
  may 
  be 
  remarked 
  in 
  

   this 
  connexion 
  that 
  the 
  accessories 
  in 
  P. 
  americana 
  do 
  not 
  behave 
  in 
  any 
  

  

  VOL. 
  XCI. 
  — 
  B. 
  2 
  B 
  

  

  