﻿308 
  

  

  Mr. 
  L. 
  T. 
  Hogben. 
  

  

  Technique 
  and 
  Material. 
  

  

  Gonads 
  from 
  about 
  three 
  hundred 
  individuals, 
  at 
  all 
  stages 
  of 
  development 
  

   from 
  the 
  early 
  instars 
  onward, 
  were 
  used 
  in 
  the 
  present 
  research. 
  To 
  

   ensure 
  a 
  plentiful 
  supply 
  of 
  cells 
  in 
  synapsis, 
  both 
  testes 
  and 
  ovaries 
  of 
  

   larvae 
  were 
  used 
  principally, 
  after 
  dissection 
  in 
  Einger's 
  fluid. 
  

  

  Repeated 
  trials 
  made 
  it 
  clear 
  that 
  acid 
  fixatives 
  like 
  Flemming's 
  reagent, 
  

   though 
  admirable 
  for 
  work 
  involving 
  counts, 
  are 
  of 
  little 
  utility 
  where 
  the 
  

   object 
  of 
  the 
  investigation 
  necessitates 
  special 
  attention 
  to 
  cleavages 
  in 
  

   chromatin 
  filaments. 
  All 
  the 
  advantages 
  of 
  Flemming's 
  normal 
  formula 
  can 
  

   be 
  obtained 
  by 
  eliminating 
  the 
  acetic 
  component, 
  so 
  that 
  swelling 
  of 
  

   chromatin 
  is 
  avoided. 
  Gatenby 
  has 
  already 
  recommended 
  this 
  modification 
  

   for 
  the 
  study 
  of 
  mitochondria. 
  Very 
  successful 
  results 
  were 
  obtained 
  by 
  a 
  

   modification 
  of 
  one 
  of 
  Eabl's 
  formulas 
  : 
  equal 
  parts 
  of 
  formol 
  and 
  1 
  per 
  cent, 
  

   platinic 
  chloride 
  were 
  mixed, 
  and 
  diluted 
  with 
  two 
  volumes 
  of 
  distilled 
  

   water. 
  The 
  mixture 
  penetrates 
  admirably 
  ; 
  and, 
  while 
  the 
  chromatin 
  

   elements 
  shrink 
  too 
  much 
  for 
  convenient 
  metaphase 
  counts, 
  for 
  the 
  examina- 
  

   tion 
  of 
  filaments, 
  where 
  cleavage 
  is 
  doubtful, 
  it 
  gives 
  an 
  admirable 
  fixation. 
  

   In 
  all 
  cases 
  where 
  iron 
  hsematoxylin 
  was 
  afterwards 
  used, 
  the 
  sections 
  were 
  

   previously 
  stained 
  with 
  a 
  transparent 
  dye, 
  and 
  ultimately 
  differentiated 
  in 
  

   dilute 
  alum 
  very 
  slowly 
  under 
  constant 
  microscopic 
  observation 
  until 
  the 
  

   pigment 
  was 
  all 
  but 
  removed 
  from 
  the 
  object 
  studied. 
  Such 
  precaution 
  is 
  

   essential 
  ; 
  in 
  Periplaneta, 
  the 
  elongated 
  annular 
  heterotype 
  chromosomes 
  

   appear 
  in 
  Haidenhein 
  preparations 
  (owing 
  to 
  the 
  elimination 
  of 
  the 
  inter- 
  

   space 
  by 
  adsorption 
  of 
  stain) 
  as 
  homogeneous 
  rods, 
  long 
  after 
  all 
  the 
  dye 
  has 
  

   been 
  extracted 
  from 
  the 
  chromatin 
  of 
  resting 
  cells. 
  The 
  importance 
  of 
  care 
  

   in 
  staining 
  is 
  sufficiently 
  evident 
  in 
  the 
  illustrations 
  of 
  authors 
  {e.g., 
  Buchner) 
  

   who 
  have 
  used 
  the 
  iron 
  method. 
  

  

  1. 
  Oogenesis 
  in 
  P. 
  americana. 
  

   As 
  in 
  other 
  Orthoptera, 
  the 
  ovarioles 
  of 
  the 
  Blattidse 
  are 
  composed 
  of 
  only 
  

   two 
  kinds 
  of 
  cellular 
  elements, 
  follicular 
  cells 
  and 
  oocytes 
  ; 
  there 
  are 
  no 
  

   nurse 
  cells. 
  In 
  the 
  imago, 
  four 
  regions 
  may 
  be 
  distinguished 
  in 
  the 
  egg 
  

   tube 
  : 
  (a) 
  a 
  portion 
  composed 
  of 
  oocytes 
  in 
  linear 
  series, 
  surrounded 
  indi- 
  

   vidually 
  with 
  follicular 
  epithelium, 
  and 
  occupying 
  altogether 
  about 
  four-fifths 
  

   of 
  the 
  entire 
  length 
  of 
  the 
  tube 
  ; 
  (b) 
  a 
  region 
  of 
  oocytes 
  not 
  as 
  yet 
  arranged 
  

   in 
  linear 
  series 
  nor 
  separately 
  invested 
  with 
  follicles, 
  but 
  already 
  displaying 
  

   the 
  nucleus 
  in 
  the 
  diffuse 
  condition 
  characteristic 
  of 
  the 
  growth 
  phase 
  ; 
  (c) 
  a 
  

   zone 
  of 
  young 
  oocytes 
  in 
  synapsis 
  and 
  of 
  oogonia 
  with 
  large 
  spherical 
  nuclei 
  ; 
  

   (d) 
  the 
  terminal 
  filament, 
  consisting 
  of 
  smaller 
  cells, 
  with 
  inconspicuous 
  and 
  

  

  