﻿572 
  J. 
  E. 
  S. 
  MOORE 
  AND 
  L. 
  E. 
  UOBINSON. 
  

  

  his 
  work 
  on 
  PjnTliocoris 
  ('Z. 
  wiss. 
  Zool./ 
  Bd. 
  li, 
  1890), 
  wliicli 
  

   led 
  to 
  its 
  consideration 
  as 
  a 
  modified 
  cliromosome, 
  endowed 
  

   with 
  special 
  functions, 
  distinct 
  from 
  those 
  of 
  the 
  normal 
  

   chromosomes 
  of 
  the 
  cell. 
  Since 
  Henking 
  published 
  this 
  

   work, 
  a 
  few 
  investigators 
  have 
  devoted 
  their 
  attention 
  

   particularly 
  to 
  this 
  subject, 
  describing 
  the 
  nucleolus 
  as 
  an 
  

   " 
  accessory 
  chromosome," 
  and 
  attempting 
  to 
  connect 
  its 
  

   function 
  with 
  such 
  interesting 
  problems 
  as 
  " 
  determination 
  

   of 
  sex" 
  and 
  '' 
  heredity." 
  

  

  In 
  the 
  male 
  reproductive 
  cell 
  of 
  Periplaneta 
  aniericana 
  

   the 
  nucleolus 
  is 
  conspicuous 
  in 
  almost 
  all 
  phases 
  of 
  the 
  

   spermatogenesis, 
  and 
  consequently 
  its 
  actual 
  changes 
  can 
  

   be 
  studied 
  without 
  any 
  great 
  difficulty. 
  

  

  (I) 
  The 
  Premaiotic 
  (Somatic) 
  Divisions. 
  — 
  Through- 
  

   out 
  the 
  somatic 
  divisions, 
  from 
  the 
  resting 
  phase 
  up 
  to 
  the 
  

   complete 
  differentiation 
  of 
  the 
  chromosomes, 
  the 
  nucleolus 
  

   is 
  prominent 
  as 
  a 
  large 
  chromatic 
  structure 
  occupying 
  a 
  

   position 
  inside 
  the 
  nuclear 
  membrane. 
  In 
  the 
  resting 
  

   somatic 
  cells 
  the 
  nuclei 
  are 
  large 
  and 
  oval 
  in 
  shape, 
  and, 
  

   on 
  account 
  of 
  the 
  small 
  quantity 
  of 
  chromatin 
  present, 
  pale 
  

   (fig. 
  1). 
  The 
  nucleolus 
  [nc.') 
  arises 
  as 
  an 
  indefinite 
  cloudy 
  

   mass 
  suspended 
  in 
  the 
  linin 
  reticulum. 
  At 
  first 
  it 
  stains 
  

   very 
  feebly, 
  but 
  rapidly 
  becoming 
  denser, 
  finally 
  retains 
  the 
  

   ordinary 
  chromatin 
  stains 
  very 
  powerfully 
  (fig. 
  2). 
  It 
  always 
  

   assumes 
  a 
  more 
  or 
  less 
  spherical 
  shape, 
  and 
  by 
  the 
  time 
  that 
  

   the 
  nucleus 
  exhibits 
  the 
  aggregation 
  of 
  chromatin 
  granules 
  

   in 
  the 
  angles 
  of 
  the 
  Hnin 
  reticulum 
  (fig. 
  2), 
  the 
  nucleolus 
  is 
  

   by 
  far 
  the 
  most 
  conspicuous 
  object 
  in 
  tlie 
  cell. 
  

  

  In 
  its 
  early 
  condition 
  the 
  nucleolus 
  is 
  usually 
  irregular 
  and 
  

   ill-defined 
  in 
  outline, 
  often 
  somcAvhat 
  stellate, 
  the 
  angular 
  

   processes 
  merging 
  insensibly 
  into 
  the 
  general 
  linin 
  reticulum. 
  

   Its 
  structure 
  at 
  first 
  is 
  not 
  homogeneous, 
  there 
  being 
  fre- 
  

   quently 
  enclosed 
  masses 
  which 
  stain 
  more 
  deeply 
  than 
  the 
  

   general 
  mass 
  (fig. 
  1). 
  As 
  the 
  chromatin 
  granules 
  increase 
  in 
  

   quantity 
  the 
  nucleolus 
  becomes 
  denser, 
  staining 
  more 
  deeply, 
  

   and 
  finally 
  reaching 
  a 
  stage 
  in 
  which 
  it 
  is 
  as 
  chromatic 
  as 
  a 
  

   fully-formed 
  chromosome. 
  The 
  outline 
  of 
  the 
  nucleolus 
  loses 
  

  

  