﻿SfEKMATOGENESIS 
  OF 
  PEKIPLAKETA 
  AMERICANA. 
  573 
  

  

  its 
  indetinito 
  nature 
  and 
  becomes 
  rounded 
  oE, 
  and 
  is 
  readily 
  

   distinguishable 
  from 
  the 
  knot-like 
  masses 
  of 
  chromatin 
  

   usually 
  termed 
  karyosomes, 
  but 
  often 
  described 
  as 
  a 
  form 
  of 
  

   nucleoli. 
  These 
  bodies 
  have 
  nothing 
  whatever 
  to 
  do 
  with 
  

   the 
  nucleolus 
  which 
  is 
  being 
  described; 
  they 
  are 
  collections 
  

   of 
  chromatic 
  substance 
  which 
  are 
  utilised, 
  finally, 
  in 
  the 
  

   formation 
  of 
  the 
  chromosomes. 
  The 
  aggregations 
  of 
  

   chromatin 
  rapidly 
  assume 
  the 
  appearance 
  of 
  definite 
  patches 
  

   on 
  the 
  periphery 
  of 
  the 
  nucleus 
  (fig. 
  3), 
  each 
  patch 
  being 
  the 
  

   early 
  representative 
  of 
  a 
  chromosome. 
  Almost 
  at 
  the 
  com- 
  

   mencement 
  of 
  aggregation 
  of 
  the 
  chromatin, 
  it 
  is 
  seen 
  that 
  

   each 
  patch 
  is 
  divided, 
  this 
  division 
  being 
  the 
  line 
  of 
  separa- 
  

   tion 
  of 
  the 
  halves 
  of 
  the 
  chromosome 
  on 
  the 
  spindle. 
  When 
  

   this 
  stage 
  is 
  reached 
  the 
  liniu 
  reticulum 
  begins 
  to 
  break 
  

   down, 
  and 
  a 
  considerable 
  amount 
  of 
  liuin 
  substance 
  collects 
  

   in 
  a 
  mass 
  round 
  the 
  nucleolus 
  (tigs. 
  3 
  and 
  4). 
  

  

  Delicate 
  strands 
  of 
  linin 
  continue 
  to 
  extend 
  between 
  the 
  

   chromosomes, 
  affording 
  them 
  support, 
  until 
  the 
  appearance 
  

   of 
  the 
  spindle. 
  The 
  chromosomes 
  become 
  denser 
  and 
  more 
  

   sharply 
  defined, 
  and 
  ultimately 
  the 
  extremities 
  of 
  each 
  half 
  

   are 
  recurved, 
  giving 
  the 
  divided 
  chromosome 
  the 
  appearance 
  

   of 
  a 
  tetrad 
  (tigs. 
  4 
  — 
  6). 
  

  

  As 
  this 
  condition 
  is 
  reached, 
  owing 
  to 
  the 
  size 
  and 
  

   density 
  of 
  the 
  chromosomes, 
  the 
  nucleolus 
  often 
  becomes 
  

   obscured, 
  but 
  its 
  presence 
  within 
  the 
  nucleus 
  can 
  be 
  verified 
  

   in 
  a 
  complete 
  cell 
  by 
  counting 
  the 
  chromatic 
  bodies 
  within 
  

   the 
  nucleus. 
  The 
  number 
  of 
  chromosomes 
  in 
  the 
  premaiotic 
  

   division 
  in 
  P. 
  americana 
  is 
  thirty-two, 
  but 
  at 
  this 
  stage 
  

   thirty-three 
  chromatic 
  bodies 
  may 
  be 
  counted 
  within 
  the 
  

   nuclear 
  membrane, 
  one 
  of 
  these 
  being 
  the 
  nucleolus. 
  

  

  The 
  archoplasm 
  (fig. 
  4, 
  a.) 
  at 
  this 
  time 
  is 
  differentiated 
  as 
  

   a 
  dense 
  cloudy 
  mass 
  of 
  cytoplasm 
  lying 
  close 
  to 
  the 
  nuclear 
  

   membrane. 
  Radiating 
  striations 
  soon 
  appear 
  in 
  the 
  archo- 
  

   plasmic 
  mass, 
  and 
  the 
  nuclear 
  membrane, 
  first 
  becoming 
  in- 
  

   definite, 
  finally 
  disappears. 
  

  

  The 
  radiating 
  strise 
  now 
  extend 
  over 
  the 
  chromosomes 
  

   which 
  become 
  massed 
  together 
  in 
  the 
  nuclear 
  space, 
  and 
  the 
  

  

  