﻿MATURATIONf, 
  ETC., 
  OF 
  THE 
  EGG 
  OF 
  THE 
  AXOLOTL. 
  425 
  

  

  the 
  persistent 
  identity 
  of 
  the 
  chromosomes 
  cannot 
  possibly 
  be 
  

   maintained 
  for 
  an 
  instant. 
  

  

  The 
  female 
  pronucleus 
  thus 
  reconstituted 
  begins 
  to 
  move 
  

   into 
  the 
  interior 
  of 
  the 
  egg; 
  at 
  the 
  same 
  time 
  it 
  enlarges 
  

   considerably, 
  and 
  becomes 
  irregularly 
  lobed. 
  It 
  is, 
  as 
  a 
  rule, 
  

   closely 
  surrounded 
  by 
  the 
  yolk-granules, 
  but 
  a 
  few 
  vacuoles 
  

   may 
  be 
  developed 
  in 
  its 
  immediate 
  proximity 
  (fig. 
  28, 
  d.) 
  ; 
  

   this, 
  however, 
  is 
  not 
  of 
  frequent 
  occurrence. 
  It 
  cannot 
  be 
  

   traced 
  to 
  any 
  action 
  of 
  the 
  preserving 
  fluid. 
  True 
  achro- 
  

   matic 
  nucleoli 
  appear 
  later 
  on 
  in 
  its 
  interior; 
  these 
  bodies 
  

   stain 
  very 
  deeply 
  with 
  the 
  plasma 
  stains, 
  eosin 
  and 
  indigo- 
  

   carmine, 
  and 
  also 
  very 
  deeply 
  with 
  iron-hsematoxyliu. 
  They 
  

   may 
  be 
  slightly 
  lobed 
  and 
  vacuolated 
  (fig. 
  27). 
  

  

  (b) 
  The 
  male 
  pronucleus. 
  — 
  Ultimately 
  the 
  male 
  pronucleus 
  

   has 
  precisely 
  the 
  same 
  structure 
  as 
  that 
  just 
  described 
  

   for 
  the 
  female, 
  but 
  this 
  structure 
  is 
  arrived 
  at 
  simply 
  by 
  a 
  

   continued 
  process 
  of 
  vacuolation. 
  At 
  no 
  time 
  in 
  the 
  trans- 
  

   formation 
  of 
  the 
  sperm-head 
  is 
  it 
  possible 
  to 
  detect 
  any 
  

   separate 
  chromosomes. 
  

  

  In 
  the 
  stage 
  last 
  described 
  the 
  sperm-head 
  was 
  in 
  the 
  form 
  

   of 
  an 
  obtuse 
  cone 
  (fig. 
  18). 
  The 
  substance 
  of 
  this 
  cone, 
  which 
  

   is 
  highly 
  chromatic, 
  now 
  becomes 
  considerably 
  vacuolated. 
  

   The 
  vacuoles 
  vary 
  in 
  size; 
  many 
  of 
  them 
  are 
  so 
  close 
  together 
  

   that 
  only 
  a 
  thin 
  separating 
  lamella 
  is 
  left. 
  By 
  a 
  continuation 
  

   of 
  this 
  process 
  the 
  nucleus 
  comes 
  to 
  assume 
  a 
  typical 
  reticular 
  

   structure 
  (figs. 
  26, 
  b. 
  ; 
  20). 
  The 
  coarse, 
  and 
  now 
  achromatic, 
  

   reticulum 
  is 
  apparently 
  derived 
  from 
  the 
  remains 
  of 
  the 
  

   lamellae, 
  while 
  the 
  chromatin 
  is 
  confined 
  to 
  the 
  large, 
  often 
  

   irregular 
  granules 
  at 
  the 
  nodes. 
  Gradually, 
  however, 
  the 
  

   reticulum 
  becomes 
  much 
  finer, 
  the 
  chromatin 
  more 
  minutely 
  

   divided 
  and 
  less 
  intense 
  in 
  its 
  staining 
  reactions, 
  while 
  true 
  

   nucleoli 
  make 
  their 
  appeai-ance 
  (figs. 
  19, 
  21). 
  The 
  male 
  pro- 
  

   nucleus 
  is 
  now 
  exactly 
  similar 
  in 
  structure 
  to 
  the 
  female. 
  

   Like 
  the 
  latter 
  also 
  it 
  is 
  at 
  first 
  rounded 
  but 
  subsequently 
  

   irregularly 
  lobed, 
  and 
  undergoes 
  a 
  marked 
  increase 
  of 
  volume. 
  

  

  Though 
  the 
  above 
  seems 
  to 
  be 
  the 
  normal 
  series 
  of 
  changes 
  

   which 
  the 
  sperm-head 
  passes 
  through, 
  a 
  slight 
  variation 
  of 
  

  

  