﻿428 
  J. 
  W. 
  JENKINSON. 
  

  

  I 
  liave 
  observed 
  the 
  two 
  halves 
  united 
  by 
  two 
  curved 
  rods, 
  

   the 
  whole 
  having 
  the 
  appearance 
  of 
  an 
  oval 
  ring 
  (fig. 
  27). 
  

  

  The 
  diverging 
  halves 
  move 
  apart 
  till 
  they 
  are 
  separated 
  by 
  

   a 
  distance 
  a 
  little 
  greater 
  than 
  the 
  longer 
  diameter 
  o£ 
  the 
  

   nucleus. 
  The 
  division 
  usually 
  occurs 
  before 
  the 
  pronuclei 
  

   have 
  met, 
  but 
  it 
  may 
  be 
  deferred 
  (fig. 
  27). 
  

  

  With 
  regard 
  to 
  the 
  mode 
  of 
  origin 
  of 
  this 
  centrosome 
  I 
  do 
  

   not 
  wish 
  to 
  speak 
  too 
  positively. 
  It 
  may 
  be 
  argued, 
  in 
  view 
  

   of 
  the 
  known 
  persistence 
  of 
  this 
  organ 
  from 
  one 
  cell-generation 
  

   to 
  the 
  next 
  in 
  cases 
  of 
  ordinary 
  division, 
  that 
  the 
  centrosome 
  

   must 
  arise 
  here 
  also 
  from 
  the 
  middle-piece, 
  which, 
  as 
  we 
  know, 
  

   is 
  itself 
  merely 
  the 
  enlarged 
  centrosome 
  of 
  the 
  spermatid. 
  In 
  

   this 
  case 
  we 
  should 
  have 
  to 
  suppose 
  that 
  the 
  middle-piece, 
  

   after 
  being 
  dissolved 
  in 
  an 
  early 
  stage 
  became 
  reprecipitated 
  

   in 
  a 
  later. 
  The 
  solution 
  and 
  reprecipitation 
  of 
  a 
  nuclein 
  is 
  

   of 
  course 
  no 
  very 
  extraordinary 
  process 
  ; 
  it 
  occurs 
  quite 
  

   normally 
  in 
  the 
  nucleus 
  in 
  the 
  disappearance 
  and 
  re-formation 
  

   of 
  the 
  chromosomes. 
  

  

  Now, 
  however 
  much 
  may 
  be 
  said 
  for 
  such 
  an 
  hypothesis 
  

   from 
  a 
  purely 
  theoretical 
  and 
  comparative 
  point 
  of 
  view, 
  it 
  is 
  

   hardly 
  supported 
  in 
  the 
  case 
  of 
  the 
  axolotl 
  by 
  any 
  positive 
  

   evidence 
  at 
  all, 
  and 
  is, 
  as 
  I 
  believe, 
  directly 
  negatived 
  by 
  the 
  

   evidence 
  which 
  I 
  am 
  able 
  to 
  bring 
  forward 
  in 
  favour 
  of 
  a 
  

   totally 
  different 
  origin 
  of 
  the 
  centrosome, 
  namely, 
  from 
  the 
  

   sperm-nucleus 
  itself. 
  

  

  I 
  have 
  observed 
  in 
  many 
  cases 
  that 
  the 
  membrane 
  of 
  the 
  

   sperm-nucleus 
  cannot 
  be 
  detected, 
  or 
  is 
  at 
  least 
  very 
  much 
  

   weakened 
  on 
  the 
  side 
  turned 
  towards 
  the 
  centi'osome 
  (figs. 
  22, 
  

   23), 
  and 
  in 
  some 
  preparations 
  the 
  centrosome 
  is 
  so 
  closely 
  

   apposed 
  to 
  this 
  side 
  of 
  the 
  nucleus 
  that 
  it 
  appears 
  to 
  be 
  

   actually 
  emerging 
  from 
  it 
  (figs. 
  24, 
  25). 
  The 
  dense 
  cloud 
  of 
  

   pigment 
  which, 
  as 
  we 
  have 
  seen, 
  obscures 
  the 
  centrosome, 
  

   appears 
  to 
  come 
  into 
  existence 
  simultaneously, 
  for 
  deeply 
  

   pigmented 
  processes 
  are 
  observed 
  passing 
  inwards 
  from 
  the 
  

   centi'osome 
  into 
  the 
  interior 
  of 
  the 
  nucleus. 
  To 
  judge 
  by 
  this 
  

   evidence, 
  then^ 
  centrosome 
  and 
  pigment 
  are 
  both 
  formed 
  not 
  

  

  