﻿436 
  J. 
  W. 
  JENKINSON. 
  

  

  blastomeres 
  go 
  through 
  precisely 
  the 
  same 
  cycle 
  of 
  changes 
  as 
  

   that 
  which 
  I 
  have 
  described 
  above 
  for 
  the 
  cleavage 
  centro- 
  

   someSj 
  and 
  that 
  this 
  body, 
  when 
  introduced 
  into 
  or 
  formed 
  

   in 
  the 
  ovum, 
  becomes 
  a 
  permanent 
  organ 
  of 
  the 
  embryonic 
  cells. 
  

  

  Before 
  leaving 
  the 
  aster 
  I 
  have 
  to 
  describe 
  certain 
  changes 
  

   that 
  take 
  place 
  in 
  its 
  peripheral 
  region. 
  

  

  We 
  have 
  seen 
  that 
  the 
  centrosphere 
  is 
  surrounded 
  by 
  

   coarse 
  radiations 
  which 
  pass 
  out 
  between 
  the 
  yoke-granules 
  

   into 
  the 
  general 
  cytoplasms, 
  and 
  appear 
  to 
  be 
  identical 
  with 
  

   one 
  half 
  of 
  the 
  radiations 
  of 
  the 
  sperm-aster. 
  These 
  radia- 
  

   tions 
  do 
  not 
  at 
  first 
  extend 
  into 
  the 
  equatorial 
  region 
  of 
  the 
  

   spindle, 
  which 
  is 
  occupied 
  only 
  by 
  a 
  mass 
  of 
  round 
  vacuoles 
  

   (figs. 
  32, 
  33) 
  ; 
  but 
  in 
  the 
  fully-formed 
  spindle 
  a 
  complete 
  

   mantle 
  of 
  radiations 
  is 
  found 
  wrapping 
  round 
  the 
  spindle 
  

   proper 
  and 
  extending 
  as 
  far 
  as 
  the 
  equator 
  (figs. 
  38, 
  41). 
  

   Here 
  the 
  radiations 
  meet 
  without, 
  as 
  far 
  as 
  I 
  can 
  see, 
  ever 
  

   intercrossing 
  with 
  those 
  derived 
  from 
  the 
  opposite 
  pole 
  ; 
  on 
  

   the 
  contrary 
  the 
  two 
  sets 
  of 
  rays 
  seem 
  to 
  diverge 
  outwards 
  

   and 
  to 
  lie 
  parallel 
  to 
  one 
  another, 
  one 
  on 
  each 
  side 
  of 
  the 
  

   equatorial 
  plane. 
  The 
  rays 
  become 
  closely 
  crowded 
  together 
  

   by 
  the 
  expansion 
  of 
  the 
  nuclear 
  spindle 
  (figs. 
  38, 
  40, 
  41), 
  and 
  

   are 
  thickly 
  beset 
  with 
  pigment 
  granules. 
  

  

  These 
  equatorial 
  astral 
  rays 
  thus 
  appear 
  to 
  be 
  a 
  completely 
  

   new 
  formation, 
  replacing 
  the 
  round 
  vacuoles 
  of 
  an 
  earlier 
  

   period 
  ; 
  but 
  whether 
  they 
  are 
  in 
  reality 
  outgrowths 
  of 
  the 
  

   previous 
  rays 
  — 
  and 
  in 
  this 
  case 
  we 
  might 
  have 
  to 
  attribute 
  

   their 
  formation 
  ultimately 
  to 
  the 
  activity 
  of 
  the 
  centrosome 
  — 
  

   or 
  whether 
  they 
  arise 
  merely 
  by 
  the 
  compression 
  of 
  the 
  

   round 
  vacuoles, 
  is 
  not 
  easy 
  to 
  determine. 
  The 
  persistence 
  of 
  

   the 
  pigment 
  granules 
  leads 
  me 
  to 
  incline 
  to 
  the 
  latter 
  view 
  ; 
  

   for 
  I 
  have 
  noticed 
  that 
  in 
  the 
  case 
  of 
  new 
  formations, 
  for 
  

   example 
  in 
  the 
  formation 
  of 
  the 
  vacuoles 
  of 
  the 
  sperm-sphere, 
  

   the 
  pigment 
  granules 
  are 
  swept 
  aside. 
  On 
  the 
  other 
  view 
  we 
  

   should 
  have 
  to 
  suppose 
  that 
  the 
  pigment 
  in 
  question 
  was 
  

   pushed 
  outwards 
  from 
  the 
  centrosome 
  by 
  the 
  continued 
  

   growth 
  of 
  the 
  rays, 
  and 
  this 
  is 
  favoured 
  by 
  the 
  fact 
  that 
  the 
  

   dense 
  pigment 
  which 
  surrounded 
  the 
  centrosome 
  at 
  its 
  first 
  

  

  