﻿46 
  

  

  nor 
  does 
  a 
  segmentative 
  cavity 
  make 
  its 
  appearance 
  until 
  

   much 
  later. 
  

  

  From 
  the 
  stage 
  shown 
  in 
  Figure 
  1, 
  up 
  to 
  the 
  stage 
  shown 
  

   in 
  Figure 
  10, 
  no 
  traces 
  of 
  a 
  segmentation 
  nucleus 
  could 
  be 
  

   made 
  out 
  in 
  the 
  living 
  egg, 
  but 
  at 
  the 
  stage 
  shown 
  in 
  Fig- 
  

   ure 
  11, 
  a 
  large, 
  circular, 
  transparent 
  body 
  appears 
  in 
  the 
  

   first 
  micromere 
  and 
  another 
  at 
  the 
  formative 
  end 
  of 
  the 
  com- 
  

   pound 
  mass 
  formed 
  by 
  the 
  fusion 
  of 
  the 
  second 
  micromere 
  

   with 
  the 
  macromere. 
  

  

  At 
  the 
  end 
  of 
  the 
  second 
  period 
  of 
  rest 
  (Figure 
  13), 
  these 
  

   bodies 
  are 
  much 
  larger, 
  and 
  their 
  outlines 
  are 
  very 
  clear. 
  

   The 
  commencement 
  of 
  the 
  second 
  period 
  of 
  activity 
  is 
  shown 
  

   in 
  Figure 
  14, 
  w^hich 
  is 
  six 
  minutes 
  after 
  Figure 
  13. 
  The 
  

   two 
  spherules 
  swell 
  up 
  and 
  become 
  much 
  more 
  conspicuous 
  

   than 
  they 
  were 
  at 
  the 
  stage 
  before, 
  although 
  they 
  are 
  still 
  

   in 
  contact 
  over 
  a 
  considerable 
  area. 
  The 
  wave-like 
  motion, 
  

   noticed 
  at 
  an 
  earlier 
  stage, 
  is 
  now 
  repeated 
  in 
  each 
  spher- 
  

   ule, 
  and 
  runs 
  over 
  the 
  surface 
  from 
  the 
  point 
  furthest 
  from 
  

   the 
  polar 
  globlue 
  towards 
  the 
  end 
  where 
  tliis 
  is 
  situated 
  ; 
  the 
  

   wave 
  continuing 
  for 
  about 
  half 
  a 
  minute. 
  At 
  the 
  time 
  this 
  

   motion 
  commences 
  a 
  remarkable 
  change 
  takes 
  place 
  in 
  the 
  

   two 
  transparent 
  vesicles 
  ah'eady 
  mentioned. 
  Each 
  of 
  these 
  be- 
  

   comes 
  irregular 
  and 
  star-shaped, 
  and 
  long 
  channels 
  radiate 
  

   from 
  it 
  into 
  the 
  substance 
  of 
  the 
  yolk, 
  as 
  shown 
  in 
  Figure 
  

   47. 
  The 
  central 
  chamber 
  then 
  instantly 
  disappears 
  ; 
  the 
  

   radiating 
  channels 
  are 
  visible 
  for 
  a 
  fraction 
  of 
  a 
  second 
  

   longer, 
  and 
  then 
  disappear, 
  and 
  the 
  places 
  which 
  the 
  two 
  

   large 
  chambers 
  had 
  occupied 
  are 
  now 
  (Figure 
  14), 
  seen 
  to 
  be 
  

   occupied 
  by 
  two 
  small 
  refractive 
  nuclei. 
  I 
  at 
  first 
  thought 
  

   that 
  the 
  radiating 
  channels 
  might 
  be 
  the 
  same 
  as 
  the 
  star- 
  

   shaped 
  figiires 
  of 
  recent 
  embryologists, 
  but 
  it 
  seems 
  more 
  

   probable 
  that 
  each 
  of 
  the 
  large 
  chambers 
  of 
  Figures 
  11, 
  12 
  

   and 
  13, 
  contains 
  a 
  nucleus 
  which 
  might 
  be 
  brought 
  out 
  by 
  re- 
  

   agents, 
  and 
  which 
  is 
  surrounded 
  by 
  a 
  more 
  fluid 
  substance, 
  

   the 
  diftusion 
  of 
  which 
  through 
  the 
  yolk 
  precedes 
  the 
  forma- 
  

   tion 
  of 
  the 
  amphiaster 
  and 
  the 
  division 
  of 
  the 
  nucleus. 
  It 
  is 
  

   possible 
  that 
  this 
  diffusion 
  is 
  the 
  cause 
  of 
  the 
  peculiar 
  star- 
  

   iike 
  arrangement 
  of 
  the 
  granules 
  of 
  the 
  yolk 
  around 
  the 
  nu- 
  

  

  