﻿88 
  

  

  it. 
  So 
  too, 
  are 
  the 
  two 
  small 
  ones 
  originating 
  from 
  the 
  

   smaller 
  cell 
  of 
  the 
  stage 
  shown 
  in 
  Fig 
  5. 
  Tlie 
  notch 
  

   which 
  is 
  moving 
  inwards 
  to 
  nip 
  off 
  the 
  small 
  cell 
  from 
  

   the 
  large 
  one 
  moves 
  so 
  fast 
  that 
  I 
  hnd 
  the 
  camera 
  liicida 
  

   of 
  use 
  only 
  so 
  far 
  as 
  it 
  enables 
  me 
  to 
  get 
  the 
  dimensions. 
  

   In 
  like 
  manner 
  tlie 
  contour 
  lines 
  on 
  the 
  other 
  side 
  are 
  

   rapidly 
  changing 
  in 
  the 
  division 
  of 
  the 
  smaller 
  cell. 
  

   Then 
  follows 
  a 
  condition 
  of 
  rest 
  shown 
  in 
  

   Fig. 
  7. 
  The 
  micromeres 
  are 
  now 
  three 
  in 
  

   jnuniber, 
  the 
  megamere 
  is 
  still 
  much 
  greater 
  

   in 
  bulk 
  than 
  all 
  three. 
  The 
  nuclei 
  again 
  

   become 
  defined 
  . 
  The 
  egg 
  is 
  passing 
  slowly 
  

   into 
  the 
  stage 
  shown 
  in 
  Fig. 
  8, 
  at 
  the 
  one 
  

   Figure 
  7. 
  pole 
  of 
  which 
  we 
  still 
  see 
  the 
  polar 
  cells 
  

   persisting. 
  The 
  thrfee 
  micromeres 
  have 
  

   subsided 
  ; 
  l)ecome 
  depressed 
  and 
  the 
  whole 
  

   outliup 
  is 
  more 
  rounded, 
  like 
  that 
  of 
  the 
  w^ 
  

   unsegniented 
  egg. 
  The 
  faint 
  indication 
  of 
  § 
  

   a 
  segmentation 
  cavity 
  or 
  space 
  shown 
  be- 
  v^^ 
  

   tween 
  the 
  micromeres 
  and 
  megamere 
  in 
  

   Fig. 
  7, 
  lias 
  disappeared. 
  The 
  end)ryo 
  is 
  Fujiire 
  8. 
  

   quiescent 
  and 
  has 
  reached 
  the 
  limit 
  of 
  peiiiaps 
  its 
  third 
  

   or 
  fourth 
  period 
  of 
  activity 
  and 
  rest. 
  The 
  succeeding 
  

   stage 
  represented 
  in 
  Fig. 
  9 
  is 
  whei-e 
  the 
  next 
  

   ])eriod 
  of 
  activity 
  has 
  reached 
  its 
  comple- 
  

   tion. 
  The 
  micromeres 
  of 
  Figs. 
  7 
  and 
  8 
  have 
  

   again 
  divided 
  and 
  one 
  or 
  two 
  micromeres 
  

   have 
  been 
  derived 
  from 
  the 
  megamere 
  ; 
  in 
  

   this 
  way 
  a 
  number 
  of 
  additional 
  nncromeres 
  

   Fiijurc 
  9. 
  has 
  been 
  the 
  result. 
  The 
  micromeres 
  are 
  

   now 
  piled 
  up 
  at 
  one 
  side, 
  or 
  rather 
  end, 
  of 
  the 
  egg^ 
  and 
  

   the 
  i^olar 
  cells 
  still 
  persist. 
  The 
  micromeres 
  display 
  a 
  

   certain 
  symmetry 
  of 
  arrangement. 
  It 
  now 
  becomes 
  ap- 
  

   parent 
  that 
  the 
  micrcmieres 
  are 
  to 
  be 
  the 
  foundation 
  of 
  

   the 
  epiblast 
  or 
  skin 
  layer 
  of 
  the 
  embryo, 
  while 
  the 
  mi- 
  

   cromere 
  is 
  to 
  become 
  the 
  hypoblast 
  or 
  inner 
  layer 
  from 
  

  

  