﻿42 
  

  

  from 
  five 
  minutes 
  to 
  an 
  Lour 
  after 
  impregnation 
  the 
  egg 
  

   becomes 
  quite 
  regularly 
  spherical, 
  as 
  shown 
  in 
  Figure 
  1, 
  and 
  

   is 
  now 
  covered 
  by 
  a 
  distinct 
  limiting 
  membrane, 
  which 
  ad- 
  

   heres 
  closely 
  to 
  the 
  surface 
  of 
  the 
  uniformly 
  granular 
  yolk. 
  

  

  The 
  changes 
  of 
  segmentation 
  take 
  place 
  so 
  very 
  rapidly 
  

   that 
  the 
  close 
  observation 
  of 
  the 
  living 
  egg 
  demanded 
  all 
  my 
  

   attention, 
  and 
  I 
  was 
  not 
  able 
  to 
  make 
  any 
  observations 
  upon 
  

   stained 
  specimens, 
  regarding 
  the 
  fate 
  of 
  the 
  germinative 
  vesi- 
  

   cle, 
  or 
  the 
  orgin 
  of 
  the 
  polar 
  globules 
  or 
  formation 
  of 
  the 
  first 
  

   segmentation 
  nucleus 
  ; 
  and 
  the 
  living 
  egg 
  is 
  suflSciently 
  opaque 
  

   to 
  prevent 
  observations 
  upon 
  this 
  point. 
  

  

  After 
  the 
  egg 
  has 
  assumed 
  the 
  spherical 
  form 
  shown 
  in 
  Fig- 
  

   ure 
  1, 
  it 
  remains 
  without 
  change 
  for 
  some 
  time, 
  usually 
  nearly 
  

   an 
  hour, 
  and 
  then 
  enters 
  upon 
  a 
  period 
  of 
  activity, 
  during 
  

   which 
  changes 
  follow 
  each 
  other 
  with 
  great 
  rapidity. 
  

  

  The 
  first 
  thirteen 
  figures 
  were 
  drawn 
  from 
  the 
  same 
  egg^ 
  

   As 
  the 
  day 
  was 
  very 
  cold, 
  the 
  changes 
  were 
  slow, 
  and 
  the 
  

   first 
  period 
  of 
  activity 
  did 
  not 
  set 
  in 
  until 
  two 
  hours 
  and 
  

   seven 
  minutes 
  after 
  impregnation, 
  but 
  the 
  series 
  of 
  changes, 
  

   shown 
  in 
  Figures 
  2-13 
  occupied 
  only 
  seventeen 
  minutes, 
  and 
  

   this 
  was 
  so 
  much 
  longer 
  than 
  usual 
  that 
  I 
  was 
  able 
  to 
  com- 
  

   mence 
  my 
  series 
  of 
  drawings 
  by 
  sketching 
  them. 
  

  

  As 
  shown 
  in 
  Figure 
  2, 
  the 
  egg 
  commences 
  its 
  activity 
  by 
  

   elongating 
  and 
  becoming 
  oval, 
  with 
  one 
  end 
  narrower 
  than 
  

   the 
  other. 
  The 
  narrow 
  end 
  is 
  to 
  become 
  the 
  nutritive 
  pole, 
  and 
  

   the 
  broad 
  end 
  the 
  formative 
  pole 
  of 
  the 
  segmenting 
  egg. 
  In 
  

   all 
  the 
  figures 
  of 
  segmenting 
  eggs 
  the 
  formative 
  pole 
  is 
  above,, 
  

   and 
  the 
  nutritive 
  below, 
  and 
  the 
  latter 
  corresponds, 
  in 
  a 
  gene- 
  

   ral 
  way, 
  to 
  the 
  dorsal 
  surface 
  of 
  the 
  embryo. 
  

  

  Contractions 
  now 
  begin 
  to 
  make 
  their 
  appearance 
  at 
  the 
  

   formative 
  end, 
  throwing 
  the 
  limiting 
  membrane 
  into 
  waves 
  or 
  

   wrinkles, 
  which 
  travel 
  rapidly 
  towards 
  the 
  formative 
  pole, 
  

   near 
  which 
  they 
  disappear. 
  

  

  The 
  wrinkles 
  are 
  shown 
  in 
  Figure 
  2. 
  It 
  is, 
  of 
  course,, 
  

   impossible 
  to 
  show 
  their 
  movement 
  in 
  a 
  drawing, 
  but 
  the 
  

   progression 
  over 
  the 
  surface 
  of 
  the 
  yolk, 
  from 
  the 
  starting- 
  

   point 
  at 
  the 
  small 
  end 
  to 
  the 
  place 
  where 
  they 
  disappear 
  near 
  

   the 
  round 
  end, 
  is 
  well 
  marked, 
  and 
  is 
  a 
  constant 
  characteristic,. 
  

  

  