﻿43 
  

  

  which 
  may 
  be 
  found 
  in 
  every 
  egg 
  by 
  patient 
  watching. 
  It 
  is~ 
  

   of 
  very 
  sliort 
  duration, 
  and 
  the 
  limiting 
  membrane 
  usually 
  

   becomes 
  smooth 
  again 
  in 
  about 
  fifteen 
  seconds 
  after 
  the 
  con- 
  

   tractions 
  commence. 
  Before 
  I 
  discovered 
  that 
  similar 
  waves 
  

   run 
  over 
  the 
  surface 
  of 
  the 
  egg 
  for 
  a 
  few 
  seconds 
  at 
  the 
  begin- 
  

   ning 
  of 
  the 
  active 
  changes 
  at 
  later 
  stages 
  of 
  segmentation, 
  T 
  

   naturally 
  inferred 
  that 
  they 
  were 
  connected 
  with 
  the 
  extru- 
  

   sion 
  of 
  the 
  polar 
  globules. 
  AVliile 
  it 
  seems 
  probable 
  that 
  they 
  

   are 
  in 
  some 
  way 
  connected 
  with 
  this 
  extrusion, 
  their 
  occurrence 
  

   at 
  later 
  stages 
  shows 
  that 
  this 
  is 
  not 
  their 
  only 
  significance. 
  

  

  So 
  far 
  as 
  I 
  am 
  aware, 
  this 
  is 
  the 
  first 
  notice 
  of 
  their 
  occur- 
  

   rence. 
  

  

  Soon 
  after 
  the 
  waves 
  commence, 
  an 
  area, 
  which 
  is 
  a 
  little 
  

   less 
  granular 
  than 
  the 
  mass 
  of 
  the 
  egg, 
  becomes 
  visible 
  at 
  the 
  

   formative 
  pole, 
  and 
  from 
  this 
  the 
  first 
  polar 
  globule 
  soon 
  

   begins 
  to 
  protrude, 
  pushing 
  out 
  the 
  external 
  egg-membrane. 
  

   Figure 
  '> 
  is 
  the 
  same 
  egg 
  two 
  minutes 
  later, 
  and 
  Figure 
  4 
  is 
  

   the 
  same 
  after 
  another 
  interval 
  of 
  two 
  minutes. 
  The 
  oval 
  

   outline 
  is 
  now 
  gradually 
  changing 
  to 
  a 
  pear 
  shape, 
  the 
  stalk 
  

   of 
  the 
  pear 
  occupying 
  the 
  nutritive 
  pole, 
  and 
  the 
  polar 
  

   globule 
  projecting 
  from 
  the 
  middle 
  of 
  the 
  broad 
  end 
  of 
  

   the 
  pear 
  at 
  the 
  formative 
  pole. 
  During 
  these 
  stages 
  the 
  

   granular 
  matter 
  of 
  the 
  yolk 
  may 
  be 
  seen 
  to 
  flow 
  in 
  a 
  steady,, 
  

   slow 
  current, 
  around 
  the 
  periphery 
  of 
  the 
  egg, 
  but, 
  as 
  far 
  as 
  I 
  

   could 
  observe, 
  the 
  current 
  has 
  no 
  definite 
  starting-point 
  or 
  

   terminus. 
  At 
  these 
  stages 
  there 
  are 
  no 
  waves 
  on 
  the 
  surface, 
  

   and 
  the 
  membrane 
  is 
  smooth. 
  It 
  is 
  interesting 
  to 
  observe 
  

   that 
  while 
  these 
  changes 
  are 
  taking 
  place 
  the 
  nutritive 
  end 
  of 
  

   the 
  egg 
  grows 
  a 
  little 
  more 
  transparent 
  than 
  the 
  formative 
  

   end, 
  a 
  reversal 
  of 
  what 
  occurs 
  in 
  almost 
  all 
  other 
  eggs 
  which 
  

   pass 
  through 
  unequal 
  or 
  irregular 
  segmentation, 
  although 
  

   Loven 
  has 
  described 
  the 
  same 
  phenomenon 
  in 
  Crenella. 
  In 
  

   a 
  short 
  time 
  three 
  planes 
  of 
  cleavage 
  run 
  in 
  towards 
  the 
  centre 
  

   of 
  the 
  egg 
  from 
  three 
  equidistant 
  points 
  on 
  the 
  periphery, 
  as 
  

   shown 
  in 
  Figure 
  5, 
  which 
  is 
  two 
  minutes 
  later 
  than 
  Figure 
  

   4, 
  although 
  the 
  changes 
  usually 
  take 
  place 
  mucli 
  more 
  rapidly. 
  

   One 
  of 
  these 
  planes 
  is 
  at 
  the 
  point 
  occupied 
  by 
  the 
  polar 
  

   globule, 
  and 
  the 
  others 
  about 
  midway 
  between 
  it 
  and 
  the: 
  

  

  