﻿48 
  

  

  as 
  the 
  plates 
  of 
  a 
  calcareous 
  shell, 
  and 
  compares 
  the 
  egg 
  to 
  

   a 
  sea-urchin. 
  

  

  To 
  return 
  to 
  the 
  segmentation 
  ; 
  immediately 
  after 
  the 
  large 
  

   vesicles 
  have 
  disappeared, 
  the 
  egg 
  has 
  the 
  appearance 
  shown 
  

   in 
  Figure 
  14. 
  One 
  minute 
  later 
  (Figure 
  15), 
  the 
  first 
  mi- 
  

   cromere, 
  c, 
  has 
  become 
  nearly 
  spherical, 
  and 
  stands 
  out 
  sharp- 
  

   ly 
  from 
  the 
  remainder 
  of 
  the 
  egg, 
  and 
  the 
  compound 
  mass, 
  d 
  

   and 
  J, 
  of 
  the 
  preceding 
  figures, 
  is 
  again 
  separated 
  into 
  the 
  

   macromere, 
  a, 
  and 
  the 
  second 
  micrornere, 
  h. 
  In 
  another 
  min- 
  

   ute 
  (Figure 
  16), 
  the 
  formative 
  pole 
  is 
  divided 
  into 
  four 
  mi- 
  

   cromeres, 
  one 
  of 
  which, 
  J, 
  is 
  only 
  slightly 
  marked 
  ofl:' 
  from 
  

   the 
  macromere, 
  while 
  the 
  three 
  others 
  are 
  more 
  distinct. 
  

   The 
  impossibility 
  of 
  seeing 
  both 
  sides 
  of 
  the 
  egg 
  at 
  once 
  

   makes 
  it 
  difficult 
  to 
  say 
  just 
  how 
  these 
  four 
  spherules 
  are 
  

   formed, 
  but 
  it 
  seems 
  most 
  pi-obable 
  that 
  two 
  of 
  them 
  are 
  

   formed 
  by 
  the 
  division 
  of 
  the 
  first 
  micromere, 
  and 
  two 
  by 
  

   the 
  division 
  of 
  the 
  second. 
  

  

  In 
  the 
  egg 
  which 
  was 
  figured 
  the 
  nearest 
  spherule 
  bears 
  

   every 
  indication 
  of 
  an 
  origin 
  by 
  the 
  division 
  of 
  the 
  first 
  mi- 
  

   cromere, 
  c, 
  into 
  two, 
  and 
  other 
  eggs 
  served 
  to 
  show 
  with 
  equal 
  

   clearness 
  that 
  one 
  of 
  them 
  is 
  also 
  separated 
  off 
  from 
  the 
  

   second 
  micromere, 
  h. 
  Certain 
  irregular 
  forms 
  of 
  segmenta- 
  

   tion, 
  which 
  will 
  be 
  described 
  later, 
  also 
  appear 
  to 
  sustain 
  this 
  

   view. 
  

  

  Owins: 
  to 
  an 
  unfortunate 
  oversio-ht, 
  the 
  dotted 
  lines 
  which 
  

   should 
  connect 
  the 
  letters 
  of 
  reference 
  with 
  the 
  parts 
  they 
  

   refer 
  to 
  were 
  not 
  copied 
  in 
  the 
  drawings 
  from 
  which 
  the 
  photo- 
  

   electrotypes 
  of 
  Plates 
  II. 
  and 
  III. 
  were 
  made; 
  but 
  I 
  hope 
  

   that 
  a 
  more 
  careful 
  description 
  will 
  supply 
  a 
  remedy 
  for 
  the 
  

   accident. 
  Two 
  minutes 
  later. 
  Figure 
  17, 
  three 
  of 
  the 
  micro- 
  

   meres, 
  the 
  first, 
  c, 
  and 
  the 
  two 
  new 
  ones, 
  d 
  d^ 
  are 
  well 
  de- 
  

   fined 
  and 
  prominent; 
  but 
  one 
  of 
  them, 
  the 
  second 
  micromere, 
  

   5, 
  has 
  again 
  begun 
  to 
  become 
  fused 
  with 
  the 
  macromere, 
  a. 
  

   After 
  another 
  interval 
  of 
  three 
  minutes 
  and 
  a 
  half, 
  Figure 
  18, 
  

   this 
  micromere 
  has 
  become 
  completely 
  fused 
  with 
  the 
  macro- 
  

   mere, 
  to 
  form 
  a 
  compound 
  mass, 
  a 
  and 
  J, 
  which 
  is 
  almost 
  

   spherical, 
  and 
  in 
  this 
  a 
  single 
  transparent 
  vesicle 
  has 
  made 
  its. 
  

   appearance. 
  The 
  other 
  three 
  ^micromeres 
  are 
  even 
  more 
  

  

  