﻿57 
  

  

  wliicli 
  I 
  liave 
  selected 
  above 
  show 
  the 
  dependence 
  of 
  the 
  young 
  

   upon 
  continuous 
  warm 
  weather. 
  

  

  The 
  past 
  spring 
  and 
  summer 
  were 
  unusually 
  cool, 
  and 
  it 
  

   was 
  not 
  until 
  the 
  middle 
  of 
  July 
  that 
  the 
  weatfier 
  was 
  warm 
  

   for 
  more 
  than 
  three 
  or 
  four 
  days 
  in 
  succession, 
  and 
  my 
  failure 
  

   to 
  iind 
  any 
  tloating 
  eujbryos 
  in 
  the 
  open 
  ocean 
  may 
  be 
  due 
  

   to 
  the 
  fact 
  tliat 
  they 
  were 
  killed 
  by 
  the 
  cold 
  as 
  fast 
  as 
  the 
  

   eggs 
  were 
  laid. 
  After 
  the 
  middle 
  of 
  July 
  I 
  found 
  a 
  few 
  em- 
  

   bryo 
  at 
  the 
  surface 
  of 
  the 
  water 
  of 
  the 
  Sound. 
  

  

  EXCEPTIONS 
  TO 
  THE 
  NORMAL 
  METHOD 
  OK 
  SEGMENTATION. 
  

  

  The 
  metliod 
  of 
  segmentation, 
  as 
  I 
  have 
  described 
  it, 
  is 
  the 
  

   normal 
  method, 
  and 
  is 
  followed 
  exactly 
  by 
  a 
  very 
  largo 
  pro- 
  

   portion 
  of 
  the 
  eggs 
  — 
  by 
  more 
  than 
  &0 
  per 
  cent, 
  of 
  them, 
  I 
  

   should 
  think; 
  but 
  a 
  few 
  eggs 
  in 
  every 
  lot 
  present 
  considera- 
  

   ble 
  variation, 
  especially 
  in 
  the 
  earlier 
  stages. 
  

  

  Plate 
  X, 
  Figures 
  54: 
  to 
  62, 
  shows 
  one 
  of 
  the 
  most 
  common 
  

   variations. 
  If 
  a 
  number 
  of 
  eggs 
  be 
  carefully 
  watched 
  during 
  

   the 
  early 
  stages 
  a 
  few 
  will 
  be 
  found 
  to 
  reach 
  the 
  stage 
  shown 
  

   in 
  Figure 
  13, 
  Plate 
  I, 
  more 
  directly 
  than 
  the 
  ordinary 
  eggs, 
  

   without 
  going 
  through 
  the 
  process 
  of 
  forming 
  the 
  second 
  mi- 
  

   cromere 
  5, 
  of 
  Plate 
  I, 
  and 
  then 
  obliterating 
  it. 
  Figure 
  54 
  is 
  

   an 
  egg 
  two 
  hours 
  and 
  seven 
  minutes 
  after 
  fertilization, 
  and 
  in 
  

   the 
  stage 
  shown 
  in 
  Figure 
  4. 
  Two 
  minutes 
  later 
  it 
  had 
  as- 
  

   sumed 
  the 
  form 
  shown 
  in 
  Figure 
  55, 
  which 
  is 
  very 
  similar 
  to 
  

   Figure 
  5, 
  except 
  that 
  the 
  three 
  lobes 
  of 
  the 
  trefoil 
  are 
  less 
  

   sharply 
  separated. 
  Two 
  minutes 
  later 
  it 
  had 
  assumed 
  the 
  

   form 
  shown 
  in 
  Figure 
  56, 
  and 
  one 
  minute 
  later 
  the 
  form 
  shown 
  

   in 
  Figure 
  57. 
  As 
  shown 
  l)y 
  these 
  figures, 
  the 
  second 
  micro- 
  

   mere 
  does 
  not 
  become 
  distinct, 
  as 
  in 
  Figure 
  6, 
  but 
  the 
  faint 
  

   indication 
  of 
  it 
  shown 
  in 
  Figure 
  55 
  quickly 
  disappears, 
  and 
  

   the 
  subsequent 
  changes 
  result 
  in 
  the 
  separation 
  of 
  the 
  egg 
  

   into 
  two 
  masses, 
  instead 
  of 
  three. 
  Figure 
  58 
  is 
  forty-five 
  

   seconds 
  later 
  than 
  Figure 
  57, 
  and 
  Figure 
  59 
  four 
  minutes 
  and 
  

   fifteen 
  seconds 
  later. 
  A 
  single 
  furrow 
  now 
  extends 
  nearly 
  

   across 
  the 
  egg, 
  from 
  the 
  polar 
  globule, 
  and 
  divides 
  it 
  into 
  two 
  

   nearly 
  separated 
  portions 
  — 
  a 
  small 
  one 
  and 
  a 
  large 
  one. 
  In 
  

  

  