﻿572 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  [84J 
  

  

  EXPLANATION 
  OF 
  PLATE 
  XIV. 
  

   Clupea 
  sapidissima. 
  (TJie 
  Common 
  Shad.) 
  

  

  Fig. 
  68. 
  The 
  freshly 
  extruded 
  egg 
  enlarged, 
  showing 
  its 
  envelope 
  much 
  wrinkled 
  and 
  

   its 
  surface 
  covered 
  with 
  small 
  round 
  vesicles. 
  

  

  Fig. 
  69. 
  An 
  optic 
  section 
  of 
  the 
  periphery 
  of 
  the 
  preceding 
  more 
  enlarged, 
  showing 
  

   the 
  zona 
  z, 
  the 
  cortical 
  layer 
  cl, 
  with 
  its 
  emhedded 
  vesicles, 
  and 
  the 
  large 
  yelk- 
  

   spheres 
  y 
  surrounded 
  by 
  their 
  films 
  of 
  protoplasm. 
  

  

  Fig. 
  70. 
  A 
  shad's 
  egg, 
  showing 
  the 
  vitellus 
  and 
  distended 
  egg-membrane, 
  natural 
  

   size. 
  

  

  Figs. 
  71, 
  72, 
  and 
  73. 
  Represent 
  three 
  stages 
  in 
  the 
  development 
  of 
  the 
  blastodisk 
  of 
  the 
  

   shad's 
  egg 
  at 
  the 
  lateral 
  pole 
  of 
  the 
  vitellus. 
  

  

  Fig. 
  74. 
  Shows 
  the 
  gradual 
  accumulation 
  of 
  the 
  germinal 
  matter 
  at 
  one 
  pole 
  of 
  the 
  

   egg, 
  the 
  polar 
  prominence 
  externally, 
  and 
  the 
  presence 
  of 
  plasmic 
  processes 
  ex- 
  

   tending 
  down 
  through 
  the 
  vitellus. 
  

  

  Fig. 
  75. 
  Shad 
  ovum 
  with 
  the 
  blastodisk 
  just 
  forming, 
  viewed 
  from 
  above. 
  ' 
  

  

  Fig. 
  76. 
  Shad 
  ovum 
  with 
  the 
  blastodisk 
  formed 
  and 
  with 
  protoplasmic 
  processes 
  pass- 
  

   ing 
  from 
  its 
  under 
  surface 
  down 
  into 
  the 
  vitellus. 
  

  

  Figs. 
  77 
  and 
  78. 
  Views 
  in 
  optic 
  section 
  of 
  shad 
  ova 
  at 
  the 
  time 
  the 
  first 
  cleavage 
  

   furrow 
  is 
  developed. 
  

  

  Fig. 
  79, 
  a, 
  b, 
  c, 
  d, 
  e,f. 
  The 
  changes 
  which 
  the 
  polar 
  prominence 
  showu 
  in 
  fig. 
  74, 
  under- 
  

   went 
  at 
  short 
  intervals 
  of 
  time, 
  during 
  half 
  an 
  hour, 
  till 
  the 
  polar 
  cells 
  were 
  de- 
  

   tached. 
  

  

  Fig. 
  80. 
  Surface 
  view 
  from 
  above 
  of 
  the 
  blastodisk 
  of 
  the 
  shad, 
  at 
  the 
  time 
  of 
  the 
  first 
  

   cleavage. 
  

  

  Fig. 
  81. 
  A 
  similar 
  view 
  of 
  an 
  older 
  blastodisk 
  at 
  the 
  time 
  of 
  the 
  completion 
  of 
  the 
  

   second 
  cleavage. 
  

  

  Fig. 
  82. 
  Side 
  view 
  of 
  a 
  similar 
  stage. 
  

  

  Fig. 
  83. 
  Side 
  view 
  of 
  blastodisk 
  which 
  has 
  abnormally 
  segmented 
  into 
  five 
  cells. 
  

  

  Fig. 
  84. 
  Blastodisk 
  actively 
  segmenting, 
  and 
  rapidly 
  approaching 
  the 
  sixteen-celled 
  

   stage. 
  The 
  irregularities 
  in 
  the 
  form 
  of 
  the 
  cells 
  is 
  due 
  to 
  the 
  unequal 
  contrac- 
  

   tractions 
  of 
  their 
  plasma. 
  

  

  Fig. 
  85. 
  Blastodisk 
  composed 
  of 
  four 
  cells 
  at 
  the 
  time 
  of 
  the 
  second 
  cleavage 
  ; 
  side 
  

   view. 
  

  

  Figs. 
  86 
  and 
  87. 
  Oblique 
  views 
  of 
  two 
  different 
  blastodisks 
  at 
  the 
  end 
  of 
  the 
  third 
  

   cleavage 
  after 
  eight 
  cells 
  have 
  been 
  developed. 
  

  

  Fig. 
  88. 
  Side 
  view 
  of 
  a 
  blastodisk 
  at 
  the 
  same 
  stage 
  as 
  the 
  preced 
  

  

  Fig. 
  89. 
  Side 
  view 
  of 
  a 
  blastodisk 
  during 
  th8 
  active 
  stage 
  of 
  the 
  fourth 
  cleavage. 
  

  

  Fig. 
  90. 
  Surface 
  view 
  of 
  a 
  blastodisk 
  which 
  has 
  advanced 
  somewhat 
  beyond 
  the 
  fifth 
  

   cleavage, 
  or 
  thirty 
  -two 
  celled 
  stage. 
  

  

  Fig. 
  91. 
  Optic 
  section 
  through 
  a 
  still 
  more 
  advanced 
  stage 
  of 
  the 
  development 
  of 
  the 
  

   blastodisk, 
  when 
  the 
  latter 
  is 
  composed 
  of 
  three 
  to 
  four 
  layers 
  of 
  cells. 
  

  

  Fig. 
  92. 
  Blastodisk 
  at 
  the 
  time 
  it 
  has 
  assumed 
  the 
  lenticular 
  form, 
  and 
  is 
  composed 
  of 
  

   very 
  small 
  cells, 
  just 
  before 
  it 
  begins 
  to 
  spread 
  over 
  the 
  yelk. 
  Optic 
  section. 
  

  

  