﻿OYSTER 
  INDUSTRY 
  OF 
  NORTH 
  CAROLINA. 
  321 
  

  

  edges 
  of 
  the 
  mantle 
  from 
  the 
  margin 
  of 
  the 
  shell, 
  while 
  the 
  latter 
  in 
  contracting 
  

   tend 
  to 
  crimp 
  or 
  fold 
  its 
  edges. 
  The 
  tentacles 
  are 
  mainly 
  innervated 
  by 
  fibers 
  

   emanating 
  from 
  the 
  hindmost 
  ganglia, 
  while 
  the 
  internal 
  organs 
  are 
  innervated 
  from 
  

   the 
  head 
  or 
  cephalic 
  ganglia. 
  The 
  hind 
  ganglia 
  also 
  preside 
  over 
  the 
  contraction 
  

   of 
  the 
  great 
  adductor 
  muscle. 
  The 
  nerve 
  threads 
  which 
  radiate 
  outward 
  from 
  it 
  to 
  

   the 
  tentacles 
  dispatch 
  the 
  warnings 
  when 
  intruders 
  are 
  at 
  hand 
  that 
  it 
  must 
  contract 
  

   and 
  close 
  the 
  shells. 
  « 
  

  

  EMBRYONIC 
  DEVELOPMENT. 
  

  

  The 
  following 
  popular 
  account 
  of 
  the 
  early 
  stages 
  in 
  the 
  develop- 
  

   ment 
  of 
  the 
  oyster 
  is 
  slightly 
  modified 
  from 
  the 
  description 
  by 
  

   Dr. 
  W. 
  K. 
  Brooks: 
  

  

  The 
  ovarian 
  eggs 
  are 
  simply 
  the 
  cells 
  of 
  an 
  organ 
  of 
  the 
  body, 
  the 
  ovary, 
  and 
  they 
  

   differ 
  from 
  the 
  ordinary 
  cells 
  only 
  in 
  being 
  much 
  larger 
  and 
  more 
  distinct 
  from 
  each 
  

   other, 
  and 
  they 
  have 
  the 
  power, 
  when 
  detached 
  from 
  the 
  body, 
  of 
  growing 
  and 
  

   dividing 
  up 
  into 
  cells, 
  which 
  shall 
  shape 
  themselves 
  into 
  a 
  new 
  organism 
  like 
  that 
  

   from 
  whose 
  body 
  the 
  egg 
  came. 
  Most 
  of 
  the 
  steps 
  in 
  this 
  wonderful 
  process 
  may 
  be 
  

   watched 
  under 
  the 
  microscope, 
  and, 
  owing 
  to 
  the 
  ease 
  with 
  which 
  the 
  eggs 
  of 
  the 
  

   oyster 
  may 
  be 
  obtained, 
  this 
  is 
  a 
  very 
  good 
  egg 
  to 
  study. 
  

  

  About 
  15 
  minutes 
  after 
  the 
  eggs 
  are 
  fertilized 
  they 
  will 
  be 
  found 
  to 
  be 
  covered 
  with 
  

   male 
  cells, 
  as 
  shown 
  in 
  plate 
  viii, 
  fig. 
  1.^ 
  In 
  about 
  an 
  hour 
  the 
  egg 
  will 
  be 
  found 
  to 
  

   have 
  changed 
  its 
  shape 
  and 
  appearance. 
  It 
  is 
  now 
  nearly 
  spherical, 
  as 
  shown 
  in 
  plate 
  

   VIII, 
  fig. 
  2, 
  and 
  the 
  germinative 
  vesicle 
  is 
  no 
  longer 
  visible. 
  The 
  male 
  cells 
  maj' 
  or 
  may 
  

   not 
  still 
  be 
  visible 
  upon 
  the 
  outer 
  surface. 
  In 
  a 
  short 
  time 
  a 
  little 
  transparent 
  point 
  

   makes 
  its 
  appearance 
  on 
  the 
  surface 
  of 
  the 
  egg 
  and 
  increases 
  in 
  size 
  and 
  soon 
  forms 
  

   a 
  little 
  projecting 
  transparent 
  knob 
  — 
  the 
  polar 
  globule 
  — 
  which 
  is 
  shown 
  in 
  fig. 
  3, 
  

   plate 
  VIII, 
  and 
  in 
  succeeding 
  figures. 
  

  

  Recent 
  investigations 
  tend 
  to 
  show 
  that 
  while 
  these 
  changes 
  are 
  taking 
  place 
  one 
  of 
  

   the 
  male 
  cells 
  penetrates 
  the 
  protoplasm 
  of 
  the 
  egg 
  and 
  unites 
  with 
  the 
  germinative 
  

   vesicle, 
  which 
  does 
  not 
  disappear 
  but 
  divides 
  into 
  two 
  parts, 
  one 
  of 
  which 
  is 
  pushed 
  

   out 
  of 
  the 
  egg 
  and 
  becomes 
  the 
  polar 
  globule, 
  while 
  the 
  other 
  remains 
  behind 
  and 
  

   becomes 
  the 
  nucleus 
  of 
  the 
  developing 
  egg, 
  but 
  changes 
  its 
  appearance 
  so 
  that 
  it 
  is 
  

   no 
  longer 
  conspicuous. 
  The 
  egg 
  now 
  becomes 
  i^ear-shaped, 
  with 
  the 
  polar 
  globule 
  

   at 
  the 
  broad 
  end 
  of 
  the 
  pear, 
  and 
  this 
  end 
  soon 
  divides 
  into 
  two 
  par-ts, 
  so 
  that 
  the 
  

   egg 
  (fig. 
  4, 
  plate 
  viii) 
  is 
  now 
  made 
  of 
  one 
  large 
  mass 
  and 
  two 
  slightly 
  smaller 
  ones^ 
  

   with 
  the 
  polar 
  globule 
  between 
  them. 
  

  

  The 
  later 
  history 
  of 
  the 
  egg 
  shows 
  that 
  at 
  this 
  early 
  stage 
  the 
  egg 
  is 
  not 
  perfectly 
  

   homogeneous, 
  but 
  that 
  the 
  protoplasm 
  which 
  is 
  to 
  give 
  rise 
  to 
  certain 
  organs 
  of 
  the 
  

   body 
  has 
  separated 
  from 
  that 
  which 
  is 
  to 
  give 
  rise 
  to 
  others. 
  

  

  The 
  upper 
  portion 
  of 
  the 
  egg 
  soon 
  divides 
  up 
  into 
  smaller 
  and 
  smaller 
  spherules, 
  

   until 
  at 
  the 
  stage 
  shown 
  in 
  figs. 
  5, 
  6, 
  and 
  7, 
  plate 
  viii, 
  we 
  have 
  a 
  layer 
  of 
  small 
  cells 
  

   wrapped 
  around 
  the 
  greater 
  part 
  of 
  the 
  surface 
  of 
  a 
  single 
  large 
  spherule, 
  and 
  the 
  

   series 
  of 
  figures 
  shows 
  that 
  the 
  latter 
  is 
  the 
  spherule 
  which 
  is 
  below 
  in 
  fig. 
  4, 
  plate 
  viii. 
  

   This 
  spherule 
  now 
  divides 
  up 
  into 
  a 
  layer 
  of 
  cells, 
  and 
  at 
  the 
  same 
  time 
  the 
  egg, 
  or 
  

   rather 
  the 
  embryo, 
  becomes 
  flattened 
  from 
  above 
  downward 
  and 
  assumes 
  the 
  shape 
  

   of 
  a 
  flat 
  oval 
  disk. 
  Figs. 
  10 
  and 
  9, 
  plate 
  viii, 
  are 
  views 
  of 
  the 
  upper 
  and 
  lower 
  surface 
  of 
  

   the 
  embryo 
  at 
  about 
  this 
  time. 
  In 
  a 
  sectional 
  view, 
  fig. 
  11, 
  plate 
  viii, 
  it 
  is 
  seen 
  to 
  be 
  

   made 
  of 
  two 
  layers 
  of 
  cells, 
  an 
  upper 
  layer 
  of 
  small 
  transparent 
  cells, 
  e 
  c, 
  which 
  are 
  

  

  a 
  Ryder, 
  John 
  A.; 
  Fishery 
  Industries 
  of 
  the 
  United 
  States, 
  pp. 
  714-715. 
  

  

  b 
  References 
  to 
  figures 
  in 
  quoted 
  portions 
  of 
  this 
  paper 
  do 
  not 
  correspond 
  with 
  the 
  originals, 
  being 
  

   altered 
  to 
  accord 
  with 
  their 
  sequence 
  in 
  the 
  present 
  article. 
  

  

  