﻿OYSTER 
  INDUSTRY 
  OF 
  NORTH 
  CAROLINA. 
  323 
  

  

  lu 
  other 
  laraellibranchs, 
  and 
  doubtless 
  also 
  in 
  the 
  03^stel•, 
  the 
  shell 
  

   beg-ins 
  as 
  a 
  deposit 
  in 
  an 
  invagination 
  or 
  pocket 
  on 
  the 
  dorsal 
  side 
  of 
  

   the 
  body. 
  In 
  its 
  manner 
  of 
  formation 
  this 
  shell 
  gland 
  resembles 
  the 
  

   primitive 
  mouth 
  for 
  which 
  it 
  has 
  been 
  more 
  than 
  once 
  mistaken 
  by 
  

   investigators. 
  In 
  some 
  forms 
  the 
  shell 
  is 
  at 
  first 
  single, 
  but 
  in 
  the 
  

   03^ster 
  the 
  two 
  are 
  said 
  to 
  be 
  separated 
  from 
  each 
  other 
  from 
  the 
  begin- 
  

   ning, 
  and 
  appear 
  independently. 
  Doctor 
  Brooks 
  says 
  further: 
  

  

  Soon 
  after 
  they 
  make 
  their 
  appearance, 
  the 
  embryos 
  cease 
  to 
  crowd 
  to 
  the 
  surface 
  

   of 
  the 
  water 
  and 
  sink 
  to 
  various 
  depths, 
  although 
  they 
  continue 
  to 
  swim 
  actively 
  in 
  

   all 
  directions, 
  and 
  may 
  still 
  be 
  found 
  occasionally 
  close 
  to 
  the 
  surface. 
  The 
  region 
  

   of 
  the 
  body 
  which 
  carries 
  the 
  cilia 
  now 
  becomes 
  sharply 
  defined, 
  as 
  a 
  circular 
  pro- 
  

   jecting 
  pad, 
  the 
  velum, 
  and 
  this 
  is 
  present 
  and 
  is 
  the 
  organ 
  of 
  locomotion 
  at 
  a 
  much 
  

   later 
  stage 
  of 
  development. 
  It 
  is 
  shown 
  at 
  the 
  right 
  side 
  of 
  the 
  figure 
  in 
  plate 
  vxii, 
  

   fig. 
  17, 
  and 
  in 
  fig. 
  18, 
  plate 
  viir, 
  it 
  is 
  seen 
  in 
  surface 
  view, 
  drawn 
  in 
  between 
  the 
  

   shells, 
  and 
  with 
  its 
  cilia 
  folded 
  down 
  and 
  at 
  rest, 
  as 
  they 
  are 
  seen 
  when 
  the 
  little 
  

   oj'ster 
  lies 
  upon 
  the 
  bottom. 
  

  

  The 
  two 
  shells 
  grow 
  rapidly, 
  and 
  soon 
  become 
  quite 
  regular 
  in 
  outline, 
  as 
  shown 
  

   in 
  plate 
  viir, 
  fig. 
  17, 
  and 
  plate 
  ix, 
  fig. 
  1, 
  but 
  for 
  some 
  time 
  they 
  are 
  much 
  smaller 
  

   than 
  the 
  body, 
  which 
  projects 
  from 
  between 
  their 
  edges 
  around 
  their 
  whole 
  circum- 
  

   ference, 
  except 
  that 
  along 
  a 
  short 
  area, 
  the 
  area 
  of 
  the 
  hinge 
  upon 
  the 
  dorsal 
  surface, 
  

   where 
  the 
  two 
  valves 
  are 
  in 
  contact. 
  . 
  

  

  The 
  two 
  shells 
  continue 
  to 
  grow 
  at 
  their 
  edges, 
  and 
  soon 
  become 
  large 
  enough 
  to 
  

   cover 
  up 
  and 
  i^roject 
  a 
  little 
  beyond 
  the 
  surface 
  of 
  the 
  body, 
  as 
  shown 
  in 
  plate 
  ix, 
  

   fig. 
  1, 
  and 
  at 
  the 
  ^'ame 
  time 
  muscular 
  fibers 
  make 
  their 
  appearance 
  and 
  are 
  so 
  

   arranged 
  that 
  they 
  can 
  draw 
  the 
  edge 
  of 
  the 
  body 
  and 
  the 
  velum 
  in 
  between 
  the 
  

   edges 
  of 
  the 
  shells 
  in 
  the 
  manner 
  shown 
  in 
  plate 
  viii, 
  fig. 
  18. 
  In 
  this 
  way 
  that 
  sur- 
  

   face 
  of 
  the 
  body 
  which 
  lines 
  the 
  shell 
  becomes 
  converted 
  into 
  the 
  two 
  lobes 
  of 
  the 
  

   mantle, 
  and 
  between 
  them 
  a 
  mantle 
  cavity 
  ia 
  formed, 
  into 
  which 
  the 
  velum 
  can 
  be 
  

   drawn 
  when 
  the 
  animal 
  is 
  at 
  rest. 
  While 
  these 
  changes 
  have 
  been 
  going 
  on 
  over 
  

   the 
  outer 
  surface 
  of 
  the 
  body 
  other 
  important 
  internal 
  modifications 
  have 
  taken 
  

   place. 
  We 
  left 
  the 
  digestive 
  tract 
  at 
  the 
  stage 
  shown 
  in 
  plate 
  viii, 
  fig. 
  16, 
  without 
  

   any 
  communication 
  with 
  the 
  exterior. 
  

  

  Soon 
  the 
  outer 
  wall 
  of 
  the 
  body 
  becomes 
  pushed 
  inward 
  to 
  form 
  the 
  true 
  mouth, 
  

   at 
  a 
  point 
  (plate 
  viir, 
  fig. 
  17) 
  which 
  is 
  upon 
  the 
  ventral 
  surface 
  and 
  almost 
  directly 
  

   opposite 
  the 
  point 
  where 
  the 
  primitive 
  mouth 
  was 
  situated 
  at 
  an 
  earlier 
  stage. 
  The 
  

   digestive 
  cavity 
  now 
  becomes 
  greatly 
  enlarged 
  and 
  cilia 
  make 
  their 
  appearance 
  upon 
  

   its 
  walls, 
  the 
  mouth 
  becomes 
  connected 
  with 
  the 
  chamber 
  which 
  is 
  thus 
  formed 
  and 
  

   which 
  becomes 
  the 
  stomach, 
  and 
  minute 
  particles 
  of 
  food 
  are 
  drawn 
  in 
  by 
  the 
  cilia 
  

   and 
  can 
  now 
  be 
  seen 
  inside 
  the 
  stomach, 
  where 
  the 
  vibration 
  of 
  the 
  cilia 
  keep 
  them 
  

   in 
  constant 
  motion. 
  Up 
  to 
  this 
  time 
  the 
  animal 
  has 
  developed 
  without 
  growing, 
  

   and 
  at 
  the 
  stage 
  shown 
  in 
  plate 
  viii, 
  fig. 
  16, 
  it 
  is 
  scarcely 
  larger 
  than 
  the 
  unfertilized 
  

   egg, 
  but 
  it 
  now 
  begins 
  to 
  increase 
  in 
  size. 
  The 
  stages 
  shown 
  in 
  plate 
  ix, 
  fig. 
  1, 
  and 
  

   plate 
  VIII, 
  fig. 
  18, 
  agree 
  pretty 
  closely 
  Avith 
  the 
  figures 
  which 
  the 
  European 
  embry- 
  

   ologists 
  give 
  of 
  the 
  oyster 
  embryo 
  at 
  the 
  time 
  when 
  it 
  escapes 
  from 
  the 
  mantle 
  

   chamber 
  of 
  its 
  parent. 
  The 
  American 
  oyster 
  reaches 
  this 
  stage 
  in 
  from 
  twenty-four 
  

   hours 
  to 
  six 
  days 
  after 
  the 
  egg 
  is 
  fertilized, 
  the 
  rate 
  of 
  development 
  being 
  deter- 
  

   mined 
  mainly 
  by 
  the 
  temperature 
  of 
  the 
  water. 
  

  

  Soon 
  after 
  the 
  mantle 
  has 
  become 
  connected 
  with 
  the 
  stomach 
  this 
  becomes 
  united 
  

   to 
  the 
  body 
  wall 
  at 
  another 
  point 
  a 
  little 
  behind 
  the 
  mantle, 
  and 
  a 
  second 
  opening, 
  

   tlie 
  anus, 
  is 
  formed. 
  The 
  tract, 
  which 
  connects 
  the 
  anus 
  with 
  the 
  stomach, 
  lengthens 
  

   and 
  forms 
  the 
  intestine, 
  and 
  soon 
  after 
  the 
  sides 
  of 
  the 
  stomach 
  become 
  folded 
  off 
  

   to 
  form 
  the 
  two 
  halves 
  of 
  the 
  liver, 
  as 
  shown 
  in 
  plate 
  ix, 
  fig. 
  L 
  Various 
  muscular 
  

  

  