﻿OYSTERS 
  AND 
  METHODS 
  OF 
  OYSTER-CULTURE. 
  279 
  

  

  intestine, 
  where 
  there 
  is 
  a 
  marked 
  constriction 
  of 
  the 
  alimentary 
  canal. 
  It 
  appears, 
  

   therefore, 
  to 
  be 
  a 
  sort 
  of 
  loose 
  valve 
  in 
  the 
  cavity 
  of 
  the 
  gut; 
  its 
  function 
  may 
  be 
  to 
  

   prevent 
  coarse 
  particles 
  of 
  food 
  from 
  passing 
  or 
  it 
  may 
  in 
  someway 
  assist 
  digestion. 
  

   In 
  specimens 
  hardened 
  in 
  acid 
  or 
  alcohol 
  this 
  rod 
  is 
  destroyed, 
  or 
  at 
  least 
  disappears, 
  

   so 
  that 
  I 
  have 
  been 
  unable 
  to 
  find 
  it. 
  The 
  greater 
  portion 
  of 
  its 
  substance 
  is 
  appar- 
  

   ently 
  made 
  up 
  of 
  water. 
  

  

  The 
  peculiar 
  double 
  indnplication 
  of 
  the 
  wall 
  of 
  the 
  intestine 
  is 
  described 
  in 
  

   another 
  place. 
  The 
  fecal 
  matters 
  are 
  extruded 
  in 
  the 
  form 
  of 
  a 
  demi-cylinder, 
  with 
  

   one 
  side 
  excavated 
  in 
  a 
  groove-like 
  manner. 
  This 
  shape 
  of 
  the 
  fecal 
  matters 
  is 
  due 
  

   to 
  the 
  presence 
  of 
  the 
  double 
  fold. 
  The 
  feces 
  themselves 
  are 
  composed 
  of 
  extremely 
  

   fine 
  particles 
  of 
  quartz 
  or 
  sand 
  grains, 
  the 
  tests 
  of 
  diatoms, 
  organic 
  matters, 
  humus, 
  

   cellulose, 
  fragments 
  of 
  the 
  chitinous 
  coverings 
  of 
  some 
  of 
  the 
  minute 
  worms 
  and 
  

   articulates, 
  etc., 
  which 
  have 
  been 
  swallowed 
  and 
  digested 
  by 
  the 
  animal. 
  The 
  anus, 
  r, 
  

   is 
  situated 
  on 
  the 
  dorsal 
  side 
  of 
  the 
  great 
  adductor 
  muscle 
  where 
  the 
  intestine 
  ends. 
  

  

  The 
  organs 
  of 
  sensation 
  of 
  the 
  oyster, 
  though 
  not 
  very 
  highly 
  developed, 
  are 
  of 
  

   sufiicient 
  importance 
  to 
  merit 
  attention. 
  The 
  auditorj' 
  sense, 
  although 
  I 
  have 
  never 
  

   been 
  able 
  to 
  dissect 
  out 
  the 
  auditory 
  vesicles, 
  I 
  am 
  satisfied 
  exists, 
  because 
  one 
  can 
  

   not 
  noisily 
  approach 
  an 
  oyster 
  bank 
  where 
  the 
  oysters 
  are 
  feeding 
  without 
  their 
  

   hearing 
  so 
  that 
  instantly 
  every 
  shell 
  is 
  closed. 
  The 
  tentacles 
  of 
  the 
  mantle 
  are 
  often 
  

   extended 
  until 
  their 
  tips 
  reach 
  beyond 
  the 
  edges 
  of 
  the 
  valves. 
  If 
  the 
  animal 
  in 
  

   this 
  condition 
  is 
  exposed 
  to 
  a 
  strong 
  light 
  the 
  shadow 
  of 
  the 
  hand 
  passing 
  over 
  it 
  is 
  

   a 
  sufficient 
  stimulus 
  to 
  cause 
  it 
  to 
  retract 
  the 
  mantle 
  and 
  tentacles 
  and 
  to 
  close 
  its 
  

   parted 
  valves. 
  The 
  mantle 
  incloses, 
  like 
  a 
  curtain, 
  the 
  internal 
  organs 
  of 
  the 
  crea- 
  

   ture 
  on 
  either 
  side, 
  and 
  lies 
  next 
  the 
  shell, 
  and, 
  as 
  already 
  stated, 
  secretes 
  and 
  

   deposits 
  the 
  layers 
  of 
  calcic 
  carbonate 
  composing 
  the 
  latter. 
  The 
  free 
  edges 
  of 
  the 
  

   mantle, 
  which 
  are 
  purplish, 
  are 
  garnished 
  with 
  small, 
  highly 
  sensitive 
  tentacles 
  of 
  

   the 
  same 
  color. 
  These 
  tentacles 
  are 
  ciliated 
  and 
  serve 
  as 
  organs 
  of 
  touch, 
  and 
  also 
  

   appear 
  to 
  be 
  to 
  some 
  extent 
  sensitive 
  to 
  light. 
  

  

  The 
  nervous 
  system 
  of 
  the 
  oyster 
  is 
  very 
  simple, 
  and, 
  as 
  elsewhere 
  stated, 
  is 
  to 
  

   some 
  extent 
  degenerate 
  in 
  character. 
  It 
  is 
  composed 
  of 
  a 
  pair 
  of 
  ganglia 
  or 
  knots 
  of 
  

   nervous 
  matter, 
  plate 
  i, 
  fig. 
  1, 
  sg, 
  which 
  lie 
  just 
  over 
  the 
  gullet, 
  and 
  from 
  these 
  a 
  pair 
  

   of 
  nervous 
  cords, 
  d, 
  pass 
  backward, 
  one 
  on 
  each 
  side, 
  to 
  join 
  the 
  hinder 
  pair 
  which 
  lie 
  

   just 
  beneath 
  the 
  adductor 
  muscle, 
  }> 
  9- 
  The 
  mantle 
  receives 
  nerve 
  branches 
  from 
  the 
  

   hindmost 
  ganglia 
  or 
  knots 
  of 
  nervous 
  matter; 
  these, 
  as 
  their 
  centers, 
  control 
  the 
  

   contraction 
  and 
  elongation 
  of 
  the 
  radiating 
  bundle 
  of 
  muscular 
  fibers, 
  as 
  well 
  as 
  

   those 
  which 
  lie 
  lengthwise 
  along 
  the 
  margin 
  ; 
  the 
  former 
  contract 
  and 
  withdraw 
  the 
  

   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 
  orgnns 
  are 
  innervated 
  from 
  

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

   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.* 
  

  

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

  

  