﻿OYSTERS 
  AND 
  METHODS 
  OF 
  OYSTER-CULTUKE. 
  273 
  

  

  of 
  different 
  character, 
  the 
  outer 
  brownish, 
  with 
  a 
  friable 
  prismatic 
  structure, 
  the 
  

   inner 
  dense 
  and 
  nacreous. 
  In 
  the 
  larva 
  there 
  is 
  no 
  such 
  distinction, 
  and 
  the 
  whole 
  

   shell 
  consists 
  of 
  a 
  glassy 
  substance 
  devoid 
  of 
  any 
  definite 
  structure. 
  

  

  The 
  hinge 
  line 
  answers, 
  as 
  in 
  the 
  adult, 
  to 
  the 
  dorsal 
  side 
  of 
  the 
  body. 
  On 
  the 
  

   opposite 
  or 
  ventral 
  side 
  the 
  wide 
  mouth 
  m 
  and 
  the 
  minute 
  vent 
  v 
  are 
  seen 
  at 
  no 
  

   great 
  distance 
  from 
  one 
  another. 
  Projecting 
  from 
  the 
  front 
  part 
  of 
  the 
  aperture 
  of 
  

   the 
  shell 
  therii 
  is 
  a 
  sort 
  of 
  outgrowtli 
  of 
  the 
  integument 
  of 
  what 
  we 
  may 
  call 
  the 
  bai'k 
  

   of 
  the 
  neck 
  into 
  a 
  large 
  oval 
  thick-rimnied 
  disk 
  termed 
  the 
  velum, 
  vl, 
  the 
  middle 
  of 
  

   which 
  presents 
  a 
  more 
  or 
  less 
  mai'ked 
  prominence. 
  The 
  rim 
  of 
  the 
  disk 
  is 
  lined 
  with 
  

   long 
  vibratilo 
  cilia, 
  and 
  it 
  is 
  the 
  lashing 
  of 
  these 
  cilia 
  which 
  propels 
  the 
  animal, 
  and, 
  

   in 
  the 
  absence 
  of 
  gills, 
  jirobably 
  subserves 
  respiration. 
  The 
  funnel-shaped 
  mouth 
  

   has 
  no 
  palps; 
  it 
  leads 
  into 
  a 
  wide 
  gullet, 
  and 
  this 
  into 
  a 
  capacious 
  stomach. 
  A 
  

   sac-like 
  process 
  of 
  the 
  stomach 
  on 
  either 
  side 
  (the 
  left 
  one, 
  ?, 
  only 
  is 
  shown 
  in 
  iig. 
  2) 
  

   represents 
  the 
  "liver." 
  The 
  narrow 
  intestine 
  is 
  already 
  partially 
  coiled 
  on 
  itself, 
  and 
  

   this 
  is 
  the 
  only 
  departure 
  from 
  perfect 
  bilateral 
  symmetry 
  in 
  the 
  whole 
  body 
  of 
  the 
  

   animal. 
  The 
  alimentary 
  canal 
  is 
  lined 
  throughout 
  with 
  ciliated 
  cells, 
  and 
  the 
  vibra- 
  

   tion 
  of 
  these 
  cilia 
  is 
  the 
  means 
  by 
  which 
  the 
  minute 
  bodies 
  which 
  serve 
  the 
  larva 
  for 
  

   food 
  are 
  drawn 
  into 
  the 
  digestive 
  cavity. 
  

  

  There 
  are 
  two 
  pairs 
  of 
  delicate 
  longitudinal 
  muscles, 
  rs 
  ri, 
  which 
  are 
  competent 
  to 
  

   draw 
  back 
  the 
  ciliated 
  velum 
  into 
  the 
  cavity 
  of 
  the 
  shell, 
  when 
  the 
  animal 
  at 
  once 
  

   sinks. 
  The 
  complete 
  closure 
  of 
  the 
  valves 
  is 
  effected, 
  as 
  in 
  the 
  adult, 
  by 
  an 
  adductor 
  

   muscle, 
  am, 
  the 
  fibers 
  of 
  which 
  pass 
  from 
  one 
  valve 
  to 
  the 
  other. 
  But 
  it 
  is 
  a 
  very 
  

   curious 
  circumstance 
  that 
  this 
  adductor 
  muscle 
  is 
  not 
  the 
  same 
  as 
  that 
  which 
  exists 
  

   in 
  the 
  adult. 
  It 
  lies, 
  in 
  fact, 
  iu 
  the 
  forepart 
  of 
  the 
  body 
  and 
  on 
  the 
  dorsal 
  side 
  of 
  

   the 
  alimentary 
  canal. 
  The 
  great 
  muscle 
  of 
  the 
  adult, 
  fig. 
  3, 
  M, 
  on 
  the 
  other 
  hand, 
  

   lies 
  on 
  the 
  ventral 
  side 
  of 
  the 
  alimentary 
  canal 
  and 
  in 
  the 
  hinder 
  part 
  of 
  the 
  body. 
  

   And 
  as 
  the 
  muscles, 
  respectively, 
  lie 
  on 
  opposite 
  sides 
  of 
  the 
  alimentary 
  canal, 
  that 
  

   of 
  the 
  adult 
  can 
  not 
  be 
  that 
  of 
  the 
  larva, 
  which 
  has 
  merely 
  shifted 
  its 
  position; 
  for 
  

   in 
  order 
  to 
  get 
  from 
  one 
  side 
  of 
  the 
  alimentary 
  canal 
  to 
  the 
  other 
  it 
  must 
  needs 
  cut 
  

   through 
  that 
  organ; 
  but 
  as 
  in 
  the 
  adult 
  no 
  adductor 
  muscle 
  is 
  discoverable 
  in 
  the 
  

   position 
  occupied 
  by 
  that 
  of 
  the 
  larva 
  or 
  anywhere 
  on 
  the 
  dorsal 
  side 
  of 
  the 
  aliment- 
  

   ary 
  canal, 
  while 
  on 
  the 
  other 
  hand 
  there 
  is 
  no 
  trace 
  of 
  any 
  adductor 
  on 
  the 
  ventral 
  

   side 
  in 
  the 
  larva, 
  it 
  follows 
  that 
  the 
  dorsal 
  or 
  anterior 
  adductor 
  of 
  the 
  larva 
  must 
  

   vanish 
  in 
  the 
  course 
  of 
  development, 
  and 
  that 
  a 
  new 
  ventral 
  or 
  posterior 
  adductor 
  

   must 
  be 
  developed 
  to 
  play 
  the 
  same 
  part 
  and 
  replace 
  the 
  original 
  muscle 
  functionally, 
  

  

  though 
  not 
  morphologically. 
  , 
  

  

  # 
  X 
  * 
  * 
  # 
  # 
  # 
  

  

  When 
  the 
  free 
  larva 
  of 
  the 
  oyster 
  settles 
  down 
  into 
  the 
  fixed 
  state, 
  the 
  left 
  lobe 
  of 
  

   the 
  mantle 
  stretches 
  beyond 
  its 
  valve, 
  and, 
  applying 
  itself 
  to 
  the 
  surface 
  of 
  the 
  stone 
  

   or 
  shell 
  to 
  which 
  the 
  valve 
  is 
  to 
  adhere, 
  secretes 
  shelly 
  matter, 
  which 
  serves 
  to 
  cement 
  

   the 
  valve 
  to 
  its 
  support. 
  As 
  the 
  animal 
  grows 
  the 
  mantle 
  deposits 
  new 
  layers 
  of 
  

   shell 
  over 
  its 
  whole 
  surface, 
  so 
  that 
  the 
  larval 
  shell 
  valves 
  become 
  separated 
  from 
  

   the 
  mantle 
  by 
  the 
  new 
  layers 
  (plate 
  viii, 
  fig. 
  3, 
  S), 
  which 
  crop 
  out 
  beyond 
  their 
  

   margins 
  and 
  acquire 
  the 
  characteristic 
  prismatic 
  and 
  nacreous 
  structure. 
  The 
  sum 
  

   mits 
  of 
  the 
  outer 
  faces 
  of 
  the 
  umbones 
  thus 
  correspond 
  with 
  the 
  places 
  of 
  the 
  larval 
  

   valves, 
  which 
  soon 
  cease 
  to 
  be 
  discernible. 
  After 
  a 
  time 
  the 
  body 
  becomes 
  convex 
  

   on 
  the 
  left 
  side 
  and 
  flat 
  on 
  the 
  right 
  ; 
  the 
  successively 
  added 
  new 
  layers 
  of 
  shell 
  mold 
  

   themselves 
  upon 
  it, 
  and 
  the 
  animal 
  acquires 
  the 
  asymmetry 
  characteristic 
  of 
  the 
  

   adult.* 
  

  

  The 
  lioriiy 
  convex 
  shell 
  of 
  the 
  fry 
  (plate 
  viii, 
  fig. 
  3, 
  L) 
  may 
  be 
  seen, 
  for 
  

   a 
  considerable 
  time 
  after 
  attachment, 
  at 
  the 
  umbo 
  or 
  beak 
  of 
  the 
  develoi)- 
  

   ing- 
  shell 
  of 
  the 
  spat 
  (plate 
  viii, 
  fig. 
  3, 
  S). 
  The 
  under 
  or 
  attached 
  valve 
  of 
  

   the 
  latter 
  at 
  first 
  conforms 
  closely 
  to 
  the 
  surface 
  to 
  which 
  it 
  has 
  become 
  

  

  * 
  Huxley, 
  Thomas 
  H. 
  Oysters 
  and 
  the 
  Oyster 
  Question. 
  The 
  English 
  Illustrated 
  

   Magazine, 
  London, 
  Oct. 
  1883 
  and 
  Nov. 
  1883, 
  vol. 
  1, 
  pp. 
  4:7-55, 
  and 
  pp. 
  112-121. 
  

  

  F. 
  C. 
  R. 
  1897 
  18 
  

  

  