﻿OYSTERS 
  AND 
  METHODS 
  OF 
  OYSTER-CULTURE. 
  267 
  

  

  margin 
  than 
  to 
  the 
  hinge; 
  it 
  is 
  a 
  well-defined 
  scar, 
  kidney-shaped 
  in 
  

   specimens 
  of 
  ordinary 
  size, 
  but 
  becoming 
  more 
  elongate 
  in 
  very 
  large 
  

   individuals; 
  in 
  young 
  specimens 
  it 
  is 
  pale, 
  but 
  it 
  afterwards 
  becomes 
  

   l)urple 
  or 
  almost 
  black. 
  The 
  left 
  or 
  lower 
  valve 
  is 
  deeply 
  concave 
  

   within, 
  the 
  upper 
  valve 
  being 
  flat 
  or, 
  usually, 
  slightly 
  concave. 
  The 
  

   animal 
  portions 
  are 
  large, 
  nearly 
  filling 
  the 
  shell, 
  and 
  the 
  mantle 
  border 
  

   is 
  comparatively 
  narrow. 
  (Plate 
  v.) 
  

  

  PACIFIC 
  COAST 
  "NATIVE," 
  OSTREA 
  LURID 
  A. 
  

  

  The 
  shell 
  of 
  this 
  species 
  is 
  thin 
  and 
  irregular, 
  varying 
  in 
  shape 
  from 
  

   almost 
  round 
  to 
  elongate 
  elliptical; 
  the 
  surface 
  is 
  sometimes 
  laminated, 
  

   but 
  is 
  never 
  ribbed; 
  the 
  color 
  is 
  variable, 
  being 
  sometimes 
  purple, 
  

   sometimes 
  dirty 
  green 
  or 
  gray; 
  the 
  inside 
  of 
  the 
  shell 
  is 
  greenish, 
  

   sometimes 
  tinged 
  with 
  purjile. 
  The 
  muscular 
  imi)ressiou 
  or 
  scar 
  is 
  

   purple, 
  but 
  paler 
  than 
  in 
  the 
  eastern 
  oyster, 
  and 
  its 
  greatest 
  length 
  is 
  

   usually 
  longitudinal 
  rather 
  than 
  transverse; 
  it 
  is 
  situated 
  about 
  mid- 
  

   way 
  between 
  the 
  hinge 
  and 
  the 
  lips 
  or 
  nibs 
  of 
  the 
  shell, 
  and 
  its 
  ventral 
  

   margin 
  is 
  usually 
  prolonged 
  toward 
  the 
  hinge. 
  There 
  is 
  rarely 
  a 
  well- 
  

   defined 
  pit 
  or 
  excavation 
  beneath 
  the 
  hinge, 
  the 
  inner 
  face 
  of 
  the 
  shell 
  

   sloping 
  off 
  gently 
  from 
  the 
  ligament. 
  The 
  lower 
  valve 
  is 
  deeper 
  than 
  

   the 
  upper 
  one, 
  but 
  is 
  rarely 
  so 
  strongly 
  concave 
  as 
  in 
  the 
  eastern 
  

   species. 
  (Plate 
  vi.) 
  

  

  REPRODUCTION 
  AND 
  DEVELOPMENT. 
  

   SEXUAL 
  CHARACTERISTICS. 
  

  

  In 
  the 
  European 
  oyster 
  the 
  individuals 
  are 
  hermaphrodites 
  — 
  that 
  is, 
  

   each 
  is 
  both 
  male 
  and 
  female; 
  in 
  the 
  common 
  eastern 
  oyster 
  the 
  sexes 
  

   are 
  sei)arate, 
  each 
  individual 
  being 
  either 
  male 
  or 
  female, 
  but 
  not 
  both. 
  

  

  Although 
  the 
  sexes 
  difier 
  remarkably 
  in 
  physiology 
  and 
  minute 
  

   anatomy, 
  it 
  is 
  not 
  possible 
  to 
  distinguish 
  male 
  from 
  female 
  by 
  any 
  

   known 
  external 
  characters. 
  It 
  is 
  only 
  by 
  an 
  examination 
  of 
  the 
  genital 
  

   glands, 
  which 
  in 
  the 
  male 
  produce 
  the 
  spermatozoa 
  or 
  milt 
  and 
  in 
  the 
  

   female 
  the 
  ova, 
  eggs, 
  or 
  spawn, 
  or 
  by 
  examining 
  the 
  genital 
  products 
  

   themselves, 
  that 
  the 
  one 
  sex 
  may 
  be 
  distinguished 
  from 
  the 
  other. 
  

  

  The 
  difl^erences 
  between 
  the 
  ovaries 
  of 
  the 
  female 
  and 
  the 
  testes 
  of 
  

   the 
  male 
  are 
  explained 
  in 
  the 
  section 
  treating 
  of 
  the 
  anatomy. 
  When 
  

   the 
  animals 
  are 
  ripe, 
  the 
  distinction 
  of 
  the 
  sexes 
  is 
  most 
  conveniently 
  

   made 
  by 
  an 
  examination 
  of 
  the 
  genital 
  products. 
  A 
  drop 
  of 
  genital 
  

   fluid 
  is 
  extracted 
  from 
  the 
  oyster 
  in 
  the 
  manner 
  described 
  under 
  the 
  

   head 
  of 
  artificial 
  fertilization 
  (p. 
  332) 
  and 
  let 
  fall 
  into 
  a 
  glass 
  of 
  clear 
  

   sea 
  water. 
  If 
  the 
  individual 
  be 
  a 
  ripe 
  female, 
  the 
  drop 
  will 
  break 
  up 
  

   into 
  a 
  uniformly 
  distributed 
  cloud, 
  which, 
  if 
  examined 
  against 
  a 
  black 
  

   background, 
  will 
  be 
  seen 
  to 
  consist 
  of 
  separate 
  minute 
  white 
  granules 
  

   or 
  eggs. 
  If 
  the 
  eggs 
  be 
  unrii)e, 
  they 
  will 
  remain 
  aggregated 
  in 
  little 
  

   compound 
  masses. 
  If 
  the 
  specimen 
  examined 
  be 
  a 
  male, 
  the 
  drop 
  of 
  

   milt 
  will 
  form 
  an 
  irregular, 
  stringy 
  cloud, 
  showing 
  a 
  tendency 
  to 
  drift 
  in 
  

  

  