﻿274 
  REPORT 
  OF 
  COMMISSIONER 
  OP 
  FISH 
  AND 
  FISHERIES 
  

  

  attached, 
  being 
  usually 
  flat, 
  but 
  afterwards, 
  as 
  a 
  rule, 
  becomiug 
  deep 
  

   and 
  strongly 
  concave, 
  through 
  an 
  upgrowing 
  along 
  the 
  edges. 
  

  

  FIXATION, 
  SET, 
  OR 
  SPATTING. 
  

  

  At 
  the 
  time 
  of 
  fixation 
  the 
  fry 
  will, 
  under 
  proper 
  conditions, 
  attach 
  

   itself 
  by 
  its 
  left 
  valve 
  to 
  any 
  hard 
  or 
  firm 
  body 
  with 
  which 
  it 
  may 
  come 
  

   in 
  contact. 
  

  

  The 
  first 
  essential 
  is 
  that 
  the 
  surface 
  should 
  be 
  clean 
  and 
  that 
  it 
  

   should 
  remain 
  so 
  a 
  sufiQcient 
  length 
  of 
  time 
  to 
  enable 
  the 
  young 
  oyster 
  

   to 
  firmly 
  establish 
  itself. 
  So 
  long 
  as 
  this 
  condition 
  obtains, 
  the 
  nature 
  

   of 
  the 
  material 
  seems 
  to 
  matter 
  but 
  little. 
  In 
  most 
  bodies 
  of 
  water 
  the 
  

   spat 
  fixes 
  itself 
  at 
  all 
  levels 
  from 
  the 
  surface 
  to 
  the 
  bottom, 
  but 
  in 
  cer- 
  

   tain 
  parts 
  of 
  the 
  coast 
  its 
  place 
  of 
  attachment 
  is 
  confined 
  to 
  the 
  zone 
  

   between 
  high 
  and 
  low 
  water, 
  the 
  mid-tide 
  mark 
  being 
  the 
  place 
  of 
  max- 
  

   imum 
  fixation. 
  It 
  has 
  been 
  suggested 
  that 
  this 
  was 
  due 
  to 
  the 
  density 
  

   of 
  the 
  water 
  i)reventing 
  the 
  sinking 
  of 
  the 
  fry. 
  There 
  are 
  a 
  number 
  

   of 
  objections 
  to 
  this 
  theory, 
  but 
  no 
  better 
  one 
  has 
  been 
  offered, 
  and 
  it 
  

   may 
  receive 
  provisional 
  acceptance. 
  

  

  GROWTH. 
  

  

  At 
  the 
  time 
  of 
  its 
  attachment 
  the 
  oyster 
  fry 
  measures 
  about 
  one- 
  

   eightieth 
  or 
  one-ninetieth 
  of 
  an 
  inch 
  in 
  diameter. 
  The 
  valves 
  of 
  the 
  

   shell 
  are 
  strongly 
  convex 
  and 
  symmetrical, 
  and 
  are 
  composed 
  of 
  a 
  

   horny 
  material 
  quite 
  different 
  from 
  the 
  finished 
  shell 
  of 
  the 
  adult. 
  

  

  The 
  mantle, 
  a 
  thin 
  flap 
  of 
  tissue 
  which 
  envelops 
  the 
  body 
  of 
  the 
  

   oyster 
  on 
  each 
  side, 
  projects 
  freely 
  from 
  between 
  the 
  lips 
  of 
  the 
  valves 
  

   and 
  is 
  the 
  organ 
  which 
  secretes 
  the 
  shell. 
  Upon 
  its 
  outer 
  surface 
  suc- 
  

   cessive 
  layers 
  of 
  horny 
  material 
  are 
  laid 
  down, 
  these 
  becoming 
  impreg- 
  

   nated 
  with 
  calcareous 
  matter 
  arranged 
  in 
  a 
  prismatic 
  manner, 
  and 
  thus 
  

   forming 
  the 
  stony 
  shell 
  which 
  characterizes 
  the 
  adult. 
  

  

  The 
  mantle 
  increases 
  pari 
  passu 
  with 
  the 
  growth 
  of 
  the 
  soft 
  parts 
  in 
  

   general, 
  and 
  as 
  it 
  is 
  always 
  capable 
  of 
  protrusion 
  a 
  little 
  beyond 
  the 
  lips 
  

   of 
  the 
  valves, 
  it 
  follows 
  that 
  each 
  successive 
  layer 
  of 
  shell 
  is 
  slightly 
  

   larger 
  than 
  that 
  which 
  preceded 
  it, 
  and 
  the 
  shell 
  increases 
  in 
  length 
  

   and 
  breadth 
  as 
  well 
  as 
  in 
  thickness. 
  From 
  the 
  nature 
  of 
  its 
  growth, 
  

   therefore, 
  the 
  youngest 
  or 
  newest 
  part 
  of 
  the 
  shell 
  is 
  on 
  the 
  inner 
  face 
  

   and 
  at 
  the 
  edges, 
  the 
  latter 
  always 
  being 
  sharp 
  and 
  thin 
  in 
  a 
  growing 
  

   oyster. 
  The 
  shell 
  of 
  the 
  young 
  oyster 
  is 
  always 
  thin 
  and 
  delicate, 
  and 
  

   is 
  generally 
  more 
  rounded 
  than 
  in 
  the 
  adult. 
  The 
  lower 
  valve 
  at 
  first 
  

   adheres 
  closely 
  to 
  the 
  body 
  to 
  which 
  it 
  is 
  attached, 
  but 
  later 
  its 
  edge 
  

   grows 
  free 
  and 
  the 
  valve, 
  as 
  a 
  whole, 
  becomes 
  deeper 
  and 
  more 
  capa- 
  

   cious 
  than 
  its 
  fellow. 
  The 
  small 
  larval 
  or 
  fry 
  shell 
  remains 
  visible 
  at 
  

   the 
  beak 
  of 
  the 
  spat 
  shell 
  for 
  a 
  considerable 
  time, 
  but 
  becomes 
  eroded 
  

   away 
  before 
  the 
  oyster 
  reaches 
  the 
  adult 
  condition. 
  

  

  The 
  soft 
  parts 
  of 
  the 
  oyster 
  assume 
  their 
  adult 
  form 
  in 
  general 
  soon 
  

   after 
  attachment, 
  although 
  the 
  genital 
  glands 
  do 
  not 
  become 
  functional 
  

   until 
  a 
  much 
  later 
  period. 
  

  

  