﻿OYSTERS 
  AND 
  METHODS 
  OF 
  OYSTER-CULTURE. 
  287 
  

  

  In 
  most 
  regions 
  which 
  have 
  been 
  investigated 
  the 
  plants 
  coustitnte 
  

   by 
  far 
  the 
  most 
  important 
  item 
  of 
  diet, 
  usually 
  over 
  90 
  per 
  cent 
  of 
  the 
  

   food 
  contents 
  of 
  the 
  stomachs 
  being 
  composed 
  of 
  vegetable 
  matter. 
  

   Of 
  this 
  diatoms 
  are 
  the 
  chief 
  constituents, 
  and 
  to 
  a 
  certain 
  extent 
  the 
  

   food 
  value 
  of 
  any 
  given 
  oyster 
  region 
  may 
  be 
  measured 
  by 
  the 
  quantity 
  

   of 
  these 
  minute 
  plants 
  which 
  it 
  is 
  callable 
  of 
  producing. 
  

  

  Diatoms 
  are 
  numerous 
  both 
  in 
  species 
  and 
  individuals, 
  and 
  all 
  possess 
  

   two 
  interesting 
  peculiarities 
  : 
  They 
  are 
  incased 
  in 
  a 
  siliceous 
  or 
  flinty 
  

   box 
  and 
  they 
  possess 
  the 
  power 
  of 
  locomotion, 
  the 
  first 
  permitting 
  their 
  

   ready 
  identification 
  in 
  the 
  stomach 
  contents 
  and 
  the 
  second 
  aiding 
  in 
  

   their 
  distribution. 
  More 
  or 
  less 
  regular 
  diurnal 
  migrations 
  of 
  swarms 
  

   to 
  and 
  from 
  the 
  surface 
  of 
  the 
  water 
  take 
  place 
  with 
  the 
  variations 
  in 
  

   the 
  light. 
  During 
  sunlight 
  they 
  rise 
  from 
  the 
  bottom, 
  and 
  are 
  then 
  

   readily 
  transported 
  by 
  the 
  currents, 
  again 
  settling 
  down 
  as 
  darkness 
  

   comes 
  on. 
  They 
  feed 
  and 
  grow 
  in 
  size 
  most 
  actively 
  during 
  the 
  day, 
  but 
  

   multiply 
  in 
  number 
  principally 
  at 
  night. 
  Diatoms 
  are 
  important, 
  not 
  

   only 
  in 
  fattening 
  the 
  oyster, 
  but 
  they 
  also 
  have 
  a 
  profound 
  influence 
  

   upon 
  its 
  flavor 
  and 
  color. 
  

  

  The 
  oyster 
  is 
  said 
  to 
  feed 
  mainly 
  during 
  flood 
  tide, 
  opening 
  its 
  shell 
  

   at 
  that 
  time 
  to 
  admit 
  the 
  influx 
  of 
  water 
  with 
  its 
  contained 
  organisms. 
  

   Investigation 
  by 
  Dr. 
  Bashford 
  Dean 
  showed 
  that 
  the 
  stomachs 
  were 
  

   practically 
  foodless 
  in 
  the 
  morning, 
  contained 
  most 
  food 
  at 
  midday, 
  

   and 
  a 
  somewhat 
  reduced 
  quantity 
  at 
  evening, 
  thus 
  suggesting 
  that 
  

   feeding 
  was 
  most 
  active 
  during 
  intense 
  daylight. 
  

  

  Dr. 
  Dean 
  remarks 
  : 
  

  

  This 
  suggestion, 
  as 
  to 
  the 
  feeding 
  habits 
  of 
  the 
  oyster, 
  is 
  not 
  a 
  surprising 
  one 
  

   when 
  we 
  remember 
  that 
  it 
  is 
  during 
  the 
  strongest 
  sunlight 
  than 
  diatoms, 
  as 
  plants 
  

   keenly 
  sensitive 
  to 
  the 
  sun, 
  are 
  most 
  active 
  and 
  are 
  known 
  to 
  migrate 
  in 
  tioating 
  

   clouds 
  from 
  the 
  bottom 
  of 
  the 
  surface. 
  

  

  As 
  is 
  mentioned 
  in 
  the 
  section 
  relating 
  to 
  the 
  anatomy 
  of 
  the 
  oyster, 
  

   the 
  water 
  drawn 
  into 
  the 
  mantle 
  cavity 
  by 
  the 
  action 
  of 
  the 
  cilia 
  is 
  

   filtered 
  through 
  the 
  rectangular 
  openings 
  in 
  the 
  gills 
  into 
  a 
  chamber 
  or 
  

   tube 
  lying 
  above 
  each 
  gill, 
  whence 
  it 
  passes 
  backward 
  and 
  out 
  of 
  the 
  

   shell 
  in 
  a 
  current 
  dorsal 
  to 
  the 
  entering 
  stream. 
  The 
  particles 
  of 
  food 
  

   in 
  the 
  inflowing 
  stream 
  become 
  entrapped 
  in 
  a 
  sticky 
  mucus 
  covering 
  

   the 
  gills, 
  and, 
  together 
  with 
  this 
  mucus, 
  in 
  part, 
  are 
  carried 
  in 
  a 
  steady 
  

   stream 
  toward 
  the 
  mouth, 
  the 
  motion 
  being 
  imparted 
  to 
  the 
  mass 
  by 
  

   the 
  rhythmic 
  action 
  of 
  the 
  cilia. 
  The 
  palps 
  and 
  mouth 
  are 
  also 
  

   ciliated, 
  which 
  insures 
  the 
  continuance 
  of 
  this 
  current 
  into 
  the 
  stomach, 
  

   where 
  the 
  food 
  particles 
  undergo 
  digestion. 
  A 
  very 
  considerable 
  pro- 
  

   portion 
  of 
  inert 
  matter, 
  sand, 
  mnd, 
  etc., 
  of 
  no 
  nutrient 
  value 
  passes 
  into 
  

   the 
  alimentary 
  tract 
  along 
  with 
  the 
  food, 
  the 
  oyster 
  having 
  no 
  means 
  

   of 
  making 
  selection. 
  

  

  The 
  temperature, 
  depth, 
  and 
  density 
  of 
  the 
  water 
  have 
  considerable 
  

   effect 
  ui)on 
  the 
  food 
  supply. 
  In 
  clear, 
  warm 
  weather 
  the 
  amount 
  of 
  

   food 
  matter 
  is 
  increased 
  by 
  the 
  natural 
  multiplication 
  of 
  the 
  minute 
  

  

  