﻿shell 
  again. 
  As 
  the 
  stream 
  of 
  water 
  passes 
  through 
  the 
  gills 
  

   the 
  blood 
  is 
  aerated 
  by 
  contact 
  with 
  it. 
  The 
  food 
  of 
  the 
  oys- 
  

   ter 
  consists 
  entirely 
  of 
  minute 
  animal 
  and 
  vegetable 
  organ- 
  

   isms 
  and 
  small 
  particles 
  of 
  organized 
  matter. 
  Ordinary 
  sea 
  

   water 
  contains 
  an 
  abundance 
  of 
  this 
  sort 
  of 
  food, 
  which 
  is 
  

   drawn 
  into 
  the 
  gills 
  with 
  the 
  water, 
  but 
  as 
  the 
  water 
  strains 
  

   through 
  the 
  pores 
  into 
  the 
  water 
  tubes, 
  the 
  food 
  particles 
  are 
  

   caught 
  on 
  the 
  surface 
  of 
  the 
  gills 
  by 
  a 
  layer 
  of 
  adhesive 
  slime 
  

   which 
  covers 
  all 
  the 
  soft 
  parts 
  of 
  the 
  body. 
  As 
  soon 
  as 
  they 
  

   are 
  entangled 
  the 
  cilia 
  strike 
  against 
  them 
  in 
  such 
  a 
  way 
  as 
  

   to 
  roll 
  or 
  slide 
  them 
  along 
  the 
  gills 
  towards 
  the 
  mouth. 
  When 
  

   they 
  reach 
  the 
  anterior 
  ends 
  of 
  the 
  gills 
  they 
  are 
  pushed 
  off 
  

   and 
  fall 
  between 
  the 
  lips, 
  and 
  these 
  again 
  are 
  covered 
  with 
  

   cilia, 
  which 
  carry 
  the 
  particles 
  forwards 
  until 
  they 
  slide 
  into 
  

   the 
  mouth, 
  which 
  is 
  always 
  wide 
  open 
  and 
  ciliated, 
  so 
  as 
  to 
  

   draw 
  the 
  food 
  through 
  the 
  oesophagus 
  into 
  the 
  stomach. 
  

   Whenever 
  the 
  shell 
  is 
  open 
  these 
  cilia 
  are 
  in 
  action, 
  and 
  as 
  

   long 
  as 
  the 
  oyster 
  is 
  breathing 
  a 
  current 
  of 
  food 
  is 
  sliding 
  

   into 
  its 
  mouth. 
  

  

  The 
  cilia 
  and 
  particles 
  of 
  food 
  are 
  too 
  small 
  to 
  be 
  seen 
  with- 
  

   out 
  a 
  microscope, 
  but 
  if 
  finely 
  powdered 
  carmine 
  be 
  sprinkled 
  

   over 
  the 
  gills 
  of 
  a 
  fresh 
  oyster, 
  which 
  has 
  been 
  carefully 
  

   opened 
  and 
  placed 
  in 
  a 
  shallow 
  dish 
  of 
  sea 
  water, 
  careful 
  ob- 
  

   servation 
  will 
  show 
  that 
  as 
  soon 
  as 
  the 
  colored 
  particles 
  touch 
  

   the 
  gills 
  they 
  begin 
  to 
  slide 
  along 
  with 
  a 
  motion 
  which 
  is 
  

   quite 
  uniform, 
  but 
  not 
  much 
  faster 
  than 
  that 
  of 
  the 
  minute 
  

   hand 
  of 
  a 
  watch. 
  

  

  This 
  slow, 
  steady, 
  gliding 
  motion, 
  without 
  any 
  visible 
  cause, 
  

   is 
  a 
  very 
  striking 
  sight, 
  and 
  with 
  a 
  little 
  care 
  the 
  particles 
  

   may 
  be 
  followed 
  up 
  to 
  and 
  into 
  the 
  mouth. 
  

  

  In 
  order 
  to 
  trace 
  the 
  course 
  of 
  the 
  digestive 
  organs, 
  the 
  

   visceral 
  mass 
  may 
  be 
  split 
  with 
  a 
  sharp 
  knife 
  or 
  razor. 
  If 
  

   the 
  split 
  is 
  pretty 
  near 
  the 
  middle 
  of 
  the 
  body, 
  each 
  half 
  will 
  

   show 
  sections 
  of 
  the 
  short, 
  folded 
  oesophagus, 
  running 
  up- 
  

   wards 
  from 
  the 
  mouth, 
  and 
  the 
  irregular 
  stomach, 
  with 
  thick 
  

   semi-transparent 
  walls, 
  surrounded 
  by 
  the 
  compact, 
  dark 
  

  

  