9 
‘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 
