110 INVERTEBRATE ZOOLOGY 
the visceral mass. With forceps and knife carefully remove 
the tough white integument which covers the left side of the 
visceral mass. The soft cream-colored mass filling the greater 
part of it is the reproductive gland, the greenish mass above is 
the liver. Imbedded in these masses lies the alimentary tract, a 
narrow, delicate tube, which will be injured in the dissection 
unless the greatest care be taken. Beginning with the mouth 
gently scrape away the soft mass which surrounds the alimen- 
tary tract, laying it entirely bare. The water in the dissecting 
pan must be frequently renewed to keep it clear, and great care 
taken not to break the canal. The mouth opens into the short 
cesophagus, after which the canal dilates to form the stomach. 
The liver surrounds the stomach and is connected with it by 
several ducts. Back of the stomach is the intestine, which first 
runs backward and downward to the posterior part of the 
visceral mass, after several turnings in the lower part of which 
it bends upward and runs forward parallel with the posterior - 
margin of the visceral mass to its dorsal border, where it leaves 
it. Here the rectum begins and passes through the heart and 
above the posterior adductor muscle to the anus. A small 
transparent rod is often present in the intestine; its function 
is unknown. 
Clams feed upon minute organisms and organic particles 
contained in the water. Some of the water in the mantle 
cavity is drawn into the mouth by the ciliated oral palps and 
passes through the alimentary tract, where the organic sub- 
stances are digested and absorbed. 
Bxercis? 9. Draw a diagrammatic view of the digestive system. 
The reproductive system. The sexes are separate. The repro- 
ductive glands (testis or ovary) are very similar to each other and 
consist of a pair of cream-colored masses which fill a greater 
part of the visceral mass. Their external openings are a pair 
of minute pores, one on each side of the visceral mass just 
