376 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
particles of sand. The finding of some animal or plant or other object 
in the stomach of the oyster does not prove that it composes any part 
of its food supply, no matter how numerous the form may be in indi- © 
viduals, but it can only offer a suggestion for further investigation. In 
order to demonstrate which of these various objects serve as food, it is 
necessary to prove not only that they are ingested, showing a possible | 
source of nutriment, but also that having passed through the digestive 
tract only the indigestible parts remain. To conclude from the fact — 
alone of the occurrence of any animal or vegetable in the stomach of 
an oyster that it forms a part of its food is no more justifiable than to 
affirm that the fishes brought up by a water-wheel are food for the 
wheel. 
The method followed by me in studying the stomach contents of the — 
oyster was as follows: The oyster was carefully opened, guarding against 
any injury from the knife except the separation of the muscle which 
connects the two valves of the shell. The oysters were, as a rule, 
examined immediately after being taken from the water, usually within 
fifteen minutes, and very rarely after as long an interval as two hours. 
After separating the gills at the oral extremity with a scalpel, so that 
the opening of the mouth was exposed, the tip of a finely drawn-out glass 
tube having a rubber ball at the other end was introduced into the stom- 
ach. The contents of the stomach were now sucked out by removing 
the hand from the hitherto compressed bulb. 
The contents of the stomach of an oyster which has recently fed—in 
other words, of every oyster collected when the shells are open—present 
a beautiful dark-golden color. A drop of this material obtained in the 
manner described above and placed under the microscope for examina- 
tion shows that the stomach of the adult oyster contains a large number 
of diatoms, embracing a great many species. The constant occurrence 
of these forms in great quantities suggested the possibility of their serv- 
ing as food. In addition to the diatoms a quantity of decaying organic 
matter at least equal in amount, and also of some of the lower alge, 
besides sand, ete., were often found. Rhizopods, a few euglenas, an 
occasional foraminiferum, and other animals of lower grade were seen, 
but only once was a copepod found; in fact, animal life was practically 
absent. 
An idea which early occurred to me was the importance of examining 
simultaneously the stomachs of the other common bivalve mollusks of 
the James River, to see if any uniformity in the nature of the food in — 
this natural group could be detected. With this object the stomachs 
of the hard clam or quahog (Mercenaria mercenaria), of the soft clam 
(Mya arenaria), and of the ribbed mussel (Modiola plicatula) were also 
examined. In all of these species the contents of the stomach were 
found to be the same as in the oyster. 
The first question to be settled was whether or not the oyster and 
these other mollusks actually digested the diatoms found in their 
