376 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



particles of saiul. The tiiidiug- of some auimal or plant or other object 

 in the stomach of the oyster does uot 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 x^ossible 

 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 oircurrence of any animal or vegetable in the stomach of 

 an oyster that it forms a i)art 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 exi)osed, 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 cojitents 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 i)ossibility 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 algje, 

 besides sand, etc., were often found. Khizopods, a few euglenas, an 

 occasional foraminiferum, and other animals of lower grade were seen, 

 but only once was a copei)od found; in fact, animal life M^as practically 

 absent. 



An idea which early occurred to me was the importance of examining 

 sinmltaneously the stomachs of the other common bivalve mollusks of 

 the James Kiver, 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 (puiliog {Mereenaria mercoiaria), of the soft clam 

 {Mya arenaria), and of tlie 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 



