730 NATURAL HISTOEY OF AQUATIC ANIMALS. 



Saint Jerome's Creek, a few miles north of the mouth of the Potomac, during the months of July, 

 August, September, and October: . 



"The food of this mollusk, as is well known, consists entirely of microscopic beings and 

 fragments of organic matter, which are carried by currents from the palps and gills, which have 

 been already described, to the large mouth of the animal at the hinge eud of the shell. The inside 

 of the gullet and stomach, like some other parts of the body, are covered with cilia, so that food 

 once fairly in the mouth will be carried by their action down to the cavity of the stomach, where 

 it is carried iuto the folds and deep pouches in its walls, and even into the openings of the bile 

 ducts, to undergo digestion or solution, so as to be fitted in its passage through the intestine to 

 be takeu into the circulation, and finally disposed of in building up the structures of the body. 



"Along with the food which is taken, a very large amount of indigestible dirt, or inorganic 

 matter, is carried in, which, in a great measure, fills up the intestine, together with the refuse or 

 waste from the body. This material, when examined, reveals the fact that the Oyster subsists 

 largely on diatoms, a low type of moving plants which swim about in the water, incased in minute 

 sandstone cases, or boxes, of the most delicate beauty of workmanship. These, when found in 

 the intestine, have usually had their living contents dissolved out by the action of the digestive 

 juices of the stomach. I have found in our own species of Oyster the shells of three different 

 genera of diatoms, viz: Campylodiscus, Coscinodiscm, and Navicula. The first is a singularly bent 

 form; the second is discoidal; and the last boat-shaped, and all are beautifully marked. Of 

 these three types, I saw a number of species, especially of the latter, but as I was not an authority 

 upon the systematic history of any of them I had to neglect the determination of the species. No 

 doubt many more forms are taken as food by the Oyster, since I saw other forms in which the 

 living matter inside the siliceous cases was brown, the same as in most of the preceding forms 

 which I have indicated. Some of these brown forms were so plentiful as to color a considerable 

 surface whereon they grew of the same tint as themselves. 



"Besides the diatoms and the spores of alga, the larvse or young of many animals, such as 

 sponges, bryozoa, hydroids, worms, mollusks, are small enough to be taken in as aliment by 

 the Oyster, though their bodies in most cases being soft and without a skeleton, it is impossible 

 to find any traces, either in the stomach or intestine, of their remains, to indicate that they have 

 formed a part of the bill of fare of the animal. What, however, demonstrates that such small 

 larval organisms do help to feed the Oyster is the i'act that at the heads of the small inlets or 

 creeks along the Chesapeake, where the water is but little affected by the tides and is somewhat 

 brackish and inclined to be stagnant, there always appears to be a relatively greater development 

 of a somewhat characteristic surface or shallow water fauna of minute forms. 



"In Saint Jerome's Creek the microscopic fauna of its headwaters is entirely different from 

 that of the body of the creek; two minute forms inhabit in vast numbers the former, while I 

 sought in vain for them in the more open and changeable waters of the main body of the inlet, 

 which are brought into active movement twice a day by the action of the tides. One of these 

 I'oniis, un infusorian, 1 one twenty-fifth of an iuch in length, was found covering every available 

 surface of attachment, so that countless multitudes of the naked young would be swimming about 

 in the water previous to building the curious spiral tubes which they inhabit admirably fitted in 

 this state as food for the Oyster. Besides the type referred to, there were a number of other 

 iufusorians, which in their so-called swarming stages of development would become available 

 as Oyster food. Of Mich types 1 noticed four different species, either belonging or very nearly 



1 On the occurrence of J'Vo jn-uducla, Wright, in the Chesapeake Bay. Am. Naturalist, 1880, pp. 810, 811. 



