20 



the body, are covered with cilia, so that food once fairly 

 in the mouth will be carried by their acrtion down to the 

 cavity of the stomach, where it is carried into 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 

 taken 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 undigestible dirt or inorganic matter is car- 

 ried in, which in a great measure fills up the intestine 

 together with the refuse or Avaste 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 encased in minute sand- 

 stone cases or boxes of the most delicate beauty of work- 

 manship. 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, Cosci- 

 nodiscus and Namcula. The hrst 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 silicious 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 con- 

 siderable surface whereon they grew, of the same tint as 

 themselves. But in no instance have I found any indi- 

 cations of the animal of the oyster becoming colored by 

 feeding on these diatoms, as it is said the European 

 oyster does when feeding on Namcula ostrearia^ which 



