26 



only .005 of an inch. Yet in this minute digestive cavity the 

 food is actually found rotating in the form of minute rounded 

 or oval bodies, which are kept in motion by the action of the 

 cilia which line the stomach. That these bodies must have 

 been of about the same size as when they were swallowed and 

 as when seen rotating in the stomach, is evident from the fact 

 that the young oysters, like the adults, are wholly without 

 teeth or triturating organs of any kind. 



This minute kind of vegetable and animal food is found 

 more or less abundantly in all sea water, and is especially abund- 

 ant during the spawning season, when the disintegration and 

 decomposition of all kinds of minute organic debris floating 

 in the water is in rapid progress, owing to the prevalent high 

 temperature of the air and Avater. It is, therefore ,probable 

 that very few otherwise suitable localities exist where it is not 

 possible to find an abundance of the proper food for the young 

 oyster during the early stages of its growth." 



The food of the adult oyster, in common with that of the 

 clam, mussel, scallop, and other molluscs of the same type, con- 

 sists almost entirely of minute plants. By far the greater num- 

 ber of these food forms belong to the class of plants known as 

 Diatoms. In the stomach of an oyster there will often be found 

 other materials besides the plants just mentioned. At the time 

 of spawning of the oyster there will be large numbers of their 

 eggs, and at all times some of the very small animals ; but when 

 a record of the stomach contents is kept for an extended period, 

 it will be found that the diatoms make up by far the largest 

 and most important part. 



All diatoms are enclosed in a flinty covering made up of 

 two valves which fit together like the two halves of a pill box. 

 The markings on the shells are characteristic ,for each of the 

 difl'erent forms, and thus allow their ready identification in 

 the stomach contents of the oyster even when nothing but the 

 empty shells remain. 



Diatoms occur in immense numbers in the waters of the 

 ocean, in the brackish waters near the shore, as well as in the 

 fresh Avater of ponds and rivers. The kinds of diatoms found 

 in these different localities differ very much in their characteris- 

 tics, and the forms on which the ovster feeds are those that are 



