FOOD OF THE OYSTER, CLAM, AND RIBBED MUSSEL. 383 



in an Erleumeyer liask with a little of the pelagic catch added, in 

 order to give it the necessary elements for the growth of the diatoms. 

 The flask was then plngged with cotton and sterilized by boiling. 

 Afterwards, when it had cooled, a few drops of the pelagic catch con- 

 taining bnt a few diatoms were introduced into this sterilized medium. 

 After some days small colonies of diatoms appeared on the wall of the 

 flask, especially on the side turned toward the light. One of these 

 colonies was removed by means of a sterilized platinum needle and 

 introduced into another Erlemeyer flask containing the same medium. 

 This culture was afterwards used for experiments. 



The experiments were carried on in the following way: A hash of 

 fish and one of shrimps was suspended in water, the suspension con- 

 taining particles not larger than a copepod. Clams were first used 

 for the experiments. A culture of diatoms in sufficient quantity to 

 cause a small, well-defined cloud in the water was offered to them by 

 means of a fine glass tube, the end of which was brought close to the 

 ventral opening of the siphon, care being taken (see figure' not to 



i5^^^gi>i*5^^r^'.3«i;5iii -•- 



touch it. The culture was now allowed to flow through, and soon 

 disappeared in the opening of the siphon. Many such cultures were 

 accepted by the clam, but when similar experiments were made with a 

 hash of fish, the result was either that the opening closed as soon as the 

 particles of fish touched it, or the suspension was accepted as before, 

 but almost as soon as taken it was forcibly ejected and often thrown 

 to a distance of six or seven inches. The shrimp hash was rejected in 

 the same manner. 



When soft clams were used, the same results were obtained, and when 

 the hash was brought between the oi)en shells of the oyster, the same 

 phenomena were observed, the suspension being rejected and the shells 

 immediately closed, while the diatoms were readily accepted. Though 

 these experiments were repeated over and over again, I always obtained 

 the same results with a single exception in the case of a soft clam, an 

 individual apparently without a discriminating taste, which accepted 

 a great quantity of the hash, but finally rejected it also. 



