124 Ame7^ica7i Fisheries Society 



ber of hours they were taken up, the contents of the 

 nets washed into a small quantity of water, and the food 

 forms counted by means of the Rafter cell, the approxi- 

 mate number of standard units per cubic centimeter in 

 each case being determined. Two parallel sets were run 

 at three different times, ranging from eight to eighteen 

 hours each. The total number of standard units per cubic 

 centimeter for the current was 2,188,800, for the still 

 water 1,612,800, giving a gain of 35.7% for the current. 

 The annual growth of the hard clams in the current 

 showed a gain of 24.5 mm. or 612% by volume as com- 

 pared with a gain in the still water of 13.62 mm. or 241% 

 which was 2.6 times as much. These figures are at best 

 only approximate but are sufficient to show that there 

 is a great discrepancy between the actual increase in 

 the food supply and the rate of growth. Numerous errors 

 are possible in this test; in the placing of the nets, in 

 the technique of counting, and by comparing the yearly 

 growth with the food supply for a short period; but 

 the vast difference is striking, since it is apparent that 

 the 35.7% gain in food cannot account for the great 

 difference in growth, and we are justified in concluding 

 that other factors, one of which is an increased supply 

 of oxygen, are even more important. 



Observations upon clams in aquaria in still or even 

 stagnant water show that they feed but a small portion 

 of the time, lying with their siphons partly extended in 

 a semi-dormant condition. In these cases, if the water 

 is slightly agitated by blowing upon the surface, the 

 clams stretch out their siphons and begin to feed active- 

 ly, showing the stimulation from the circulation of the 

 water. Practically no growth has been obtained from 

 clams in still water aquaria, in spite of the fact that 

 they have been well supplied with food forms. A pos- 

 sible explanation is that current serves in some way to 

 stimulate the feeding of the clam and in this manner 

 increases its powers of assimilation. 



Lime Furnisher. — Current also furnishes the clam 

 with the lime salts in solution in the water, which are 



