B elding. — Conditions Regulating Clam Growth 123 



Oxygen Bearer. — The relation between the amount of 

 food, the supply of oxygen and the feeding of the clam 

 in a current is comparatively intricate and the exact 

 proportion that each factor contributes to the increase 

 in growth, as far as figures are concerned, is somewhat 

 problematical. Oxygen, the most important, aifects 

 growth in two ways, first by increasing the metabolism 

 of the body, and second by stimulating the feeding activi- 

 ties of the clam, but so closely are these actions connected 

 that it is impossible to determine their relative values. 

 Oxygen is needed for life and with an increase in the 

 amount of available oxygen the bodily functions are per- 

 formed more readily. The usual supposition that the 

 effect of current upon clam growth was entirely due to 

 the actual increase in food forms was disproved in 1907 

 by an experiment, which demonstrated that the increase 

 in the food supply was only a partial explanation. The 

 results indicated that the beneficial action of the current 

 consisted rather in increasing the clam's power of assimi- 

 lating food. By the following method an approximate 

 idea of the actual increase in the food supply as compared 

 with the total increase in growth for hard clams in still 

 water and in a current was obtained. 



At Monomoy Point, Massachusetts, the rate of growth 

 had been followed for several years for two experimental 

 beds of hard clams, the one in still water showing a slow 

 growth, the other with a good circulation of water having 

 a much greater increase. To test the relative difference 

 in the amount of food forms at a definite point on these 

 beds small nets of silk bolting cloth. No, 11, two inches 

 in diameter and four inches long, were so arranged that 

 they would rotate on an iron rod after the manner of 

 weathervanes. When in position the nets remained 

 extended in the water and on the slightest motion would 

 swing on a pivot, thus always presenting the opening 

 of the net to the current. One net was placed over the 

 bed in still water, the other, identical in every respect, 

 was situated over the bed in the current for the same 

 length of time. After having been down a certain num- 



