292 Our Food Mollusks 



passively by tide currents ; but because the young always 

 settle in considerable numbers on old natural beds, some 

 of those carried away by the retreating tide must be 

 brought back by the flood. But in selecting bottoms for 

 artificial beds, localities possibly might be found that are 

 favorable for planted clams, but on which there would 

 be little or no natural set of the young because of peculi- 

 arities of currents. 



It is certain that the young clam makes no selection 

 whatever of bottoms on which to settle, though curious 

 segregations of minute clams that are often met with 

 might suggest some such power. Here and there it will 

 be found that sea-weeds bear newly settled clams in 

 great numbers. Certain strips of beach also have been 

 observed on which multitudes of small soft clams have 

 settled, the margins of the tracts being sharply limited. 

 On adjacent bottoms very few are to be found. Prob- 

 ably these great inequalities in distribution are due en- 

 tirely to peculiarities of water currents. When a certain 

 stage of development is reached, the swimming form set- 

 tles, wherever it happens to be. More will fall where 

 large volumes of water pass in the form of sharply de- 

 fined currents than where there is little movement of 

 water. As so often happens in nature, the seed is sown 

 broadcast. While in this case it can usually live only on 

 certain restricted tracts between tide lines, it falls in 

 deep water and shallow alike, probably thousands of 

 times more often where death is inevitable than where 

 farther development is possible. 



During the swimming period there has been formed 

 far back on the under side of the foot a gland for secret- 

 ing a transparent fluid which, on being ejected into the 

 water, hardens into a minute, tough thread known as the 



