308 Our Food Mollusks 



Sometimes the set is quite evenly spread over a flat. 

 Most often it is very irregular, being generally thin, 

 but very dense in a few spots. These dense segrega- 

 tions, that every clammer knows, are caused by sharply 

 defined currents that have passed near spawning clams. 

 Every day during the breeding season some swimming 

 individuals reach the stage of development in which they 

 sink to the bottom, and a more or less steady shower of 

 them continues to fall for several weeks. More swim- 

 ming forms will pass over the bottom that underlies a 

 current than elsewhere, and this will receive an unusually 

 large number of the settling individuals. Some modi- 

 fication of a current, as an eddy on its margin, may 

 sweep together astonishingly great accumulations. Such 

 segregations are common, and the fate of the young 

 clams comprising them has been studied and described. 



Two such areas, for example, lying under parallel and 

 sharply defined currents that were separated by a dense 

 mat of eel-grass, were nearly two hundred yards long 

 (Figure 61). Each was but two or three yards wide. 

 In the middle of the breeding season they were as densely 

 packed as it was possible for them to be. Before the 

 end of the summer all had died from overcrowding. 



A similar segregation, occurring on the flats near Ips- 

 wich, in Massachusetts, the fate of which, however, was 

 not witnessed, has been well described by Mr. J. R. 

 Stevenson. " Often," he writes, " they are so numerous 

 that only a small portion can burrow, the rest being but 

 half in the sand, or merely resting upon its surface, the 

 sport of every storm. Such an area I found during No- 

 vember, 1906, in Plum Island Sound, upon the east side 

 of Rowley Reef. The narrow channel here washes the 

 eastern thatch bank. Upon the west side of this channel 



