The Life History of the Soft Clam 291 



great numbers by many swimming enemies, and Mr. D. 

 L. Belding, Biologist of the Massachusetts Fish and 

 Game Commission, has recently made observations 

 which show that cold rains are very fatal to them. 

 " During a long, cold rain," he writes, " counts were 

 made of the number of larvae in a certain amount of 

 water which passed through the plankton net : before 

 the rain, 30,000; after nine hours, 15,000; after fifteen 

 hours, 3,000. After the rain had ceased, the number of 

 larvae gradually increased until it was the same as at 

 the first count." This is interesting, because the varia- 

 tion in the " set " in different years seems, as in the case 

 of the oyster, to be best explained by these and other sud- 

 den lowerings of temperature during the swimming 

 period. 



From this time on, the habits of the young clam be- 

 come very different from those of the young oyster of 

 the same age. While the latter settles and at once be- 

 comes fixed to some foreign object for the rest of its life, 

 the young Mya must still expose itself to many dangers 

 before reaching a safe resting-place in the bottom. 



During the later part of the swimming stage, a well 

 developed, muscular foot appears, extending along the 

 whole lower or ventral side of the body. It is now rela- 

 tively very large, as it is in the adult hard clam or little 

 neck, but later it will become proportionately much re- 

 duced in size. Siphon and gills, also, have made their 

 appearance. The velum, a projecting pad covered with 

 the swimming cilia, gradually disappears, and the small 

 clam settles to the bottom. 



During the few days of the swimming period, the 

 young clam may have been carried some distance from its 

 starting-point, not only by its power of locomotion, but 



