CHAPTER XIX 

 THE LIFE HISTORY OF THE SOFT CLAM 



N Mya, as in the oyster of our Atlantic coast, 

 the sexes are separate. South of Cape Cod 

 fs,i£ tne breeding season begins about the middle 

 of June, reaches its height during the last two 

 weeks of July, and continues until September. North 

 of Cape Cod the season begins somewhat later, probably 

 on account of the difference in temperature. 



As in most other bivalves, male and female cells are 

 extruded into the water, where they unite. As might be 

 expected, the early stages of development are similar 

 to those of the oyster, resulting in the formation of a 

 swimming embryo that rotates spirally as it passes 

 through the water. When the embryonic shell appears, 

 the animal has a diameter of about one three-hundredth 

 of an inch. The entire swimming period covers from 

 three to six days, varying considerably with changes in 

 the temperature of the water. A fall of temperature 

 checks, and a rise to a certain optimum accelerates de- 

 velopment. The numbers over some flats during the 

 height of the reproductive season are very great. A 

 small surface net a foot in diameter, on being towed a 

 hundred yards through the water, has been observed to 

 capture from twenty-five to thirty thousand of the swim- 

 ming young. 



At this time the young are undoubtedly destroyed in 



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