340 Our Food Mollusks 



curate guesses as to the time of breeding and the length 

 of life. We now possess a thorough study of the 

 anatomy and development of the giant scallop by Pro- 

 fessor G. A. Drew, and an interesting investigation of 

 the development and habits of the shallow water form 

 has been made by Mr. D. L. Belding. 



In the giant scallop the sexes are separate, but the 

 shallow water form is hermaphroditic. In both cases 

 the ovaries are easily recognized without dissection dur- 

 ing the breeding season by their bright salmon-pink color. 



The spawning season of Pectan irradians begins about 

 the first of June in New England, and ends in early 

 August, weather causing some variation. Probably it 

 begins earlier in warm southern waters. The ripe eggs 

 of this form, one four-hundredth of an inch in diameter, 

 are extruded into the water, and there meet the male 

 cells. Usually in hermaphroditic animals one set of sex- 

 ual cells is matured and discharged before the other, ap- 

 parently in order that self-fertilization may be prevented. 

 But in an aquarium a scallop sometimes discharges ova 

 and spermatozoa together, and these unite with each 

 other. More frequently one set is discharged, and then, 

 after an interval, the other, and under natural conditions 

 cross-fertilization would most often occur. 



The segmentation of the fertilized egg is of the same 

 general character as that of oyster and clam eggs. It 

 also, from fifteen to twenty hours after fertilization, be- 

 comes a swimming embryo or veliger and, suspended by 

 the activities of its cilia, is carried about by water cur- 

 rents. The velum or prominence bearing swimming cilia 

 has made its appearance, and a shell is secreted that is 

 soon large enough to cover the entire body. The velum 

 is extended out beyond the shell margin when in func- 



