OF MASSACHUSETTS. 83 



growth (Fig. 85). Risser (2) has observed a similar occurrence with 

 the growth of Rhode Island scallops, but declared that there is a com- 

 plete check at this period, and to it attributes the origin of the annual 

 growth line. This report has demonstrated that the growth line is 

 formed at an early period, about May 1, by the resuming of shell 

 formation after the nongrowth of the winter months, and has nothing 

 to do with the spawning season. Likewise, no decided check in the 

 growth of Massachusetts scallops is found during the spawning season, 

 but rather the scallop continues to grow at about half its normal rate. 

 The monthly rate of growth was determined for 1,900 scallops in four 

 wire netting pens at Monomoy Point during 1906. It was found, by 

 considering the entire summer's growth (May 1 to December 1) as 

 100 per cent., that the growth during May was 19.76 per cent., during 

 June 8.33 per cent., during July 10.35 per cent., during August 20.39 

 per cent., showing that the rate of growth for the month preceding and 

 succeeding the spawning season was over twice as fast as for the 

 spawning months. 



The reason for this slow growth can be attributed to the coincidence 

 with the spawning season, and is best explained by assuming that the 

 activities of the animal were directed for that period upon the propaga- 

 tion of its species, and less energy was used for the secretion of shell. 

 Temperature, the great factor in determining growth, does not have any 

 influence here, as the water during June and July was warmer than 

 during May and colder than August. In fact, all natural conditions 

 affecting the rate of growth were eliminated, leaving the spawning 

 season as the direct cause in the lessening of the rate of growth. 



Growth of the Young Scallop. — The young scallop at the age of 

 forty-eight hours has increased in size by the formation of the embry- 

 onic shell. Previous to this time the ciliated larva was scarcely larger 

 than the original egg. The period of first shell formation marks the 

 beginning of real growth, which continues for the entire life of the 

 scallop during the summer months. Since the growth during early life 

 has been described in chapter III., it is only necessary to consider the 

 growth after the scallop has become readily visible to the naked eye, 

 i.e., about %5 of an inch in size. 



The time of appearance of the set depends upon two factors, (1) 

 locality; (2) year. During 1906 the visible appearance of "set" was 

 recorded as follows: (1) Powder Hole, Chatham, August 7; (2) Stage 

 Harbor, Chatham, July 24; (3) Edgartown, August 3; North Fal- 

 mouth (Buzzard's Bay), July 20; Marion, July 20; showing a difference 

 of fourteen days between two bodies of water not 10 miles apart, and 

 an extreme variation of eighteen days. At Monomoy, between 1905 

 and 1909, the sets have appeared as early as July 24 and as late as 

 August 7, showing the influence of seasonal change. (These dates do 

 not indicate the first appearance, but when the average set was readily 



