OF MASSACHUSETTS. 



77 



grows half the time, as all shell formation is accomplished during 

 the summer months and no increase in size is found during the cold 

 weather. This gives the scallop a resting time between the period of 

 youth and adult, and again during its old age, as the average life of 

 the animal is from twenty to twenty-six months. 



In following the life of the scallop born in July, growth ceases dur- 

 ing December and is again resumed May 1 of the following year, when 

 the temperature of the water has reached 45° to 50°F. The same seal- 

 lop ceases growth in the fall, usually in the latter part of November 

 (slightly earlier than the young set of that year), when the water has 

 again fallen below 45°. Thus, every scallop has two periods of growth, 

 corresponding to the two summers of its existence, and two resting 

 periods during the winters. The cause of this cessation of growth is 

 explained under the topic " Effect of Temperature." 



By monthly measurements of the scallops confined in pens at Mono- 

 moy Point during 1906, the relative value of each month was calculated 

 and the variation in growth for different parts of the summer was de- 

 termined. In the following table each mouth is given a numerical 

 number, representing the gain per cent, for the month, the entire year 

 being considered as 100 per cent. (Figs. 84, 85) : — 



1 Decrease in June and July due to spawning. 



Length of Life. — Briefly stated, the normal Uf e of the scallop is 

 from twenty to twenty-six months, relatively few scallops passing the 

 two-year limit. 



Previous to 1906, when this problem was first satisfactorily solved 

 by the commission, the question most often propounded by the practical 

 scallop fisherman was, " How long does the scallop live ? " In spite of 

 the diversity of opinion, which credited the scallop with living anywhere 

 from two to five years, the majority of the scallopers believed that two 

 years marked the limit of its life, a view which coincided with the 

 results of the investigation. Both IngersoU (8) and Risser (2) agreed 

 with this view, but were unable at the time of writing to furnish definite 

 proofs. So it fell to our lot to obtain, through a series of observations 



