OF MASSACHUSETTS. 23 



they were not taken, as nearly all die from natural causes before a 

 second season. 



The Spawning Season. — In Massachusetts waters, owing to the 

 diversity of conditions as regards locality, environment and seasonal 

 changes, it is difficult to define the spawning season exactly and only 

 general limits can be given when the entire territory is considered. As 

 a rule, temperature seems to be the controlling factor, as is demon- 

 strated by the variation of the season according to locality and years. 

 The entire period roughly covers two months, averaging from the middle 

 of June to the middle of August (Fig. 83). The height of the. spawning 

 occurs during the first weeks in July, and although the season drags on 

 for a month longer, the greater part of the mature eggs have been liber- 

 ated. Different localities, with the same general limits, often vary in 

 having the height of the spawning at different times, While the spawn- 

 ing of the scallop as a class extends for two months, the duration of the 

 season for the individual runs anywhere from one day to several weeks. 



(a) Spawning Season at Monomoy Point. — During the summers of 

 1906 and 1907 the spawning season of the scallop was followed in the 

 waters of the Powder Hole at Monomoy Point, and supplementary 

 observations were made during ]908 and 1909. During the first two 

 years conditions in this locality were practically the same, thus eliminat- 

 ing nearly all variation factors except seasonal change. It is, there- 

 fore, fair to assume that the following variations are mostly due to 

 the difference in the temperature of the two years. 



In comparing the two years 1906 and 1907 the following points will 

 be considered: (1) date of first spawning; (2) length of time spawn 

 could be obtained for successful artificial fertilization; (3) date of 

 appearance of the set on raft spat collectors. 



(1) Careful observations were made in regard to the beginning of 

 the spawning season, and the start was accurately determined for this 

 locality. In 1906 scallops first extruded eggs and spermatozoa on 

 June 12, and in 1907 on June 21, a variation of nine days. The average 

 temperature of the water on June 12, 1906, was 61.5° F., on June 21, 

 1907, 61.5° F. June 4, 1906, was equivalent to June 18, 1907, in 

 regard to the temperature, which reached 60° for the first time on these 

 dates, showing that the seasonal variation in temperature was about 

 two weeks. In both cases there had been a previous rise in temperature. 

 By June 20 this difference had vanished and the daily temperatures for 

 the two years were approximately the same (Fig. 81). 



(2) For successful artificial fertilization spawn could be obtained 

 for both years as late as July 20. Mature eggs and active spermatozoa 

 were found in the reproductive organs later, but the scallops did not 

 give forth spawn readily after this date. The records made with the 

 color chart show that the spawning season is not complete before the 

 middle of August. 



