OF MASSACHUSETTS. 21 



in chajjter VII., in small aquaria during the period of observation, and 

 were replaced in their native element between times. Possible error 

 arises from the unnatural conditions, which may render the spawning 

 abnormal. Unfortunately no satisfactory method of eliminating this 

 error could be devised. These observations, however, have been par- 

 tially confirmed in other ways. 



(1) When the scallop spawns, which sex cell is liberated first f 

 Observations on 38 scallops showed that 19 produced spermatozoa, 



17 eggs, and 2 a mixture of both at the first discharge. In general, the 

 scallop continues shooting for a number of discharges the kind of sex 

 cell with which it starts, and although scallops are hermaphroditic, only 

 a single kind is usually given off at any one time, the length of the 

 period varying from a few minutes to five or six hours. It can be safely 

 concluded that it is purely a matter of chance which sex cell is given 

 off, and that the tendency toward one kind may be a precaution against 

 self-fertilization. 



(2) How long are the intervals between discharges? 



The intervals between discharges vary from one-half a minute to 

 forty-five minutes, or even days. After a series of rapid discharges the 

 resting period appears to be longer. One scallop was observed to give 

 as many as five successive discharges, while two are of frequent occur- 

 rence. Other specimens have been observed to shoot spawn at intervals 

 of two or three minutes for over five hours. The scallop possibly can 

 adapt itself to existing conditions and spawn only at favorable times. 

 If the germ cells are set free at intervening periods over a long space of 

 time there is a greater chance of surviving. 



(5) Do scallops throw all their spawn in one day? 



Numbered scallops were placed in separate aquaria for periods of 

 two hours for several days, a record being kept of the spawning of 

 each individual. After each test the animals were suspended in wire 

 baskets from a raft at a depth of 10 feet in water, which was consider- 

 ably cooler than the sun-warmed water in the aquaria, probably pre- 

 venting further shooting of spawn. Although only 25 per cent, threw 

 spawn we can infer that scallops shoot their sex products little by little, 

 as the same individuals were found to give forth spawn after an interval 

 of several days. This fact indicates that the spawning season for one 

 scallop probably extends over a period of days and even weeks. Eec- 

 ords with color charts, upon scallops of another set, likewise show 

 that spawning is gradual. 



(4) Do scallops spawn at any particular time of day? 



Scallops have been observed to spawn as early as 8.15 a.m. (July 13, 

 1907) and as late as 4.30 p.m. (July 12, 1909), and at various times 

 between these hours. Although sunlight is more favorable, the scallop 

 will spawn on cloudy days and probably at night, as the time of spawn- 

 ing is largely determined by the temperature. 



