84 COMMISSION OF CONSERVATION 



The length of the period of an oyster's free-swimming life may be 

 considered to be between three weeks and a month. The period of five 

 hours from fertilization to the beginning of swimming locomotion is so 

 short as to scarcely need consideration in this connection. The period 

 of thirty-two hours from fertilization to the first beginnings of the 

 shell is likewise a comparatively short time. The period from fertilization 

 to the earliest plankton stages, i.e., to the larva ( such as raised by 

 Brooks) with a straight-hinge shell sufficient to enclose the soft parts, is 

 as closely as we can calculate, perhaps six days. This with the three 

 weeks of growth from the youngest to the oldest plankton stages, makes 

 approximately a month for the whole period. 



Swarming can be made of great advantage to man in that, by re- 

 peatedly taking and examining plankton, he may learn the time of the 

 first appearence of oyster larvse in the water and keep informed as to 

 their numbers and growth, and thereby be able to judge the best time for 

 putting out cultch. 



Spatting is the natural and normal fixation of full-grown oyster larvie 

 on to shells, rocks or other solid objects in the sea-water of oyster areas. 

 The actual process, we may feel assured, has never been observed, but 

 spat have been discovered so close after being fixed that their fixation was 

 the only recognizable and essential difference between them and the oldest 

 free-swimming larvae. The first apparent difference in structure to arise 

 is the deposit of a rim of new shell, the spat shell, which soon grows to 

 such an extent as to make the spat easily visible and recognizable as 

 a minute oyster. Older and larger spat have long been known by men 

 who have had to do with oysters. They seem generally to make their 

 appearance so suddenly that it is customary among fishermen to speak 

 of a "fall of spat." 



The time of the year at which spatting takes place has not received 

 much attention from those who have studied the development of the 

 oyster. Perhaps this is due to the failure to separate spatting from 

 spawning. ' So long as it was believed that fixation takes place in a brief 

 time after the eggs are spawned there was no particular advantage in con- 

 sidering the two periods separately. 



Sprat (1690) wrote: "In the month of May the oysters cast their Spawn (which the 

 Dredgers call their Spat)." 



Winslow (1882): "The oyster embryo is predisposed at least to fix itself very soon 

 after the process of segmentation is completed." 



Rice (1885): " The attachment takes place in about two days from the time of 

 fertilization." 



Jackson (1888) "when oysters were setting most abundantly in 



July and early August." 



Nelson (1901): " The fry, after about five days, develop a two-valvcd shell,and then 

 they seek a place to settle down on." 



The first spat of the season 1904 that I observed was taken on the 

 10th August. That this date is sufficiently near the mark is proved by 



