RESUME OF THE STAGES OF DEVELOPMENT 79 



to determine the period with certainty. I believe that, while it may- 

 fluctuate to some extent according to season and locality, it will be found 

 for the great mass of oysters to fall about the end of June and first half 

 of July. 



The temperature of water in the region of oyster beds along our coast, 

 at the beginning of spawning, approximates to 20° C. (= 68° F.). In 

 1909 the surface water above the government reserve beds at Shediac, 

 N.B., reached 17-5° C. on July 7, and an artificial fertilization experiment 

 succeeding in developing numerous oyster eggs to the free-swimming larva 

 stage. On August 7 the highest temperature, 23° C, was noted (at 

 Caraquet), and on September 2 the temperature, 18° C. was already be- 

 ginning to lower (at Malpeque). This was an unusually late and cool 

 season and illustrates the dependence of spawning upon temperature, for 

 the first young shelled stages of living oyster larvse were observed in the 

 plankton collections on July 22 (at Cocagne). 



The number of egg-producing oysters is of course only a fraction of the 

 whole number of oysters in a bed. There are as many males as females. 

 Immature oysters do not spawn. 



The number of eggs spawned by a single oyster of average size was 

 estimated by Brooks (1880) to be about 9,000,000, and for a very large 

 oyster about 60,000,000. In a later work (1905) he gives 16,000,000 as 

 the average. Prince (1895) mentions 50,000,000 to 100,000,000. Nelson 

 (1900) gives 30,000,000. The method of estimation consists in measuring 

 the cubic contents of the ovary, or of the mass of ova extracted, and, after 

 making allowance for surrounding and intervening tissue, calculating the 

 number of times the remaining volume would contain that of a single egg. 

 The actual number is of less real value than the fact that it is, at all events, 

 very large. 



On an undisturbed oyster bed of some years standing, the chances 

 are that the actual number of oysters from year to year does not change 

 to a very great extent. In such a case the collossal number of eggs spawned 

 serves solely to make good the loss through death from natural causes, 

 and illustrates the lavish method of nature in preserving the average 

 number of individuals. 



The fate of most eggs is in some way to meet with destruction, the 

 manner of which will depend upon their chance circumstances. They 

 may fail to be fertilized. At one place they may fall in masses so great 

 that the under ones are smothered ; at another place they may sink into 

 mud and meet with a similar fate. Here falling sediment or drifting sand 

 may encompass them; there they may be eagerly devoured by some 

 animal. Currents may drift them out to sea where they are lost, or throw 

 them up on the beach where they are dried. Those that escape such 

 accidents uninjured develop into larvae. 



