1116 U. S. BUREAU OF FISHEEIES 



dion membrane and is probably located in the body of the sperma- 

 tozoa, the hypothesis Avas advanced that it acts upon oysters through 

 the digestive tract. Indirect evidence in support of this vieAv is 

 found in the fact that particles suspended in the water surrounding 

 the gills reach the stomach in about 10 minutes. Experiments car- 

 ried out with Japanese oysters supported all the findings made in the 

 experiments with the eastern species. The only difference Avas that 

 the critical temperature below which spaAvning of the Japanese 

 oyster does not occur, is 25° C. (77° F.) instead of 20° C. (60° F.) 

 as has been determined for the American species; and that without 

 the addition of sperm a temperature of 30° C. (86° F.) instead of 

 27° C. (81° F.) induces spawning of the Japanese oyster. The 

 males of Ostrea gigas responcl to the addition of eggs even at a tempera- 

 ture of 10° C. (50° F.). Since the temperature of Puget Sound 

 rarely reaches 15° C. the failure of this species to propagate here is 

 explained. 



Potential fecuiiditrj of oysters. — The potential fecundity of 

 oysters — that is. the number of eggs developed by the female — was 

 studied by Dr. Paul sS. Galtsoff at XVoods Hole laboratory. A female 

 oyster, placed in a glass tank and having an upper valve attached to 

 a recording apparatus, was induced to spawn. After the reaction was 

 finished, the Avater Avas vigorously stirred and the number of eggs 

 was enumerated by taking four samples of 100 cubic centimeters of 

 water and counting the eggs in a Sedgwick Kafter camera. It Avas 

 found that the female. Avhicli Avas 5 inches long and 4 inches Avide, 

 discharged 109,000,000 eggs (this figure is correct AA^thin 10 per 

 cent). This figure is much higher than all estimates made by pre- 

 vious observers (from 2.000,000 to 60,000,000). When this oyster 

 was dissected, it Avas found that the gonads Avere still full of eggs, the 

 thickness of the gonad layer being about 0.7 centimeter. Since 

 l^revious experiments have shoAvn that one female may spawn 6 or 7 

 times during the season, the conclusion can be reached that one oyster 

 ma}' produce nearly half a billion eggs. 



Effect of temperature on heart heat. — A study of the effect of 

 temperature on heart beat was carried out by H. F. Prytherch at the 

 laboratory of the UniA^ersity of Pennsylvania. 



In their natural environment, oysters are subjected to Avater 

 temperatures ranging from approximately 0° to 30° C. (32° to 

 86° F.). By observing the heart beat at different temperatures 

 throughout this range, Ave are able to determine the relative degree 

 of activity of the metabolic and other physiological processes of the 

 organism, such as feeding, respiration, development of the gonads, 

 etc. The average of all these experiments shoAvs clearly that an 

 increase in temperature produces an increase in the rate of beat. 

 The heart beat Avas observed to stop at low temperatures ranging 

 from 2.5° to 5° C. (36.5° to 41° F.). Avhich supplies further evidence 

 of the hibernation of the oyster during cold Aveather. The study of 

 heart beat also shoAvs the relative importance of Avater temperature 

 (luring the spring and summer months on the growth, development, 

 and ripening of the reproductiA'e products. Since metabolic proc- 

 esses are directly proportional to temperature, it is evident that 

 fluctuations from the normal temperature Avill have a direct bearing 

 on the oyster industry. 



