PROGEESS IN BIOLOGICAL INQUIKIES, 19 31 511 



The latent periods of spawning reactions — that is, the time elapsed 

 from the moment the 05'ster was exposed to a given temperature 

 until the beginning of spawning — varies from 20 to 257 minutes and 

 apparently is not correlated with the temperature, the quickness of 

 the response probably depending on the condition of the organism 

 itself. 



The fact that the females can be stimulated hj a temperature of 

 24.6° C. or higher suggested the possibility that similar effects might 

 be obtained by a longer exposure to temperatures between 20° and 

 24.5° C. The results of a large number of experiments, of which only 

 three will be described here, show that this is very doubtful. On 

 July 10, three ripe females were taken from the tank, in which the 

 temperature during the previous week fluctuated between 18.5° and 

 19.5° C. and placed in an aquarium filled with filtered sea water. The 

 temperature was kept at 22.6° but occasionally rose to 23.4°. The 

 shell movement of each oyster was recorded on the kymograph. The 

 first oyster was kept for 5 hours and 22 minutes, the second for 29 

 hours and 53 minutes, and the third one for 73 hours and 13 minutes. 

 The water in the aquaria in which the second and third oysters were 

 kept was changed twice a day. None of the oysters spawned during 

 that time, but each of them spawned after sperm were added to the 

 water, the latent periods being 16, 24, and 15 minutes, respectively. 



It is interesting to note that in both cases of stimulation, either by 

 the temperature or by the sperm, the reaction is alike and is char- 

 acterized by a series of rhythmical contractions of the adductor 

 muscle and of the mantle. From that an inference can be made that 

 both factors release some mechanism in the organism of the female 

 which in turn stimulates the muscle and causes the discharge of 

 eggs from the ovary. In this respect the reaction is not specific. It 

 is, however, specific in the sense that sperm of other mollusks (My a, 

 Mj^tilus) fail to induce spawning of the oyster. No positive results 

 were obtained also when the sperm of 0. cucuUata was added to the 

 female of 0. virginica and vice versa. 



From a biological point of view stimulation of spawning either 

 by the temperature or by the sperm- and-egg suspension is of great 

 interest. It provides a mechanism which insures successful propaga- 

 tion of the species. Should the temperature of the sea water fail 

 to reach the effective point which would induce shedding of eggs by 

 the females, still the spawning of the latter could be provoked by 

 the sperm discharge of the males, which are more susceptible to the 

 increase in temperature. In most of the cases observed by Doctor 

 Galtsoff, when several oysters were kept together the males spawned 

 first and induced the shedding of eggs by the females. The process, 

 once started, spreads by mutual stimulation of the two sexes through- 

 out the whole oyster bed and results in simultaneous spawning of 

 the oyster population. 



SOUTH ATLANTIC OYSTER STUDIES 



Investigations and experiments of a practical and scientific nature 

 are being conducted from North Carolina to Florida under the super- 

 vision of Dr. H. F. Prytherch, director of the Beaufort (N. C.) lab- 

 oratory, which serves as the headquarters for this work. In 



