spawning curve appears in hundreds of records 

 obtained in the laboratory in the course of several 

 years of studies. It does not occur after the 

 spawning season is over and cannot be provoked 

 by temperature or chemical stimulation of the 

 oysters devoid of mature eggs. Injections of low 

 concentrations of adrenalin cause rhythmical con- 

 tractions of the adductor muscle but of an entirely 

 different type. The spawning reaction is always 

 followed by a refractory period of two to several 

 days during which the female is not responsive 

 to stimulation. 



SPAWNING REACTION OF THE MALE 



Spawning of the male does not involve the par- 

 ticipation of the mantle and adductor muscle. 

 Sperm is discharged from the spermary into the 

 epibranchial chamber by ciliary motion inside the 

 genital ducts and is swept away by the respiratory 

 current (figs. 282 and 283). The pallium remains 

 wide open and quiescent. Muscular contractions 

 of the adductor play no role in the release and dis- 

 charge of sperm, and there is no visible change in 

 the velocity of the cloacal current during ejacu- 

 lation (Galtsoff, 1938a) . Shedding of sperm occurs 

 sometimes in sudden outbursts of brief duration 

 which may be repeated at frequent intervals. 

 Toward the end of the reproductive season the dis- 

 charge of sperm may continue for several hours 



without interruption until the male is completely 

 spent. Ejaculation proceeds either from one or 

 from both spermiducts simultaneously. In the 

 latter case the flow of milky water containing 

 suspended spermatozoa can be seen emerging from 

 the cloaca and from the promyal chamber simul- 

 taneously. The males of C gigas and C. coin- 

 mercialis behave in a manner similar to the males 

 of C. virginica. 



Males of C. virginica are more responsive to 

 spawning stimuli than the females of the species. 

 They are more readily stunulated by rising 

 temperature, and shedding of sperm is easily 

 induced by various substances; a suspension of 

 eggs or filtered egg water (sea water in which eggs 

 were kept for some time) ; eggs of various bivalves 

 {Pecten irradians, Mercenaria mercenaria, Mytilus 

 edulis) ; and eggs of starfish, Asteriasforbesi. 



The latent period of stimulation varies depend- 

 ing on the substance used and its concentration, 

 but in general it is much shorter than in female 

 spawning. Suspension of eggs or egg water of 

 C. virginica induces spawning of the male within 

 5 to 6 seconds at 24° to 25° C; eggs of Pecten 

 irradians are more effective, provoking a response 

 in a male oyster in 4.6 to 4.8 seconds; the latent 

 period in the case of clam eggs (Alya arenaria, 

 Mercenaria mercenaria) is from 8 to 9 seconds at 



^^^^^ Jk. 



_A_-_k^ 



_jw^ 



vWt4aUJvl4v^^ 



Figure 282. — Shell movements of three males of C. lirgimca recorded during the shedding of sperm. There was no 

 change in muscular contraction before, during, or after spawning. Temperature 23.5° C. Time interval, 1 minute. 



310 



FISH AND WILDLIFE SERVICE 



