BULLETIN OF THE UNITED STATES FISH COMMISSION. 233 



which have been advanced. Some authors have asserted that fecunda- 

 tiou takes place iu the ovary by a contact effected between the two gen- 

 crating elements, when these elements, which are formed in one and 

 the same gland, both arrive at the condition of maturity, so that all the 

 eggs would be fecuiulated when they pass into the oviducts. It has also 

 been stated that the embryo is comidetel^' formed (that is, provided 

 with shells) when it passes from the ovary into the mantle of the mother 

 oyster. This latter opinion is entirely erroneous, ibr by examining the 

 white spawn of oysters it will be seen that the eggs which compose it 

 are mostly in the very first stage of their development. 



One of our most distinguished naturalists, Lacaze-Duthiers, has 

 found the truth by showing that the oyster is a hermaphrodite, perform- 

 ing by turns, but never simultaneously, the functions of each sex ; and 

 that the fecundation of the eggs which probably takes place in the gen- 

 erative orifices, is accomplished by the participation of another oyster. 

 The observations which we made in the laboratory of M. Balbiani, at 

 the College of France, corroborate this opinion of the great French 

 'Zoologist, which is also shared by Mobius. We have never yet found, 

 in one and the same gland, eggs and siiermatozoa, the two generative 

 elements, in the same stage of development; and we have never seen 

 these two elements reach maturity at the same time. From this we have 

 drawn the logical conclusion that they do not come in contact with each 

 other.* 



The spawning season of the Ostrea edtiUs occurs at different jieriods 

 and varies very much in length. Sometimes it commences in April and 

 does not end till some time in September. Even in December oysters 

 containing embryos have been found. Sometimes the spawning season 

 does not begin till May or June and ends in August. It is regulated 

 by the temperature of the season and by the mildness or severity of 

 the preceding winter. In Juno and July, however, the emission of 

 spawn is generally most abundant. 



The activity of the reproductive organ is, so to speak, constant. 

 After the embryos have been emitted the oyster, which has become 

 very lean, begins to i)ick up again, and soon arrives at a state of reple- 

 tion similar to tliat which it possessed before spawning, but which is 

 due to the presence of fat around the gland. This is tlie time when it is 

 most sought after for the market. But wliile the accumulation of fat 

 is going on epithelial cells develop, wliich later are transformed and 

 bring forth the generative elements. When the weather is mild, even 

 in winter, the transformation takes place very rapidly. We have fre- 



* It will he seen further on that the eggs of the Ostrea cdulis perish iu pure eea-water. 

 This is not the case with zoosperms. These, while they are inside the gland, are not 

 vigorous, no matter what stage of devel(>i>iiient they have reached. But as soon as 

 they are brouglit in contact with sea-water they become animated and begin to vi- 

 brate. It would seem that they do not acquire their fecundating quality until they 

 have been iu the water for a while. This would be another argument against auto- 

 fecundation. 



