Miscellaneous. 329 
this, nothing has yet been quite demonstrated. Considering that 
the genital gland rarely presents the two sexes at the same degree 
of maturity, it is probable that it does not fecundate itself. 
The Portuguese oyster, on the contrary, is unisexual. That is 
incontestable. We have opened a great number of them, taken at 
all the phases of the reproductive period ; and all were either ex- 
clusively males or exclusively females. 
On the other hand, contrary to what takes place with the common 
oyster, in which fecundation is accomplished within the valves, the 
ova are expelled from the shell; it is in the bosom of the water that 
they meet with the fecundating element. In fact neither ova nor 
embryos are ever found in the mantle of O. angulata. This is 
moreover corroborated by the fact that the ova and embryos of the 
Portuguese oyster are developed in the pure sea-water, while those 
of the common oyster, atleast during the whole period of the gesta- 
tion of the ovum and till the moment when the embryo abandons 
the maternal shelter, cannot live out of the liquid contained in the 
shell, which liquid, according to an analysis made in M, Berthelot’s 
laboratory, contains a notable proportion of albumen. In vain we 
tried to preserve, in sea-water aerated and renewed, any embryos of 
O. edulis to complete development, whether they were in the state 
of white or of grey spat: the white embryos succumbed after two 
er three days, the grey ones after twelve or fifteen, although they 
had within reach collectors to which they could attach themselves. 
These facts constitute an essential difference between the two 
species, which excludes every hypothesis of crossing and must cause 
the rejection of the theory of hybridation advocated by some ostrei- 
culturists. We have moreover made some direct experiments at 
hybridation, which issued in a negative result. Thus, at different 
times during last year and this, we placed ova from Portuguese 
oysters in contact with zoosperms taken from common oysters, and 
conversely ; but never, under the conditions of our experiments, 
have the elements naturally and instinctively come together, never 
has there been any trace of fecundation or development. 
The sexual elements of O. angulata being, as we have said, clearly 
separate, we had a glimpse of the possibility of accomplishing arti- 
ficial fecundation. Theexample of Brooks, of Baltimore University, 
who made successful attempts at artificial fecundation with Ostrea 
virginiana, was also encouraging. 
After much feeling our way, we adopted the following method. 
With a little practice, it is easy to distinguish the sexes with the naked 
eye. By means of a camel’s-hair pencil we detach the ova from the 
ovary, and deposit them in a vessel filled with sea-water—a phial, 
for example. In order to disaggregate them and clear them from 
the foreign matters with which they may be encompassed, the phial 
is agitated for a few moments, and then the liquid allowed to 
settle. The ova which are fit for fecundation sink to the bottom of 
the vessel; what remains in suspension must be eliminated. 
The liquid is decanted, and fresh sea-water poured in; and it is 
sufficient to add a small portion of seminal liquor in order that the 
Ann. & Mag. N. Hist. Ser. 5. Vol. x. 22 
