35 
PART II— EMBRYOLOGY. 
THE SEXES OF THE OYSTER. 
A list of the contradictory opinions which various writers 
have expressed regarding the distinctness of the sexes of the 
oyster is hardly worth publishing, since all the thoroughly 
competent observers who have investigated the subject in 
modern times agree that each oyster is, at the breeding season, 
•either a male or a female. 
During my investigations I submitted more than a thousand 
•oysters to microscopic examination. My studies were carried 
on during the breeding season, and I did not find a single 
hermaphrodite. The male cells are so small compared with 
the eggs that it would be impossible to state that a mass of 
oggs taken from the ovary contained no spermatozoa, although 
they could not escape detection if they were at all abundant. 
On the other hand, a single egg in the field of the micro- 
scope in a drop of male fluid would be very conspicuous, and 
could not escape detection ; and the fact that not a single case 
of this kind occurred is sufficient to establish the distinctness 
of the sexes at the breeding season. 
A short time since, October 25th, I examined a number of 
oysters with the same result. I found six females with ovaries 
filled with nearly ripe ovarian eggs, and eight males whose 
testes were filled with spermatozoa, most of which were im- 
mature, but some of them fully developed and active. 
One of the males and one female were hardened in chromic 
acid, and a number of microscopic sections were cut from 
various parts of the reproductive organs of each. Hone of the 
ovarian follicles or parts of follicles of the female contained 
anything but eggs, and not a single egg at any stage of devel- 
opment was found in any part of the body of the male. 
