36 
In order to show how conspicuously the characteristics of 
the sexes are shown in these sections I have made careful 
drawings of two of them. Figure 53 is a section of part 
of the visceral mass of the female, showing nine ovarian 
follicles cut in various directions. Each follicle contains a 
nearly central cavity, and around this, on all sides, the 
opaque granular eggs project from the basement membrane 
of the follicle, to which they are attached either directly or 
by long stalks. Each egg contains a large, conspicuous, oval, 
transparent nucleus, and a single nucleolus, which is on that 
side of the nucleus which is nearest the point of attachment 
to the membrane. The eggs are so crowded that they are 
flattened and rendered polygonal by mutual pressure, and in 
some places there is a very regular alternation of those with 
and those without stalks. 
Figure 67 is a section of a portion of the visceral mass 
of a male, as seen with the same magnifying power. The 
space nearest the basement membrane of each follicle is 
here occupied by a thick layer of small cells, the mother 
cells of the spermatozoa, and the centre of the follicle, instead 
of being empty, as in the female, is filled with a mass of sper- 
matozoa, which have been set free. Some of the follicles 
shown in this section open by slightly constricted orifices into 
a large oval duct, with a lining of epithelial cells. These 
ducts are filled with nearly ripe spermatozoa, which have been 
forced into them from the follicles, and even in the hardened 
specimen traces of the movement of the spermatozoa frotn 
the cavities of the follicles into that of the duct are retained. 
A comparison of this figure with the one just described shows 
the male follicle to be so different from the female follicle in 
structure and appearance that the occurrence of a male folli- 
cle in a section of the ovary, or of a female follicle in a section 
of the testis, could not escape instant detection, and it is also 
plain that one of the very characteristic ovarian eggs shown 
in Figure 53, could hardly fail to attract attention at once if 
it should occur in a section of the testis. 
My observations tend to show, then, that the sexes are sep- 
arate in the American oyster of the Chesapeake Bay during 
