11 
If the point of a knife be pushed into the reproductive or- 
gan a milk-like fluid will ooze out of the cut, and a little of 
it may be taken up on a knife blade and transferred to a glass 
slide for examination. The drop of fluid should be thoroughly 
mixed with a drop of sea water and placed on the slide, and 
gently covered with a cover-glass, and examined with a mag- 
nifying power of about one hundred diameters. If the speci- 
men is a female, this power will show that the white fluid is 
almost entirely made up of irregular pear-shaped ovarian 
eggs (Figure 49), each of which contains a large circular 
transparent germinative vesicle surrounded by a layer of 
granular slightly opaque yolk. It is almost impossible to de- 
scribe the slight differences which distinguish the perfectly 
ripe egg from those which are nearly ripe but not capable of 
fertilization, although a very little experience will enable one 
to tell whether it is worth while to attempt the fertilization 
of the eggs of any given female. 
When the drop of fluid is thoroughly mixed with the sea- 
water, the eggs should appear clean, sharply defined, separate 
from each other, and pretty uniformly distributed through the 
drop, as shown in the figure. If they adhere to each other, 
or if their outlines are indistinct, or if there is much fine 
granular matter scattered between the eggs, it is probable that 
the attempt at artificial fertilization will at best be only par- 
tially successful. 
When a perfectly ripe female is found, it should be set aside 
and the search continued for a male. The question of the 
sex of the oyster has long been a matter of dispute, and the 
subject will be fully discussed in another place. All that 
concerns us now is to know that for all practical purposes the 
sexes are separate in the European as well as the American 
oyster. At the breeding season each individual is either ex- 
clusively a male or exclusively a female. Out of several 
thousand which I examined, I have not found one which con- 
tained both eggs and male cells, and all the best authorities 
upon the European oyster make the same statement, although 
there is some reason for the belief that an oyster may give 
