82 Sir Everard Home on the changes the ovum of the frog 
their full size, nor to have received their proportion of jelly, 
till they arrive at a cavity close to the termination of each 
oviduct, formed by a very considerable enlargement of those 
tubes, corresponding, in many respects to the cloaca in 
which the pullet's egg is retained till the shell becomes 
hard: 
These large bags, in which the oviducts of the frog termi- 
nate, when distended with ova, put on an appearance so like 
the enlarged horns of the uterus of the quadruped when they 
are filled with young ones, that they have by some anatomists 
been called a double uterus. This, however, is an improper 
appellation. 
When the bva are deposited in these reservoirs, they be- 
come completely formed, and in a state to be impregnated 
by the male influence, which is applied to them in the act 
of their expulsion. As they are pressed upon each other, 
by being confined in a small space, the gelatinous covering 
takes on an hexagonal figure, in the centre of which is the 
ovum. 
The ova, when examined by a magnifying glass in a strong 
light, exhibit an appearance so similar to the molecule in the 
pullet's egg, as to be readily mistaken for it ; but a more 
attentive inspection shows, that it is only a white portion 
in the ovum, seen through the covering of the vesicle.. When 
the vesicle is punctured by the point of a needle, the contents 
are so fluid as readily to run out, leaving the strong trans- 
parent memb^'anous bag lined with a fluid nigrum pigmentum, 
empty. 
Immediately after impregnation there is no change in the 
appearance of the jelly, nor of the vesicle contained in it, in 
