349 
during incubation in the common fowl. 
quadrupeds, there is a natural opening in the external mem- 
brane ; in the bird, the natural opening is in the internal one, 
which in its structure bears a resemblance to the chorion. 
EXPLANATION OF THE PLATES. 
Plate XXXII. 
Fig. 1. The ovarium of a hen that had been laying for 
some time. Natural size. 
Fig. 2. A yelk taken out of its bag, and lying in its natural 
position horizontally. Natural size. 
Fig. 3. A small portion of the yelk, with the molecule ly- 
ing on the bare surface of the yelk within the aperture of the 
inner membrane of the yelk ; the external membrane is turned 
aside, and shows a concave aperture which circumscribes 
exactly the molecule. Magnified 5 diameters. 
Fig. 4. The bare molecule after being hardened in distilled 
vinegar, laid on a black ground. Magnified 10 diameters. 
Fig. 5. The globules of which the inner areola is chiefly 
composed. Magnified 400 diameters. 
Fig. 6. An egg found in the oviduct of the same hen from 
which the above ovarium was taken. Natural size. 
Fig. 7. The same egg, its soft and semi-transparent shell 
being removed, the albumen and yelk are enclosed in the 
double membrane which lines the shell. Natural size. 
Fig. 8. A small portion of the yelk of the same egg, with 
the molecule lying on its bare surface within the orifice of 
the inner membrane, and the external membrane turned aside. 
Magnified 5 diameters. 
Fig. 9. The same molecule hardened, and laid on a black 
ground. Magnified 10 diameters. 
