24,0 Sir Eyerard Home on the ova of the Opossum tribe. 
Fig. g. The globules of the yelk diluted with water, mag- 
nified four hundred diameters. 
Plate XIX. 
Ovarium of the Hen. 
Fig. l. Front view of the ovarium of alien : natural size. 
Fig. 2. A small portion of the same, with some very 
young yelks : natural size. 
Fig. 3. The same small portion, magnified five diameters. 
Fig. 4. Back view of the ovarium of the hen : natural size. 
Since this Paper was sent to the press, the author has received, 
through the kindness of Governor Mac Ouarrie and Sir John 
Jemison, four specimens of female Ornithorhynchi Paradoxi 
from New South Wales, and finds in all of them, .as well as in 
every other specimen that has come under his observation, 
that there are yelk-bags only in the left ovarium, showing that 
both ovaria are not generally in use at the same time. This is 
an approach to the bird, in which there is only one, lying on 
the left side. 
In the chick of the common fowl before it is hatched, there 
is a small portion of an oviduct on the right side, but his 
disappears before the chick is completely formed. 
