2$6 
Sir Everard Home on the 
these circumstances are represented, but the uses of the 
different parts, I readily confess, I was at that time unable 
accurately to comprehend. 
The mode of formation of the ova in the Koli and the 
Wombat of New South Wales, and in the great and small 
Opossum of North America, constitutes the second link in this 
chain of gradation. 
In none of these- different genera are there corpora lutea 
in the ovaria, but in their place a certain number of yelk-bags 
of different sizes ; and these are so completely imbedded in 
the substance of the ovarium, that to common observation 
they appear to be so many corpora lutea. There is no 
thickened glandular structure surrounding the Fallopian tubes 
near their termination in the uterus. Instead of one uterus 
having two Fallopian tubes, there are two uteri and one tube 
to each.; and in proof that the ovum in each uterus is im- 
pregnated separately in its own cavity, the point of the penis 
jn the male is so formed as to throw the semen into both. 
The lateral tubes, by which the foetus is aerated in the kan- 
garoo, are formed in these genera in a different manner ; there 
is only one to each uterus, and this, instead of communica- 
ting with the uterus at the fundus, opens into it at the cervix. 
The yelk-bags are shown in the annexed drawing. I have 
not had an opportunity of examining the ovum of any of 
these animals in utero, but Mr. Bell, a very intelligent sur- 
geon, transmitted an account to Sir Joseph Banks, of the dis- 
section of a female koli, in which he met with an imperfectly 
formed embryo in each of the uteri, surrounded by a mass of 
albumen. The young of all these genera are expelled from 
the uterus into the marsupium, and become attached to the 
prominent points of the nipples. 
