L 234 j 
XVI. On the Ova of the different tribes of Opossum and Orni - 
thorhynchus . By Sir Everard Home, Bart . V. P. R. S. 
Read March 25, 1819. 
Now it is determined that the ova of quadrupeds in general 
are formed in corpora lutea, and that in all such animals 
the ova become attached to the uterus, and by this means 
the foetus receives its support and increase ; we are enabled 
to ascertain the modes of formation of the ova of the opos- 
sum tribes, which from the want of this previous knowledge 
have not been investigated with the smallest degree of success. 
This becomes the best apology that can be made for the fai- 
lure of every former attempt. 
In this enquiry it will be found, that the ova of all the 
animals of these tribes are not formed in the same manner, 
and that the differences met with, make two distinct links 
between quadrupeds in general and the ornithorhynchi ; 
these again approach so nearly to the bird, as to complete 
the links of gradation between the human species and the 
feathered race, so far at least, as concerns their mode of 
generation. 
The mode of formation of the ova in the kangaroo, consti- 
tutes the first link in this beautiful series. 
In the kangaroo, Mr. Bauer has found the corpus luteum, 
similar to that in quadrupeds ; it is represented in the annexed 
drawing. Indeed it is to Mr. Bauer's talents and microsco- 
pical observations that we are indebted for all our infor- 
mation upon this subject. 
