Mode of Generation of the Kangaroo. 235 
In other quadrupeds the influence of the semen is ascertained 
to have reached the fallopian tube, by well attested cases of the 
foetus never arriving at the uterus. In this animal such an effect 
is rendered difficult, and not very probable ; it is therefore 
more natural to suppose the impregnation takes place in the 
same way as in the detached foetuses of other animals. 
This mode of nourishing the young resembles, in some re- 
spects, what takes place in the dog-fish, whose egg is deposited 
in the oviduct, and hatched there. The yelk of the egg in the 
bird being conveyed into the belly at the time of its being 
hatched, made me desirous to see if any of the gelatinous sub- 
stance of the uterus was conveyed into the belly of the young 
kanguroo, but I could not on dissection find any such appear- 
ance ; and as it is to be immediately attached to the nipple, 
there is no apparent necessity for such a provision. 
The egg of the turtle and dog-fish, which live in water, is 
similar to the contents of the uterus in the kanguroo in being 
composed of one substance only, which renders it probable that 
in birds it is made up of two substances, on account of the 
young being longer unable to procure its own food. 
If we consider the varieties which occur in the formation of 
different animals as so many parts of the same system, the 
mode of generation just described will be found, in this chain 
of gradations of nature, to form a link between animals whose 
young are nourished by means of a connection with the uterus, 
and those that are nourished independant of it. 
