62 MAMMALIAN DESCENT. [Lect. Ill, 



sac, as in some Sharks, grow into more than a tem- 

 porary union with the oviduct, or uterus, so as to derive 

 nourishment from its walls. Hence the small size of 

 the young of these creatures at birth, the food-yoUc 

 being so soon exhausted, and no other pre-natal supply 

 being at hand. 



Two newly-born young of the large Kangaroo 

 {Mcbcropus major) sent to me by Dr Bennett of Sydney, 

 were not so large as new-born Eats, i.e., they were, 

 about an inch long. Yet these small Kangaroos, whose 



Fio. 8. — New-born young from the poucli of Kangaroo (Macropus Major), 

 magnified 2| diameters. 



parents are the size of Sheep, like the sedentary Oyster 

 "attend at ease moist nutriment," being attached to 

 the teats, and there abiding. The embryo of the 

 Marsupial is comparable in some degree to that of 

 many fishes, in which the food-yolk is soon exhausted,. 



