62 



MAMMALIAN DESCENT. 



[Lect. IIL 



sac, as in some Sharks, grow into more tlian 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-yolk 

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

 being at hand. 



Two newly-l^orn young of the large Kangaroo- 

 [Macropus 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 



Fig. 8.--New-boru young from the poucli of Kangaroo {Macro23Us Major), 



magnified 2g diameters. 



parents are the size of Sheep, like the sedentary Oyster 

 '^attend at ease moist nutriment," beino- 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, 



