GENERAL STRUCTURE OF MAMMAIS, ~ 91 
them); and the Whale tribe are adapted in their general 
form to lead the life of fishes (among which they are still 
commonly ranked by persons ignorant of natural history). 
Notwithstanding these marked differences in external form, 
there is a great correspondence as to internal structure ; for 
bats and whales, as well as ordinary quadrupeds, produce 
their young alive, and suckle them afterwards ; they are also 
warm-blooded, breathing air, and having an active circulation. 
The bodies of Mammals are, for the most part, more or less 
completely covered with hair, which serves to keep in their 
warmth ; and this is seldom absent, except in such as inhabit 
warm climates and do not require this provision. In the 
“Whales, the same end is answered by the thick layer of oi! in 
‘the substance of the skin, constituting the blubber ; and Man 
‘is left to form a protective covering for his body by the exer- 
‘cise of his own ingenuity. The general arrangement of the 
_Sub-maxillary Gland Parotid Gland 
Fig. 30.—Inrerior or 4 Mowxkey. 
| = organs of Mammals will be seen from the accom- 
= figure of the body of a Monkey, laid open in such 
; 
