INTEODUCTORY. 
Mammals may be delined as vertebrated * air-breathing warm- 
blooded animals, generally more or less clothed with hair, in 
which the females are provided with mammary, or milk, glands — 
these being also present, though small and fnnctionless, in the 
males. With the exception of the Australasian Monotremes, 
which lay eggs, the young are brought forth alive. The limbs 
are usually four in number, the hind pair being, how’ever, 
sometimes modified into swimming-paddles or suppressed 
altogether, while the front ones are in some cases developed 
into wings, and in others into flippers. The tail may be rudi- 
mentary, as in Man and the higher Apes ; long and simple, 
as in Cats ; prehensile f, ‘Ls in the American Monkeys and 
Opossums ; provided with a long tassel for driving away insects 
from the skin, as in Elephants, Cattle, &c. ; or, finally, modified 
into a swimming-organ, either by the outgrowth of broad 
flukes ” as in Whales, or by being flattened vertically as in 
Beavers, or from side to side as in the Musk-rat, the African 
Fotamogale, and others. 
The heart of Mammalia consists of two completely separated 
divisions, each with an u])per and lower chamber (auricle and 
ventricle). The blood has a high temperature, exce])t in some 
of the lowest forms, such as the Spiny Anteaters, or Echidnas, of 
Australasia. 
* /. e. with a backhoue. 
t 1. e. witli the power of curling round and grasping objects. 
B 
