232 ANIMAL FORMS 
The opossums, fairly abundant ‘throughout the warmer 
portions of this country, are rat-like creatures, with scaly 
tails, yellowish-white fur, large head, and pointed snout. 
Except at the breeding season they lead solitary lives, 
sleeping in the holes of trees by day and at night feeding 
on roots, birds, and fruits. 
The kangaroos; familiar from specimens in menageries 
or museums; chiefly, inhabit the plains of Australia: The 
giant -gray: kangaroos (Macropus giganteus), attaining a 
height of over six feet, go in herds, and owing to the great 
development, of their hind limbs and tails are able, when 
alarmed, to travel with the swiftness of a horse. Several 
smaller species, some no-larger than rabbits, live among 
the brush, and like their larger relatives crop the grass and 
tender herbage with sharp incisor teeth. 
While the marsupials do not lay eggs as does the duck- 
mole, they allow them to develop within the body for a 
very short time only. Hence the young, when born, are 
scarcely more than an inch in length, and are blind, naked, 
and_perfectly helpless. -At once they are placed by the 
mother in the pouch of skin, or marsupium, on the under 
side of her body. In this the young are suckled and pro- 
tected until able to gather their own food and fight their 
own way. 
218. Rodents or gnawers (Glires).—The rodents are a 
large group of mammals, including such forms as the rats, 
mice, squirrels, gophers, and rabbits. They are readily dis- 
tinguished by their clawed feet adapted for climbing or 
‘burrowing, and by large curved incisor teeth. Unlike 
ordinary teeth, they grow continually, and, owing to the 
restriction of the hard enamel to their front surfaces, wear 
away behind faster than in front, thus producing a chisel- 
like cutting edge. 
The largest of our native rodents is the porcupine 
(Erethizon dorsatus), which ranges from Maine to Mexico, 
and attains a length of nearly three feet. Many of the hairs 
