The moles do not _hibernate_; the bats do. Give the reason for the difference. If bats are aroused out of a trance-like condition in winter, they may die of starvation. Why? The mother bat carries the young about with her, since, unlike birds, she has no nest. How are the young nourished? _Order_ ____. _Why?_ ____. (Key, p. 193.) [Illustration: FIG. 371.--POUCHED GOPHER (_Geomys bursarius_) × ¹⁄₄, a large, burrowing field rat, with cheek pouches for carrying grain.] [Illustration: FIG. 372.--Hind foot _a_, fore foot _b_, tail _c_, of BEAVER.] [Illustration: FIG. 373.--BEAVER.] [Illustration: FIG. 374.--POSITION OF LIMBS IN RABBIT.] =The Gnawing Mammals.=--These animals form the most numerous order of mammals. They _lack canine_ teeth. Inference? The incisors are four in number in all species except the rabbits, which have six (see Fig. 345). They are readily recognized by their _large incisors_. These teeth grow throughout life, and if they are not constantly worn away by gnawing upon hard food, they become inconveniently long, and may prevent closing of the mouth and cause starvation. The hard enamel is all on the front surface, the dentine in the rear being softer; hence the incisors sharpen themselves by use to a chisel-like edge. The molars are set close together and have their upper surfaces level with each other. The ridges on them run crosswise so as to form a continuous filelike surface for reducing the food still finer after it has been gnawed off (Fig. 345). The lower jaw fits into grooves in place of sockets. This allows the jaw to work back and forth instead of sidewise. The rabbits and some squirrels have a hare lip; _i.e._ the upper lip is split. What advantage is this in eating? In England the species that burrow are called rabbits; those that do not are called hares. Name six enemies of rabbits. Why does a rabbit usually sit motionless unless approached very close? Do you usually see one before it dashes off? A rabbit has from three to five litters of from three to six young each year. Squirrels have fewer and smaller litters. Why must the rabbit multiply more rapidly than the squirrel in order to survive? English rabbits have increased in Australia until they are a plague. Sheep raising is interfered with by the loss of grass. The Australians now ship them to England in cold storage for food. Rabbits and most rodents lead a watchful, timid, and alert life. An exception is the porcupine, which, because of the defense of its barbed quills, is dull and sluggish. The common rodents are:-- squirrels rabbits rats mice beavers muskrats porcupines guinea pig pouched gopher prairie dog prairie squirrel chipmunk ground hog field mouse