Fig. 369.—Skeleton of Bat.
As with the mole, the skeletal adaptations of the bat are most remarkable in the hand. How many fingers? (Fig. [369].) How many nails on the hand? Use of nail when at rest? When creeping? (Fig. [369].) Instead of feathers, the flying organs are made of a pair of extended folds of the skin supported by elongated bones, which form a framework like the ribs of an umbrella or a fan. How many digits are prolonged? Does the fold of the skin extend to the hind legs? The tail? Are the finger bones or the palm bones more prolonged to form the wing skeleton?
Fig. 370.—Vampire (Phyllostoma spectrum) of South America. × ⅙.
The skin of the wing is rich in blood vessels and nerves, and serves, by its sensitiveness to the slightest current of air, to guide the bat in the thickest darkness. Would you judge that the bat has sharp sight? Acute hearing?
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].)
Fig. 371.—Pouched Gopher (Geomys bursarius) × ¼, a large, burrowing field rat, with cheek pouches for carrying grain.
Fig. 372.—Hind foot a, fore foot b, tail c, of Beaver.