114 MAMMALS

habits, and are found in both hemispheres, the Asiatic
species all living in barren districts. One of the
species (A. monax) is the woodchuck, so often men-
tioned in American books.

The flying squirrels are of considerable age, their
remains having been unearthed in the middle tertiaries
of Europe. Nowadays there is but one European
species, the polatouche (Sczuropterus volans), which is
found in Russia and Siberia, and is a handsome little
animal about six inches long, tawny above and white
below. In North America there is but one species
(S. volucella), whichis greyish aboveand cream-coloured
below. All the other species are found in India or
Malaysia ; some of them will glide for eighty yards
in the air from tree to tree, but their flight is always
slightly downwards.

The beavers havea family tothemselves(Castor¢de).
One of the fossil beavers was five feet long, and there
were several species of them. There are but two living
species, Castor fiber of the Old World, and C. cana-
denszs of the New, and these are the largest of the
rodents except the capybara. They are also the most
intelligent, particularly the American beaver. He is
not only a mere burrower as his European relative is
becoming to be, but an architect and an engineer. He
builds his lodge of wood of his own felling, and these
lodges are in towns, and in association with his fellow-
townsmen; he builds a dam to keep the water ata
convenient level, and even excavates a canal to bring
the trees along on whose bark and wood he feeds. The
work he does is wonderful. Mr. Baillie-Grohman
describes how he once watched a party at work. ‘It