Character of the Order--A well-defined Group--Teeth Evidence--Kinds and Number of Teeth--The Incisors: their Growth, Renewal, and Composition--The Molars--The Gnawing Process--Skeleton--Brain--Senses--Body--Insectivora and Rodentia--Food of Rodents--Classification--THE SIMPLE-TOOTHED RODENTS--Characteristics--THE SQUIRREL-LIKE RODENTS--SCIURIDÆ--Distinctive Features--THE COMMON SQUIRREL--Form--Distribution--Food--Bad Qualities--Habits--THE GREY SQUIRREL--THE FOX SQUIRREL--Flying Squirrels--Their Parachute Membrane--THE TAGUAN--Appearance--Habits--Other Species--THE POLATOUCHE--THE ASSAPAN--The Genus _Xerus_--THE GROUND SQUIRRELS--THE COMMON CHIPMUNK--THE MARMOTS--Distinguishing Features--THE SPERMOPHILES--THE GOPHER--THE SISEL, OR SUSLIK--THE BARKING SQUIRRELS--THE PRAIRIE DOG--Description--Species--Habits--Burrows--Fellow-inmates in their “Villages”--THE TRUE MARMOTS--THE BOBAC--THE ALPINE MARMOT--THE WOODCHUCK--THE HOARY MARMOT, OR WHISTLER--ANOMALURIDÆ--Tail Peculiarity--Distinctive Features--HAPLODONTIDÆ--Description--THE SEWELLEL--CASTORIDÆ--THE BEAVER--Skeletal Peculiarities--General Form--Appearance--Distribution--The Beavers of the Old and New World--Habits--Wonderful Sagacity--The Building Instinct--Their Method of Working--The various Stages--Their Lodges--Their Dams--Activity by Night--Flesh--Hunted--The _Castoreum_. While the last few chapters have been devoted to orders which contain the largest and most powerful of terrestrial mammalia, we have now to treat of a group, all the members of which are of comparatively small size. “Mice, rats, and such small deer,” to use Shakspere’s phrase, make up a great proportion of the order Rodentia. The biggest of them is only about the size of a small Pig; and perhaps the common House Rat, or, at any rate, the common Squirrel, may be taken as showing the average dimensions of a Rodent. But, although from this point of view they may be looked upon as “a feeble folk,” their numerous species render them a most important section of the mammalian fauna of nearly all countries, and this importance is greatly increased, practically, by the immense number of individuals by which each species is usually represented.