Many interesting small mammals are nocturnal or lead such obscure and hidden lives that they are rarely observed except by naturalists. Of these are the numerous species of shrews, which include the smallest mammals in the world. These tiny beasts all live among the vegetation and debris on the surface of the ground or in little burrows below. With the moles they are members of the order Insectivora and depend mainly on insects and meat for food. Despite their minute size, they are possessed of an indomitable courage and ferocity, which leads them without hesitation to attack and kill mice many times their own weight. The genus _Sorex_, of which the common shrew is a member, is circumpolar in distribution, the various species ranging through England, the European mainland, Asia, and North America as far south as Guatemala. The common shrew is a purely North American animal, occupying all the northern part of the continent from the Arctic shores of Alaska and Canada south to northern Nevada, South Dakota, Illinois, and Pennsylvania, and along the Allegheny and high Rocky Mountains to North Carolina and New Mexico. Its vertical range extends from the seacoast up to timberline in the Rocky Mountains. The common shrew is the smallest of the mammals in all the northern parts of this continent, and one marvels at the possibility of such a tiny morsel of flesh and blood withstanding the rigors of the arctic winters. It measures about four inches in total length and weighs about forty-five grains; the body and tail are slender, the nose long and sharp, and the rim of the ears shows a little above the dense velvety fur. By these characters it may be distinguished from the larger, more heavily proportioned (and darker-colored) short-tailed shrews which abound with it in certain parts of its range. Its smaller size and grayish brown color are the main superficial differences between it and other American members of the same genus. The climatic differences in its wide range have developed several geographic races, none of which, however, show strongly marked characters. This shrew appears to have a most catholic taste, so far as its surroundings are concerned, for it appears to frequent every type of situation where shelter and food can be found. It abounds among the peat beds and sphagnum mosses of the desolate barrens bordering on the Arctic coast, as well as amid the rotten stumps, old logs, fallen leaves, and other vegetable debris on the floor of the forests farther south. It will be found also in the rank matted vegetation about marshes, in old fields and occasional sphagnum swamps in the southern parts of its range.