Of the hares and rabbits the cottontail (_Lepus nuttalii_) and the common jack-rabbit (_L. campestris_) are the best known. The cottontail is found all over the United States, but shows some variation in the different regions. There are several species of jack-rabbits, all limited to the plains and mountain regions west of the Mississippi River. The food of rabbits is strictly vegetable, consisting of succulent roots, branches, or leaves. Rabbits are very prolific and yearly rear from three to six broods of from three to six young each. There are two North American species of porcupines, an Eastern one, _Erethizon dorsatus_, and a Western one, _E. epixanthus_. The quills in both these species are short, being only an inch or two in length, and are barbed. In some foreign porcupines they are a foot long. They are loosely attached in the skin and may be readily pulled out, but they cannot be shot out by the porcupine, as is popularly told. The little guinea-pigs (_Cavia_), kept as pets, are South American animals related to the porcupines. The pocket gophers, of which there are several species mostly inhabiting the central plains, are rodents found only in North America. They all live underground, making extensive galleries and feeding chiefly on bulbous roots. The mice and rats constitute a large family of which the house-mice and rats, the various field-mice, the wood-rat (_Neotoma pennsylvanica_) and the muskrat (_Fiber zibethicus_) are familiar representatives. The common brown rat (_Mus decumanus_) was introduced into this country from Europe about 1775, and has now nearly wholly supplanted the black rat (_M. rattus_), also a European species, introduced about 1544. The beaver (_Castor canadensis_) is the largest rodent. It seems to be doomed to extermination through the relentless hunting of it for its fur. The woodchuck or ground-hog (_Arctomys monax_) is another familiar rodent larger than most members of the order. The chipmunks and ground-squirrels are commonly known rodents found all over the country. They are the terrestrial members of the squirrel family, the best known arboreal members of which are the red squirrel (_Sciurus hudsonicus_), the fox-squirrel (_S. ludovicianus_), and the gray or black squirrel (_S. carolinensis_). The little flying squirrel (_Sciuropterus volans_) is abundant in the Eastern States.