FAMILY X.—DIPODIDÆ (THE JERBOAS).
The JERBOAS are a more extensive and much more widely distributed family of hopping Rodents. In these we find the organisation for jumping brought to greater perfection than in any other group. The body is light and slender, the hind limbs much elongated, the fore limbs very small, and the tail long and usually tufted at the end. The number of toes on the hind feet varies from three to five, and the metatarsal bones are very often united so as to form what is called a “cannon bone” in the Horse. The incisor teeth are compressed; the molars sometimes four, but usually three in each series, rooted or rootless, not tuberculate; the infra-orbital opening is rounded and very large, and the zygomatic arch slender. The great home of these animals is the vast steppe region which stretches from South-eastern Europe across the greater part of Central Asia, but they extend southwards round the eastern extremity of the Mediterranean, through Syria and Arabia to Egypt and Africa, over a great part of which they are found, and eastward to India, Afghanistan, and Ceylon. A single species occurs at the Cape of Good Hope; and another is found in North America. We may commence by noticing this last species, as it not only makes the nearest approach to those of preceding families, especially the Muridæ, but differs from the rest of the Jerboas in characters of such importance, that Dr. Coues maintains its right to form a separate family (Zapodidæ).
SKULL OF THE CAPE JUMPING HARE.
The AMERICAN JUMPING MOUSE (Zapus[54] hudsonius) has a wide range, extending across the continent of North America from sea to sea, and from Labrador, Hudson’s Bay, and the Great Slave Lake in the north, to Virginia and the elevated portions of Arizona and New Mexico in the south. It is an elegant little mouse-like creature, rather more than three inches long, and furnished with a cylindrical tail, which exceeds the head and body in length by about two inches. Its hind limbs are not quite so disproportionately developed as in the other members of the family. Its fur in summer is of a brown colour above, becoming yellowish on the sides and white below; in the winter the brown tint covers the whole surface. The ears, which are not very large, are black, with a light-coloured rim; the hind feet are greyish, and the fore feet whitish on the upper surface; and the tail, which tapers to an exceedingly fine point, where there is a fine pencil of hairs, is ringed and nearly naked.
The characters in which this animal differs from its nearest relatives are as follows:—In the upper jaw there are four rooted molars on each side, the first being very small, the second the largest, and the rest gradually diminishing in size; the fore feet have the thumbs rudimentary, and the hind feet have five toes, all of which touch the ground; the metatarsal bones are separate; and the soles of the feet naked, with granules and small horny shields.
AMERICAN JUMPING MOUSE.
The American Jumping Mouse is found in meadows in the neighbourhood of woods and copses. It is nocturnal in its activity, sleeping during the day in its burrow, which is usually about two feet deep, and coming forth at night. It is sociable in its habits, and excessively active, covering from three to five feet of ground at each leap, so that it is a matter of no little difficulty to capture a specimen in the open. In the woods it is worse, as the little creature will bound over bushes, and get out of sight in a moment. Its food consists of seeds of various kinds, and it is exceedingly fond of beech-mast. For protection from the cold of winter the Jumping Mouse makes a little hollow clay ball, within which it coils itself up, and goes comfortably to sleep. The nest is made about six inches under the surface of the ground, and is composed of fine grass, sometimes mixed with feathers, wool, and hair; and in this the female produces from two to four young, probably several times in the course of the summer, as the nests and young are to be found from May to August.
