Other African forms constitute the small sub-family of the TREE MICE (_Dendromyinæ_), which are entirely confined to the southern portion of the continent. They are characterised by having the incisors rounded and grooved in front, the infra-orbital opening not narrow below, and the coronoid process of the lower jaw very small. The ears are clothed with hairs; and the feet, which are five-toed, are furnished with long claws, which are serviceable to the little rat-like animals in climbing up the trunks of trees. The BLACK-STREAKED TREE MOUSE (_Dendromys mesomelas_) is a rather pretty little species, of a greyish colour, with a black line down the middle of the back. It is slender in form, with a long, scaly tail, rounded ears, and the two outer toes in each foot shorter than the rest. _Steatomys pratensis_, from Mozambique, is stouter in form than the preceding, and has a short, densely hairy tail; and in _Lophuromys ater_, from the same locality, the incisors are not grooved, and the fur is developed into fine flattened bristles. The GERBILLES (_Gerbillinæ_) are distinguished from all other Muridæ (although approached by _Hapalotis_) by the great length of the hind limbs, which are converted into powerful leaping organs, somewhat as in the Jerboas and Kangaroos, although not quite to the same extent. Like all the preceding forms, they have the molars furnished with roots, but not with tuberculate crowns, these being divided into transverse plates formed by separate elliptical or rhomboidal coats of enamel. The incisor teeth are narrow, the infra-orbital opening as in the Murinæ, and the tail long and hairy. The Gerbilles are plump little animals, with a short neck, a broad head, and a pointed muzzle. The feet are five-toed, but the thumb on the fore feet is reduced to a mere wart-like process with a flat nail. They are confined to the Eastern hemisphere, and, indeed, to the African continent, the south of Asia, as far as India, and the south-east of Europe, where they live both in cultivated districts and in the driest deserts, and often occur in great numbers, when they may cause considerable damage to the neighbouring crops. They shelter themselves during the day in shallow burrows, and come forth in the evening in search of their food, which consists chiefly of grain and roots. They store up great quantities of the ears of corn in their subterranean dwellings, and in many places the poorer inhabitants search after these stores, and by digging them out procure a good supply of grain. They are very prolific, the females producing large families several times in the year. [Illustration: MOLAR TEETH OF THE GERBILLE.]