The body in the Rodents is generally plump and short, and the head is borne upon a short neck. The limbs also are usually short, so that the belly is close to the ground; but in some cases all four legs are of moderate length, or, as already stated, the hind legs are enormously developed, forming powerful leaping organs. In general structure, as to a certain extent in habits, there is, in fact, a most striking parallelism between the Rodentia and the Insectivora (_see_ Vol. I., p. 343); in both we find arboreal and terrestrial forms, and among the latter some specially organised for burrowing in the earth, and others equally adapted for springing lightly over its surface; a few, also, in both orders, are aquatic. But here the parallel ceases. The dentition in the two groups is widely divergent, and, as might be anticipated from this circumstance, the food is very different; for, although some Rodents, such as the common Mouse and Rat, are omnivorous, there is no doubt that, as a whole, the Rodents must be regarded as vegetarians. Grass and the leaves of plants and trees furnish some of them with nourishment; whilst others feed upon fruits, seeds, and nuts, in the consumption of which last the powerful incisor teeth come into play. Many species lay up stores of food for the winter season, of which they pass more or less in a state of torpidity; and some of these are provided with cheek-pouches, often of considerable size, in which to convey their harvest into their store-houses.