A more interesting animal is the Ctenomys magellanica, a little less than the rat in size, with a shorter tail, pale grey fur, and red incisors. It is called _tuco-tuco_ from its voice, and _oculto_ from its habits; for it is a dweller underground, and requires a loose, sandy soil in which, like the mole, it may _swim_ beneath the surface. Consequently the pampa, with its heavy, moist mould, is not the tuco's proper place; nevertheless, wherever there is a stretch of sandy soil, or a range of dunes, there it is found living; not seen, but heard; for all day long and all night sounds its voice, resonant and loud, like a succession of blows from a hammer; as if a company of gnomes were toiling far down underfoot, beating on their anvils, first with strong measured strokes, then with lighter and faster, and with a swing and rhythm as if the little men were beating in time to some rude chant unheard above the surface. How came these isolated colonies of a species so subterranean in habits, and requiring a sandy soil to move in, so far from their proper district--that sterile country from which they are separated by wide, unsuitable areas? They cannot perform long overland journeys like the rat. Perhaps the dunes have travelled, carrying their little cattle with them. Greatest among the carnivores are the two cat-monarchs of South America, the jaguar and puma. Whatever may be their relative positions elsewhere, on the pampas the puma is mightiest, being much more abundant and better able to thrive than its spotted rival. Versatile in its preying habits, its presence on the pampa is not surprising; but probably only an extreme abundance of large mammalian prey, which has not existed in recent times, could have, tempted an animal of the river and forest-loving habits of the jaguar to colonize this cold, treeless, and comparatively waterless desert. There are two other important cats. The grass-cat, not unlike Felis catus in its robust form and dark colour, but a larger, more powerful animal, inexpressibly savage in disposition. The second, Felis geoffroyi, is a larger and more beautiful animal, coloured like a leopard; it is called wood-cat, and, as the name would seem to indicate, is an intruder from wooded districts north of the pampas.