little creature, with a low gurgling language, like running babbling
waters; in habits resembling its domestic pied relation the guinea pig.
It loves to run on clean ground, and on the pampas makes little
rat-roads all about its hiding-place, which little roads tell a story to
the fox, and such like; therefore the little cavy's habits, and the
habits of all cavies, I fancy, are not so well suited to the humid
grassy region as to other districts, with sterile ground to run and play
upon, and thickets in which to hide.

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,