A common rodent is the coypú--Myiopotamus coypú--yellowish in colour with bright red incisors; a rat in shape, and as large as an otter. It is aquatic, lives in holes in the banks, and where there are no banks it makes a platform nest among the rushes. Of an evening they are all out swimming and playing in the water, conversing together in their strange tones, which sound like the moans and cries of wounded and suffering men; and among them the mother-coypú is seen with her progeny, numbering eight or nine, with as many on her back as she can accommodate, while the others swim after her, crying for a ride. With reference to this animal, which, as we have seen, is prolific, a strange thing once happened in Buenos Ayres. The coypú was much more abundant fifty years ago than now, and its skin, which has a fine fur under the long coarse hair, was largely exported to Europe. About that time the Dictator Rosas issued a decree prohibiting the hunting of the coypú. The result was that the animals increased and multiplied exceedingly, and, abandoning their aquatic habits, they became terrestrial and migratory, and swarmed everywhere in search of food. Suddenly a mysterious malady fell on them, from which they quickly perished, and became almost extinct. What a blessed thing it would be for poor rabbit-worried Australia if a similar plague should visit that country, and fall on the right animal! On the other hand, what a calamity if the infection, wide-spread, incurable, and swift as the wind in its course, should attack the too-numerous sheep! And who knows what mysterious, unheard-of retributions that revengeful deity Nature may not be meditating in her secret heart for the loss of her wild four-footed children slain by settlers, and the spoiling of her ancient beautiful order! A small pampa rodent worthy of notice is the Cavia australis, called _cui_ in the vernacular from its voice: a timid, social, mouse-coloured 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.