The specific name of the Restless Cavy seems to be derived from its popular name in the country where it occurs. According to Mr. Darwin, it is very common about the banks of the La Plata, sometimes frequenting sandy hillocks, and the hedge-rows formed of the agave and the prickly pear, but apparently preferring marshy places covered with aquatic plants. In dry places it makes a burrow; but when it frequents wet localities contents itself with the concealment afforded to it by the herbage. Rengger describes it also as generally haunting moist situations in Paraguay, and he adds that it keeps near the borders of forests, but is never found either in the forests or in the open fields. It lives in small societies of from six to fifteen individuals, in the impenetrable thickets of Bromelias, where its presence is revealed by the numerous beaten paths which it produces by going to and fro. In Bolivia, according to Mr. Bridges, it is peculiar to the low lands, and there takes shelter among the loose stones of the walls enclosing the fields. It is active in search of food early in the morning and in the evening, but will also come forth on gloomy days. Rengger and Azara both agree in the statement that the female produces only one or two young at a time; but the former says that this takes place only once in the year, whilst the latter describes the animal as breeding all the year round, and, indeed, in this way accounts for its abundance, notwithstanding its being preyed upon so extensively by rapacious birds and quadrupeds. The question whether our common Guinea-pig is really the domesticated descendant of the animal just described can hardly be regarded as finally settled, and, indeed, independently of colour, there are sufficient differences between them to justify some doubt on the subject. The name Guinea-pig may, as Mr. Waterhouse suggests, be a mistake for Guiana-pig, and the first specimens may very probably have come from that part of America. Its prevalent colours, as is well known, are combinations of white, black, and yellow, and as these colours are shown in the drawings of Aldrovandus, dating back to within fifty years of the discovery of South America, there seems every reason to believe that the animal must have been long domesticated in America prior to its introduction into Europe. On the other hand, Dr. Rengger says that he saw fourteen Apereas representing the fifth or sixth generation from a single couple domesticated about seven years before, and that these exhibited no difference of colouring from the wild animal. Several allied species inhabit the great plains of South America.