Amongst the Rodentia, no members of the Lagomorpha (hares, rabbits and picas) are known to hibernate, although some of the species, like the mountain hare (_Lepus timidus_), extend far to the north in the palaearctic region, and the picas (_Ochotona_) live at high altitudes in the Himalayas and Central Asia, where the cold of winter is excessive, and where the snow lies deep for many months. It is probable that the picas live in fissures and burrows beneath the snow, and feed on stores of food accumulated during the summer and autumn. The Hystrico-morpha also are non-hibernators. It is true that the common porcupine (_Hystrix cristata_) of south Europe and north Africa is alleged to hibernate; the statement cannot, however, be accepted without confirmation, because the cold is seldom excessive in the countries it frequents, and specimens exhibited in the Zoological Gardens in London remain active throughout the year, although kept in enclosures without artificial heat of any kind. Even the most northerly representative of this group, the Canadian porcupine (_Erethizon dorsatus_), which inhabits forest-covered tracts in the United States and Canada, may be trapped and shot in the winter. Some members of this group, like capybaras (_Hydrochaerus capybara_) and coypus (_Myocastors coypus_) which live in tropical America, are unaffected by the winter cold of temperate countries, and live in the open all the year round in parks and zoological gardens in England. Several of the genera of Myomorpha contain species inhabiting the northern hemisphere, which habitually hibernate. The three European genera of dormice (_Myoxidae_), namely _Muscardinus_, _Eliomys_ and _Glis_, sleep soundly practically throughout the winter; and examples of the South African genus _Graphiurus_ practise the same habit when imported to Europe. If a warm spell in the winter rouses dormice from their slumbers, they feed upon nuts or other food accumulated during the autumn, but do not as a rule leave the nests constructed for shelter during the winter. According to the weather, the sleep lasts from about five to seven months. In the family _Muridae_, the true mice and rats (_Murinae_) and the voles and lemmings (_Arvicolinae_) seem to remain active through the winter, although some species, like the lemmings, range far to the north in Europe and Asia; but the white-footed mice (_Hesperomys_) of North America, belonging to the _Cricetinae_, spend the winter sleeping in underground burrows, where food is laid up for consumption in the early spring. The Canadian jumping mouse (_Zapus hudsonianus_), one of the Jaculidae, also hibernates, although the sleep is frequently interrupted by milder days. Some of the most northerly species of jerboas (Jaculidae), namely _Alactaga decumana_ of the Kirghiz Steppes and _A. indica_ of Afghanistan, sleep from September or October till April; and the Egyptian species (_Jaculus jaculus_) and the