It is evident that such animals as the lapp, lemming, musk-ox, or reindeer must push southward on the approach of winter. Their migrations are by no means unexpected; nor would the mere land journey of birds create amazement when we know the real causes; but to cross the great inland sea anywhere, save at its entrance, must be considered a great feat when performed by tiny warblers, and birds not physically adapted for long flights; for instance, the willow warbler or the land-rail, crossing the broadest parts of the Mediterranean, must traverse at least six hundred miles. No doubt the heated winds from the desert exert a great influence in determining the route to be taken by migratory birds, especially in the countries that come directly under their operation; and at no seasons are their presence more apparent than during the spring and autumn; for not only then do they blow their greatest violence, but are also most keenly felt by contrast with the previous hot or cold months. Thus the winds that beckon the bird in autumn to come southward, drive it back again to Europe in spring. Much, however, depends on the constitutional powers of the individual species, which vary greatly in members of the same family; for instance, the little chiffchaff often makes its appearance in England as early as the middle of March, whilst its congener, the willow warbler, is seldom seen before the end of April; the spotted fly-catcher and night-jar arrive toward the end of May, and depart again early in September. Bird migrations may be said to be either complete or partial; some birds totally abandon Europe during winter, and take up their residence in north Africa; others repair merely to the more genial climates of the south of Europe; whilst many remain, but in diminished numbers, throughout the year, the majority resorting to milder temperatures. For example, the swallow tribe leave Europe entirely; the wagtails have their winter homes among the oases of the desert and on the banks of the Nile, whilst a few tarry in southern Europe, and with their brethren in spring push northward. A good many stone-chats spend the winter in Britain, whilst the majority move southward; not so with their close ally, the whin-chat, which disappears entirely during the cold season, and, with the migratory portion of the last-named species, seeks the more genial climates of north Africa. Thus, in all probability, there are individual stone-chats that have alternately braved the cold of the north and the more cheerful winter of the Sahara; for we cannot suppose that there is a set that invariably stop in the north, and another that constancy leave at the approach of winter. At all events, here is displayed a flexibility of constitution often considered characteristic of man alone. Although the regular birds of passage maintain much exactitude with reference to their arrivals and departures, others seem to err greatly when compelled by weather or other causes to trust to their