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Show lG ISLAND LIFE. [rAnT I. the Himalayas there are numbers of birds '~hich have very res t n·c t ed ranges, b u t those of the N. e ilghernes are perhaps better known several species of laughmg thrushes and some other birds b:ing found only on the summits of these mountains. The most wonderfully restricted ranges are, however, to be found among. the humming-birds of trop~ca~ America. The great volcanic peaks of Chimborazo and P1ehmcha h~ve each a peculiar species of humming-bird co.nfinecl to a .belt JUSt below the limits of perpetual snow, w h1le the extmct volcano of Chiriqui in V eragua has a species confined to its wooded crater. One of the most strange and beautiful of the humming-birds (Loddigesia mirabilis) was obtained once only, more than forty years ago, near Chachapoyas in the Andes of northern Peru ; and though Mr. Gould has sent many drawings of the bird to people visiting the district and has for many years offered a high re·ward for a specimen, no other has ever been seen! 1 The above details will sufficiently explain what is meant by the "specific area" or range of a species. The very wide and very narrow ranges are exceptional, the great majority of species both of mammals and birds ranging over moderately wide areas, which present no striking contrasts in climate and physical conditions. Thus a large proportion of European birds range over the whole continent in an east and west direction, but considerable numbers are restricted either to the northern or the southern half. In Africa some species range over all the continent south of the desert, while large numbers are restricted to the equatorial forests, or to the upland plains. In North America, if we exclude the tropical and the arctic portions, a considerable number of species range over all the temperate parts of the continent, while still more are restricted to the east, the centre, or the west, respectively. Gene1·ic A1·eas.-Having thus obtained a tolerably clear idea of the main facts as to the distribution of isolated species, let us now consider those collections of closely-allied species termed genera. What a genus is will be sufficiently understood by a few illustrations. All the different kinds of dogs, jackals, and ' t Since these lines were written, the report comes that fresh specimens have been found in the same locality. CITAP. 11.] THE ELEMENTARY FACTS OF DISTRIBUTION. 17 ~volves be_long to the dog genus, Canis; the tiger, lion, leopard, Jaguar, and the .wild cats, to the cat genus, Felis; the blackbird, song-thrush, m1ssel-thrusb, fieldfare, and many others, to the thrush genus, Turd us; the crow, rook, raven, and jackdaw, to the crow genus: Corvus; but the magpie belongs to another, though closely-allied genus, Pica, distinguished by the different form and proportions of its wings and tail from all the species of the crow genus. The number of species in a genus varies greatly, from one up to several hundreds. The giraffe, the glutton, the walrus, the bearded reedling, the secretary-bird, and many others, have no close allies, and each forms a genus by itself. The beaver genus, Castor, anJ the camel genus, Camelus, each consist of two species. On the other hand, the deer genus, Cervus bas forty species ; the mouse and rat genus, }Ius more than a hundred species; and there is about the same number of the thrush genus; while among the lower classes of animals genera are often very extensive, the fine genus Papilio, or swallow-tailed butterflies, containing more than four hundred species; and Cicindela, which includes o~r native tiger beetles, has about the same number. Many genera of shells are very extensive, and one of them-the· gerius Helix, including the commonest snails, and ranging. all over the world-is probably the most extensive in theanimal kingdom, numbering about two thousand described species. Separate and overlapping Areas.-The species of a genus are distributed in two ways. Either they occupy distinct areas which do not touch each other and are sometimes widely separated, or they touch and occasionally overlap each other, each species occupying an area of its own which rarely coincides exactly with that of any other species of the same genus. In some cases, when a river, a mountain-chain, or a change of conditions as from pasture to desert or forest, determines the range of species, the areas of two species of the same genus may just meet, one beginning where the other ends; but this is comparatively rare. It occurs, however, in the Amazon valley, where several species of monkeys, birds, and insects come up to the south bank of the river but do not pass it, c |