hese mountains. The most wonderfully restricted ranges are, however, to be
found among the humming-birds of tropical America. The great volcanic peaks
of Chimborazo and Pichincha have each a peculiar species of humming-bird
confined to a belt just below the limits of perpetual snow, while the
extinct volcano of Chiriqui in Veragua 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 sent
many drawings of the bird to people visiting the district and for many
years offered a high reward for a specimen, no other has ever been seen![4]

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 {17} more are restricted to
the east, the centre, or the west, respectively.

_Generic Areas._--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 wolves belong to the dog genus, Canis; the tiger,
lion, leopard, jaguar, and the wild cats, to the cat genus, Felis; the
blackbird, song-thrush, missel-thrush, fieldfare, and many others to the
thrush genus, Turdus; 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 g