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all told, which leaves 784 forms that may be distinctively termed "land-birds," and whose distribution over the continent is more or less governed by the existence of a continuous land surface. Of these 784 species only 438, or less than 56 per cent. of the whole, are to be found in the western half of Australia, and only eighty-eight of these are common over both halves of the continent. Although the conditions for living are not greatly different in east and west, it is seen that no less than 44 per cent. of the forms of bird life still cling to that long narrow tract of Eastern Australia which, with the exception of Bass Strait, extends unbroken from Cape York on Torres Strait to the southernmost point of Tasmania. In that long and mountainous tract two very distinct sub-regions of bird life appear. One is the Cape York Peninsula, which contains many forms of both mammalian and bird life that do not occur in the Northern Territory on the western side of the Carpentaria Gulf. Zoologically it is closely allied to New Guinea and contains two small tree-climbing kangaroos, three "birds of Paradise," a "cassowary," two "brush turkeys," and a host of fruit-eating pigeons. The other district or sub-region is practically the coast slopes of New South Wales, in which occur the famous lyre bird family, an enormous development of sea-coast birds, and a relative paucity of variety among the parrots and cockatoos. Inland from the ocean slopes of Queensland and New South Wales the bird life of the plains and the scattered scrubs begins; the forest bird life is absent; the watercourses and occasional swamps develop a fauna of remarkable sameness, and this feature is characteristic right across Central Australia to the shores of the Indian Ocean.

The bird life of the western half of Australia is far older in origin than its mammalian life, but, like the latter, has spread to the Western Australian coast by three distinct routes. One stream has come down from the Northern Territory through the Kimberley district, and sent a few stragglers as far southward as the North-West Cape. From Central Australia most of the forms common to the whole western region have come, a few forms only reaching right to the nor'-west coast. Along the south coast, as formerly existent, the third stream came; and in the extreme south-west corner of the continent can now be witnessed the extent of variation into peculiarly restricted species which have evolved as the result of long isolation from the original family groups in the east. Of 264 species of land-birds in this south-west corner no fewer than 193 have come from South Australia—that is to say, from the land round Spencer Gulf and the lower reaches of the Murray River, a region itself possessing but 323 species of land- and river-birds. From Central Australia and Western Queensland—a region containing 186 characteristic bird forms—fifty-two species have passed into Western Australia. Of the 297 species of land birds recorded as occurring in the Kimberley and nor'-west divisions of the State there are 138 species directly common with that part of North Australia west of the Gulf of Carpentaria, and have their closest affinities with Indian and Indo-Malayan forms. The three streams of immigration—the northern, central, and southern—are thus equally clearly marked. The total number of land- and sea-birds recorded for Western Australia (and at the present time regarded as well-established species) is 491. Of this total fifty-three are sea-birds and 438 land-birds. Of the latter some 383 species have come in as colonists from North or East Australia, leaving but forty-five species, or some ${\displaystyle \scriptstyle {10{\frac {1}{2}}}}$ per cent., as autochthonous species or variants evolved within the State itself.

It is the number of species restricted to particular districts or regions which marks off the distinctive life-regions of the world or of a country. The complete separation between the northern, western, and southern parts of Western Australia from its central portion is clearly shown in the following tabulation:—

The distinction between the north and south parts of the State is thus seen to be a strongly marked one, and without any well-defined intermediate or mixed zone. In the north there are 104 species which do not spread southward, and in the south there are sixty-three species which do not spread northward. The little red-breasts or "robins" of the south are not identical with the "robins" of the north, nor are they with those of the interior or central region. Neither are the magpies, the shrike-tits, or the tree-creepers identical. Even