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of the Yane-tse-kiang; also North Africa and Arabia, to about the line of the tropic of Cancer.

2. Ethiopian, including Africa south of the tropic of Cancer, as well as the southern part of Arabia, with Madagascar and the adjacent islands.

3. Oriental, or Indo-Malay, comprising India and Ceylon, the Indo-Chinese countries and southern China, and the Malay Archipelago as far as the Philippines, Borneo and Java.

4. Australian, composed of the remainder of the Malay Archipelago, Australia, New Zealand and all the tropical islands of the Pacific, as far east as the Marquesas and the Low Archipelago.

5. Neotropical, which comprises South America and the adjacent islands, the West Indies or Antilles, and Central America and Mexico.

6. Nearctic, consisting of temperate and arctic North America, with Greenland.

"These six regions," remarks Dr Wallace, "although all of primary importance from their extent, and well marked by their total assemblage of animal forms, vary greatly in their zoological richness, their degree of isolation and their relationship to each other. The Australian region is the most peculiar and the most isolated, but it is comparatively small and poor in the higher animals. The Neotropical region comes next in peculiarity and isolation, but it is extensive and excessively rich in all forms of life. The Ethiopian and Oriental regions are also very rich, but they have much in common. The Palaearctic and Nearctic regions being wholly temperate are less rich, and they too have many resemblances to each other; but while the Nearctic region has many groups in common with the Neotropical, the Palaearctic is closely connected with the Oriental and Ethiopian regions."

In Dr Sclater's original scheme the first four of the above regions were bracketed together under the designation of Palaeogaea, and the fifth and sixth, or those belonging to the New World, as Neogaea. T. H. Huxley, in a paper on the distribution of game-birds, published in the Proceedings of the Zoological Society of London for 1868, instead of dividing the world into an eastern and a western division, adopted a northern and a southern division, calling the former Arctogaea, and the latter (which included Australasia and the Neotropical region of Messrs Sclater and Wallace, but not the Ethiopian region) Notogaea.

In 1874 Dr Sclater,^[1] taking mammals as well as birds into consideration, adopted Huxley's Arctogaea as the major northern division to include the Nearctic, Palaearctic, Oriental and Ethiopian regions; and instead of Huxley's Notogaea recognized three primary divisions, namely, Dendrogaea for the Neotropical region, Antarctogaea for the Australian region (in a somewhat restricted sense), and Ornithogaea for New Zealand and Polynesia.

The tendency of these amendments on the original scheme of a simple division into six regions was to recognize three primary divisions of higher rank than such "regions." This view was adopted in 1890 by Dr W. T. Blanford,^[2] who proposed to designate these three major divisions of the earth's land surface respectively the Australian, the South American and the Arctogaean regions. A weak point in this scheme is that since the term "region" is likewise applied to the subdivisions of Arctogaea, there is a danger of confusion between the primary and secondary divisions. An amendment proposed anonymously ^[3]in 1893 was to substitute the names Notogaea, Neogaea and Arctogaea for the three primary divisions of Dr Blanford. Yet another emendation, suggested by R. Lydekker^[4] and subsequently adopted by Prof. H. F. Osborn,^[5] was to designate these three primary divisions as "realms," and to reserve the name "region" for their subdivisions.

Emendations on the original scheme also included modifications in the limits of the regions themselves. In 1878, for instance, Dr A. Heilprin^[6] (in accordance with a suggestion of Prof. A. Newton) proposed to nuite the Nearctic with the Palaearctic region under the name of Holarctic; separating at the same time from the former a "transitional" Sonoran, and from the latter a similar Mediterranean, or Tyrrhenian, region, while he also recognized a distinct Polynesian region, distinguished in the main by negative characters. The Sonoran region was subsequently adopted by Dr C. H. Merriam^[7] in 1892, and later on by Dr Blanford in the address already cited, the title being, however, changed to Medio-Columbian. A most important proposal was also embodied in Dr Blanford's scheme, namely, the separation from the Ethiopian region of Madagascar and the Comoro islands to form a separate Malagasy region. Another modification of the original scheme was to transfer the island of Celebes, together with Lombok, Flores and Timor, from the Australian to the Oriental region, or to regard them as representing a transitional region between the two.^[8] The effect of this change was practically to abolish "Wallace's line" (the deep channel between the islands of Bali and Lombok and thence northward through the Macassar Strait), the deepest channel being really situated to the eastward of Timor.

The later evolution of the scheme, as presented by Dr Max Weber,^[9] may be tabularized, with some slight alteration, as follows, the "realms" being printed in capitals, the regions and sub-regions in ordinary type, and the transitional regions in italics:—

I. Arctogaea
1. Holarctic.		2. Ethiopian.	3 . Malagasy.	4. Oriental.
|	|
Nearctic Sonoran	Palaearctic Mediterranean			Austro-Malayan
II. Neogaea				III. Notogaea.
5. Neotropical.				6. Australian
				(?) 7 . Polynesian
				(?) 8. Hawaiian.

In the accompanying map the Sonoran and Mediterranean transitional regions are represented as equivalent in value to the main regions, and the Austro-Malayan transitional region is not indicated. The recognition of a Polynesian and still more of a Hawaiian region, is provisional.

The most distinct of the three primary realms is undoubtedly Notogaea, the Australian section of which is the sole habitat of egg-laying mammals (Monotremata) and of a great Notogaea. variety of marsupials, inclusive of the whole of the diprotodonts, with the exception of the few (cuscuses) found in the Austro-Malayan transitional region. Apart from monotremes and marsupials, the only indigenous mammals found in Notogaea are rodents and bats, with perhaps a pig in New Guinea; although it is most probable that the latter is introduced, as is almost certainly the dingo, or native dog, in Australia. The rodents are all referable to the family Muridae, and are mostly of peculiar types, such as the golden water-rat (Hydromys) and the jerboa-rats (Conilurus, Notomys, &c.); they are, however, in many instances more or less nearly related to species found in Celebes, the mountains of the Philippines and Borneo, and apparently represent an ancient fauna. The mammalian fauna of Notogaea is practically limited to the Australian region, its indigenous representatives in New Zealand being only a couple of bats, The monotremes are in all probability the survivors of a group which was widely spread in Jurassic times; while marsupials, as represented by the American opossums (Didelphyidae), had a very wide range even as late as the Oligocene division of the Tertiary period. The diprotodont marsupials may not improbably have originated within the Australian region, or this region conjointly with the Austro-Malayan transitional region.

Notogaea is likewise the home of a number of peculiar types of birds, some of which range, however, into the Austro-Malayan area, that is to say, Celebes and Ceram. In the Australian region the

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1. Manchester Science Lectures, ser. 5 and 6, p. 202 seq.
2. Proc. Geol. Soc. (London, 1890), p. 76.
3. Natural Science, iii. 289.
4. Geographical Distribution of Mammals (London, 1896), p. 27.
5. "Correlation between Tertiary Mammal Horizons of Europe and America," Annals New York Academy, xiii. 48 (1900).
6. The Geographical and Geological Distribution of Animals (London, 1878).
7. "The Geographical Distribution of Life in North America with special reference to the Mammalia," Proc. Biol. Soc, Washington, vol. vii. pp. 1-64 (1892).
8. See W. L. Sclater, "The Geography of Mammals," part v., Geographical Journal, 1896; M. Weber, "On the Origin of the Fauna of Celebes," Ann. Mag. Nat. Hist., ser. 7, vol. iii. pp. 121-136 (1899), and Der Indo-australische Archipel und die Ceschichte seiner Tierwelt (Jena, 1902); Lydekker, "Celebes; a Problem in Distribution," Knowledge, vol. xxi. pp . 175-177 (1898); see also Deer of All Lands, p. 168 (1898).
9. Die Saugetiere (Jena, 1904), p. 308.