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explained in Chapter IX. As a matter of convenience, and for other reasons adduced in the same chapter, the detailed exposition of the geographical distribution of the animals of the several regions in Part III. commences with the Palaearctic and terminates with the Nearctic region. Objections to the system of Circumpolar Zones.—Mr. Allen's system of “realms" founded on climatic zones (given at p. 61), having recently appeared in an ornithological work of considerable detail and research, calls for a few remarks. The author continually refers to the “law of the distribution of life in circumpolar zones,” as if it were one generally accepted and that admits of no dispute. But this supposed “law” only applies to the smallest details of distribution—to the range and increasing or decreasing numbers of species as we pass from north to south, or the reverse; while it has little bearing on the great features of zoological geography—the limitation of groups of genera and families to certain areas. It is analogous to the “law of adaptation” in the organisation of animals, by which members of various groups are suited for an aerial, an aquatic, a desert, or an arboreal life; are herbivorous, carnivorous, or insectivorous; are fitted to live underground, or in fresh waters, or on polar ice. It was once thought that these adaptive peculiarities were suitable foundations for a classification,-that whales were fishes, and bats birds; and even to this day there are naturalists who cannot recognise the essential diversity of structure in such groups as swifts and swallows, sun-birds and humming-birds, under the superficial disguise caused by adaptation to a similar mode of life. The application of Mr. Allen's principle leads to equally erroneous results, as may be well seen by considering his separation of “the southern third of Australia” to unite it with New Zealand as one of his secondary zoological divisions. If there is one country in the world whose fauna is strictly homogeneous, that country is Australia; while New Guinea on the one hand, and New Zealand on the other, are as sharply differentiated from Australia as any adjacent parts of the same primary zoological division can possibly be. Yet the “law of circumpolar distribution” leads to the division of Australia by an arbitrary east and west line, and a union of the northern two-thirds with New Guinea, the southern third with New Zealand. Hardly less unnatural is the supposed equivalence of South Africa (the African temperate realm) to all tropical Africa and Asia, including Madagascar (the IndoAfrican tropical realm). South Africa has, it is true, some striking peculiarities; but they are absolutely unimportant as compared with the great and radical differences between tropical Africa and tropical Asia. On these examples we may fairly rest our rejection of Mr. Allen's scheme.
We must however say a few words on the zoo-geographical nomenclature proposed in the same paper, which seems also very objectionable. The following terms are proposed: realm, region, province, district, fauna and flora ; the first being the highest, the last the lowest and smallest sub-division. Considering that most of these terms have been used in very different senses already, and that no means of settling their equivalence in different parts of the globe has been even suggested, such a complex system must lead to endless confusion. Until the whole subject is far better known and its first principles agreed upon, the simpler and the fewer the terms employed the better; and as “region” was employed for the primary divisions by Mr. Sclater, eighteen years ago, and again by Mr. Andrew Murray, in his Geographical Distribution of Mammals; nothing but obscurity can result from each writer using some new, and doubtfully better, term. For the sub-divisions of the regions no advantage is gained by the use of a distinct term—“province”—which has been used (by Swainson) for the primary divisions, and which does not itself tell you what rank it holds; whereas the term “sub-region" speaks for itself as being unmistakably next in subordination to region, and this clearness of meaning gives it the preference over any independent term. As to minor named sub-divisions, they seem at present uncalled for; and till the greater divisions are themselves generally agreed on, it seems better to adopt no technical names for what must, for a long time to come, be indeterminate.
Does the Arctic Fauna characterize an independent Region.— The proposal to consider the Arctic regions as constituting one of the primary zoological divisions of the globe, has been advocated by many naturalists. Professor Huxley seems to consider it advisable, and Mr. Allen unhesitatingly adopts it, as well as an “antarctic” region to balance it in the southern hemisphere. The reason why an “Arctic Region” finds no place in this work may therefore be here stated. No species or group of animals can properly be classed as “arctic,” which does not exclusively inhabit or greatly preponderate in arctic lands. For the purpose of establishing the need of an “arctic "zoological region, we should consider chiefly such groups as are circumpolar as well as arctic; because, if they are confined to, or greatly preponderate in, either the eastern or western hemispheres, they can be at once allocated to the Nearctic or Palaearctic regions, and can therefore afford no justification for establishing a new primary division of the globe. Thus restricted, only three genera of land mammalia are truly arctic : Gulo, Myodes, and Rangifer. Two species of widely dispersed genera are also exclusively arctic, Ursus maritimus and Vulpes lagopus. Exclusively arctic birds are not much more numerous. Of land birds there are only three genera (each consisting of but a single species), Pinicola, Nyctea, and Surnia. Lagopus is circumpolar, but the genus has too wide an extension in the temperate zone to be considered arctic. Among aquatic birds we have the genus of ducks, Somateria; three genera of Uriidae, Uria, Catarractes, and Mergulus; and the small family Alcidae, consisting of the genera Alca and Fratercula. Our total then is, three genera of mammalia, three of land, and six of aquatic birds, including one peculiar family. In the southern hemisphere there is only the single genus Aptenodytes that can be classed as antarctic ; and even that is more properly south temperate. In dealing with this arctic fauna we have two courses open to us; we must either group them with the other species and genera which are common to the two northern regions, or we must form a separate primary region for them. As a matter of convenience the former plan seems the best; and it is that which is in accordance with our treatment of other intermediate tracts which contain special forms of life. The great desert zone, extending from the Atlantic shores of the Sahara across Arabia to Central Asia, is a connecting link between the Palaearctic, Ethiopian, and Oriental regions, and contains a number of “desert” forms wholly or almost wholly restricted to it; but the attempt to define it as a separate region would introduce difficulty and confusion. Neither to the “desert” nor to the “arctic” regions could any defined limits, either geographical or zoological, be placed; and the attempt to determine what species or genera should be allotted to them would prove an insoluble problem. The reason perhaps is, that both are essentially unstable, to a much greater extent than those great masses of land with more or less defined barriers, which constitute our six regions. The Arctic Zone has been, within a recent geological period, both vastly more extensive and vastly less extensive than it is at present. At a not distant epoch it extended over half of Europe and of North America. At an earlier date it appears to have vanished altogether; since a luxuriant vegetation of tall deciduous trees and broad-leaved evergreens flourished within ten degrees of the Pole ! The great deserts have not improbably been equally fluctuating; hence neither the one nor the other can present that marked individuality in their forms of life, which seems to have arisen only when extensive tracts of land have retained some considerable stability both of surface and climatal conditions, during periods sufficient for the development and co-adaptation of their several assemblages of plants and animals. We must also consider that there is no geographical difficulty in dividing the Arctic Zone between the two northern regions. The only debateable lands, Greenland and Iceland, are generally admitted to belong respectively to America and Europe. Neither is there any zoological difficulty; for the land mammalia and birds are on the whole wonderfully restricted to their respective regions even in high latitudes; and the aquatic forms are, for our present purpose, of much less importance. As a primary division the “Arctic region” would be out of all proportion to the other six, whether as regards its few peculiar types or the limited number of forms and species actually inhabiting it; but it comes in well as a connecting link between two regions, where the peculiar forms of both are specially modified; and is in this respect quite analogous to the great desert zone above referred to. I now proceed to characterize briefly the six regions adopted in the present work, together with the sub-regions into which they may be most conveniently and naturally divided, as shown in our general map. Palaearctic Region.—This very extensive region comprises all temperate Europe and Asia, from Iceland to Behring's Straits and from the Azores to Japan. Its southern boundary is somewhat indefinite, but it seems advisable to comprise in it all the extra-tropical part of the Sahara and Arabia, and all Persia, Cabul, and Beloochistan to the Indus. It comes down to a little below the upper limit of forests in the Himalayas, and includes the larger northern half of China, not quite so far down the coast as Amoy. It has been said that this region differs from the Oriental by negative characters only; a host of tropical families and genera being absent, while there is little or nothing but peculiar species to characterize it absolutely. This however is not true. The Palaearctic region is well characterized by possessing 3 families of vertebrata peculiar to it, as well as 35 peculiar genera of mammalia, and 57 of birds, constituting about one-third of the total number it possesses. These are amply sufficient to characterize a region positively; but we must also consider the absence of many important groups of the Oriental, Ethiopian, and Nearctic regions; and we shall then find, that taking positive and negative characters together, and making some allowance for the necessary poverty of a temperate as compared with tropical regions, the Palaearctic is almost as strongly marked and well defined as any other. Sub-divisions of the Palaearctic Region.—These are by no means