« EelmineJätka »
of its inhabitants, by which the present state of things has been brought about. For this purpose we require a group which shall be dependent for its means of dispersal on the distribution of land and water, and on the presence or absence of lofty mountains, desert plains or plateaux, and great forests ; since these are the chief physical features of the earth's surface whose modifications at successive periods we wish to discover. It is also essential that they should not be subject to dispersal by many accidental causes; as this would inevitably in time tend to obliterate the effect of natural barriers, and produce a scattered distribution, the causes of which we could only guess at. Again, it is necessary that they should be so highly organized as not to be absolutely dependent on other groups of animals, and with so much power of adaptation as to be able to exist in one form or another over the whole globe. And lastly, it is highly important that the whole group should be pretty well known, and that a fairly natural classification, especially of its minor divisions such as families and genera, should have been arrived at; the reason for which last proviso is explained in our next chapter, on classification.
Now in every one of these points the mammalia are preeminent; and they possess the additional advantage of being the most highly developed class of organized beings, and that to which we ourselves belong. We should therefore construct our typical or standard Zoological Regions in the first place, from a consideration of the distribution of mammalia, only bringing to our aid the distribution of other groups to determine doubtful points. Regions so established will be most closely in accordance with those long-enduring features of physical geography, on which the distribution of all forms of life fundamentally depend; and all discrepancies in the distribution of other classes of animals must be capable of being explained, either by their exceptional means of dispersion or by special conditions affecting their perpetuation and increase in each locality.
If these considerations are well founded, the objections of those who study insects or molluscs, for example,- that our regions are not true for their departments of nature—cannot be
maintained. For they will find that a careful consideration of the exceptional means of dispersal and conditions of existence of each group, will explain most of the divergences from the normal distribution of higher animals.
We shall thus be led to an intelligent comprehension of the phenomena of distribution in all groups, which would not be the case if every specialist formed regions for his own particular study. In many cases we should find that no satisfactory division of the earth could be made to correspond with the distribution even of an entire class; but we should have the coleopterist and the lepidopterist each with his own Geography. And even this would probably not suffice, for it is very doubtful if the detailed distribution of the Longicornes, so closely dependent on woody vegetation, could be made to agree with that of the Staphylinidæ or the Carabide which abound in many of the most barren regions, or with that of the Scarabeidæ, largely dependent on the presence of herbivorous mammalia. And when each of these enquirers had settled a division of the earth into “ regions ” which exhibited with tolerable accuracy the phenomena of distribution of his own group, we should have gained nothing whatever but a very complex mode of exhibiting the bare facts of distribution. We should then have to begin to work out the causes of the divergence of one group from another in this respect; but as each worker would refer to his own set of regions as the type, the whole subject would become involved in inextricable confusion. These considerations seem to make it imperative that one set of “regions” should be established as typical for Zoology; and it is hoped the reasons here advanced will satisfy most naturalists that these regions can be best determined, in the first place, by a study of the distribution of the mammalia, supplemented in doubtful cases by that of the other vertebrates. We will now proceed to a discussion of what these regions are.
Various Zoological Regions proposed since 1857.-It has already been pointed out that a very large number of birds are limited by the same kind of barriers as mammalia; it will therefore not be surprising that a system of regions formed to suit the
one, should very nearly represent the distribution of the other.
1. The Palæarctic Region; including Europe, Temperate Asia,
2. The Ethiopian Region ; Africa south of the Atlas, Madagascar, and the Mascarene Islands, with Southern Arabia.
3. The Indian Region ; including India south of the Himalayas, to South China, and to Borneo and Java.
4. The Australian Region ; including Celebes and Lombock, eastward to Australia and the Pacific Islands.
5. The Nearctic Region; including Greenland, and N. America, to Northern Mexico.
6. The Neotropical Region; including South America, the Antilles, and Southern Mexico.
This division of the earth received great support from Dr. Günther, who, in the Proceedings of the Zoological Society for 1858, showed that the geographical distribution of Reptiles agreed with it very closely, the principal difference being that the reptiles of Japan have a more Indian character than the birds, this being especially the case with the snakes. In the volume for 1868 of the same work, Professor Huxley discusses at considerable length the primary and secondary zoological divisions of the earth. He gives reasons for thinking that the most. radical primary division, both as regards birds and mammals, is into a Northern and Southern hemisphere (Arctogæa and Notogæa), the former, however, embracing all Africa, while the latter includes only Australasia and the Neotropical or Austro-Columbian region. Mr. Sclater had grouped his regions primarily into Palæogæa and Neogæa, the Old and New Worlds of geographers; a division which strikingly accords with the distribution of the passerine birds, but not so well with that of mammalia or reptiles. Professor Huxley points out that the Nearctic, Palæarctic, Indian, and Ethiopian regions of Mr. Sclater have a much greater resemblance to each other than any one of them has to Australia or to South America ; and he further suggests that New Zealand alone has peculiarities which might entitle it to rank as a primary region
along with Australasia and South America; and that a Circumpolar Province might be conveniently recognised as of equal rank with the Palæarctic and Nearctic provinces.
In 1866, Mr. Andrew Murray published a large and copiously illustrated volume on the Geographical Distribution of Mammals, in which he maintains that the great and primary mammalian regions are only four : 1st. The Palæarctic region of Mr. Sclater, extended to include the Sahara and Nubia ; 2nd. the Indo-African region, including the Indian and Ethiopian regions of Mr. Sclater; 3rd. the Australian region (unaltered); 4th. 'the American region, including both North and South America. These are the regions as described by Mr. Murray, but his coloured map of “Great Mammalian Regions” shows all Arctic America to a little south of the Isothermal of 32° Fahr. as forming with Europe and North Asia one great region.
At the meeting of the British Association at Exeter in 1869, Mr. W. T. Blanford read a paper on the Fauna of British India, in which he maintained that a large portion of the peninsula of India had derived its Fauna mainly from Africa; and that the term “Indian region ” of Mr. Sclater was misleading, because India proper, if it belongs to it at all, is the least typical portion of it. He therefore proposes to call it the “ Malayan region,” because in the Malay countries it is most highly developed. Ceylon and the mountain ranges of Southern India have marked Malay affinities.
In 1871 Mr. E. Blyth published in Nature “A suggested new Division of the Earth into Zoological Regions,” in which he indicates seven primary divisions or regions, subdivided into twenty-six sub-regions. The seven regions are defined as follows: 1. The Boreal region; including the whole of the Palæarctic and Nearctic regions of Mr. Sclater along with the West Indies, Central America, the whole chain of the Andes, with Chili and Patagonia. 2. The Columbian region; consisting of the remaining part of South America. 3. The Ethiopian region; comprising besides that region of Mr. Sclater, the valley of the Jordan, Arabia, and the desert country towards India, with all the plains and table lands of India and the northern
half of Ceylon. 4 The Lemurian region; consisting of Madagascar and its adjacent islands. 5. The Austral-Asian region; which is the Indian region of Mr. Sclater without the portion taken to be added to the Ethiopian region. 6. The Melanesian region; which is the Australian region of Mr. Sclater without New Zealand and the Pacific Islands, which form 7. the Polynesian region. Mr. Blyth thinks this is “a true classification of zoological regions as regards mammalia and birds.”
In an elaborate paper on the birds of Eastern North America, their distribution and migrations (Bulletin of Museum of Comparative Zoology, Cambridge, Massachusetts, Vol. 2), Mr. J. A. Allen proposes a division of the earth in accordance with what he terms," the law of circumpolar distribution of life in zones,” as follows: 1. Arctic realm. 2. North temperate realm. 3. American tropical realm. 4. Indo-African tropical realm. 5. South American tropical realm. 6. African temperate realm. 7. Antarctic realm. 8. Australian realm. Some of these are subdivided into regions; (2) consisting of the American and the Europæo-Asiatic regions ; (4) into the African and Indian regions ; (8) into the tropical Australian region, and one comprising the southern part of Australia and New Zealand. The other realms each form a single region.
Discussion of proposed Regions.—Before proceeding to define the regions adopted in this work, it may be as well to make a few remarks on some of the preceding classifications, and to give the reasons which seem to render it advisable to adopt very few of the suggested improvements on Mr. Sclater's original proposal. Mr. Blyth's scheme is one of the least natural, and also the most inconvenient. There can be little use in the knowledge that a group of animals is found in the Boreal Region, if their habitat might still be either Patagonia, the West Indies, or Japan; and it is difficult to see on what principle the Madagascar group of islands is made of equal rank with this enormous region, seeing that its forms of life have marked African affinities. Neither does it seem advisable to adopt the Polynesian Region, or that comprising New Zealand alone (as hinted at by Professor Huxley and since adopted by