Imágenes de páginas
PDF
EPUB

forms and intruders from the south. Bears, Beavers, Sheep, and Deer similar; Prong-buck, Pouched Mice, and Musquash peculiar; Raccoon and Opossum, probably derived from the south

6.—Palsarctic Region

Name.irakaibs, ancient, and ap/ero?, north, as embracing the whole northern area of the Old World.

Extent.—Whole of the Eastern Hemisphere north of a line on the south of the Atlas, and running eastward through the south of Palestine and Persia, along the Himalayas, through Central Asia and the centre of China to the Pacific.

Characteristics.—Absence of Monkeys, Lemurs, and Frugivorous Bats; abundance of Carnivores—Ounce, Lynxes, Wolves, Foxes, Bears, and Weasels; Rodents— Marmots, Beavers, Pikas; Ungulates — Sheep, Deer, Chamois, and Musk-deer; no Elephants nor Hyrax.

This division of the Earth's surface into six regions was first proposed by one of the authors of the present work in an essay on the distribution of the Class of birds read before the Linnsean Society in 1857 (9). It was further elaborated and upheld in an address given to Section D. of the British Association at the Bristol Meeting in 1875 (10), and in a Paper published in The Ibis in 1891 (11). The same system was adopted by Mr. Wallace in his standard work on "Geographical Distribution" (13), and was there shown to be applicable to the other principal groups of terrestrial animals. Moreover, the names then bestowed on the six great primary Regions are now in general use among naturalists in all countries. Mr. Wallace, who has devoted many pages to the discussion of this subject,1 has come to the conclusion that, admitting that these six regions are not precisely equal in rank, and that some of them are more isolated than the others, they are in geographical equality, compactness of area, and facility of definition beyond all comparison better than any others which have been suggested for the purpose of facilitating the study of geographical distribution.

Notwithstanding Mr. Wallace's strong support, however, it is right to say that this system has not been universally accepted. Professor Huxley (6) in 1868 proposed to separate the world into two divisions—Arctogaea and Notogaea, the former containing the Nearctic, Palaearctic, Ethiopian, and Oriental Regions, and the latter the Neotropical and Australian Regions. He adopted the Nearctic, Palaearctic, Ethiopian, and Oriental Regions as subdivisions of Arctogaea, and only stipulated for the formation of a Circum-polar province independent of the Nearctic and Palaearctic Regions. Notogaea Professor Huxley divided into three provinces (a) the Austro-Columbian ( = the Neotropical), (6) the Australian (= the Australian Region minus New Zealand), and (c) the New Zealand province.

From this it will be seen that Professor Huxley's scheme does not really diverge materially from the system here employed; the chief points of difference being (a) the uniting together of the Australian and Neotropical Regions into Notogaea; (b) the formation of independent Circumpolar and New Zealand provinces. With regard to the first point, almost the only bond of union between the Australian and Neotropical Regions, so far as mammals, at any rate, are concerned, is the presence of Marsupials 1 "Geographical Distribution of Animals," vol. i., chap. iv.

in both regions. But the Marsupials of Australia seem to have but a very remote connection with those of South America, and there is at present no palseontological evidence of the former occurrence of the Australian forms, or of forms allied to them, outside of Australia itself.1 On the other hand, the presence of fossil opossums (Didelphyidm) in the Eocene beds of France, shows that the South American forms were formerly more widely spread.

Professor Huxley has also cited the Parrots (Psittacomorphm) "as helping, together with the three-toed Ratitm, to bind together the widely-separated portions of the south world" But on referring to the account of the distribution of the Parrots in Salvadori's recently published catalogue (8), it will be found that out of the six families into which he divides the group, five are practically confined to the Australian Region, and that the remaining one is widely spread throughout the tropical regions of both hemispheres. The most recent arrangement of this family, therefore, gives little support to Professor Huxley's arguments.

Looking, again, to the distribution of the Ratitm (wingless birds), we find the Neotropical form (the Rhea) more closely connected with the Ostrich, the Ethiopian form, and that they both differ considerably from the Emus, Cassowaries, and Kiwis, the three Australian representatives of this order. Thus, then, there seems to be

1 Recently Sefior Ameghino has described from the Santa Cruz beds of Patagonia, which are probably of Eocene age, certain fossil mammals which he has referred to the Dasyurida, one of the Australian families. Again, Mr. Thomas' Canolates (see P. Z. S. 1895), is also believed to be allied to the Australian Diprotodonts. If these relationships should turn out to be correct, it will indicate further evidence of some connection between South America and Australia, though at a considerably remote epoch of geological time.

scarcely any ground for connecting the Neotropical and Australian Regions under one name.

Before discussing the other differences between this scheme and that of Huxley, it will be as well to mention the diverging views of some other naturalists. Of these the chief is Professor Heilprin, of Philadelphia, who in his "Geographical and Geological Distribution of Animals," (5)" in accordance with a suggestion by Professor Newton," has proposed to unite the Nearctic and Palaearctic Regions into a single realm—the "Holarctic"—and to separate the Pacific Islands from Australia as the "Polynesian Realm." Again, Mr. J. A. Allen, of New York, in his recently published essays (1 and 2), has shown considerable independence of thought in this matter. In the introduction to the later of them, which deals chiefly with the distribution of North American mammals, Mr. Allen gives an account of the influences which, in his opinion, mainly determine the geographical distribution of life, dwelling first on the great importance of temperature and moisture, and afterwards on the inter-relation of landareas, which, he says, is "co-eval and perhaps more than co-ordinate with climate in its influence upon the distribution of life." Next, Mr. Allen treats of the seven primary life-regions, or " realms" as he terms them, into which he proposes to divide the Earth. These are:—

1. An Arctic Realm, occupying all the country in both hemispheres north of the isotherm 32° F., this boundary corresponding very closely to that of the northern limit of trees.

2. A North Temperate Realm, occupying the whole of the northern hemisphere between the isotherms of 32° and 70° F.

3. An American Tropical Realm, consisting of Tropical America.

4. A n Indo-African Realm, consisting of Africa, except the northern border, and Tropical Asia and its islands.

5. A South American Temperate Realm, embracing extra-tropical South America

6. An Australian Realm, equivalent to our Australian Region.

7. A Lemurian Realm, containing Madagascar and its islands.

Mr. Allen's views on Distribution have been criticised and answered by another American naturalist, Mr. Gill (4), who has proposed a division of the Earth into nine "realms." These, as will be seen, although not differing in many cases from regions adopted by former authorities, are distinguished by an entirely new set of names, as follows:—

(1) The Anglo-gaean ( = Nearctic Region).

(2) The Eury-gsean ( = Palaearctic Region).

(3) The Indo-gaean (= Oriental Region).

(4) The Afro-gaean ( = Ethiopian Region).

(5) The Dendro-gsean ( = the tropical half of the Neotropical Region).

(6) The Amphi-gsean ( = the temperate half of the Neotropical Region).

(7) The Austro-gaean ( = Australia, New Guinea, and the adjacent islands).

(8) The Ornitho-gaean (= New Zealand).

(9) The Neso-gsean ( = Polynesia).

Dr. Bowdler Sharpe (12) has also recently published his views on the zoo-geographical areas, as worked out from the distribution of birds. Dealing here only with the division of the Earth into Regions, we notice that

« AnteriorContinuar »