« AnteriorContinuar »
geography, and consider how the earth's surface may be most naturally divided into Primary Regions, taking the amount of similarity and dissimilarity of animal life as our sole guide. In order to endeavour to solve this problem, let us select the mammals, as the most highly organised and altogether the best-known group of the animal kingdom, and examine the geographical distribution of this class of animals over the world's surface.
Mammals are divided by naturalists into eleven large groups, called "Orders." As regards their distribution, however, these Orders fall into two very different categories, according as they live on land or in the water—terrestrial and marine. For out of the eleven Orders, one of the principal divisions of the Carnivora—the Pinnipeds or seals, and two other Orders in their entirety—(the Cetaceans or whales, and the Sirenians or Manatees) are specially adapted for existence in water. Land is, therefore, a barrier to their extension, whereas, on the contrary, in the case of the ordinary terrestrial mammals, land is the means by which they extend their ranges, and seas and rivers form their restraining boundaries.
We will for the present put aside the marine mammals, and address ourselves to the discussion of the distribution of the nine terrestrial Orders, namely:—
Now, as is generally agreed by naturalists, one of the most certain and best ascertained points in the classification of mammals is, that these nine Orders can be grouped
primarily in three natural divisions (which may, in fact, be considered as Sub-classes) of nearly equal value. These three Sub-classes are, as named by Professor Huxley—the Prototheria, embracing only the Order Monotremata— the Metatheria, equivalent to the Order Marsupialia, and the Eutheria, which includes all the remaining Orders from the Edentata to the Primates. Let us, therefore, consider the distribution of the members of these three Sub-classes on the earth's surface. When we come to examine the ranges of these groups on the map, we shall find that the Monotremes are wholly confined to Australia and New Guinea; that the Marsupials predominate in Australia, and are only met with elsewhere in South America (one or two species of Opossum occurring in North America, but being probably only recent intruders from the south); and that the typical mammals or Eutheria occupy the rest of the world.
Again, after examining the distribution of the seven Orders of typical mammals, we remark the following significant facts:—
1. The absence of Insectivores in South America.
2. The great prevalence of Edentates in the same country; the Sloths, Armadilloes, and Ant-eaters, constituting three out of the five known families of this Order, being entirely confined to South and Central America.
Taking these main facts as our guide, we may divide the land-surface of the Earth as follows, into three divisions:—
(1) Land where Marsupials prevail; no Eutheriaiis except Rodents and Bats; Monotremes
Australia, New Guinea^
(2) Land where Euther
ians and Marsupials
(3) Land where Euther
ians only occur; few
America south of the Isth- \
Europe, Asia, Africa, Asia-
The fault of this division is that it leaves the great mass of land in the Northern Hemisphere undivided and rather unmanageable. But this northern land is easily separable into four sections, although it should be understood that these four sections are not of equivalent value to the two other primary divisions. Thus we obtain a division of the land-area of the globe for mammals into six areas, which are called Regions (see Plate I., p. 16), and which may be shortly defined and named as follows:—
Australia, New Guinea, and adjacent| islands up to Wallace's line .
j- I. Australian Region.
i fCentral America south of the Isthmus-!
g -J of Tehuantepec, the West Indies, and J- II. Neotropical Region.
Africa south of the Atlas, and Madagascar III. Ethiopian Region.
South Asia, the Philippines and Islands of-j the Indian Archipelago down to Wal- J- IV. Oriental Region. lace's line, and Celebes J
1 As will be shown later on, this statement is not absolutely correct as regards North America, as at least one species of marsupial occurs within its limits.
«, _ [ North America down to the Isthmus) TT .. „ . || ofTehuantepec . . . ) ^-Nearctu Region.
a 5 Europe, Africa north of the Atlas, and) TrT „ , .. „ . <S -Tr' \ VI. Palaarctic Hegum.
^ ~ v Northern Asia . . . . ) J
We will now take a brief survey of the principal features of these six regions—as shown in the accompanying chart (Plate I., p. 16) and their most characteristic mammal-forms.
Extent.—Australia, New Guinea, and Moluccas up to Wallace's line, New Zealand, and the numerous islands of the Pacific.
Characteristics.—Absence of nearly all Eutherian Mammals, except a few Rodents and Bats; presence of six distinct families of Marsupials with one hundred species, and the only two known forms of Monotremes.
Name.—i/e6?, new, and Tpcm-ucos, i.e., tropical land of the New World.
Extent.—America, south of the Isthmus of Tehuantepec, and the West Indies.
Characteristics.—Monkeys of the peculiar families CebidsR and Hapalidm; absence of Frugivorous Bats, and presence of Vampires (Phyllostomatidm); abundance of the Porcupine family; absence of Insectivores and Civets, also of Elephants; presence of Tapirs; no Ruminants except Deer and Lamas; presence of Sloths, Ant-eaters, and Armadilloes; one family of Marsupials— Opossums.
3. —Ethiopian Region
Name.—'AWUnres, ancient name for negroes.
Extent.—Africa, south of the Atlas; Arabia up to the Persian Gulf, and Madagascar.
Characteristics. — Chimpanzee and other Monkeys; absence of Bears and Deer; presence of Lion, African Elephant, Hyrax, Rhinoceros, Hippopotamus, Wart-hog, numerous Antelopes, Giraffe, Pangolin, Ant-bear—general richness in large and highly-organised Ungulates.
4. —Oriental Region
Extent.—Southern Asia, south of the Pakearctic Region, and islands of Indian Archipelago down to Wallace's line, including Celebes.
Characteristics.—Orangs, Gibbons, and other peculiar Monkeys. Flying Lemur, Tiger, and other cats, Indian Elephant, Rhinoceros, Malayan Tapir, Manis.
Generally, it may be said that the peculiar forms of the Oriental Region are fewer than in the Ethiopian Region, and that the Oriental Region has Bears, Deer, and Tapirs, which are wanting in the latter.
5. —Nearctic Region
Name.—veo?, new, and ap/cros, north, i.e., northern district of the New World.
Extent.—North America, down to the Isthmus of Tehuan tepee.
Characteristics.—General mammal-fauna, very like that of the Palaearctic Region, but mixed up with endemic