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TABLE OF REGIONS AND SUB-REGIONS--continued.
III. Oriental ...... 1. Hindostan (or Central Ind.) Transition to Ethiopian.
Transition to Australian. IV. Australian... 1. Austro-Malaya.
Transition to Oriental. 2. Australia. 3. Polynesia. 4. New Zealand.
Transition to Neotropical. V. Neotropical.. 1. Chili (or S. Temp. Am.) Transition to Australian.
Transition to Palæarctic.
CLASSIFICATION AS AFFECTING THE STUDY OF GEOGRAPHICAL
A LITTLE consideration will convince us, that no inquiry into the causes and laws which determine the geographical distribution of animals or plants can lead to satisfactory results, unless we have a tolerably accurate knowledge of the affinities of the several species, genera, and families to each other; in other words, we require a natural classification to work upon. Let us, for example, take three animals—a, b, and c-which have a general external resemblance to each other, and are usually considered to be really allied; and let us suppose that a and b inhabit the same or adjacent districts, while c is found far away on the other side of the globe, with no animals at all resembling it in any of the intervening countries. We should here have a difficult problem to solve; for we should have to show that the general laws by which we account for the main features of distribution, will explain this exceptional case. But now, suppose some comparative anatomist takes these animals in hand, and finds that the resemblance of c to a and b is only superficial, while their internal structure exhibits marked and important differences; and that c really belongs to another group of animals, d, which inhabits the very region in which c was found—and we should no longer have anything to explain. This is no imaginary case. Up to a very few years ago a curious Mexican animal, Bassaris astuta, was almost always classed in the civet family (Viverridæ), a group entirely con
fined to Africa and Asia ; but it has now been conclusively shown by Professor Flower that its real affinities are with the racoons (Procyonidæ), a group confined to North and South America. In another case, however, an equally careful examination shows, that an animal peculiar to the Himalayas (Ælurus fulgens) has its nearest ally in the Cercoleptes of South America. Here, therefore, the geographical difficulty really exists, and any satisfactory theory of the causes that have led to the existing distribution of living things, must be able to account, more or less definitely, for this and other anomalies. From these cases it will be evident, that if any class or order of animals is very imperfectly known and its classification altogether artificial, it is useless to attempt to account for the anomalies its distribution may present; since those anomalies may be, to a great extent, due to false notions as to the affinities of its component species.
According to the laws and causes of distribution discussed in the preceding chapters, we should find limited and defined distribution to be the rule, universal or indefinite distribution to be the exception, in every natural group corresponding to what are usually regarded as families and genera; and so much is this the case in nature, that when we find a group of this nominal rank scattered as it were at random over the earth, we have a strong presumption that it is not natural ; but is, to a considerable extent, a haphazard collection of species. Of course this reasoning will only apply, in cases where there are no unusual means of dispersal, nor any exceptional causes which might determine a scattered distribution.
From the considerations now adduced it becomes evident, that it is of the first importance for the success of our inquiry to secure a natural classification of animals, especially as regards the families and genera. The higher groups, such as classes and orders, are of less importance for our purpose; because they are almost always widely and often universally distributed, except those which are so small as to be evidently the nearly extinct representatives of a once more extensive series of forms. We now proceed to explain the classification to be adopted, as low down as the series of families. To these, equivalent English
names are given wherever they exist, in order that readers possessing no technical knowledge, may form some conception of the meaning of the term " family” in zoology.
The primary divisions of the animal kingdom according to two eminent modern authorities are as follows:
For reasons already stated it is only with the fifth, seventh, and eighth of these groups that the present work proposes to deal; and even with the fifth and seventh only partially and in the most general way.
The classes of the vertebrata, according to both the authors above quoted, are: 1. Mammalia. 2. Aves. 3. Reptilia. 4. Amphibia. 5. Pisces, in which order they will be taken here.
The sub-classes and orders of mammalia are as follows:
11. Edentata Didelphia ...... 12. Marsupialia ... Ornitħodelphia 13. Monotremata
The above series of orders is arranged according to Professor Flower's Osteology of Mammalia, and they will follow in this succession throughout my work. Professor Huxley arranges the same orders in a different series.
In determining the manner in which the several orders shall be subdivided into families, I have been guided in my choice of classifications mainly by the degree of attention the author appears to have paid to the group, and his known ability as a systematic zoologist; and in a less degree by considerations of convenience as regards the special purposes of geographical distribution. In many cases it is a matter of great doubt whether a certain group should form several distinct families or be united into one or two; but one method may bring out the peculiarities of distribution much better than the other, and this is, in our case, a sufficient reason for adopting it.
For the Primates I follow, with some modifications, the classification of Mr. St. George Mivart given in his article " Apes" in the new edition of the Encyclopædia Britannica, and in his paper in the Proceedings of the Zoological Society of London, 1865, p. 547. It is as follows:
Order-PRIMATES, divided into two Sub-orders :
2. Semnopithecidæ Old-world Monkeys.
Tarsiers. 8. Chiromyidae
Omitting man (for reasons stated in the preface) the three first families are considered by Professor Mivart to be subfamilies of Simiidæ; but as the geographical distribution of the Old World apes is especially interesting, it is thought