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SECTION I.—INTRODUCTORY REMARKS
The three Orders, to which it is proposed to devote the present chapter, contain the most difficult and least known members of the whole class. They are very numerous, especially the two latter groups, nearly all of small size, and in most parts of the world have been very imperfectly studied. Within these last few years large additions have been made to our knowledge of them, especially in the case of the Rodents, and their proper systematic arrangement is still a matter of much discussion amongst naturalists. Under these circumstances, and looking to the fact that these small mammals are of much less general interest than their larger brethren, it is not proposed to go very fully into the subject of their geographical distribution, but merely to point out some of the leading and less controvertible facts known upon this part of their history. We will commence with the Insectivores, which are generally allowed to be in many respects allied to the Carnivores, although they present certain points in their structure which appear to show a probability of their original descent from much lower forms.
SECTION II.—DISTRIBUTION OF INSECTIVORES
The Insectivores are for the most part widely scattered over the earth's surface, but not very numerous in species except in certain localities. In the Australian Region they are entirely absent, their place in nature being there taken by the Insectivorous Marsupials, and in the Neotropical Region, they have only penetrated as far south as certain districts in the Northern Andes. In this case also we may suppose that their functions are performed by the smaller Opossums (Didelphyidæ), which subsist almost entirely upon insects. In almost every other part of the earth, as we shall see, the Insectivores are represented either by special types or by members of the widely-spread group of Shrews.
As will be seen by the tables given below (p. 260) the Insectivores, according to a moderate estimate, are supposed to number about 230 species, divisible into forty-one genera. These genera are grouped in ten families, on the distribution of each of which a few words may be said.
At the head of the Order it is best to place the Kaguan, or Flying Lemur as it is commonly called, though its structure is so peculiar and its affinities so little obvious that it might perhaps be more properly ranked in an Order by itself. Of this family only a single genus (Galeopithecus) with two species is known, one found in the Malay Peninsula and the islands of the Eastern Archipelago, and a second, smaller form in the Philippine group. The Galeopithecidæ, therefore, may be placed as a characteristic form of the Oriental Region.
The second family of Insectivora, the Tupaiida, or
Tree-shrews, with two genera and about fifteen species, is likewise confined to the Oriental Region, and forms another characteristic group of that Region.
In the third family of Insectivorous Mammals the Macroscelidæ, or Jumping Shrews, which, though held to represent the Tree-shrews in Africa, are very different in appearance and are essentially terrestrial in their habits, must be considered as a purely Ethiopian type, though one form (Macroscelides rozeti) has crossed the limits of the Ethiopian Region into Algeria.
The fourth family of Insectivora, the Erinaceidæ, or Hedgehogs, are rather more widely diffused. The true Hedgehogs (Erinaceus), of which about fourteen species are known, are spread all over the Ethiopian Region except Madagascar, and are likewise found in the Oriental and Palæarctic Regions. The second genus of Erinaceidæ (Gymnura), of which two species are distinguished, is restricted to the Oriental Region.
In the fifth sub-family of this Order the Soricidæ, or Shrews, we find the most numerous and the most widely extended mammals of this group. Though these little animals are still very imperfectly known and many more species must remain to be discovered, they already number some 125 species. These are spread over nearly the whole earth except the Australian Region and the Neotropical Region, where, however, in the northern borders two or three species are known to occur. The Musk-shrews (Crocidura) are the most numerous of all the genera, more than eighty species of these little animals having been already described. They are found in Africa and Madagascar and are also numerous in the Oriental and Palaarctic Regions, but do not occur at all in the New World. Others of the eleven genera of this family, however, are based on one or two species and have a much more limited distribution, such as the Water-shrew (Crossopus) of Europe and Northern Asia, and Nectogale, the Webfooted Shrew of Tibet.
After the Shrews follow the Moles (Talpida) of which about eleven genera are known containing altogether about twenty-three species. The Moles are specially characteristic of the Palæarctic and Nearctic Regions, to which nearly all the genera and species are confined, but one or two species of true Moles (Talpa) have invaded the confines of the Oriental Region.
The seventh family of Insectivores (Potamogalidæ) contains only two isolated forms—Potamogale from West Africa and Geogale from Madagascar. This group must therefore be attributed to the Ethiopian Region.
Allied to the last-named family, but still more closely to the Tenrecs which follow them, are the two species of the remarkable genus Solenodon, to find which we must go, strangely enough, as far as the West Indian Islands. Here linger the last representatives of this singular group of Insectivores, one species, Solenodon paradoxus, being restricted to Hayti and the other, S. cubanus, to Cuba.
The Tenrecs (Centetids), which form the ninth family of Insectivorous Mammals, number as many as twentyone species which belong to seven genera, of which the distribution may be very shortly described, as they all belong to the island of Madagascar, and constitute one of the most curious of the primitive forms of animal life that render the Malagasy Sub-region so remarkable.
Finally, closing the Order of Insectivores, we find the
Golden Moles (Chrysochloride), a family containing but one genus, Chrysochloris, with seven species all confined to the Ethiopian Region.
Summary and Deductions as regards the Insectivores
Table of the families and genera of the Order Insectivora, showing the approximate number of species in each of the Regions.