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1. The Order of Chiroptera, or Bats, contains about 530 known species which are divided into ninety-five genera and six families.
2. They are found in every part of the world except within the Arctic and Antarctic Circles, and even in many islands where no other mammals occur.
3. The Fruit-bats (Pteropodidm) are met with only in the Old World, and mainly within the tropics.
4. The Vampires (Phyllostomatidm) are entirely restricted to the Neotropical Region, except two or three species (out of eighty) which have passed over the boundaries into the Nearctic Region.
5. Two forms of the Vampires (Desmodus and DlphyUa), having their dentition and digestive organs specially modified for that purpose, feed on the blood of living animals.
Section IV.—Distribution Of Rodents
Rodents are by far the most numerous of all the Orders of Mammals, comprising, according to a moderate calculation, nearly 1400 species which are arranged in 159 genera belonging to twenty-one distinct families. They are also among the most universally distributed of terrestrial mammals, being found in all latitudes high and low, and abundant in every part of the earth except Australia, where they are feebly represented by a few genera and species. The Rodents, especially the Mice (Muridm), to which family rather more than half their number belong, are still imperfectly known; their arrangement and classification have recently undergone important changes, and continual discoveries of new species and new alliances are made by several busy naturalists who are engaged mainly on a study of the smaller mammals. Under these circumstances it is hardly necessary for our present purpose to mention more than the names of most of the twenty-one families which constitute this complicated group, but we shall endeavour to pick out, as we go through them, some of the most noticeable facts connected with the distribution of these mammals.
Adopting Mr. Thomas's recent classification of the genera of this group1 (with a few slight deviations) as the best authority, we find the Anomaluridm, a singular group of Flying-Squirrel-like Rodents, at the head of the Order. This family, with its three genera (Anomalurus, Idiurus, and Zenkerella), is purely Ethiopian, the eleven or twelve species which are referred to it occurring only in tropical Africa. Passing on to the next family, the Squirrels (Sciuridm), we have an extensive group of about 240 species divided into eleven genera distributed nearly all over the earth's surface, with the exception of the Australian Region and Madagascar, where they are entirely deficient. The most numerous genus is that of the true Squirrels (Sciurus) which, subject to the exception just mentioned, is fairly distributed over the whole of the earth.
The Castoridm, or Beavers, which come next, are represented in the present day only by the genus Castor, with two species, one of which occurs in the high latitudes of the Palsearctic and the other in those of the Nearctic
1 "On the genera of Rodents," P. Z. S. 1896, p. 1012. Cf. Palmer, «' Science," N. 8., vi, p. 103 (1897).
Region. These two species are closely allied and perhaps scarcely distinguishable.
The Haplodontiidm, or Sewellels, allied to the Squirrels, contain only the single genus HaplocUyntia, the species of which are confined to the Nearctic Region.
In the fourth family of the Rodents we meet with more familiar objects. The Gliridm, or Dormice, with six genera and about nineteen or twenty species, "have a curious distribution, being found only in the Ethiopian, Oriental, and Palaearctic Regions. Each of these Regions, however, has its peculiar genera, true Glis and its allies belonging to the Palaearctic Region, whilst Graphiurus is strictly Ethiopian, and the two remaining genera are restricted to the Oriental Region.
We now come to the Mice, or Muridm, which, as already indicated, are exceedingly numerous and all-pervading creatures. Mr. Thomas places the 730 species of this family in seventy-eight genera. Mice are most numerous, perhaps, in the tropics, but are also well represented in Arctic latitudes, and in the shape of Lemmings (Lemmus), extend far towards the Pole.
They are not abundant in Australia proper, being represented there chiefly by the peculiar genus Hydramys and a few species of Mils. In Madagascar the seven genera of Muridm met with are likewise altogether restricted to that anomalous island.
The Mole-rats (Spalaeidm), whichL follow next in Mr. Thomas's series, are a small and peculiar group, the members of which imitate the subterranean life of the Moles. The typical genus Spalax, with eight species, is confined to the Palaearctic Region, whilst the Bamboo Rats (Rhizomys), represent the group in the Oriental Region and Tachyoryctes in the Ethiopian Region.
The Pocket-gophers (Ge&myidm), which are entirely restricted to the Nearctic Region, contain only two genera and nine species. Allied to them are the Heteromyidm, a more numerous group of seventy or eighty species, entirely restricted to the New World, and, with the exception of a few stray species of Pocket-mice (Heteromys), to the Nearctic Region.
The tenth family of Rodents, the Bathyergidm, belong entirely to the Ethiopian Region, over which they are thinly represented by fifteen or sixteen species. The Naked Sand-Rat of Southern Abyssinia and Somaliland (Hcterocephalus glaber), is one of the most extraordinary-looking Mammals in the world, being almost entirely without hair and covered with a yellowish naked skin; it is subterranean in its habits.
The Dipodidm, or Jerboas, which we now come to, are well known for the great length of the hind limbs and the kangaroo-like manner of their progression; they consist of six genera and about thirty-three species, all of which, except one (Zapus), are restricted to the Palaearctic Region. The six species of Zapus, are spread over the Nearctic Region from the far North down to Mexico, where, however, they are restricted to the highlands.
Allied to the Jerboas is the Jumping-Hare (Pedetes coffer), which forms an allied family of itself, and is restricted to Southern and South-eastern Africa.
We now arrive at the series of Porcupiny Rodents, of which as many as seven families are usually recognized. These are mostly found in the Neotropical Region,
and four of them indeed, the Chinchillidm, Dasyproctidm,