VOLE (Germ. Wiihlniaus, Fr. Campagnol). This word, little known as it is to the majority of English people, is the proper name for a genus containing three of the com-monest of our English mammals, namely, the water, bank, and field voles,animals generally called " water-rat," " red field-mouse," and " short-tailed field-mouse " respect-ively. The scientific name for the group is Arvicola, a genus which, with the lemmings and two or three other genera, forms the subfamily Arvicolinse of the great Rodent family Muridx, whose proper place in the general system is shown under MAMMALIA (vol. xv. p. 419).
The voles, as a whole, are distinguished by their squat and heavy shape, their slower and less graceful move-ments, very small blunt snout,
eyes. inconspicuous ears, and shortened limbs and tail, in all of which points they are markedly contrasted with the true rats and mice of the genus Mus, the only animals with which they can be confounded. Molars of Water-Vole (Arvicola amphibius); But by far the top view, most important characteristic of the voles lies in their molar teeth, which have been said to form " the perfection of Rodent dentition " from their wonderful specialization and adaptation to the purpose of grinding vegetable substances. These teeth, three in number on each side of each jaw, are rootless, that is to say, they go on grow-ing during the whole life of the animal at the same rate
that they are worn down by use, just as is the case with the incisors, whose rootless condition is a characteristic of the whole Rodent order. Each tooth consists of a variable number of prismatic pillars formed externally of enamel and internally of the softer dentine, their section, as produced naturally by wear, being as is shown in the woodcut, a figure which may be compared with that given of the true murine dentition under MOUSE (vol. xvii. p. 5). The general prismatic appearance of the teeth, how-ever, is only due to the bending in at regular distances of the external enamel walls of the tooth, to such an extent that the enamel touches that at the opposite side of the tooth and thus shuts off a greater or less number of dentinal spaces, triangular in section. Owing to the manner of growth of the teeth their general pattern of spaces and angles is but little affected by age and wear, remaining practically the same throughout the life of the animal. On this account the variations in the pattern have been very generally used as a means of characterizing the different genera, subgenera, and species of the group, although their value for this purpose has of late been questioned, and a new classification proposed, entirely ignoring the tooth-characters, and based more upon external peculiarities.
Without entering into the characters of the different sub-groups of the voles, it may suffice to say that each of the three species found in Great Britain belongs to a dis-tinct subgenus of Arvicola, and therefore the three together give a fair idea of the extent to which the subgenera differ from one another. These three species are the following :
1. The common Water-Vole (Arvicola amphibius) is as large as the house-rat, with which it is so often confused, but possesses of course the bluff-headed appearance and short tail characteristic of the voles. Its fur is long, soft, and thick, of a uniform grizzled brown all over, except when, as is not uncommon, it is wholly black. Its tail is about half the length of its head and body, and its hind feet are unusually long and powerful, although not webbed, and have five rounded pads on their lower surfaces. Its molar teeth (see woodcut) present the following number of prismatic spaces:in the upper jaw the first, or anterior, has 5, the second 4. and the third 4, of which the last is very irregular in shape, and is sometimes itself divided into two, making 5 in all; in the lower jaw the first has 7 spaces, of which the 3 anterior are generally not fully separated from one another, the second has 5, and the third 3. These numbers for the different teeth are taken as the characters of the subgenus Paludicola of Dr Blasius, by whom this method of subdividing the group was first introduced. The water-vole is one of the commonest English mammals, and is perhaps the most often actually seen of all, owing to its diurnal instead of nocturnal habits. It frequents rivers and streams, burrowing deeply into their banks, and in this way often causing considerable damage. Its food consists almost wholly of water-weeds, rushes, and other vegetable substances, but, like so many other rodents, it will also eat animal food on occasion, in the shape of insects, mice, or young birds. The female has during the warm season of the year three or four litters, each of from two to seven young. The range of the water-rat extends over the whole of Europe and North Asia, from England to China, but is not found in Ireland, where, curiously, no species of Arvicola is indigenous.
2. The next British species, representing the subgenus Agricola of Dr Blasius, is the common Field-Vole, or short-tailed field-mouse (Arvicola agrcstis), about the size of a house-mouse, but with a short stumpy body, and a tail only about one-third the length of the head and body combined. Its hind feet have six pads on their inferior surfaces. Its colour is dull grizzled brown above, and greyish-white below. Its molar teeth have respectively 5, 5, and 6 prismatic spaces above, and 9, 5, and 3 below. The field-vole is one of the commonest of our smaller mammals, and frequents fields, woods, and gardens in enormous numbers, often doing very considerable damage in the latter owing to its fondness for garden produce of all kinds. It is spread over the wdiole of Great Britain from the Hebrides southwards. Abroad its range extends from Finland to North Italy and from France and Spain to Russia.
3. The Bank-Vole (Arvicola glareolus) is of much the size and general appearance of the common field-vole, but may be dis-tinguished by its more or less rusty or rufous-coloured back, its larger ears, and its comparatively longer tail, which attains to about half the length of the head and body. Its molar teeth present characters so different from those of all other voles as to have caused it to be often looked upon as belonging to an entirely distinct genus, for which the name of Evotomys is used.
Their chief distinction lies in the fact that, unlike those of all other voles, their pulp-cavities close up in adult life, and they form distinct roots, more resembling those of the ordinary rats and mice. The enamel spaces of these teeth number respec-tively 5, 4, and 5 above, and 7, 3, and 3 below. The habits of this species are in every way similar to those of the field-vole. Its range in Great Britain extends northwards to Morayshire, beyond which it has not yet been observed. Abroad it is found all along the north temperate zone from France to China, and is replaced in North America by a closely allied animal known as Arvicola gapperi. It is probable, however, that both these forms, A. gapperi and A. glareolus, are only southern climatic offshoots of a still more northern species, the Arvicola rutilus of northern Europe, Siberia, and Arctic America.
The foreign species of vole number about 40, of which
about 10 are European, 20 Asiatic, and 10 North American,
none being found either in Africa, India (except in the
extreme north), Australia, or South America. The group
is therefore one peculiarly characteristic of the temperate
parts of the northern hemisphere. (o. T.)