DENTITION of THE
THICK-LEGGED BAT.

LINNÆUS, in his “Systema Naturæ,” united all the Bats known to him (with the exception of a single species, which, by a curious perversion of judgment he referred to a distinct genus, and placed in quite a different order) under the single genus Vespertilio. Later writers, finding it necessary, as their knowledge of these animals increased, to divide the Bats into many genera, have gradually, as it were, cut off portions of the old Linnæan genus and given them new names, always retaining the old name for the group which might be considered to include the most typical forms of the original genus Vespertilio, the ordinary Bats of European countries. Of these, only two are noticed in the last edition of the work of the great Swedish naturalist, and even these are now referred to two distinct genera, and the generic name of Vespertilio is now retained by only one of the few species with which Linnæus was acquainted. The genus, however, as at present restricted, contains a great number of species, all of which present the characters of what may be called an average Bat, forming, as it were, the centre (or part of the centre) round which the other groups forming the order may be ideally arranged, and hence it very appropriately bears the old name Vespertilio, as Bat par excellence, constitutes the type of the family Vespertilionidæ, and gives its name to the Vespertilionine alliance. In point of fact the genus Vespertilio and the family Vespertilionidæ may be regarded as the ideal centre of the whole order. As in other groups of the same kind the number of species contained in the family is very considerable, and their structural differences are generally minute, these, indeed, being the characteristics usually presented by what are called typical groups, the study of which is on this account attended with peculiar difficulties.

Except in one Australian genus (Nyctophilus), which has been removed here from among the Megaderms by MM. Tomes and Dobson, the nostrils in the Vespertilionidæ are simple round or crescentic apertures placed at the extremity of the muzzle, and not surrounded by leaf-like appendages. The tail is always long, contained in the membrane between the legs, which it traverses from base to apex, usually leaving a single joint projecting beyond the membrane; the ears are of moderate or large size, are generally separate, and are furnished with large tragi. With regard to the teeth, the upper incisors are separated in the middle by a wide space and placed close to the canines. The number of incisor teeth in the upper jaw varies, being generally four, standing in pairs in the pre-maxillary bones, but in some species there is only one incisor on each side, and this difference may not be associated with any other characters sufficient to justify the generic separation of the species. The lower incisors are almost always six in number; one genus only has four. The canines are of moderate length and strength. The pre-molars again are exceedingly variable; there may be three or two on each side in both jaws, or one on each side in the upper and two in the lower jaw, but the occurrence of two above and three below is very rare. As a rule, when there are more than one pre-molar on each side in the upper jaw, the hindmost of them which is close to the true molars is larger than the one or two nearer the canine (see [figure, p. 292]), and the latter are often inserted within the line of the row of teeth. The true molars are three on each side in both jaws; they are well-developed, and show the characteristic sharp W-shaped cusps very distinctly.

BRITISH BATS AT HOME.

[❏
LARGER IMAGE]

The Vespertilionidæ are all, so far as is known, strictly insectivorous in their habits. They are found generally distributed throughout the temperate and warm regions of both hemispheres. It is to this family that nearly all the European Bats belong, and it includes all the British species, except the two Horseshoe Bats which have been already described.

LONG-EARED BATS IN FLIGHT.

THE LONG-EARED BAT.[182]