The general nervous systent in the Cheiro ptera does not exhibit any very remarkable peculiarity, but some of the organs of sense require a particular notice.
Organs qf the Senses.—The organ of vision is principally remarkable for its diminutive size. The eye in many of the insectivorous group, in which the external ear is very largely developed, is placed within the margin of the auricle and almost concealed by hair. In the frugivorous group, on the other hand, it is of the usual proportional size. The organ of hearing, on the contrary, though in the latter forms not more developed than in most other quadrupeds, in the former seems to take the place of the diminutive organ of vision, being greatly extended both in its external and internal organization. The external ear in Pteropus is of the usual form and dimensions, and the eminences are not in any respect extra ordinary : but in most of the insectivorous Bats the conch of the ear is enormously large; in many species being considerably larger and longer than the head, and in the common long eared Bat of this country, Plecotus auritus, it is nearly as long as the body. The tragus is proportionally larger than in any other animals; in most species it is more or less lanceolate in its form; in Vespertilio spasma it is -forked, and in the great Bat of Britain, Vespertilio noctula, it is short, blunted, with a rounded head, thickish, and I have observed it beset with numerous minute glands, which do not occur in those species having the thin lan ceolate form of this part. Its use is probably to prevent the rush of air into the open ear during flight; and where it does not exist, as in the Horse-shoe 13ats ( Rhinolophus), its place is supplied by a large rounded lobe which is capable of still more effectually closing the external meatus.
In the internal ear there is an equal diver sity of structure in the two groups in question. The cochlea is particularly developed in the insectivorous group; being much larger than the semicircular canals; the circumference of that of _Rhinolophus is no less than four times the circumference of the canals, and its cavity exhibits ten times the diameter of one of them. In Pteropus this disproportion is very much less. The meatus is short and, as well as the tympanic cavity, extremely large and open.
But it is in the sense of touch probably that the most extraordinary and interesting pecu liarities are to be observed. Spallanzani hay-, ing observed the povver which these animals possess of flying with perfect accuracy in the dark, and of avoiding every obstacle that pre sents itself with the same unerring certainty as in the light, instituted a series of experiments, the results of which proved that bats when deprived of sight by the extirpation of the eyes, and, as far as possible, of hearing and smell by the obliteration of the external pas sages of those senses, were still capable of directing their flight with the same security and accuracy as before, directing their course through passages only just large enough to admit them without coming into contact with the sides, and even avoiding numerous small threads which were stretched across the room in various directions, the wings never, even by accident, touching any of them. These
marvellous results led him to believe that these animals are endowed with a sixth sense, the immediate operation as well as the locality of which is, of course, unknown to and unap preciable by us : but the sagacity of Cuvier removed the mystery without weakening the interest of these curious facts, by referring to the flying membrane as the seat of this extra ordinary faculty. According to this view of the subject, the whole surface of the vvings on both sides may be considered as an enor mously expanded organ of touch, of the most exquisite sensibility to the peculiar sensation for which it is intended ; and it is, therefore, by the varied modification of the impulsion of the atmosphere upon this surface, that the knowledge of the propinquity of foreign bodies is communicated. This membrane is every where furnished with oblique or transverse bands, consisting of lines of minute dots re sembling in some measure strings of very small glands or cutaneous follicles. May there not be some connexion between these peculiar little bodies and the extraordinary function just described ? The tendency to an extraordinary develop ment of the dermal system is not confined to the organs now mentioned, of the senses of touch and of hearing. The organ nf smell is in many insectivorous Bats, as in the whole family Rhinolophidee, furni shed with fol aceous appendages, formed of the integument doubled, folded, and cut into the most curious and grotesque forms. These nasal leaflets are found principally or exclusively to belong to a group, the habits of which are more com pletely lucifugous and retired than any others; they are found in the darkest penetralia of caverns, and other places where there is not even the imperfect light which the other genera of Bats enjoy. It is probable that this deve lopment of skin around the nose is intended to give increased power and delicacy to the organ of smell, as well as to regulate the access of the odoriferous particles, and thus to super sede the sense of vision, in situations where the latter would be unavailable.