filaments from the subdermal plexus. HUNTER placed his demonstrations of this structure in the series of tactile organs, and remarks: These villi are soft and pliable, they float in water, and each is longer or shorter according to the size of the animal. In the Spermaceti Whale they are about a quarter of an inch long; in the Grampus, Bottle-nose, much shorter; in all they are extremely vascular; ' they are sheathed in corresponding hollows of the epiderm.'

The naked skin in Cetacea is even, smooth, and polished, in most instances: the numerous longitudinal plaits along the under and forepart of the body in fin-whales (Balaenoptera, fig. 217, c), would allow of transverse expansion; yet the thorax which they cover needs not such provision. It is peculiar to the swifterswimming whales that pursue mackerel and herring, and may serve to warn them of shoals, by appreciation of an impulse of the water rebounding therefrom, and so conveying a sense of the propinquity of sunken rocks or sand-banks. Sensitiveness to movements of the ambient ocean is indicated by certain observed phenomena. Thus whale-fishers aver that when a straggler is attacked its fellows will bear down from some miles' distance, as if to its assistance; and it may be that they are attracted by perception of the vibration of the water caused by the struggles of the harpooned whale or cachalot. But, in the main, tactile or discriminative sensibility is very low in the Cetacean order. The thick hard and short vibrissæ on the lips of Sirenia, appear to relate rather to prehension than exploration of food.

The extent of surface and delicate organisation of the parts of the skin forming the wings and ear-conchs of those of the Battribe that pursue volant insects (vol. ii. fig. 156), and the antennal nose-leaves of many species (Rhinolophida), relate to the perception of atmospheric impulses rebounding from surfaces near which the Bat approaches in flight. Thus, when deprived of sight, and with the ears and nostrils plugged up, as in Spallanzani's questionable experiments, he avers that the Bat was capable of directing its flight with the same security and accuracy as before, guiding its course through passages just large enough to admit it 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 touching any of them. The delicate sensibility of the membranous integument meets all the conditions of the crepuscular or nocturnal flying of the bat, without involving a new and peculiar sixth sense,' as deduced 1 xx. vol. iii. p. 57, nos. 1403-1405.

character of vibrissæ are, in like manner, adapted to receive and communicate the impressions affecting particular species, or special localities--eyebrows, cheeks, lips-where they may be developed. Whiskers are long and fine in the crepuscular cats; still longer in the nocturnal aye-aye.

The corpuscular thickenings of the neurilemma with the soft centre to which the terminal nerve-filament may be traced (Pacinian bodies,' vol. i. p. 324, figs. 213, 214) are related to the present simplest and most diffused kind of sensation. The degree in which any given part of integument can discriminate two distinct contacts is shown by the intermediate distance at which they begin to be felt as a single impression. Obtuse points of a pair of compasses, e. g. applied, to the skin, with successive degrees of approximation until they feel as one point, have shown the different discriminating power of different parts of the surface of the human body, which, in the main, is expressive of the degrees of general sensibility of such parts. The following are instances in the decreasing ratio of acuteness of feeling or discriminating power:-tip of the tongue, palmar surface of terminal joint of finger, red surface of lip, tip of nose, palm of hand, skin of cheek, sole of foot (parts of), buttocks and adjoining part of thighs, loins, back.'

As the seats of special sense are almost devoid of common sensation, so surfaces with peculiar kinds of the latter, as the teat, penis, or the skin of the axilla, palm and sole susceptible of the sensation called ' tickling,' have low degrees of tactile discrimination. For the phenomena and relations of the sense of temperature, see LXVIII".

The horn-cased feet of the Ungulates, devoid of prehensile power, need no nicety of touch; but they have a sensitiveness by which the degrees of firmness of soil, e. g., may be appreciated; and this is due to the disposition of a highly vascular and nervous stratum into fine and long villi on the sole, and into numerous close-set lamellæ, fig. 17,2 17, which, interdigitating with soft horny lamellæ in the inner surface of the wall of the hoof, relate, at the same time, to its renewal and firm attachment to the terminal phalanx.

In Cetacea the peripheral surface of the derm is produced into fine and long papillæ, highly vascular, and connected with nerve

the tubes whose buried base receives the sensitive nerve, in certain Fishes (voli p. 325), was first appreciated by HUNTER. xx. vol. iii. p. 55.

1 For further details and gradations see LXVIII". vol. ii. p. 516, and LXIX". 2 xx. vol. iii. p. 58, preps. nos. 1410-1413.

filaments from the subdermal plexus. HUNTER placed his demonstrations of this structure in the series of tactile organs, and remarks :— These villi are soft and pliable, they float in water, and each is longer or shorter according to the size of the animal. In the Spermaceti Whale they are about a quarter of an inch long; in the Grampus, Bottle-nose, much shorter; in all they are extremely vascular; they are sheathed in corresponding hollows of the epiderm.'

The naked skin in Cetacea is even, smooth, and polished, in most instances: the numerous longitudinal plaits along the under and forepart of the body in fin-whales (Balanoptera, fig. 217, c), would allow of transverse expansion; yet the thorax which they cover needs not such provision. It is peculiar to the swifterswimming whales that pursue mackerel and herring, and may serve to warn them of shoals, by appreciation of an impulse of the water rebounding therefrom, and so conveying a sense of the propinquity of sunken rocks or sand-banks. Sensitiveness to movements of the ambient ocean is indicated by certain observed phenomena. Thus whale-fishers aver that when a straggler is attacked its fellows will bear down from some miles' distance, as if to its assistance; and it may be that they are attracted by perception of the vibration of the water caused by the struggles of the harpooned whale or cachalot. But, in the main, tactile or discriminative sensibility is very low in the Cetacean order. The thick hard and short vibrissæ on the lips of Sirenia, appear to relate rather to prehension than exploration of food.

The extent of surface and delicate organisation of the parts of the skin forming the wings and ear-conchs of those of the Battribe that pursue volant insects (vol. ii. fig. 156), and the antennal nose-leaves of many species (Rhinolophida), relate to the perception of atmospheric impulses rebounding from surfaces near which the Bat approaches in flight. Thus, when deprived of sight, and with the ears and nostrils plugged up, as in Spallanzani's questionable experiments, he avers that the Bat was capable of directing its flight with the same security and accuracy as before, guiding its course through passages just large enough to admit it 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 touching any of them. The delicate sensibility of the membranous integument meets all the conditions of the crepuscular or nocturnal flying of the bat, without involving a new and peculiar sixth sense,' as deduced 1 xx. vol. iii. p. 57, nos. 1403-1405.

by the narrator of the above experiments. Like the antennæ of some insects, the ear- and nose-leaves of some Bats have rapid vibratile movements; such, at least, have been observed in captive specimens, each pinna moving independently of the other: it looked as if he were feeling for sound and smell.' The nasal leaf is livid or flesh-coloured in Rhinolophus. In the bats of passive food, such as the Vampires (Desmodi) that are attracted by scent in a direct flight to the large living body they suck, and, when gorged, flit lazily back to drowse away a long digestion in their murky retreats; or such as the Roussettes (Pteropi) that wing their way to fruit trees, and, after feeding, suspend themselves in sleep to the branches; the auricular and nasal tegumentary appendages are small and simple: such sensitive tactile guides or warners in flight are only needed in the bats of active food, which must follow in swift evolutions, like the swallows, but in gloom, the volatile insects that people the summer air at dawn or dusk.

141

§ 214. Organ of taste.-The tongue attains in mammals its full development as an organ of taste; and, as respects the extent and organisation of the gustative surface, in the highest degree in Man, fig. 141. The chief distinction of this from a tactile surface is that the sensitive papillæ are on processes rising above the epithelial level, said processes being commonly called 'papillæ.' As we descend in the mammalian series the mechanical offices of the tongue predominate over the sensitive ones. In the Giraffe, Pangolins, Anteaters, and Echidna, its most obvious office is that of prehension; and in the Ornithorhynchus it supports teeth, horny like those of the jaws, and it has mechanical modifications in relation to the cheek pouches. In all Mammals the dorsum of the tongue is more or less papil1 LXXIX. p. 65.

lose, and in most the papilla offer the three conditions called 'conical, fig. 150, fungiform,' fig. 149, and fossulate,' fig. 148, f.

The tongue is well developed and freely movable in all Marsupials, and the epithelium covering the conical papillæ is rarely condensed into spines. In the carnivorous species, as the Dasyuri, the conical papillæ are minute and soft, but directed backward, so as to give a slight roughness to the tongue when stroked in the opposite direction: under a lens they appear like fine shagreen. Near the base of the tongue in Dasyurus viverrinus there are three fossulate papillæ, in triangle, with the apex toward the epiglottis. A small fibrous or sclerous rudiment of the 'glosso-hyal,' called 'worm,' or lytta, lies lengthwise beneath the tip of the tongue. In the Perameles, besides the minute and generally diffused simple papillæ, there are fungiform ones, of larger size, placed at distances of nearly a line apart, and raised about a third of a line above the surface of the dorsum. The fossulate papillæ correspond in number and arrangement with those of the Dasyures, but the entire tongue is relatively longer and more slender, especially in Per. lagotis. In some species of Opossum, as Didelphys Philander, the margin of the tongue is fringed with a series of fine long papillæ. In Didelphis virginiana the conical papillæ of the fore part of the dorsum are retroverted and sheathed with hard epithelium. In the Phalangers there is a thickening at the edge of the frænum linguæ, but no true lytta: the dorsal papillæ resemble those of the Dasyures, but are somewhat more obtuse. In the Kangaroo there is a callous ridge along the middle of the under surface of the free extremity of the tongue, and a corresponding furrow along the dorsum; the latter is common to all the Marsupials. In the Wombat and Koala the dorsum of the tongue rises somewhat abruptly from a furrow surrounding its base; its form is narrow, moderately deep, diminishing in this respect to the tip, which is rounded. In both the Kangaroo and Koala there is a single large fossulate papilla near the base of the tongue. In Dendrolagus there are three such, arranged in a triangle with the apex turned forward.

Most Rodentia show two well-marked divisions of their usually deep and compressed tongue: an anterior, which from its vascular and papillose surface is the main seat of taste, and a posterior or intermolar tract, which rises somewhat abruptly above the level of the preceding and brings the food to that of the triturating surface of the molars.

The tongue seems to fill the narrow mouth of Rodents more compactly than usual, commonly bearing the impress of the