From these experiments it was perfectly clear that in threading the galleries of caverns and other narrow and pitch-dark places to which Bats commonly resort for their diurnal repose, these animals were guided by some other sense than that of sight, and the worthy abbé set himself to ascertain what this sense might be. He commenced operations by covering the body of one of his blind Bats with varnish, and found that this had no effect in rendering its movements uncertain. He then stopped up the ears with wax, and finally with melted sealing-wax, and still the Bats obstinately persisted in avoiding obstacles placed in their way. Consequently they did not hear their way in the dark. There remained the senses of smell and taste. To test the former the nostrils were stuffed up, but the only effect of this operation was to bring the creature speedily to the ground, owing to difficulty of breathing. Little fragments of sponge impregnated with musk, camphor, or storax were fastened in front of the nostrils, and then the Bats flew about as freely as ever, and showed the same power of avoiding contact with objects in their path. The removal of the tongue, as might be expected, produced no result.
HEAD OF LONG-EARED BAT.
Many of Spallanzani’s experiments were repeated by M. de Jurine, of Geneva, and with similar results, although Jurine found that when the ears were effectually stopped the Bats struck their wings against any object that came in their way.
Spallanzani found further that when the head of a Bat was enclosed in a small paper bag, or even wrapped in some fine light stuff, the animal could not be induced to fly. Coupling this observation with the results of his other experiments, he came to the conclusion that the mysterious faculty possessed by Bats of finding their way in the darkest places was due to some special sense with which they were endowed, and which was seated in some unknown organ situated in the head. Cuvier, however, who was the first really to appreciate the results of these experiments, arrived at the conclusion, now generally accepted, that the wonderful power possessed by Bats of directing their flight in places so dark as to render the sharpest eyes useless, was due to an exceptional development of the sense of touch, residing especially in the great delicate membranous expanse of the wings. These organs are really of the most delicate structure, and traversed by nerves, the fine ramifications of which terminate in little loops, like those found in those parts of the skin in man in which the sense of touch is manifested with the greatest perfection; and their surface is covered with rows of small thickened points, or papillæ, which may very probably have something to do with the perception of exceedingly delicate tactile impressions. Further, the wings of Bats are very copiously supplied with blood-vessels, and according to Dr. Wharton Jones even the veins are furnished with contractile walls, so that the circulation of the blood in them must be exceedingly active. In fact, according to Professor St. George Mivart, we have here a condition of things which may be in some degree analogous to a state of inflammation, which would doubtless considerably heighten the sensibility of the parts. But besides the wing-membranes many Bats, as we have seen, possess greatly enlarged ears, and also curious leaf-like and membranous appendages attached to the region of the nose, all of which no doubt partake of the sensibility of the wing-membranes, and assist in no small degree in guiding their possessors. In fact, from some observations recorded in Bell’s “British Quadrupeds” with regard to two British species (the Pipistrelle and the Horseshoe Bat), it would appear that the species with nasal appendages show greater acuteness of perception than those with simple noses, and many of them are known to frequent the darkest places of retreat, and to fly later than some of their less highly endowed fellows.
HEAD OF THE SPECTACLED
VAMPIRE (STENODERMA
PERSPICILLATUM.)
The food of the great majority of Bats consists of insects, which they capture on the wing. The members of one large family, however, and some species of another, feed upon fruits; whilst a few find at least a part of their nourishment in the blood of other animals. They generally fly in the twilight of the evening and morning, retiring to obscure places during the day, although some species will occasionally come out of their concealment by daylight.
In temperate and cold climates they pass the winter in a torpid state suspended by their hinder claws in their ordinary places of daily retreat, where they are often to be found in immense numbers. An American gentleman, describing a cave in the Western Territories, where the excrements of Bats had formed so large a deposit of “guano” that it was proposed to utilise it as manure, was asked by a friend of ours about the number of Bats in the cavern. He said, “Well, I guess when we went in there was about as much Bats as air in it.” There is doubtless a slight tinge of occidental hyperbole about this statement, but the following sober details, although also from the Western continent, may serve to show what multitudes of these creatures may collect together when left undisturbed in a suitable haunt. The story is told in the introduction to Dr. Allen’s “Monograph of the Bats of North America,” and is a description by M. Figaniere, Portuguese Minister to the United States, of the incidents attending his occupation of a new house in May, 1860:—