CHAPTER I.

INTRODUCTION.--CLASSIFICATION OF BATS.--THE FRUIT-EATING BATS.

One of Æsop’s Fables--Opinions of the Ancients regarding Bats--Scaliger’s Statement of the Puzzle--Opinions of the Middle Ages--The True Position of the Bats--The Wing of the Bat--General Structure: The Breast-bone, Arms, Fingers, “Wing-membrane,” Wings, Skull, Ribs, Pelvis, Legs--In Repose--Walking--The Teats--Organs of the Senses--“Blind as a Bat”--The Eyes--Spallanzani’s Experiments--The Bat’s Power of Directing its Flight in the Darkest Places--Their Food--In Winter-Quarters--A Battue of Bats--FRUGIVOROUS AND INSECTIVOROUS BATS.

One of those ancient fables ascribed to Æsop, which were the delight of our younger days, contains a description of a battle between the birds and the beasts. The grounds of the quarrel we do not remember, and indeed the moral of the fable was tacked on to the conduct of the Bat. Availing himself of his combination of fur and wings, that astute animal hovered over the field of battle, and took his place on one side or the other, according to the direction in which the tide of success appeared to be turning, with the purpose, of course, of claiming in any case to be on the side of the victors. But this finesse was unsuccessful; the traitor was scouted by both parties, and has ever since been compelled to make his appearance in public only at night. Passing over the ingenious explanation thus afforded of the nocturnal habits of the Bats, this fable reflects pretty clearly the state of uncertainty in which the ancients were as to their precise nature. The union of a Mouse-like body with long wings was a great puzzle to people who had no sound principles of natural history classification to go upon; and even among the naturalists of antiquity there was much doubt as to the true position to be assigned to animals so singularly endowed. Aristotle seems to have thought they were birds with wings of skin; and Pliny describes them as the only birds which bring forth their young alive and suckle them. Among the Jews it is perfectly clear that the Bat was reckoned a bird; it is distinctly included among the unclean fowls in Leviticus (xi. 19), and Deuteronomy (xiv. 18). The obfuscation displayed by ancient writers with respect to the Bat is well shown in the following passage, in which Scaliger summarises their opinions:--“It is indeed,” he says, “an animal of marvellous structure; biped, quadruped; walking, but not with feet; flying, but not with feathers; seeing without light, in the light, blind; it uses light beyond the light, but wants light in the light; a bird with teeth, without a beak, with teats, with milk, bearing its young even when flying.” Can it be wondered at that such a creature should be a puzzle?

Nevertheless, some ancient writers seem to have entertained clearer notions on the subject, such as Macrobius, who maintained that as the Bat walked like a quadruped it ought to be classed with quadrupeds, for which he is blamed by Jonston, who speaks with approval of Plato’s opinion, according to which this unfortunate animal is neither bird nor beast, an opinion which partially prevailed to a rather late date. Throughout the Middle Ages, however, the general opinion even of professed naturalists was that Bats were birds; and we find this notion prevailing down to the time of Aldrovandus, in the latter part of the sixteenth century, and of Jonston, whose gigantic compilation was published in 1657. It is a question whether this notion that Bats are birds has even yet been entirely dispelled in the popular mind, and no doubt many people still regard them as birds, because they can fly, just as Whales and Seals are considered fishes, because they swim, and Centipedes and Scorpions reptiles, because they crawl. John Ray, the father of modern zoology, writing in 1683, was the first to refer the Bats to their true position among the Mammalia (animals which suckle their young), and in this course he was followed by Linnæus, who actually placed these puzzles of former naturalists in his highest order of Mammals, the Primates, along with man and the Apes. The position assigned to them by Linnæus in the series of animals they have virtually retained in nearly all systems to the present day.

By all modern zoologists the Chiroptera have been regarded as a distinct order of the Mammalia, characterised especially by their possession of the power of flight, and the consequent modification of the structure of their fore limbs, which is indicated in the name given to the group (Chiroptera--hand-wings). They are, in fact, the only true flying Mammals, and, indeed, the only truly flying Vertebrates except birds, for the so-called flying Squirrels, flying Lemurs, and flying Opossums are only furnished with a broad fold of skin on each side of the body, which, when expanded by the spreading of the limbs, acts as a sort of parachute to sustain them for a time in the air. This is also the case with the flying Dragons, although in them the membrane is stiffened by means of a portion of the ribs; and even in the flying fishes, in which the organs of aerial locomotion are formed by the fore-limbs, these merely sustain the fish in the air for a time by the increased surface they give it, but do not serve as real wings, like those of Bats and birds.

There is, however, an important difference in the structure of the wing in the Bats and birds although the general principle on which the organs of flight are constructed is the same. In both (as indeed also in flying insects), this principle consists in having a strong framework, to which an up and down movement can be communicated, along the front of the wing, enabling it to strike the air with more or less force during its downward passage, whilst the effective surface of the organ is of a flexible or elastic nature, being formed in the bird by the long feathers which are implanted in the skin clothing the bones of the wing, and in the Bat by a thin leathery membrane which is stretched between the bones of the fore and hind limbs. Upon these leathern wings the Bats flit about noiselessly in the twilight or in the darkness of the night. They are able to advance with considerable speed, and also to turn and wheel about in their course with great facility.

Of course, as in birds, the principal modification of structure exhibited in these animals is connected with their power of flight, and manifested in the fore-limbs. These, although most disproportionately developed, still, however, display the same bones which have been described in the arms of the Monkeys and Lemurs, as will be seen in our figure of the skeleton of the European Mouse-coloured Bat. We find in them a strong humerus (_a_) of moderate length, articulating with large shoulder-blades (_b_), which cover a considerable portion of the back of the chest, and are kept apart by well-developed collar-bones (_c_), springing in front from a breast-bone (sternum, _s_), which, although distinctly showing Mammalian characters, projects in such a manner as to serve the purpose of the deep keel in the breast-bone of birds, and give attachment to the powerful muscles required to set the wings in motion (see accompanying figure). The humerus is followed by the bones of the fore-arm (_d_), the radius and ulna, of which, however, the latter is generally very small, and reduced to a mere rudiment immovably fixed to the radius towards the end nearest the body. This section is the longest part of the arm, and the simplicity of its structure is in connection with the fact that, as in birds, there is here no occasion for any movement of rotation in the arm, such as enables the fore-limbs of many Mammals to be applied to a variety of uses. At the extremity of the radius are the carpal or wrist-bones (_e_), which are small but numerous, and furnish surfaces for the articulation of the bones of the fingers. Of these, the first, or thumb (_f_), is short, and composed of three joints, a metacarpal and two phalanges, the last of which bears a strong curved claw, of great use to the animal in clinging to various surfaces, and in walking on the ground. Of the other four fingers, the metacarpal bones (_g_) are very long and slender, forming, indeed, the greater part of the fingers; they taper towards their tips, but at the tips themselves are slightly enlarged. The first, or index finger, in most Bats is composed of the metacarpal bone alone, but in some this is followed by two short phalanges. The other fingers possess either two or three phalanges. In general only the thumb possesses a claw, but in some Bats there is one also on the index finger.

To convert this framework into an organ of flight its various parts are, as already stated, united by a membrane of more or less leathery appearance, although often so thin and delicate as to be somewhat translucent. It is an expansion or wide fold of the skin of the body like those forming the parachutes of the flying Squirrels, &c., and often called by the same name--_patagium_. We shall employ the simpler, if rather longer term, “wing-membrane.” The bones of the arm, with their accompanying muscles, and those of the fingers, are enclosed between the two layers of skin of which the membrane is composed, and which they serve to extend and support. In front of the arm there is a small portion of membrane filling up the angle of the elbow, and called the antebrachial membrane. The thumb is left free. Behind the arm is the great expanse of the wing, which springs from the sides of the body, and is also attached to the hind legs, generally extending down to the ankle.

The wings are expanded by the spreading of the fingers, which radiate from the wrist something like the sticks of a fan. The second, or middle finger, which is the longest, runs to the extreme tip of the wing, but before reaching this it generally joins the extremity of the first, or index finger, which thus acts as a sort of stay to it, and the two fingers together form a tolerably stiff support for the outer margin of the wing. The other two fingers (the third and fourth) traverse the wing to its hinder border, where they carry out the membrane into small pointed projections; so that when the wing is expanded, this border shows two points besides that at the apex of the wing, and three more or less rounded notches, the last of which is between the tip of the fourth finger and the attachment of the membrane to the hinder limb.

In most Bats the membrane does not stop short at the legs, but encloses them after the same fashion as the arms, leaving only the foot and sometimes a part of the shank free. The portion of membrane that passes within the legs, sometimes filling up the whole space between them and enclosing the whole or a part of the tail, sometimes forming only a narrow border to these limbs, is called the interfemoral or intercrural membrane, and the characters furnished by it and its relations to other parts are of great importance in the classification of Bats.

The rest of the structure of these animals may be dismissed in a few words. The skull, and all the other parts of the skeleton, are generally light and delicate in their construction, as might be expected in animals destined to support themselves in the air; but there is no trace of those pneumatic cavities which, in birds, enable the air to penetrate all parts of the skeleton. The jaws are well armed with teeth, which differ in their character in accordance with the food consumed by the animals. The ribs are well developed, and enclose a large chest cavity. The pelvis (_p_) is long, slender, and somewhat bird-like in some respects; the legs are short, generally slender, and articulated in such a manner that when used in walking the knees are directed backwards, like our elbows; the fibula (the second bone in the shank) is usually imperfectly developed, in the same way as the ulna in the fore-arm; and the foot consists of five distinct toes, armed with small but sharp claws, by which the animals suspend themselves from the surface of rocks, walls, and other objects, in the dark retreats to which they retire for their repose. From the heel-bone (_calcaneum_) in most Bats there springs a cartilaginous or bony rod or spur, which is regarded by some zoologists as forming part of the bone itself. This spur, which is often of considerable length, runs along the margin of the interfemoral membrane, which it no doubt helps materially to stretch. When long, and more or less curved, it often causes a projection of the side of the interfemoral membrane, as shown in the figure of the Marsh Bat (p. 259). The tail is very variable in length.

In repose, or rather when not flying, the wings of the Bat are folded up by a reversal of the process by which they were extended for flight; the long fingers are drawn together, and up towards the fore-arm, and the membrane forms leathery folds at the sides of the body. This is also their position when the animal is walking or running on the ground (see the engraving on the next page), which it does in a somewhat awkward fashion, by the action of its hind feet and the claws of its thumbs. When seen thus engaged there can be little doubt as to the quadruped nature of the Bat. Our little European species have a Mouse-like appearance, which fully justifies their old popular name.

The teats are usually situated on the breast; but sometimes they are placed quite on the sides, immediately beneath what we must call the armpits. They are two in number. In addition to these chest or pectoral teats, some species have been described as possessing a second pair of such organs situated on the groin, but recent investigations prove clearly that these are merely nipple-like warts.

The organs of the senses are well developed. The ears are almost always of considerable size, sometimes very large and membranous, and in most cases there is in front of the cavity a sort of lobe of variable form, called the earlet, or tragus, representing the little rounded lobe which, in the human ear, projects from behind the cheek over the opening (see the woodcut of the Head of the Long-eared Bat). The nostrils are either simple slits or apertures at the end of the muzzle, or surrounded by leaf-like organs, often of the most extraordinary forms (see the Head of the Spectacled Vampire, p. 264, and other illustrations later on), in fact, this tendency of the skin in Bats to run out into membranous expansions is one of their most remarkable characteristics, and, from their mode of life, this great development of the skin system would seem to be almost essential to their existence.

The old proverbial expression, “As blind as a Bat,” is certainly not founded on a due appreciation of facts, for Bats are by no means blind; on the contrary, they are furnished with very efficient eyes, although, in most cases, these are little bead-like organs, very unlike the eyes usually seen in animals whose activity is nocturnal or crepuscular. But it would appear that the office of the eyes in guiding these animals is, at all events, supplemented by some other means. Towards the end of the last century, the Abbé Spallanzani made some exceedingly interesting, although certainly cruel experiments on various species of Bats. He blinded these animals, sometimes by burning the eyes with a red-hot wire, sometimes by removing the organs altogether, and even filling up the orbits with wax, and then allowed them to fly. In spite of the mutilation, the unfortunate little creatures continued quite lively, and flew about as well as those which still retained their eyes; they did not strike against the walls of the room, or the objects in it, avoided a stick held up before them, and showed a greater desire to keep out of the way of a Cat or the hand of a man than to escape contact with inanimate objects. One of these blinded Bats was set free in a long underground passage, which turned at right angles about its middle. It flew through the two branches of this passage, and turned, without approaching the side walls. During its flight it detected a small cavity in the roof at a distance of eighteen inches, and immediately changed its course in order to conceal itself in this retreat. In a garden a sort of cage was prepared, with nets, and from its top sixteen strings were allowed to hang down. Two Bats were introduced into this enclosure, one blinded, the other with its eyes perfect. Both flew about freely, never touching the strings with more than the tips of the wings. Finally, the blind Bat discovered that the meshes of the enclosing net were large enough for it to get through, and made its escape; and, after flying about for a time, made its way rapidly and directly to the only roof in the neighbourhood, in which it disappeared. In a room containing numerous branches of trees, or in which silk threads, stretched by small weights, were suspended from the ceiling, the Bats, though blinded, avoided all these obstacles; and when, after tiring themselves with their aerial evolutions, they settled on some object for the sake of rest, they would immediately rise again on an attempt being made to seize them with the hand.

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.

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.

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:--

“The weather,” he says, “which was beautiful, balmy, and warm, invited us towards evening to out-door enjoyment and rest, after a fatiguing day of travel and active labour; but chairs, settees, and benches were scarcely occupied by us on the piazza and lawn, when to our amazement, and the horror of the female portion of our party, small black Bats made their appearance in immense numbers, flickering around the premises, rushing in and out of doors and through open windows, almost obscuring the early twilight, and causing a general stampede of the ladies, who fled, covering their heads with their hands, fearing that the dreaded little vampires might make a lodgment in their hair.

“This remarkable exhibition much increased our disappointment in regard to the habitable condition of our acquisition, and was entirely unexpected, inasmuch as the unwelcome neighbours were in their dormant state, and ensconced out of sight when the property was examined previous to purchase.

“Evening after evening did we patiently, though not complacently, watch this periodical exodus of dusky wings into light from their lurking-places one after another, and in some instances in couples, and even triples, according as the size of the holes or apertures from which they emerged in the slate roofing would permit. Their excursions invariably commenced with the cry of the _Whippoorwill_, both at coming evening and early dawn, and it was observed that they always first directed their flight towards the river, undoubtedly to damp their Mouse-like snouts, but not their spirits, for it was likewise observed that they returned to play hide and seek, and indulge in all other imaginable gambols: when, after gratifying their love of sport, and satisfying their voracious appetites (as the absence of Mosquitoes and Gnats testified), they would re-enter their habitation, and again emerge at the first signal of their feathered trumpeter. Thus I ascertained one very important fact, namely, that the Bat, or the species which annoyed us, ate and drank twice in twenty-four hours. Such appeared their habit, such, therefore, was their indispensable need.” After trying various remedies, none of which seemed to abate the nuisance, M. Figaniere adopted the following plan:--

“When the Bats’ _réveillé_ was sounded by the bugle of the _Whippoorwill_, all the hands of our establishment, men and boys, each armed with a wooden implement (shaped like a cricket-bat), marched to the third floor, ‘on murderous deeds with thoughts intent.’ A lighted lantern was placed in the middle of one of the rooms, divested of all furniture, to allure the hidden foe from their strongholds. After closing the window to prevent all escape into the open air, the assailants distributed at regular distances to avoid clubbing each other, awaited the appearance of the Bats enticed into the room by the artificial light and impelled by their own natural craving. The slaughter commenced, and progressed with sanguinary vigour for several hours, or until brought to a close by the weariness of dealing blows that made the enemy bite the dust, and overpowered by the heat and closeness of the apartment. This plan succeeded perfectly. After a few evenings of similar exercise, in which the _batteurs_ became quite expert in the use of their weapons, every wielding of the wooden bat bringing down an expiring namesake, the war terminated by the extermination of every individual of the enemy in the main building. However, there still was the cockloft of the laundry, which gave evidence of a large population. In this case I had recourse to a plan which had been recommended, but was not carried out in regard to the dwelling-house. I employed a slater to remove a portion of the slating, which required repairing. This process discovered some fifteen hundred or two thousand Bats, of which the larger number were killed, and the remainder sought the barn, trees, and other places of concealment in the neighbourhood.

“To remove the very disagreeable odour which remained in the upper part of the house, various kinds of disinfectants were employed with some advantage; but the most effectual method resorted to was that of opening holes of about four inches square, two at each gable end, to permit a current of air to pass through. These holes were covered with wire gauze to prevent the re-entrance of any of the remainder of the army of the enemy which might hover around the premises. At the end of five years the odour has now nearly disappeared, being hardly perceptible during a continuance of very damp weather.”

The great number of species of Bats which have been described from various parts of the world, but especially from tropical and sub-tropical regions, display two very strongly-marked types of structure, associated in general with very different habits and modes of life. Some are exclusively confined to a fruit diet, or consume animal food only as an exceptional dainty; whilst the others almost as exclusively find their nourishment in the swarms of insects which everywhere people the air. Of the latter, however, some few feed upon fruits, and others are said to diversify their insect fare by occasionally sucking the blood of other animals, and even of man himself. In the Frugivorous, or Fruit-eating Bats, the crowns of the molar teeth are smooth, with a central furrow running in the direction of the length of the jaw; in the Insectivorous forms, on the contrary, the molars show sharp tubercles separated by transverse furrows, generally producing a sort of W-like pattern on each tooth. These two types of tooth-structure are associated in each case with other characters. The Bats are thus divided into two great groups, generally regarded as sub-orders.