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.
SKELETON OF THE MOUSE-COLOURED BAT (VESPERTILIO MURINUS.) (From De Blainville).
a, humerus; b, shoulder-blade; c, collar-bone; d, fore-arm (radius, with the ulna at the elbow); e, wrist-bones (carpal-bones); f, thumb; g g, metacarpal bones; s s, breast-bone (sternum); p, pelvis; i i, heel-spur.
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.
THE STERNUM OF
FLYING FOX (PTEROPUS).