Next in advance of the Insectivora stands the order Chiroptera ("hand-wing"), which is the tribe of bats, divisible into two suborders—the large, diurnal fruit bats, and the small, nocturnal insect-catching bats and the vampires. No fossil remains bridging the gap between these two orders has been discovered, nor can anyone yet explain the steps in the acquirement of the bats' power of flight.

Bats are simply flying mammals, necessarily small, with the bones of the forelimbs light, hollow, and greatly elongated, the middle finger in some cases exceeding the total length of the body. These lengthened digits support between themselves and the hinder limbs a membrane that opens and closes much like an umbrella. This wing membrane consists of a double layer of skin, one continuous with the hide of the back, the other with that of the abdomen, fused together. The surface of the wing is covered with microscopically minute hairs. To these hairs and the bulbous underlying "end organs" are attributed the bat's exalted sense of touch. The expanse of these leathery wings is far greater than that of most birds relatively to the size of the body, but the muscles are weaker; and the exterior thumb, with its strong claw, by means of which bats scramble about rocks and buildings, recalls the similar organ in archÆopteryx. The hind limbs are small, while the knee bends backward because of the outward twist of the limb. This makes the foot almost useless for walking, but fits it, with its peculiarly strengthened ankle, to be extended straight backward and serve as a means of hanging the body head downwards—the bat's ordinary attitude in rest or sleep.

Bats usually produce two young at a birth, and the mother carries them about with her, they clinging to her breast, where she keeps them warm by folding them within her wings when they and she are hanging to the branch of a tree. Nothing is made in the way of a nest.

The fruit-eating bats (division Megachiroptera) are distributed in some seventy species from East Africa to the East Indies, Japan, Australia, and Polynesia. They vary in size from an ounce in weight to some as large as big squirrels, and in form from the grotesque "hammerhead" of Africa to the many rust-red East Indian species that come naturally by their name of "flying foxes," and approach foxes in size. These bats feed on all sweet fruits, and in some regions, as Java, no delicate fruit can be raised unless the tree is protected by nets. It is at night that they make their forays, sleeping during the day in great companies among the branches of some chosen tree.

Where a fig tree attracts a crowd of them, we are told by Eastern writers, the roughest fighting begins over coveted plunder, each one screaming, clawing, biting, and struggling to seize something and get away to a secure retreat to enjoy it. No doubt these squabbles are rendered more violent by the dissipated habits in which the bats indulge during their nocturnal expeditions, for, according to Dr. Francis Day and other observers, "they often pass the night drinking the toddy from the chatties in the coconut trees, which results either in their returning home in the early morning in a state of extreme and riotous intoxication, or in being found the next day at the foot of the trees, sleeping off the effects of their midnight debauch."

The second division (Microchiroptera) contains the carnivorous bats, which include five families, two of which, the nose-leafed and the desert bats, belong to the warmer parts of the Old World, and the others are tropical (EmballonuridÆ, and PhyllostomidÆ), or have an almost cosmopolitan range (VespertilionidÆ). In general the bats of this division are night flyers, and retire during the day to caves, hollow trees, and dark places in old buildings. Such haunts contain great deposits of black guano, which in many places is gathered as a most valuable fertilizer. The rock tombs and temples of Egypt and the East are haunted by thousands of these tenants, and are occupied the year through; but in cool countries the bats migrate or may go into a partial hibernation. The food of most of them, and especially of the VespertilionidÆ, to which all those of the United States and western Europe belong, is exclusively insects, caught on the wing in the twilight hours or in moonlight; and the service thus done to mankind is of much importance. In the tropics, however, several species, especially of the family PhyllostomidÆ, feed largely on fruit, being provided with long, brush-tipped tongues with which they scrape out the soft interior of the banana and similar fruits. Two species of this family are the famous "vampires" of the American tropics. The name recalls the superstition rife in Europe in the Middle Ages as to blood-exhausting fiends which were fabled to lull their victims into unconsciousness by the slow flapping of their wings, and then deprive them of life. The foremost of these vampires is a small reddish species (Desmodus rufus), whose front teeth are like keen daggers, while the cheek teeth have disappeared, having nothing to do, since the animal subsists wholly on a liquid diet.