THE BATS--WING-HANDED MAMMALS
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.