that
prodigious activity which almost tempts one to rank them among flying,
rather than among ordinary climbing mammals.

Mr. Martin has given so excellent and graphic an account of the
movements of a _Hylobates agilis_, living in the Zooelogical Gardens,
in 1840, that I will quote it in full:

"It is almost impossible to convey in words an idea of the quickness
and graceful address of her movements: they may indeed be termed
aerial, as she seems merely to touch in her progress the branches
among which she exhibits her evolutions. In these feats her hands and
arms are the sole organs of locomotion, her body, hanging as if
suspended by a rope, sustained by one hand (the right, for example),
she launches herself, by an energetic movement, to a distant branch,
which she catches with the left hand; but her hold is less than
momentary; the impulse for the next launch is acquired; the branch
then aimed at is attained by the right hand again, and quitted
instantaneously, and so on, in alternate succession. In this manner
spaces of twelve and eighteen feet are cleared, with the greatest ease
and uninterruptedly, for hours together, without the slightest
appearance of fatigue being manifested; and it is evident that, if
more space could be allowed, distances very greatly exceeding eighteen
feet would be as easily cleared; so that Duvaucel's assertion that he
has seen these animals launch themselves from one branch to another,
forty feet asunder, startling as it is, may be well credited.
Sometimes, on seizing a branch in her progress, she will throw
herself, by the power of one arm only, completely round it, making a
revolution with such rapidity as almost to deceive the eye, and
continue her progress with undiminished velocity. It is singular to
observe how suddenly this Gibbon can stop, when the impetus giving by
the rapidity and distance of her swinging leaps would seem to require
a gradual abatement of her movements. In the very midst of her flight
a branch is seized, the body raised, and she is seen, as if by magic,
quietly seated on it, grasping it with her feet. As suddenly she again
throws herself into action.

"The following facts will convey some notion of her dexterity and
quickness. A live bird was let loose in her apartment; she marked its
flight, made a long swing to a distant branch, caught the bird with
one hand in her passage, and attained the branch with her other hand,
her aim, both at the bird and at the b