with the Chimpanzee, the whole of the narrow, long
sole of the foot is placed upon the ground at once and raised at once,
without any elasticity of step."

[Illustration: FIG. 8.--Gibbon ('H. pileatus'), after Wolf.]

After this mass of concurrent and independent testimony, it cannot
reasonably be doubted that the Gibbons commonly and habitually assume
the erect attitude.

But level ground is not the place where these animals can display their
very remarkable and peculiar locomotive powers, and that prodigious
activity which almost tempts one to rank them among flying, rather than
among ordinary climbing mammals.

Mr. Martin (l.c. p. 430) has given so excellent and graphic an account
of the movements of a 'Hylobates agilis', living in the Zoological
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 given by the rapidity
and distance of her swinging leaps would seem to require a gradual
abatement of her movements. In