altogether upright.

But Mr. Martin, who also speaks from direct observation, says of the
Gibbons generally:

"Pre-eminently qualified for arboreal habits, and displaying among the
branches amazing activity, the Gibbons are not so awkward or
embarrassed on a level surface as might be imagined. They walk erect
with a waddling or unsteady gait, but at a quick pace, the equilibrium
of the body requiring to be kept up, either by touching the ground
with the knuckles, first on one side then on the other, or by
uplifting the arms so as to poise it. As 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."

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 has given so excellent and graphic an account of the
movements of a _Hylobates agilis_, living in the Zoölogical 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