soon as it
comes in contact with air, explodes with a sound resembling a miniature
gun. Westwood mentions, on the authority of Burchell, that on one
occasion, "whilst resting for the night on the banks of one of the
large South American rivers, he went out with a lantern to make an
astronomical observation, accompanied by one of his black servant boys;
and as they were proceeding, their attention was directed to numerous
beetles running about upon the shore, which, when captured, proved to be
specimens of a large species of Brachinus. On being seized they
immediately began to play off their artillery, burning and staining the
flesh to such a degree that only a few specimens could be captured with
the naked hand, and leaving a mark which remained a considerable time.
Upon observing the whitish vapour with which the explosions were
accompanied, the negro exclaimed in his broken English, with evident
surprise, 'Ah, massa, they make smoke!'"

Many other remarkable illustrations might be quoted; as for instance the
web of the Spider, the pit of the Ant Lion, the mephitic odour of the
Skunk.

SENSES

We generally attribute to animals five senses more or less resembling
our own. But even as regards our own senses we really know or
understand very little. Take the question of colour. The rainbow is
commonly said to consist of seven colours--red, orange, yellow, green,
blue, indigo, and violet.

But it is now known that all our colour sensations are mixtures of three
simple colours, red, green, and violet. We are, however, absolutely
ignorant how we perceive these colours. Thomas Young suggested that we
have three different systems of nerve fibres, and Helmholtz regards this
as "a not improbable supposition"; but so far as microscopical
examination is concerned, there is no evidence whatever for it.

Or take again the sense of Hearing. The vibrations of the air no doubt
play upon the drum of the ear, and the waves thus produced are conducted
through a complex chain of small bones to the fenestra ovalis and so to
the inner ear or labyrinth. But beyond this all is uncertainty. The
labyrinth consists mainly of two parts (1) the cochlea, and (2) the
semicircular canals, which are three in number, standing at right angles
to one another. It has been supposed that they enable us to maintain
the equilibrium of the body, but no satisfactory explanation of their
function has yet been given. In the cochlea, Corti discovered a
re