markable organ consisting of some four thousand complex arches, which
increase regularly in length and diminish in height. They are connected
at one end with the fibres of the auditory nerve, and Helmholtz has
suggested that the waves of sound play on them, like the fingers of a
performer on the keys of a piano, each separate arch corresponding to a
different sound. We thus obtain a glimpse, though but a glimpse, of the
manner in which perhaps we hear; but when we pass on to the senses of
smell and taste, all we know is that the extreme nerve fibres terminate
in certain cells which differ in form from those of the general surface;
but in what manner the innumerable differences of taste or smell are
communicated to the brain, we are absolutely ignorant.

If then we know so little about ourselves, no wonder that with reference
to other animals our ignorance is extreme.

We are too apt to suppose that the senses of animals must closely
resemble, and be confined to ours.

No one can doubt that the sensations of other animals differ in many
ways from ours. Their organs are sometimes constructed on different
principles, and situated in very unexpected places. There are animals
which have eyes on their backs, ears in their legs, and sing through
their sides.

We all know that the senses of animals are in many cases much more acute
than ours, as for instance the power of scent in the dog, of sight in
the eagle. Moreover, our eye is much more sensitive to some colours than
to others; least so to crimson, then successively to red, orange,
yellow, blue, and green; the sensitiveness for green being as much as
750 times as great as for red. This alone may make objects appear of
very different colours to different animals.

Nor is the difference one of degree merely. The rainbow, as we see it,
consists of seven colours--red, orange, yellow, green, blue, indigo, and
violet. But though the red and violet are the limits of the visible
spectrum, they are not the limits of the spectrum itself, there are
rays, though invisible to us, beyond the red at the one end, and beyond
the violet at the other: the existence of the ultra red can be
demonstrated by the thermometer; while the ultra violet are capable of
taking a photograph. But though the red and violet are respectively the
limits of our vision, I have shown[16] by experiments which have been
repeated and confirmed by other naturalists, that some of the lower
animals are capable of