cover the bark of trees! Here is abundant
opportunity for any observer of living nature to help toward the solution
of these problems.

In a battle there are always two sides and at its finish one side always
runs away while the other pursues. Thus it is in the wars of nature, only
here the timid ones are always ready to flee, while the strong are equally
prepared to pursue. It is only by constant vigilance that the little mice
can save themselves from disappearing down the throats of their enemies,
as under cover of darkness they snatch nervous mouthfuls of grain in the
fields,--and hence their gray colour and their large, watchful eyes; but
on the other hand, the baby owls in their hollow tree would starve if the
parents were never able to swoop down in the darkness and surprise a mouse
now and then,--hence the gray plumage and great eyes of the parent owls.

The most convincing proof of the reality of protective coloration is in
the change of plumage or fur of some of the wild creatures to suit the
season. In the far north, the grouse or ptarmigan, as they are called, do
not keep feathers of the same colour the year round, as does our ruffed
grouse; but change their dress no fewer than three times. When rocks and
moss are buried deep beneath the snow, and a keen-eyed hawk appears, the
white-feathered ptarmigan crouches and becomes an inanimate mound. Later
in the year, with the increasing warmth, patches of gray and brown earth
appear, and simultaneously, as if its feathers were really snowflakes,
splashes of brown replace the pure white of the bird's plumage, and
equally baffle the eye. Seeing one of these birds by itself, we could
readily tell, from the colour of its plumage, the time of year and general
aspect of the country from which it came. Its plumage is like a mirror
which reflects the snow, the moss, or the lichens in turn. It is, indeed,
a feathered chameleon, but with changes of colour taking place more slowly
than is the case in the reptile.

We may discover changes somewhat similar, but furry instead of feathery,
in the woods about our home. The fiercest of all the animals of our
continent still evades the exterminating inroads of man; indeed it often
puts his traps to shame, and wages destructive warfare in his very midst.
I speak of the weasel,--the least of all his family, and yet, for his
size, the most bloodthirsty and widely dreaded little demon of all the
countryside. His is a name to conjure wi