ge is absolutely necessary to success in the struggle for
existence.

Now, how has this curious uniformity of dress in arctic animals been
brought about? Why, simply by that unyielding principle of Nature which
condemns the less adapted for ever to extinction, and exalts the better
adapted to the high places of her hierarchy in their stead. The
ptarmigan and the snow-buntings that look most like the snow have for
ages been least likely to attract the unfavourable attention of arctic
fox or prowling ermine; the fox or ermine that came most silently and
most unperceived across the shifting drifts has been most likely to
steal unawares upon the heedless flocks of ptarmigan and snow-bunting.
In the one case protective colouring preserves the animal from himself
being devoured; in the other case it enables him the more easily to
devour others. And since 'Eat or be eaten' is the shrill sentence of
Nature upon all animal life, the final result is the unbroken whiteness
of the arctic fauna in all its developments of fur or feather.

Where the colouring of nature is absolutely uniform, as among the arctic
snows or the chilly mountain tops, the colouring of the animals is
uniform too. Where it is slightly diversified from point to point, as in
the sands of the desert, the animals that imitate it are speckled or
diversified with various soft neutral tints. All the birds, reptiles,
and insects of Sahara, says Canon Tristram, copy closely the grey or
isabelline colour of the boundless sands that stretch around them. Lord
George Campbell, in his amusing 'Log Letters from the "Challenger,"'
mentions a butterfly on the shore at Amboyna which looked exactly like a
bit of the beach, until it spread its wings and fluttered away gaily to
leeward. Soles and other flat-fish similarly resemble the sands or banks
on which they lie, and accommodate themselves specifically to the
particular colour of their special bottom. Thus the flounder imitates
the muddy bars at the mouths of rivers, where he loves to half bury
himself in the congenial ooze; the sole, who rather affects clean hard
sand-banks, is simply sandy and speckled with grey; the plaice, who goes
in by preference for a bed of mixed pebbles, has red and yellow spots
scattered up and down irregularly among the brown, to look as much as
possible like agates and carnelians: the brill, who hugs a still rougher
ledge, has gone so far as to acquire raised lumps or tubercles on his
upper surf