The upper photograph shows the Warty Chameleon inflated and conspicuous.
At another time, however, with compressed body and adjusted coloration,
the animal is very inconspicuous. The lower photograph shows the sudden
protrusion of the very long tongue on a fly.]
[Illustration: SEASONAL COLOUR-CHANGE: A SUMMER SCENE IN NORTH
SCANDINAVIA
Showing a brown Variable Hare, Willow Grouse, and Arctic Fox, all
inconspicuous in their coloration when seen in their natural
surroundings.]
The mountain hare may escape the fox the more readily because its
whiteness makes it so inconspicuous against a background of snow; and
yet, at other times, we have seen the creature standing out like a
target on the dark moorland. So it cuts both ways. The ermine has almost
no enemies except the gamekeeper, but its winter whiteness may help it
to sneak upon its victims, such as grouse or rabbit, when there is snow
upon the ground. In both cases, however, the probability is that the
constitutional rhythm which leads to white hair in winter has been
fostered and fixed for a reason quite apart from protection. The fact is
that for a warm-blooded creature, whether bird or mammal, the
physiologically best dress is a white one, for there is less radiation
of the precious animal heat from white plumage or white pelage than from
any other colour. The quality of warm-bloodedness is a prerogative of
birds and mammals, and it means that the body keeps an almost constant
temperature, day and night, year in and year out. This is effected by
automatic internal adjustments which regulate the supply of heat,
chiefly from the muscles, to the loss of heat, chiefly through the skin
and from the lungs. The chief importance of this internal heat is that
it facilitates the smooth continuance of the chemical processes on which
life depends. If the temperature falls, as in hibernating mammals (whose
warm-bloodedness is imperfect), the rate of the vital process is slowed
down--sometimes dangerously. Thus we see how the white coat helps the
life of the creature.
§ 3