MIDWINTER 131 
degrees of perfection, to adjust the internal produc- 
tion of heat to the external loss of it, and thus keep 
an approximately constant body-temperature all the 
year round. In some mammals in which this 
“thermotaxis” arrangement is less. perfect than 
usual, there is a breakdown when the cold comes 
on. The creature gives up the contest and sinks 
into deep slumber in some confined space, to the 
temperature of which that of the sleeper approxi- 
mates. If the external temperature does not fall too 
far, this hibernation may be life-saving. Similar, 
but less effective, is the lethargy of cold-blooded 
animals like tortoises and frogs, the vital collapse 
of snails and chrysalids, and the inactivity of many 
humble creatures in sheltered nooks and crannies. 
They evade the winter by their extreme passivity; 
they cannot carry on, but they do not die. 
We are led to think of stores, whether inside the 
body in the form of fat which may be slowly burnt 
away in winter months, or outside the body in the 
form of nut-pits, seed-granaries, meat-larders, and 
what not. The climax on the instinctive tack of. 
evolution is to be found in the societary stores made 
by ants and bees. Of another solution we are 
reminded by the ptarmigan and the hare that we 
startled, good examples of creatures that turn 
pale under the spell of winter till they are white 
as the snow itself. The white cloak may help in 
concealment and in the chase; it also furnishes the 
physiologically most comfortable dress for a warm- 
blooded animal in very cold surroundings. We 
