THE LIFE OF MAMMALS 
development of the habit, until finally it has crystallized into 
an instinct of self-preservation. 
The process of acquirement may have been something like 
this: Remembering that the search for food is the foremost 
anxiety and occupation of these little creatures, it would be 
increasingly stimulated as the ripening season of the seeds and 
nuts on which they depend advanced, and the impulse to in- 
cessant industry, so necessary in the poorer parts of the year, 
would now be overworked, and each animal, in his haste to be 
up and doing, would constantly bring home more food than 
would be consumed, so that it would pile up in the accustomed 
“dining room.” The gradual failure of outdoor supplies, as 
winter came on, would lead to the eating, with increasing fre- 
quency, of those fragments casually saved in and about the 
burrow or house, which, from their nature, would not have 
decayed. The animal which had been most busy and clever in 
food gathering would own the largest amount of the leavings 
of these autumnal feasts. Having the most food he would be 
among those of the colony or neighborhood strongest and most 
likely to survive, and to give to his offspring the tendency to 
strength and industry which had been his salvation. This 
would be continued and shaped by the process of natural 
selection into a valuable, instinctive habit of gathering food in 
large quantities as winter provender. 
Another noticeable point in the habits of these miners is this: Although 
often the very image of nervous activity, these and other burrowing animals 
shut themselves for long periods into almost air-tight apartments under 
ground, and yet seem to suffer no harm; but it is possible the scarcity of 
oxygen, or, rather, the accumulation of carbonic elements, may aid in in- 
ducing the trance of hibernation, to be considered when we come to the 
marmots. 
As to the ways of the chipmunks (ground squirrels of the 
genus Tamias), and of the “gray gophers” or prairie ground 
squirrels (genus Spermophilus) of the western plains, one can- 
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