
IN NATURAL HISTORY 5 
livelihood. Insects in turn are directly or indirectly dependent on flow- 
ers, and when in northern regions the approach of winter puts an end to 
the flowers, insects begin to disappear. With the withdrawal of their 
food supply, bats must either migrate, die, or in some manner survive 
without food. To a limited extent bats do migrate; but the majority 
exist without eating by hibernating during the winter—the same cold 
which puts an end to flowers and insects checking the circulation of 
blood, and permitting the bats to exist for a long time with very little 
bodily waste. This very curious condition has not been brought about 
by any direct effort on the part of the bats, but, it is believed, simply 
by the weeding out of those that were unable to lie torpid, and the sur- 
vival of those in which the bodily functions and waste of flesh were 
checked without destroying lifc. 
It must always be borne in mind that the survival of the fittest is by 
no means the survival of the strongest: for while size and strength 
count for much in the struggle between animals of the same kind, they 
count for little in combating nature, a fact which we see over and over 
again in studying the history of the past. Those great reptiles, the Dino- 
saurs, mightiest of all land animals, were swept out of existence while 
the smaller and weaker mammals survived. And, after these had at- 
tained to supremacy, the lumbering Titanotheres succumbed ia their 
turn, and other types, smaller and weaker but better adapted to the 
_ changes that were taking place, succeeded them. Small animals, as a 
rule, have certain advantages over their larger relatives in the struggle for 
existence; they breed more rapidly, reach maturity sooner, are more 
readily concealed, and require less food: so that they are able to subsist 
through periods of drouth and cold which cut off the supply of food of the 
large animals and cause them to perish of starvation. As a result of the 
weeding out process, the influence of their surroundings, and what seems 
an inborn tendency to vary,' animals changed more or less in form and 
habits, becoming adapted to the changing conditions under which they 
lived, resulting in the Evolution of new kinds of animals. In this man- 
ner very wonderful modifications have been brought about: for we see 
some animals dwelling in the heat of the tropics, and others equally at 
home amid the snow and ice of arctic regions; some passing their lives 
high on the mountain tops, some dwelling a mile or more in the depths 
of the ocean where the temperature is but little above freezing, and some 
quite at home in springs whose waters almost reach the boiling point. 
'There are two very different views in regard to this point, one that change in the surroundings 
causes the changes in the animals, the other that it simply allows the tendency to vary to assert 
itself. Both are probably true, as is the case with both sides in many quarreis—perhaps in most. 
