g2 THE MEANING OF EVOLUTION 
their place in the struggle for life outside and hunt 
their own living, one or more of them has succumbed. 
After the battle for food comes the struggle for 
shelter. For most animals there is no such thing as 
shelter. They are exposed to the inclemencies of the 
weather and to the depredations of their enemies with- 
out the means of retiring into any situation which 
might protect them. In the higher animals, especially 
when they are warmer blooded and their bodies must 
be kept at a higher temperature, some form of cover- 
ing has come to be almost universal. 
Though comparatively few animals are prepared to 
seek shelter from the cold, all of them have enemies 
against whom they must battle. These foes may wish 
to eat them or may simply wish to get them out of 
the way. In either event this struggle is so persist- 
ent and so keen that after starvation it is probably the 
source of the largest loss to the animal kingdom. 
Considering first the feeding habits of animals, we 
find they are exceedingly varied. Some creatures sim- 
ply engulf other and more minute animals, often only 
microscopic in size, in such quantities as to satisfy 
their hunger. Others, feeding upon larger plants or 
animals, must have some means of breaking off par- 
ticles of this food; still others confine themselves en- 
tirely to nutritious fluids, and must have organs 
adapted to this particular type of food. 
