ANIMALS MADE USEFUL 13 
grow and develop; and then die. Asa distinct organism 
an animal begins in an egg. Birth, growth, development 
and maturity all succeed in due time and in due order. 
Death inevitably results, either accidentally during some 
stage of the life cycle, or in the end when maturity is com- 
plete. From egg to egg is the life cycle. The three in- 
evitable certainties in the life of every animal are birth, 
growth and death. 
3. Struggle for existence—Between life and death 
there is a constant struggle for existence. This is espe- 
cially true of the wild 
forms. Animals require 
food for satisfying hun- 
ger, drink for appeas- 
ing thirst and abiding 
places for rest or rear- 
ing the young. Their 
food consists of plants 
or of other animals that RETURN OF THE FORAGER 
live on plants. Without In the wild, life is a continuous struggle for 
existence, 
plants there could be 
no plant-eating animals; and, without these, flesh-eating 
species would not be able to exist. 
This struggle for existence is observed in two ways: In the 
species, as between the sheep of the fields, the stronger securing the 
best and richest food, the weaker being crowded to the rear or to 
scanty pastures; and as between individuals of different species, as 
the wolf or coyote with the sheep, or the hawk or fox with the 
poultry. 
Another condition in this struggle is to meet the changes of the 
seasons. Vast numbers of wild animals die in winter from cold, 
or starve when the snows cover the food, or die of thirst when the 
streams disappear in summer. Thus the number of animals in the 
wild reaching maturity is but a small part of those that are born. 
4. Crowd of animals.—In nature, therefore, a continu- 
ous crowding of animal life affects not only the species 
