THE ECONOMIC BIOLOGY OF VERTEBRATES 483 



ornaments, buttons, handles, etc. Ivory comes from the tusks 

 (teeth) of the elephant and walrus. 



Transportation. Of much greater importance than these last 

 items, is the use of many mammals as beasts of burden. The 

 horse is easily first, with oxen, camels, dogs, goats, llamas, rein- 

 deer, water buffaloes, and elephants used in different countries to 

 a greater or less extent. 



Pets. Mammals have been used by many as companions and 

 pets; in this class the dog is first, the horse, cat, and occasionally 

 other forms being admitted to this select society. 



Among the mammals, also, are most of the " domestic " ani- 

 mals which man has learned to tame and breed for many of the 

 uses just mentioned. Here again, the dog comes first, as it was 

 probably derived from a domesticated wolf which primitive man 

 tamed for his company, protection, and aid in the hunt. Prob- 

 ably cattle or sheep were next controlled by man, though the 

 horse may have preceded them in learning to carry his master 

 in battle or the chase. To this list man is still adding useful 

 species either by breeding from present forms, or by taming new 

 ones when their value is discovered. 



The other side of the account is represented by a few harmful 

 mammals, dangerous either to man himself, to his domestic ani- 

 mals, or to his crops. Among these are the large carnivora, such 

 as the tiger, lion, wolf, etc., which attack man or his flocks. In 

 this country carnivora destroy about $15,000,000 worth of stock 

 per year. The rodents, especially rats, mice, and squirrels do 

 enormous harm by destroying grains and other food stuffs. In 

 the case of the rat alone, the wastage amounts to about 

 $200,000,000 annually. Furthermore, rats and some squirrels are 

 infested with fleas which transmit the plague to man, and thus 

 are even more seriously harmful. As a whole it will be seen that 

 the mammals are not only extremely useful, but absolutely essen- 

 tial to man; without them our present civilization and mode of 

 life would be impossible. 



