312 THE VERTEBRATE ANIMALS 



animal known as mammals. These characters are the possessions 

 of a hairy covering, of lungs, and warm blood. They bear young 

 developed to a form similar to their own, 1 and nurse them with 

 milk secreted by glands known as the mammary glands; hence 

 the term " mammal." 



Instincts. Mammals are considered the highest of vertebrate 

 animals, not only because of their complicated structure, but be- 

 cause their instincts are so well developed. Monkeys certainly 

 seem to have many of the mental attributes of man. 



Professor Thorndike'of Columbia University sums up their habits 

 of learning as follows : 



" In their method of learning, although monkeys do not reach the 

 human stage of a rich life of ideas, yet they carry the animal method of 

 learning, by the selection of impulses and association of them with differ- 

 ent sense-impressions, to a point beyond that reached by any other of 

 the lower animals. In this, too, they resemble man ; for he differs from 

 the lower animals not only in the possession of a new sort of intelligence, 

 but also in the tremendous extension of that sort which he has in common 

 with them. A fish learns slowly a few simple habits. Man learns quickly 

 an infinitude of habits that may be highly complex. Dogs and cats learn 

 more than the fish, while monkeys learn more than they. In the number 

 of things he learns, the complex habits he can form, the variety of lines 

 along which he can learn them, and in their permanence when once formed, 

 the monkey justifies his inclusion with man in a separate mental genus." 



Adaptations in Mammalia. Of the thirty-five hundred species, 

 most inhabit continents ; few species are found on different islands, 

 and some, as the whale, inhabit the ocean. They vary in size from 

 the whale and the elephant to tiny shrew mice and moles. Adapta- 

 tions to different habitat and methods of life abound ; the seal and 

 whale have the limbs modified into flippers, the sloth and squirrel 

 have limbs peculiarly adapted to climbing, while the bats have the 

 fore limbs modeled for flight. 



Carnivorous Mammals. As the word " carnivorous " denotes, 

 these animals are to a large extent flesh eaters. In a wild state 

 they hunt their prey, which is caught and torn with the aid of 

 well-developed claws and long, sharp teeth. These teeth, so well 

 developed in the dog, are known as canine teeth or dog teeth. All 

 flesh-eating mammals are wandering hunters in a state of nature ; 



1 With the exception of the monotremes. 



