CLASSIFICATION OF ANIMALS AND PLANTS 139 



only a backbone, but also hair, milk-organs, and diaphragm ; 

 all carnivores are alike in having mouth and digestive organs 

 t adapted to meat-eating in a way not found in other mammals ; 

 and dogs and wolves are nearer alike in all respects than 

 they are like any other animals. It is all a question of re- 

 semblances resemblances in detail between individuals of 

 a species, and more and more general resemblances as we pass 

 from species to larger and larger groups (genera, orders, 

 classes), until we find in divisions or phyla only such general 

 resemblances as the backbone, which characterizes vertebrates. 

 These resemblances, or points of structure which mark the 

 animals or plants belonging to any particular group, are the 

 characteristics. For example, the backbone is a characteristic 

 of vertebrates, for no lower animals have it ; and hair, milk- 

 glands, and the diaphragm are characteristics of mammals; 

 the formation of seeds in a peculiar manner is a characteristic 

 of seed-plants ; the arrangement of flowers in a peculiar head 

 is a characteristic of composites. So for each large or small 

 group of animals and plants, from species to primary divisions, 

 there are distinguishing marks based on resemblances. 



130. The Reasons for Classification. Probably the first 

 reason why men of science have classified animals and plants 

 is that it has seemed natural to group together the similar 

 things in nature. The fact is that we seem naturally inclined 

 to associate together things which are alike, and thereby 

 distinguish between the unlike. Without any idea of classify- 

 ing in a scientific way, we are constantly noting the character- 

 istics of people we see; and we compare and distinguish 

 between people of different races (white, black, red, etc.), of 

 nations (German, English, French, Swedish, etc.), of people 

 from different regions of a country (Northern, Southern, and 

 Western in United States), and of individuals in families. 

 If we see two or more strangers who look alike, we think of 

 them as closely related, and in the same family. If we see 

 that the members of several families have some general simi- 



