CHARACTERS OF VERTEBRATES. 163 



rated, and now the creature has added to it wings by means 

 of which it has new means of locomotion. This, however, 

 refers only to the most prominent types. 



If the table is to be arranged to show the highest animals 

 in the highest part of the column, it would be arranged as 

 follows : 



( Insects. 

 ( AIR-BREATHING ARTHROPODS. .| Myriapods. 



ARTHEOPODS. J ' S P iders - 



' WATER-BREATHING ARTHROPODS.^ Crustaceans. 



This is classification : to classify animals is to bring those 

 creatures together which have certain leading features in 

 common. And these classes may be divided again and again 

 into smaller groups. 



As, for example, the insects proper : if the pupils were to 

 divide them into smaller groups, the beetles would come 

 together as one group, no matter what their shape or size ; 

 moths would form another group ; the bugs another group, 

 and so on. 



CHAPTER XXII. 



CHARACTERS OF VERTEBRATES. 



147. THE lessons thus far presented have been upon creat- 

 ures belonging to three great divisions of the animal kingdom, 

 the Mollusks, the Arthropods, and the Worms. There are 

 many other groups which represent other great divisions of 

 the animal kingdom, of which no mention has yet been made, 



