lo THE COMMON FROG. [chap. 



reptiles, and fishes, and thus shows that it differs from 

 the immense majority of animals — the Invertebi'ata — 

 and pertains unmistakeably to the seventh sub-king- 

 dom of animals — the Vci'tcbrata. 



Now every sub-kingdom of animals is further 

 divided into a greater or lesser number of subordinate 

 (though still large) groups, termed classes. Each class 

 is again subdivided into a certain number of smaller 

 and more subordinate groups, each of which is termed 

 an order. Each order is made up oi farnilies, each 

 family being, of course, smaller and more subordinate 

 than an order. Every family consists again of still 

 more subordinate groups, each of which is termed a 

 gentis. And every genus comprises one or more 

 species. 



In zoology, every animal bears a name composed 

 of two words. The first of these is a substantive, and 

 denotes the genus to which any given animal belongs. 

 The second word is an adjective — or a word used in 

 an adjective sense — and denotes which species of the 

 genus that given animal is. Thus the Chimpanzee is 

 called Troglodytes nigcr; it is the species Niger of the 

 genus Tivglodytes, which genus contains also another 

 species, namely, the Gorilla. 



