220 THE FROG CHAP. 



Vertebrata, the many-legged, armoured forms in the 

 phylum Arthropoda. Similarly, soft-bodied animals 

 with shells, such as mussels and snails, form the phylum 

 Mollusca ; various worms, such as the earthworm, the 

 phylum Annulata ; polypes and jelly-fishes the phylum 

 Ccdenterata ; the simplest animals, mostly minute, 

 such as Amoeba, the phylum Protozoa. Finally, the 

 various phyla recognised by zoologists together con- 

 stitute the kingdom Animalia. 



Thus the animal kingdom is divided into phyla, the 

 phyla into classes, the classes into orders, the orders 

 into families, the families into genera, and the genera 

 into species ; while the species themselves are assem- 

 blages of individual animals agreeing with one another 

 in certain definite characteristics. It will be seen that 

 the individual is the only term in the series which has a 

 real existence ; all the others are mere groups, formed, 

 more or less arbitrarily, by man. 



Thus the zoological position of the common frog is 

 expressed as follows : 



Kingdom ANIMALIA. 



Phylum VERTEBRATA. 

 Class AMPHIBIA. 

 Order ANURA. 



Family Ranidcu . 

 Genus Rana . 



Species temporaria . 



Let us now briefly consider some of the reasons which 

 have led zoologists to adopt the system of classification 

 now in general use. 



It is obvious that there are various ways in which 

 animals may be classified, and the question arises 

 Which of these, if any, is the right one ? Is there any 



