Wood frog Grass frog 



{Rana {Rana 



sylvatica) pipiens) 



Bullfrog 



(Rana 

 catesbiana) 



Spotted 



salamander Common toad 



{Ambystoma (Bufo 



maculatum) amencanus) 



RELATED GENERA 



The grass frog, the wood frog, and the bullfrog are distinct species of the genus 

 Rana, the Latin name for frog. Frogs and toads are grouped in the same family. 

 These and other genera, together with the salamanders and other "relatives", make 

 up the class Amphibia — animals that live both on land and in water 



When we ask a question like "What kind of frog . . .?" we already say 

 that "frog" is a general name including two or more species. Such a group 

 of species we call a genus (plural, gejiera). 



As in all classifying, we sort animals and plants on the basis of resem- 

 blances and differences. And we consider them "related" according to the 

 degrees of resemblance. Thus we speak of frogs and toads being related, 

 as of the same family, although we do not have to decide what species was 

 their common ancestor, or even whether they actually had any common 

 ancestors. In fact, Linnaeus himself believed that each species had existed 

 as we see it from the very beginning. 



How Are the Larger Groups Related? 



Kinds of Divisions The main branches of both the plant "kingdom" 

 and the animal "kingdom" are called phyla (meaning "tribes"; singular, 

 phylum) after Linnaeus's plan. These phyla are divided into classes} In 

 some phyla there are but a few classes; in other phyla there are many. In 

 some phyla the classes are rather distinct; in others there seem to be "re- 

 lated" forms that are not so easily grouped by their characters. Accordingly, 



^Note that here the word class is used in a very special sense, meaning one of the chief di- 

 visions of a phylum, not merely any grouping whatever for which we may have a name. Note 

 also the special use of the word family in classifying plants and animals. 



38 



