CHAPTER XIII 



THE FROG (continued] : MEANING OF THE TERM SPECIES 



THE PRINCIPLES OF CLASSIFICATION EVOLUTION 

 ONTOGENY AND PHYLOGENY HEREDITY AND 

 VARIATION STRUGGLE FOR EXISTENCE NATURAL 

 AND ARTIFICIAL SELECTION ORIGIN OF SPECIES 



THE frog which you have been studying is the only 

 one commonly found in Great Britain. Another kind, 

 very similar to it, is, like the common frog, abundant in 

 Germany and other parts of the European continent, but 

 is rare in this country, only occurring in some places in 

 the eastern counties ; and various other frogs, differing 

 in certain minor respects from these are found in different 

 parts of the world. This fact is expressed in the language 

 of systematic zoology by saying that there are various 

 species of frogs, belonging to the same genus, which are 

 distinguished from one another by certain definite 

 characteristics as regards form, structure, and colour. 



According to the system of binomial nomenclature 

 introduced by Linnaeus, each kind of animal receives 

 two names one, the generic name, common to all the 

 species of the genus ; the other the specific name, peculiar 

 to the species in question. Both generic and specific 

 names are Latin in form, and are commonly Latin or 

 Greek in origin, although frequently modern names of 



