IO INTRODUCTION 



name, the first being written with a capital letter, the second 

 with a small letter unless it is derived from a proper name, 

 when it may be written with a capital, although the tendency 

 among scientists to-day is to begin all specific names with small 

 letters. Thus the dog is known scientifically as Cants familiaris, 

 the wolf as Canis lupus, the fox as Cants vulpes, — they are 

 different species of the same genus, Canis ; in the same way the 

 common cat is Felis domes tica, the lion Felis leo, and the tiger 

 Felis tigris. 



So there are in general as many kinds of animals as there are 

 species, and each has a name which can be used and under- 

 stood by all scientists, whatever their nationality. In reality 

 there are more kinds of animals than there are species, for, as 

 we noted above, species may be divided into varieties ; there 

 are many kinds of domestic dogs and cats, and many other 

 species of animals are likewise varied ; hence we may have 

 several varieties of the same species ; thus the lion of Barbarv 

 is called Felis ho barbarus ; somewhat different is the lion of 

 Persia, called Felis leo persicus ; while the lion of Senegal is 

 again sufficiently different to be considered a distinct variety, 

 Felis leo senegalensis. 



The system of nomenclature suggested by Linnaeus has been 

 taken as the foundation of all biological classification, the classi- 

 fication of living things. It sometimes happens that an animal 

 discovered and named by one scientist is later discovered and 

 named differently by another who is ignorant of the earlier 

 author's work. In all cases, however, the name accepted as 

 permanent is that which was first published; after the name of 

 the species there is frequently written the initial or abbreviated 

 name of the writer who first distinguished it; thus, the name of 

 the clog may be written Canis familiaris Linn., indicating that 

 Linnaeus was the author of this name. 



It is a matter of common observation that no two men are 

 exactly alike ; so no two other animals are exactly alike, and 

 this is not surprising, since every individual is the result of the 

 fusion of two unlike germ cells arising from two different indi- 

 viduals. But this individual variation does not exceed certain 

 limits ; the question arises, When are differences sufficiently 

 great to place plants or animals in distinct varieties of the 



