2 ZOOLOGY 



navie, common to all species of the genus ; the other the sjxcific 

 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 persons or places, with 

 Latinised terminations, are employed. In giving the name of an 

 animal, the generic name is always placed first, and is written 

 with a capital letter, the specific name following it, and being 

 written, as a rule, with a small letter. For instance, to take the 

 examples already referred to, the Domestic Cat is called Felis 

 Jomestica, the European Wild Cat F. catus, the Leopard F. ^lardus, 

 the Tiger F. tirjris, the Lion F-. Ico. Thus the systematic name of an 

 animal is something more than a mere appellation, since it indicates 

 the affinity of the species with other members of the same genus : 

 to name an animal is, in fact, to classify it. 



It is a matter of common observation that no two individuals of 

 a species are ever exactly alike: two tabby Cats, for instance, 

 however they may resemble one another in the general characters 

 of their colour and markings, invariably present differences in 

 detail by which they can be readily distinguished. Individual 

 variations of this kind are of universal occurrence. Moreover, it 

 often happens that the members of a species are divisible into 

 groups distinguishable by fairly constant characters : among 

 Domestic Cats, for instance, we find white, black, tabby, gray, and 

 tortoiseshell Cats, besides the large long-haired Persian breed, and 

 the tailless Manx Cat. All these are distinguished as varieties of 

 the single species Felis domestica. 



It is often difficult to decide whether two kinds of animals should 

 be considered as distinct species or as varieties of a single species, and 

 no universal rule can be given for determining this point. Among 

 the higher animals mutual fertility is a fair practical test, the 

 varieties of a species usually breeding freely with one another and 

 producing fertile offspring, while distinct species either do not 

 breed together or produce infertile hybrids or mules. Compare, 

 for instance, the fertile mongrels produced by the union of the 

 various breeds of Domestic Dog with the infertile mule produced by 

 the union of the Horse and Ass. But this rule is not without 

 exception, and in the case of wild animals is, more often than not, 

 impossible of application : failing it, the only criterion of a " good 

 species " is usually the presence of constant differences from allied 

 species. Suppose, for instance, that a naturalist receives for 

 description a number of skins of wild Cats, and finds, after an 

 accurate examination, that in some specimens the tail is two-thirds 

 the length of the body and the skin of a uniform reddish tint with 

 a few markings on the head, while in the rest the tail is nearly half 

 as long as the body, and the skin tawny with black stripes. If 

 there are no intermediate gradations between these two sets of 

 individuals, they will be placed without hesitation in distinct 



