INTKODUCTIDX. 1 3 



and if their peculiarities are permanent, and are handed down c(in- 

 stantly by inheritance, then we get ^"rctce." Thus we may sup- 

 pose (though some doubt it) that all known dogs belong to and 

 constitute one species. But we know that individual dogs, such as 

 the greyhound, the maatiflF, the terrier, the bull-dog, and the like, 

 differ from one another so greatly that we can always recognise 

 them with cei'tainty. These, therefore, constitute so many varieties 

 of the dog. It need only be added that the greatest of all diffi- 

 culties which the practical naturalist has to confront is the difficulty 

 of determining precisely what constitutes a species as distinguished 

 from a variet//. In other words, there are innumerable cases in' 

 which it is almost impossible to tell whether we are dealing with 

 two closely allied species, or with a species and its variety ; and in 

 no case can any definite rule of guidance be laid down by which this 

 difficulty can be got rid of. 



The classification now adopted by naturalists will perhaps be 

 better understood if we take an actual example, and see how it is 

 applied in practice. If we regard the domestic dog, with all its 

 subordinate varieties, as a single speeies, we have to notice, in the 

 first place, that it is known technically by a double name, and is 

 called the Canis familiaris. All species are thus known by "bi- 

 nomial" designations, the second name being like a man's Christian 

 name, and being distinctive of the individual, whilst ihe first name 

 is like a man's surname, and indicates the group, or, technically, 

 '''genus" to which the individual belongs. The dog, then, whilst 

 individually recognised by the epithet ^^ familiaris" belongs to the 

 " genus " Canis, in which are included other related species, such as 

 the Wolf {Canis lupus) and the Jackal (dinis aureus). The genus 

 Canis, again, belongs to the "family" Ca/iidce, including other 

 genera, such as the Foxes ( Yulpes). The family Canidce, again, is 

 one of a number of families, such as the Lions, Tigers, and Cats 

 {Felidce), the Bears and Racoons ( Ursidoe), the Hysenas (JSycenidce), 

 &c., which together constitute the '•'■order" of the Carnivora or 

 Beasts of Prey. The Carnivora, again, constitute one of many 

 orders of Quadrupeds, which are distinguished by suckling their 

 young and by other common characters, and which collectively con- 

 stitute the ''^ class" Mammalia. Finally, the class Mammalia is 

 united with the classes of the Birds, Reptiles, Amphibians, and 

 Fishes, to constitute the great primary division of Vcrtehrata or 

 " Vertebrate Animals ; " since all these classes agree with one 

 another in the fundamental character of possessing a backbone or 

 " vertebral column," or an equivalent structure. 



Condensing the above, the zoological position of the Dog, expressed 

 in full, would be as follows : — 

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