PRINCIPLES OF CLASSIFICATION. 31 



genus Linaria or Linnet, there are in this country alone, five 

 species, the green linnet or greenfinch, the brown linnet, the 

 mountain linnet or twite, the smaller redpoll, and the mealy 

 redpoll, the habits, food, and general conformation of all being 

 very nearly the same, whilst there are differences between them 

 sufficiently constant to prevent their ever being confounded. But 

 the genus Linaria is united with many other genera, which are 

 chiefly distinguished from it by some slight variations in the 

 form of the bill, into the family of Fringillidce or Finches ; which 

 includes the well-known Goldfinch, Hawfinch, Bullfinch, Gros- 

 beak, Sparrow, Chaffinch, Brambling, and many other birds, all 

 having a stout conical bill, slightly bent down near its point. 

 This family, with others in which the shape of the bill, and 

 the general formation of the body, are more or less unlike what 

 is seen in it, constitutes the section Conirostres (or conical-billed 

 birds) of the order Insessores, or Perchers. 



10. Thus it is seen that, as we pass up from species to genera, 

 from genera to families, from families to orders, and from orders 

 to classes, the characters of agreement become fewer and fewer ; 

 whilst those of difference manifest themselves more and more 

 strongly. And when we arrive at classes, we may generally say 

 that the points of difference are stronger than those of agreement , 

 so that, if two animals belong to distinct classes, they may be 

 considered more unlike than they are like ; whilst, if they belong 

 to the same class, they may be regarded as more like than they 

 are unlike. 



1 1 . One other example may be introduced, to show the utility 

 of even a very moderate knowledge of the principles of classifi- 

 cation, in enabling us to retain and apply a large amount of 

 information ; which, if we had to derive it from the study of 

 each individual animal, could scarcely be embraced by a single 

 mind. The Common Dog is a species of the genus Canis, 

 belonging to the family Canida, of the order Carnivora, of the 

 class Mammalia, of the sub-kingdom Vertebrata. The informa- 

 tion conveyed to us by these last terms has already been noticed. 

 From the simple name vertebrated animal, we learn that it has an 

 internal skeleton, with a jointed backbone and skull, containing 



