278 FIRST PRINCIPLES OF NATURAL CLASSIFICATION. 



tions to the foregoing rule that at present occur to us ; 

 they relate almost as much to the size as to the shape 

 of an ohject ; but peculiarities drawn from the latter 

 circumstance are much more to be depended upon than 

 those of the former. 



(339.) A form is modified by difference in its pro- 

 portions. Hence, the comparative shortness or longness 

 of an animal, or of its parts, when compared to another 

 which it closely resembles, is (with the exceptions last 

 mentioned) usually a sign that it is a distinct species. 

 The comparative length of the tail in quadrupeds and 

 birds, and of the wings in birds and insects, are excel- 

 lent specific distinctions : the antenna? of insects do not 

 supply, in all cases, so good a criterion ; for they often 

 ,vary considerably, both as to structure and length, in 

 the sexes of the same species : the same uncertainty 

 attends the employment of specific characters drawn 

 from their legs. In birds and quadrupeds, however, 

 the structure of these latter members afford distinctions 

 for groups; and these latter modifications give us a cer- 

 tain index for the determination of species. The 

 entomologist should pay particular attention to the pro- 

 portions of two insects, which come so close to each 

 other, that he may be in doubt as to their specific dif- 

 ference : the greater enlargement of the thorax, the 

 wings, the feet, or even of the antennae, may frequently 

 indicate a real difference. 



(340.) The most general distinction of species is 

 manifested by their colours : among these, however, we 

 must not include black ; for not only are nearly all the 

 species of entire families (as the Harpalida; MacL.) and 

 sub-families (Edolina Sw.) of this colour, but nearly 

 the whole of the saprophagous beetles are of the same 

 sombre hue. Colours, among quadrupeds, unless when 

 domesticated, seldom vary in individuals of the same 

 species ; and still more rarely among birds, when arrived 

 at maturity. It should be remembered, however, that 

 in the feathered creation,, young birds are almost always 

 clothed in the garb of their mother ; and that among the 



