246 STUDY OF NATURAL HISTORY. 



cock is known by its immense fan-shaped tail ; the 

 pheasant, by having the same member long and 

 pointed ; and the turkey, again, is pre-eminent for 

 its naked face, fleshy horn, and wattles. Here we 

 perceive the force of the Linnaean axiom. We 

 take a confessedly natural group like the present, 

 and discover what are its general characters, and 

 then descend to its variations. Had we done the 

 reverse, and set out upon a theory that a fan-shaped 

 tail, or a pointed one, or a naked face, were not to 

 be admitted as generic characters in any group, we 

 should be proceeding upon an arbitrary opinion, 

 the absurdity of which would be manifested in the 

 case before us ; because, by acting upon it here, we 

 should be obliged to distinguish a peacock from a 

 turkey by some obscure and inconspicuous charac- 

 ters, which none but the comparative anatomist or 

 the professed ornithologist would understand. Such 

 a system might, indeed, be intelligible to them, but it 

 would be almost useless to the great bulk of mankind. 

 (170.) The best characters for groups are those 

 drawn from their external aspect; and it matters 

 not in what this peculiarity of aspect consists, be- 

 cause it is almost universally accompanied by minute 

 points of difference, which, upon strict examination 

 are sure to be detected. The latter, however, should 

 not be brought in the foreground, and placed before 

 the former, merely because it has been the custom 

 for systematists to attach a fancied importance to 

 minute characters, and to neglect those which will 

 answer the same purpose of distinction, and yet be 

 obvious to every one. If, for instance, the sapro- 

 phagous and thalerophagous beetles can be equally 



