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 Linnean 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 
