SPECIFIC CHAUACTEPvS OF BIRDS. 521 
deux cercles, gris bianc et cendre brun,^' and that of the 
other as " couleur de noisette." 
Now, in forming an estimate of the sufficiency of such 
characters as these for fulfilling the objects intended, name- 
ly, the distinction of specific forms, the questions which 
necessarily occur are, — Do they possess the essential requi- 
sites ? Are they taken from obvious parts ? From positive, 
certain, fixed, determinate organs or circumstances? Are 
they liable to misinterpretation, or are they ambiguous.^ 
And, lastly, are they essentially distinctive ? 
It may be observed, in the first place, and before pro- 
ceeding to the solution of these questions, that characters 
taken, not from forms, but from qualities, and those, too, 
not essential, as is the case with colour, cannot well be said 
to be peculiarly fitted for distinguishing specific Jbrms. 
But as this may have something of sophistry in it, inas- 
much as specific form being an abstract idea, it may as well 
be rendered tangible to the comprehension, through the 
medium of qualities as of forms,—- or, at the best, may not 
be an obvious objection, the idea simply of species may be 
substituted for that of specific forms. 
With regard to obviousness, no one surely will deny 
that these characters are taken from obvious parts ; and 
the quality of those obvious parts on which they depend is 
not merely obvious, but that which, next to the size and 
general contour of a bird, impresses itself the most forcibly 
upon the mind, and, on taking a very hasty glance, it is 
almost the only property retained by the perceptive faculty. 
This, however, of itself will not constitute an incontro- 
vertible quaUfication, for, in most respects, it is on a simi- 
lar footing with Size, which, in all departments of physio- 
graphy, has been not without reason rejected as a specific 
character. 
