ON GENERIC CHARACTERS. I43 
the characters by which such divisions are to be 
defined, are most judicious when they are drawn 
from two structures: first, from that structure of 
the animal itself, which it possesses in common with 
all others of the genus; and secondly, from’ that 
peculiarity which renders it analogous to many 
others out of its own genus. 
(167.) An instance, taken from an ornithological 
group, will illustrate the foregoing remarks. The 
genus Sylvicola (North. Zool. ii. 205.), or titmice 
warblers, comprehends so large an assemblage of 
species, that we are able to trace,and demonstrate, its 
circular succession. All these birds agree, more or 
less, in the form of their wings; the first quill of 
which is nearly as long the second. This being the 
most prevalent character, we select it as the chief 
mark of discrimination, without stopping to enquire 
whether other groups are to be also characterised 
by these organs; for this, we see, most assuredly 7s. 
We find, however, that among all the birds thus 
brought together, we have different modifications of 
the other organs: some have the bill more conic 
and entire, others have it depressed and notched ; 
in two or three, it is very sharp pointed, and even 
eurved; while a few depart from all the rest, in 
having feet adapted for climbing. Now, it is ma- 
nifest, that if we had set out with presupposing that 
all birds were to be classed by the bill and the 
feet, and that all other characters were of little or 
no moment, this most natural group would never 
have been detected. It is also clear, that, being 
discovered, we cannot draw our essential and primary 
characters from any of those organs which, as above 
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