‘236 STUDY OF NATURAL HISTORY. 
CHAP. VY. 
ON THE CHARACTERS OF NATURAL GROUPS. 
(162.) THE characters by which natural groups, 
like those we have hitherto contemplated, are 
to be known and designated, has been a fruitful 
subject of disquisition among writers. It has 
been customary, until within the last few years, for 
naturalists to decide, a@ priort, upon those charac- 
ters which a group of species, or a single one, 
should possess, in order to constitute a genus. This 
mode of proceeding, as may naturally be supposed, 
led every one to follow his own opinion; so that 
almost every part of an animal, in turn, had been 
singled out as the most important for this purpose. 
Thus, Linnzeus founded his genera of birds entirely 
on the form of the bill and the construction of the 
feet; totally disregarding the formation of their 
wings,—which is one of the chief characteristics 
of birds,—and entirely overlooking their manners, 
habits, and food. In entomology, however, he con- 
structed his genera on a totally different principle. 
Here he considers the wings of insects as, affording 
the most important characters; and he has accord- 
ingly founded all his great divisions, and most of his 
lesser ones, in the different modifications which these 
members present; while the mouth and the feet, 
which were so highly regarded in his arrangement 
of birds, are scarcely noticed in his classification of 
