VARIATION OF CHARACTERS. 241 
determined, whereas habits are only to be traced 
from the living subject. Every one, for instance, 
can see whether a bird has its claws acute and very 
much curved, or whether they are comparatively 
straight and obtuse: now we know, from obsery- 
ation, that these modifications indicate two very 
different habits ; the first belonging to birds which 
always perch upon boughs, and the latter distinguish- 
ing such as live chiefly upon the ground. These 
habits, however, can never be known to the student 
as matters of fact, who merely sees such birds in a 
museum: we are therefore to direct his attention, 
in the first place, to circumstances or characters 
which it is in his power to see and verify; and 
afterwards to show the particular influence of such 
characters on habits and economy. 
(166.) The essential or most prevalent characters 
of our group, as a whole, having been ascertained, 
we are then to examine it more in detail, tracing 
the mode in which these characters vary, and as- 
certaining how far, and in what way, this variation 
is accompanied by a difference of habit and economy. 
There is, for instance, a whole family of beetles 
(the Petalocera Saprophaga of M‘Leay) which 
feed on living vegetables, in contradistinction to 
another, which devour them only in a decayed or 
putrescent state: but among those which agree in 
feeding upon living plants, we find some restrict 
their diet to the petals of flowers, others select only 
the green leaves, and many live upon the juices of 
the stem. Here, then, we have modifications of the 
same habit; and it is our business to trace such 
variations, whether in form or in economy, through 
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