174 STUDY OF NATURAL HISTORY. 
we have just alluded to. Now, this knowledge is 
to be acquired in two ways; either by actual 
observation, or by inductive reasoning. The first, 
of course, is the most simple and the most complete, 
and lies within the reach, under favourable circum- 
stances, of every observer. The latter, on the other 
hand, is more confined, and can only be arrived at 
by a long course of study. The former is a mere 
exercise of vision; but upon the latter we have ge- 
nerally to reason analogically. We then find that 
certain modifications of form indicate certain habits ; 
and that this reciprocity is so universal, that we are 
enabled to decide whether a bird, whose skin only 
we have seen, lives in general upon the ground, or 
among trees; whether it eats insects, or seeds, or 
both; or whether a beetle feeds upon green or upon 
decomposed vegetables. 
(118.) To illustrate the importance of that minutely 
accurate observation which is necessary in ascertain- 
ing the habits and economy of animals, and at the 
same time to exemplify the diversity of ways by 
which nature effects the same object, let us ima- 
gine a noble forest tree, in whose luxuriant foliage 
the birds of the air find shelter, and whose leaves 
supply food to hosts of insects. In this respect, 
the tree may be considered a world in itself, filled 
with different tribes of inhabitants, differing not 
only in their aspect, but even in the stations or 
countries they inhabit, and assimilating as litfle 
together as the inhabitants of Tartary do with . 
those of England. First, let us look to those insects, 
which, being destined to live upon vegetable food, 
are instinctively directed to seek it here: some, as 
