178 STUDY OF NATURAL HISTORY. 
increased. Thus, in America, the warblers are par- 
ticularly numerous, and not only feed upon creeping 
insects, but also upon those winged tribes which 
frequent the foliage for shelter. The more we see 
of the economy of animals, the more do we find 
stratagem opposed to stratagem: so that modes of 
defence or of self-preservation, which even the 
reason of man would suppose perfectly effectual, 
are still found to be unavailing, in all cases, against 
the address of those enemies whose attacks are to 
be dreaded. In the foregoing remarks, we have 
been insensibly led to illustrate more than one of 
the positions before touched upon. ‘The student, 
however, will thus perceive, to the full extent, the 
indispensable necessity of observing and recording 
every fact, even the most apparently trivial, con- 
nected with the habits of animals. 
(120.) But, however attentively we may study 
the manners of living animals, there must ever re- 
main a large proportion whose economy has never 
been recorded, and of which we can consequently 
know nothing from actual observation. Here, then, 
we must have recourse to analogical reasoning. It 
is found that certain habits are always indicated by 
a correspondence of structure. Among birds, for 
instance, we observe that all those which live ha- 
bitually upon the ground, like the partridge, the 
turkey, and the domestic fowl, have strong, ele- 
_ vated legs; while in birds which rest only upon 
trees, like the swallow, these members are short and 
weak. We know, from experience, the universality 
of these facts; and we thence conclude that all birds 
so constructed, have corresponding habits, although 
