“INFLUENCE OF ANALOGY. 179 
we have never seen them alive, nor have any testimony 
to the absolute fact from others. It is obvious, 
again, that birds or insects having long and very 
pointed wings, are endowed with great powers of 
flight; for we see this structure is universal among 
the swallows, the humming birds, and the dragon 
flies. We can be in no danger, therefore, of mistake, 
in deciding on the slowness or quickness of flight 
in a bird, although we may never have seen it alive. 
The form, therefore, —vay, as it is sometimes called, 
the conformation of aranimal, —will generally reveal, 
to the experienced naturalist, the leading points of 
its natural economy. But these deductions can 
only be arrived at when the student has made con- 
siderable proficiency in the science; and has, by 
a diligent comparison of the structure of species 
with reference to their natural economy, duly 
qualified himself for forming opinions which have 
not yet been confirmed by his own observation. 
Leaving this subject, therefore, as more suited to 
another part of this discourse, let us enquire into 
the second division of our subject ; namely, the pro- 
perties of animals in regard to their influence or 
uses in the economy of nature. 
(121.) So far as we have hitherto proceeded, the 
knowledge to be acquired results from simple ex- 
perience; that is, it regards isolated facts, upon 
which there can be no dispute. The structure of 
an animal, and its habits or manners, are inde- 
pendent of all theory; and, when fully ascertained, 
are so many truths which may recorded in our 
chronicles, and appealed to by all parties as matters 
of indisputable authority. But, when we come to 
Ried 
