180 STUDY OF NATURAL HISTORY. 
enquiries touching the purposes for which an animal 
has been created, and what influence it possesses in 
the economy of the universe, we pass the boundaries 
of simple fact, and are compelled, in most cases, to 
rely upon theory. True it is, as in the instances 
just given, we can be at no loss to discover the 
more general uses of animals: for example, we know 
that some supply food to others, or hasten the de- 
composition of decayed matter; that some promote 
the fecundation of plants, or check the exuberance 
of vegetation. These may still be admitted in the 
list of unquestionable truths, because they are mani- 
fest to ordinary observers. But when we enquire 
into more minute particulars, and speculate on the 
reasons why the flamingo, for instance, has such 
disproportionately long legs; what particular pur- 
poses of nature are fulfilled by the ostrich; or 
what are the particular uses for which such an 
apparently anomalous animal as the ornithorynchus, 
—half quadruped, half bird,—was created; when, 
in short, we attempt to discover the uses of such 
animals of which direct evidence cannot be pro- 
duced ; we enter upon a boundless region of specu- 
lation and theory,—a region which the student 
should avoid, and where the more experienced 
naturalist will do well to proceed with caution. 
In the mean time, such considerations should not 
deter us from accumulating facts connected with . 
animal economy, or from recording such inferences 
as may be plausibly drawn from them; leaving the 
validity of these inferences to be confirmed or dis- 
proved by longer experience. 
(122.) There is a third consideration regarding 
