CLAWS OF BIRDS. 971 
results two essential advantages to the bird: first, 
by having longer and more slender feet, it walks 
upon the earth with greater facility than any of its 
family; and, secondly, it does this without any pain, 
impediment from, or risk of injury to, the ends of 
its claws. This explanation, which has never been, 
we believe, before attempted, is one out of a 
thousand proofs of those gradations in the animal 
world which demonstrate natural series, but which 
some writers have had the hardihood to deny, as if 
the most acknowledged truths and the most obvious 
facts were to be made matters of doubt and of dif- 
ficulty. We have before us, at this moment, a 
beautiful series of species, showing every possible 
link of gradation, from the ground parrakeets of 
Australia to those of tropical America, which we 
know, from personal experience, live wholly among 
trees. This, also, will serve as an example of that 
minuteness of investigation which the student is to 
pursue, if he wishes to draw just inferences from the 
structure in animals of whose habits and economy, 
when alive, he is entirely ignorant. 
(185.) There are several other modifications of foot 
among the perching birds, which can here receive 
only a slight notice, sufficient to show the value of 
essential characters drawn from these organs. The 
structure of the claws, as just explained in the 
instance of the ground parrots, is almost sufficient 
in itself, for the discrimination of natural groups, 
or analogical types. Great curvature of these 
members indicates one of two habits, which are 
readily determined by other considerations. Either 
such birds are rapacious, in which case the claws 
