CLAWS OF BIRDS. 271 



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 



