POSITION IN PERCHIA'G. 67 



they should be enabled to remain on their -watch- 

 towers, and mark its progress. But here, as in all 

 other cases, the purpose of nature is accomplished, 

 and accomplished by apparatus the most effective, 

 and at the same time the most simple. 



It is chiefly by the pulling of the tendons which 

 close the toes, by the mere action of bending the 

 joints of the leg, that this firmness on the perch is 

 maintained. Their tendons pull all the phalanges 

 of the toes ; and thus the same action, and that not a 

 muscular exertion, which would tire, but a state of 

 greater repose than when the legs are not bent, 

 enables the bird to hold on with the whole foot, and 

 the hold taken by the elastic pads and tubercles is 

 far more firm upon a hard substance than if it were 

 taken by means of claws. The rock perchers also, 

 in general, use their claws in clutching and killing 

 their prey, so that they could not be used in keeping 

 the perch without blunting their points, and thus 

 unfitting them for their proper purposes; neither 

 could a hold merely by means of the claws be kept 

 for any length of time, unless the hold were above 

 the body, and kept by the pressure of that. All 

 perchers by the claws for repose perch with the back 

 undermost, or at least in such a way as that the weight 

 hangs upon the claws as upon hooks, the form of 

 which is maintained either by stops of bone, or by 

 the weight of the dependent body pulling the tendons, 

 and the firmness is given wholly by the latter. 



Those provisions for the secure maintenance of 

 their place, in animals, arising from structure merely, 

 and not requiring any muscular exertion, or other 

 effort on their part, which can in any way fatigue 

 them by its continuance, are among the most striking 

 instances of that superiority of design and adaptation 



F2 



