PROGRESSION IN OR THROUGH THE AIR. 



131 



from all I could determine, perfect. When one wing only 

 was cut, flight was irregular or lopsided, as in experiment 26. 



From experiments 26 and 27, as well as experiments 7 

 and 8, it would seem that the wing does not of necessity 

 require to present an unbroken or continuous surface to the 

 air, such as is witnessed in the pinion of the bat, and that the 

 feathers, when present, may be separated from each other 

 without destroying the utility of the pinion. In the raven 

 and many other birds the extremities of the first four or 

 five primaries divaricate in a marked manner. A similar 

 condition is met with in the Alucita hexadadyla, where the 

 delicate feathery-looking processes composing the wing are 

 widely removed from each other. The wing, however, ceteris 

 paribus, is strongest when the feathers are not separated from 

 each other, and when they overlap, as then they are arranged 

 so as mutually to support each other. 



Exp, 28. Eemoved half of the primary feathers from either 

 wing transversely, i.e. in the direction of the short axis of the 

 wing. Flight very slightly, if at all, impaired when only one 

 wing was operated upon. When both were cut, the bird flew 

 heavily, and came to the ground at no very great distance. 

 This mutilation was not followed by the same result in ex- 

 periments 6 and 1 1 . On the whole, I am inclined to believe 

 that the area of the wing can be curtailed with least injury 

 in the direction of its long axis, by removing successive por- 

 tions from its posterior margin. 



jExp. 29. The carpal or wrist-joint of either pinion ren- 

 dered immobile by lashing the wings to slender reeds, the 

 elbow-joints being left free. The bird, on leaving the hand, 

 fluttered its wings vigorously, but after a brief flight came 

 heavily to the ground, thus showing that a certain degree of 

 twisting and folding, or flexing of the wings, is necessary to 

 the flight of the bird, and that, however the superficies and 

 shape of the pinions may be altered, the movements thereof 

 must not be interfered with. 1 tied up the wings of a pigeon 

 in the same manner, with a precisely similar result. 



The birds operated upon were, I may observe, caught in a 

 net, and the experiments made within a few minutes from 

 the time of capture. 



