DR PETTIGREW ON THE PHYSIOLOGY OF WINGS. 391 



The wings of bats and birds are mobile because of their numerous joints 

 (shoulder, elbow, wrist, meta carpal, &c), and because of the muscles and fibro- 

 elastic ligaments which operate upon these joints. They are also flexible and 

 elastic, the one (the bat) because of its long, thin tapering fingers and envelop- 

 ing membrane ; the other (the bird) because of its tapering, primary, secondary, 

 and tertiary feathers. 



The insect wing is also mobile, the insect having the power not only of 

 moving the pinion in various directions at its root, but of causing the move- 

 ments generated at the roots to extend intelligently along the margins. The 

 insect wing is flexible and elastic in the same sense that the wing of the bat 

 and bird are flexible and elastic. The mobility, flexibility, and elasticity peculiar 

 to the living wing is more intimately blended in the wing of the insect than in 

 that of either the bat or bird. This arises from the fact that the wing of the 

 insect is usually in one piece, and jointed only at its root. 



The Wing at all times thoroughly under Control. — The advantage which the 

 wing derives from being movable in all its parts, consists in this, that it can be 

 wielded intelligently even to its extremity. This enables the insect, bat, and 

 bird, to tread and rise upon the air as a master — to subjugate it in fact. The 

 wing, no doubt, abstracts an upward and onward recoil from the air, but in 

 doing this it exercises a selective and controlling power ; it seizes one current, 

 evades another, and creates a third ; it feels and paws the air as a quadruped 

 would feel and paw a treacherous yielding surface. It is not difficult to com- 

 prehend why this should be so. If the flying creature is living, endowed with 

 volition, and capable of directing its own course, it is surely more reasonable 

 to suppose that it transmits to its travelling surfaces the peculiar movements 

 necessary to progression, than that those movements should be the result of 

 impact from fortuitous currents which it has no means of regulating. That the 

 bird requires to control the wing, and that the wing requires to be in a condition 

 to obey the behests of the will of the bird, is pretty evident from the fact that 

 most of our domestic fowls can fly for considerable distances when they are 

 young and when their wings are flexible ; whereas when they are old and the 

 wings stiff, they either do not fly at all or only for short distances, and with great 

 difficulty. This is particularly the case with tame swans. This remark also holds 

 true of the steamer or race-horse duck {Anas brachyptera), the younger speci- 

 mens of which only are volant. In the older birds the wings become too rigid 

 and the bodies too heavy for flight. Who that has watched a sea-mew struggling 

 bravely with the storm, could doubt for an instant that not only the wings but 

 every individual feather of the wing was perfectly under control ? The whole 

 bird is an embodiment of animation and power. The intelligent active eye, the 

 easy graceful oscillation of the head and neck, the folding or partial folding of 

 one or both wings, nay more, the slight tremor or quiver of the individual 



VOL. XXVI. PART II. 5 I 



