PROGRESSION IN OR THROUGH THE AIR. 



137 



In all the wings which I have examined, whether in the 

 insect, bat, or bird, the wing is recovered, flexed, or drawn 

 towards the body by the action of elastic ligaments, these 

 structures, by their mere contraction, causing the wing, when 

 fully extended and presenting its maximum of surface, to 

 resume its position of rest and plane of least resistance. The 

 principal effort required in flight is, therefore, made during 

 extension, and at the beginning of the down stroke. The 

 elastic ligaments are variously formed, and the amount of 

 contraction which they undergo is in all cases accurately 

 adapted to the size . and form of the wing, and the rapidity 

 with which it is worked ; the contraction being greatest in 

 the short-winged and heavy-bodied insects and birds, and 



Fig. 62, — Left wing of the albatross, d, e, / Anterior or thick margin of pinion. 

 by a, c Posterior or thin margin, composed of the primary (b), secondary (a), 

 and tertiary (c) feathers. In this wing the first primary is the longest, the 

 primary coverts and subcoverts being unusually long and strong. The 

 secondary coverts and subcoverts occujiy the body of the wmg {e,d), and are 

 so numerous as effectually to prevent any escai)e of air between them dur- 

 ing the return or up stroke. This wing, which I have in my possession, 

 measures over six feet in length. — Original. 



least in the light-bodied and ample-winged ones, particularly 

 such as skim or glide. The mechanical action of the elastic 

 ligaments, I need scarcely remark, insures an additional 

 period of repose to the wing at each stroke ; and this is a 

 point of some importance, as showing that the lengthened 

 and laborious flights of insects and birds are not without 

 their stated intervals of rest. 



All wings are furnished at their roots with some form of 

 universal joint which enables them to move not only in an 



little shorter ; and in the swallows this is still more the case, the first quill 

 being the longest, the rest rapidly diminishing in length."— Macgillivray, 

 Hist. Brit. Birds, vol. i. p. 82. " The hawks have been classed as noble or 

 ignoble, according to the length and sharpness of their wings ; and the fal- 

 cons, or long-winged hawks, are distinguished from the short-winged ones by 

 the second feather of the wing being either the longest or equal in length to 



the third, and by the nature of the stoop made in pursuit of their prey." 



Falconry in the British Isles, by F. H. Salvin and W. Brodrick. Lond. 1855 

 p. 28. 



