MUSEUM OF COMPARATIVE ZOOLOGY. 227 



The wing also varies considerably in form with age. In many of the 

 song-birds, at least, and also in the raptorial birds, the wing becomes 

 more pointed with the second and third moultings of the remiges. 

 Birds of the first year hence have, even after the flight feathers are 

 fully grown, a shorter and more rounded fore-wing, as a general rule, 

 than birds of two or three years of age. These differences of course 

 result from variations in the relative length of the primaries, the outer 

 primaries being the last to acquire their ultimate proportions, as they 

 are also the last primaries to be renewed in the annual moult. A 

 similar change with age occurs in the form of the inner point of the 

 wing, or that formed by the inner secondaries. These, like the pri- 

 maries, are subject to a gradual increase in length for a time with each 

 moult, they likewise being the latest of the secondaries to acquire their 

 mature size, as they are also the last of the secondaries changed in 

 each normal moult. Thus, through the gradual elongation of the outer 

 primaries and the inner secondaries, a slight change is produced in the 

 general form of the wing. It is, however, only slight, and since some 

 young birds have as pointed wings as any of the same species which 

 are fully adult, and some adult birds have wings as much rounded as 

 the full-grown young, the rule is subject to many exceptions. The 

 sexes of the same species also often differ similarly with the young and 

 old in respect to the form of the wing. This is more especially the 

 case in those species in which the female is much smaller and much 

 duller colored than the male, the structural inferiority of the female to 

 the male being thus evident in various features. 



"While the wing may be regarded, as already stated, as generally 

 smaller and more rounded in the younger individuals, it not unfre- 

 quently happens that the specimens having the greatest alar extent are 

 immature birds. This has been particularly noticed in the eagles and 

 hawks, as well as in some of the gulls, in which it is so frequent as to 

 have attracted the attention of numerous observers.* The feathers of the 

 wings and tail are not only longer, but they are also broader, and hence 

 in the expanded wing present a greater resisting surface to the air. 

 Two explanations of this fact present themselves. First, in the cases 

 referx-ed to, the birds may have been born at a very northern locality, 

 whence only the younger birds ever descend so far south. Second, the 

 greater lack of power in the muscles of flight in the young birds, as 



* See American Naturalist, Vol. Ill, 1S69, p. 617. 



