SEXUAL DIFFERENCES IN WING OF SKY LARK. 105 
angle of which the extremity of the third primary is the apex, 
or a regularly graded oblique line. It is therefore not strictly 
correct to say that the second to fourth primaries of the Sky 
Lark are almost of equal length, inasmuch as there is frequently 
(probably always) a considerable discrepancy in the length of those 
of the female. 
The secondaries of the male are distinctly longer than in the 
female and slightly less contracted towards the tips, which are 
bilobed (or, more strictly, bispatulate) in both sexes, the lobe or 
spatula terminating the outer web being longer in proportion 
to that of the inner web than in the female: this is especially 
noticeable in the larger and presumably older birds. 
There can be little doubt that the slightly greater width at 
the extremity of these feathers and their more even termination 
offer better resistance to the air, in flight, than those of the 
female, and, combined with the increase of length in these 
feathers, help materially in supporting the bird when soaring. 
A comparison of a series of Sky Larks in the flesh shows that 
the males are distinctly larger than the females, and, comparing 
the general outline of the expanded wings, it will be at once 
observed that those of the males are decidedly longer in pro- 
portion to their width than those of the females. 
When one critically examines the feathering, to see where 
the principal difference in measurement exists, it at once appears 
that the uncovered portion of the primaries in the male is dis- 
proportionately greater than in the female, and the emargination 
of the outer web in the third and fourth primaries commences 
considerably farther from their extremities, about half the edge 
of the outer web in the exposed portion being emarginate in 
the males, and about two-fifths in the females. 
Later on I hope to publish additional notes on sexual wing- 
structure in other birds. As arule, the male wing is specially 
modified to enable the bird to overtake its female; but some- 
times the development seems to serve the purpose of sustained 
rather than rapid flight; and it must be remembered that in 
certain birds (such as the Dunlin) in which the wings of both 
sexes agree in expanse and hardly differ in the structure of the 
feathering, the inferior size and weight of the body in the male 
give him a considerable advantage in flight. 
