94 THE FLIGHT OF BIRDS 
curve begins. Further out the whole breadth of 
wing is curved; for s@he distance from the front 
margin there is an upward slope, then a downward 
slope sets in. In the nearer region, also, there is not 
a simple curve maintained throughout, but the 
feathers in one part are more bent down than in 
another, so that the back edge presents a curiously 
undulating line. The Sparrow-Hawk’s wing has 
similar curves, but they are much less pronounced. 
What the exact significance of all this complication 
may be, presenting so marked a contrast to the 
uniform curves of an aeroplane, it is difficult to say. 
Probably there is some significance, since in birds 
that are strong on the wing the whole mechanism 
of flight down to minute details is so efficient. 
Sometimes we may see the wing-curves in their 
full beauty in a live bird, but it is only for a moment, 
and one wishes to look at them quietly and study 
them. The thing is, if one has a freshly-killed 
specimen, to cut off the wings close to the body and 
pin them out back downwards at their full stretch. 
Treated thus the wing retains its curves and a great 
deal of its beauty. If it is pinned face downwards 
and flattened, it conveys by no means so good an 
idea of what it was during the life of the bird. I 
have tried by photographs to show the outlines of 
various types of wing, the depth of their concavities, 
and the undulating curves seen in, for instance, the 
Curlew’s wings. Some points come out distinctly, 
others the camera fails to see or does not see clearly. 
To show the gradual tapering and flattening of 
the farther half, perhaps no wings are better than 
those of the Gannet and the Tern (Pl. xiv), and 
