Finally, turn to the flies. Herein it will be seen that there is but a single pair of wings, the hind pair having become reduced to mere stumps, known as “balancers.”
Much, very much more, might have been said of these wings: but our conversation is of birds. We cannot, however, properly appreciate either the essential characters of their wings, or their flight, without some such standards of comparison as is afforded by the wings of other creatures.
A Primaries. B Secondaries. C Tectrices. D Bastard Wing.
The upper figure shows the under side of wing with the coverts removed to show attachment of flight feathers to skeleton.
The lower figure shows the quill or flight feathers and the coverts in their natural condition.