show that as each wing is made up of a plurality
of feathers, overlapping each other, they form a
sort of a valved surface, opening so as to permit
air to pass through them during the period of
their upward movement, and closing up as the
wing descends.

It is difficult to perform this experiment with
wings, so as to show such an individual feather
movement. It is certain that there is nothing in
the structure of the wing bone and the feather
connection which points to any individual feather
movement, and our observation is, that each
feather is entirely too rigid to permit of such an
opening up between them.

It is obvious that the wing is built up in that
way for an entirely different reason. Soaring
birds, which do not depend on the flapping motion,
have the same overlapping feather formation.

WEBBED WINGS.--Furthermore, there are numerous
flying creatures which do not have
feathered wings, but web-like structures, or like the
house fly, in one continuous and unbroken
plane.

That birds which fly with flapping wings derive
their support from the air, is undoubtedly true,
and that the lift produced is due, not to the form,