Igo Natural and Artificial Flight. (April, 
and secondary feathers, the precise angles necessary for 
flight. It, in fact, insures that the wing, and the curtain or 
fringe of the wing, shall be screwed into and down upon the 
air in extension, and unscrewed or withdrawn from the air 
during flexion. The wing of the bat and bird may therefore 
be compared to a huge gimlet or auger, the axis of the 
gimlet representing the bones of the wing; the flanges or 
spiral thread of the gimlet, the volant membrane or rowing 
feathers.” 
“ The Wing Twists and Untwists during its Action.—That 
the wing twists upon itself structurally, not only in the 
insect, but also in the bat and bird, any one may readily 
satisfy himself by a careful examination, and that it twists 
upon itself during its action I have had the most convincing 
and repeated proofs. The twisting in question is most 
marked in the posterior or thin margin of the wing, the 
anterior and thicker margin performing more the part of an 
axis. As a result of this arrangement, the anterior or 
thick margin cuts into the air quietly, and as it were by 
stealth, the posterior one producing on all occasions a 
violent commotion, especially perceptible if a flame be 
exposed behind the insect. Indeed, it is a matter for 
surprise that the spiral conformation of the pinion, and its 
spiral mode of action, should have eluded observation so 
long; and I shall be pardoned for dilating upon the subject 
when I state my conviction that it forms the fundamental 
and distinguishing feature in flight, and must be taken into 
account by all those who seek to solve this most involved 
and interesting problem by artificial means. The importance 
of the twisted configuration or screw-like form of the wing 
cannot be over-estimated. That this shape is intimately asso- 
ciated with flight is apparent from the fact that the rowing 
feathers of the wing of the bird are every one of them 
distin@tly spiral in their nature; in fact, one entire rowing 
feather is equivalent—morphologically and physiologically— 
to one entire insect wing. In the wing of the martin, 
where the bones of the pinion are short and in some 
respects rudimentary, the primary and secondary feathers 
are greatly developed, and banked up in such a manner that 
the wing as a whole presents the same curves as those dis- 
played by the insect’s wing, or by the wing of the eagle, 
where the bones, muscles, and feathers have attained a 
maximum development. The conformation of the wing is 
such that it presents a waved appearance in every direCtion 
—the waves running longitudinally, transversely, and 
obliquely. The greater portion of the pinion may con- 
