188 Natural and Artificial Flight. (April, 
conical on se¢tion from within outwards and from before 
backwards ; this shape converting the pinion into a delicately 
graduated instrument, balanced with the utmost nicety to 
satisfy the requirements of the muscular system on the one 
hand and the resistance and resiliency of the air on the 
other. 
The neure or nervures in the inse¢t’s wing are arranged 
at the axis or root of the pinion, after the manner of a fan 
or spiral stair ; the anterior one occupying a higher position 
than that farther back, and so of the others. As this 
arrangement extends also to the margins, the wings are more 
or less twisted upon themselves, and present a certain degree 
of convexity on their superior or upper surface, and a 
corresponding concavity on their inferior or under surface ; 
their free edges supplying those fine curves which act with 
such efficacy upon the air, in obtaining the maximum of 
resistance and the minimum of displacement ; or what is the 
same thing, the maximum of support with the minimum of 
ship. (Video of Fig. 1, and 7g, sa, of Fig. A.) «sao 
alte Bry 
= 
- 
Fig. 1 repesents the oblique dire€tion of the Wasp seen from above and laterally. Shows 
stroke of the wing in the flight of the how the wing twists upon itself during 
insect (wasp)—hew the wing is twisted its aGtion, the posterior or thin margin 
upon itself at the end of the up (a) and 
down (0) strokes, and how the tip of the 
wing, during its vibration, describes a 
being inclined alternately forwards (g) and 
backwards (¥) at the end of the downstroke, 
and backwards (a) and forwards (s) at the 
figure-of-8 track in space (a, ¢, 0). end of the up stroke. It also shows how 
the margins of the wing form figure-of-8 
curves, and how the margins and tip of 
the wing form figure-of-8 tracks in space 
(I, 2, 3) 4, 5, 6, 7, 8, 9, 10, II, 12, 13, 14). 
All wings obtain their leverage by presenting oblique surfaces 
to the air, the degree of obliquity gradually increasing in a 
direction from behind forwards and downwards during 
-extension, when the sudden or effective stroke is being given, 
and gradually decreasing in an opposite direction during 
flexion, or when the wing is being more slowly recovered 
preparatory to making a second stroke. The down stroke 
in inse¢ts—and this holds true also of birds—is therefore 
