204 THE INTEGUMENT A L SKELETON OF THE IMAGO. 



the wing apex; o represents the thoracic attachment of the 

 remigium and the radiating lines represent the successive 

 positions of the anterior margin of the wing, seen in per- 

 spective. 



Starting from the point h on the curve, the wing plane is 

 approximately vertical, the dorsal surfaces of the two wings 

 turned towards each other, and the apex of the wing in front 

 of the wing-root. In passing from h to a, the anterior borders 

 of the two wings are nearer each other than the posterior 

 borders, so that the insect is driven forwards by the backward 

 movement of the wings. 



FIG. 36. A Curve showing the loci of a point at the tip of the wing during flight, 

 seen from below the horizontal plane passing through the wing-roots. 



During the descent of the wing from a to b, the plane of the 

 wing is at right angles to its movement, so that the insect is 

 borne upwards, and at b the wings lie in the horizontal plane. 

 From b to c the wing slopes so that its plane corresponds with 

 the plane of movement, the front edge of the wing cutting the 

 air. 



The movement of the wing in the plane ob od is due to the 

 combined swing of the propterygium on the axis of the dens, 

 and the extension of the propterygium. 



