I 



ANATOMY AND PHYSIOLOGY 



57 



the folded wing (Fig. 74, B) exhibits a costal joint (a), a fold parallel 

 to the transverse vein (b) , and a complex joint at d. The wing rotates 

 upon the articular head (ah) and when folded back beneath the wing- 

 covers the inner end of the cotyla (c) is brought into contact with a 

 chitinous sclerite of the thorax, which stops the further movement 

 of the cotyla medianward, and as the wing swings farther back the 

 middle system of veins (m) is pushed outward and anteriorly. This 

 motion, combined with the backward movement of the wing as a whole, 

 produces the folding of the 

 distal end of the wing. There 

 are no traces of muscles or 

 elastic ligaments in the wing 

 which could aid in the folding. 

 Mechanics of Flight. The 

 mechanism of insect flight is 

 much less complex than one 

 might anticipate. Indeed, 

 owing to the structure of the 

 wing itself, simple up and 

 down movements are suffi- 

 cient for the simplest kind of c 

 flight. During oscillation, 

 the plane of the wing changes, 

 as may be demonstrated by P 



holding a detached wing by 



its base and blowing at riffht FlG> 74- Wing of Leptinotarsa decemlineata. A, 



n S I1L spread; B, folded; a, costal joint; ah, articular head; 



angles tO its SUrf ace ; the mem- an, anterior system of veins; b, transverse vein; c, 



, r , i . . , j cotyla; d, joint; m, middle system of veins; p, poste- 



brane of the wing then yields rior system of ve i ns . After TOWER. 

 to the pressure of the air while 



the rigid anterior margin does not, to any great extent. Similarly, 

 as the wing moves downward the membrane is inclined upward by the 

 resistance of the air, and as the wing moves upward the membrane 

 bends downward. Therefore, by becoming deflected, the wing encoun- 

 ters a certain amount of resistance from behind, which is sufficient to 

 propel the insect. The faster the wings vibrate, the greater the deflec- 

 tion, the greater the resistance from behind, and the faster the flight 

 of the insect. 



The path traced in the air by a rapidly vibrating wing may be deter- 

 mined by fastening a bit of gold leaf to the tip of the wing and allowing 

 the insect a wasp, for example to vibrate its wings in the sunlight, 



