THE FLIGHT OF INSECTS 



of the body is flattened by vertical muscles (ik, mn\ during the 

 contraction of which the wings rise. There are also longitudinal 

 muscles (/, o, p], by the action of which the thorax is shortened 

 and the wings lowered. In Dragon-Flies, insects possessing quite 

 extraordinary flying powers, and in which the two pairs of wings 

 are capable of independent action as well as able to work together, 

 the muscular arrangements are very complicated. In addition to 

 elevator and depressor muscles there are others by which the 

 wings can be rotated and other- 

 wise adjusted. 



Flight of Insects. - - Marey 

 and others have made elaborate 

 experiments on the flight of in- 

 sects, but the small size of these 

 creatures and the great rapidity 

 of their movements make such 

 investigations exceedingly diffi- 

 cult. By allowing the wing-tips 

 of captive insects to just brush 

 against strips of blackened paper 

 stretched upon revolving cylin- 

 ders, Marey obtained curves 



which enabled him to calculate the rate of movement, some of 

 his results being as follows: 



Fig. 840. Wasp flying in the Sun, showing curves 

 described by wings. To the tip of each a fragment of 

 gold-leaf had previously been attached 



Common Fly 



Drone-Fly 



Bee 



Wasp 



Humming-Bird Moth 

 Dragon-Fly ... 

 White Butterfly 



Wing-beats per Second. 



330 

 240 



110 



72 

 28 



The rate is clearly greatest in insects of small size, and no 

 doubt in these captive specimens it was diminished by friction 

 against the blackened paper. 



By attaching a fragment of gold-leaf to the tip of the front- 

 wing in a Wasp, the same observer demonstrated the complexity 

 of the actual movement (fig. 840). And by this and other means 

 it has been shown that the wing-tip describes a figure-of-8 curve. 

 Photography is here difficult of application, but it has at least 

 shown that the plane of the wing is inclined during the upward 



