MECHANISM OF FLIGHT 



149 



movements of the wings would lead us, he says, to suppose that 

 there exists in insects a very complex set of muscles of flight, 

 but in reality, he claims, there are only the two elevator and 

 depressor muscles of each wing. 1 And Marey says that when we 

 examine more closely the mechanical conditions of the flight of 

 insects, we see that an upward and downward motion given by the 

 muscles is sufficient to produce all these successive acts, so well co- 

 ordinated with each other ; the resistance of the air effecting all the 

 other movements. He also refers to the experiments of Giraud 

 which prove that the insect needs for flight a rigid main-rib and a 

 flexible membrane. 



If we take off the wing of an insect, and holding it by the small 

 joint which connects it with the thorax, expose it to a current of air, 



FIG. 163. The two upper lines are produced by the contacts of a drone's wing on a smoked 

 cylinder. In the middle are recorded the vibrations of a tuning-fork (250 vibrations per second) for 

 comparison with the frequency of the wing movements. Below are seen the movements of the 

 wing of a bee. After Marey. 



we see that the plane of the wing is inclined more and more as it is 

 subjected to a more powerful impulse of the wind. The anterior 

 nervure resists, but the membranous portion which is prolonged 

 behind bends on account of its greater pliancy'. 



The wings of insects may be regarded simply as vibrating wires, 

 and hence the frequency of their movements can be calculated by 

 the note produced. Their movements can be recorded directly on a 

 revolving cylinder, previously blackened with smoke, the slightest 

 touch of the tip of the wing removing the black and exposing the 

 white paper beneath ; Fig. 163 was obtained in this way. By this 

 method it was calculated that in the common fly the wings made 330 

 strokes per second, the bee 190, the Macroglossus T, the dragon-fly 



1 Von Lendenfeld, however, points out the fact that Straus-Durckheim proved 

 that the wings of beetles are moved by a complicated system of numerous muscles. 

 " In the Lepidoptera I have never found less than six muscles to each wing, as also 

 in the Hymenoptera and Diptera." " The motions of the wings of Libellulidse are the 

 combined working of numerous muscles and cords, and of a great number of chitinous 

 pieces connected by joints." 



