ANATOMY AND PHYSIOLOGY 63 



oscillation, the plane of the wing changes, as may be demon- 

 strated by holding a detached wing by its base and blowing at 

 right angles to its surface ; the membrane of the wing then yields 

 to the pressure of the air while the rigid anterior margin does 

 not, to any great extent. Similarly, as the wing moves down- 

 ward the membrane is inclined upward by the resistance of the 

 air, and as the wing moves upward the membrane bends down- 

 ward. Therefore, by becoming deflected, the wing encounters 

 a certain amount of resistance from 

 behind, which is sufficient to propel 

 the insect. The faster the wings 

 vibrate, the greater the deflection, 

 the greater the resistance from be- 

 hind, and the faster the flight of the 

 insect. 



The path traced in the air by Trajectory of the wing of an 



. . insect. 



a rapidly vibrating wing may be 



determined 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, against a dark background. Under 

 these conditions, the trajectory of the wing appears as a lumi- 

 nous elongate figure 8. During flight, the trajectory consists 

 of a continuous series of these figures, as in Fig. 73. 



Marey, the chief authority on animal locomotion, used 

 chronophotography, among other methods, in studying the 

 process of flight, and obtained at first twenty, and later one 

 hundred and ten, successive photographs per second of a bee 

 in flight. As the wings were vibrating 190 times per second, 

 however, the images evidently represented isolated and not 

 consecutive phases of wing movement. Nevertheless, the 

 images could be interpreted without difficulty, in the light of 

 the results obtained by other methods. At length he obtained 

 sharp but isolated images of vibrating wings with an exposure 

 of only 1/25,000 of a second. 



The frequency of wing vibration may be ascertained from 

 the note made by the wing if it vibrates rapidly enough to 



