242 MOVEMENT 



Now, in moving to and fro, the wing struck the cylinder 

 alternately with the hairy and smooth surface, which 

 proved that the wing underwent a change in inclina- 

 tion. This fact is important to bear in mind, for it 

 materially elucidates the mechanism of flight. Such 

 is the information derived from recording insect move- 

 ment by means of mechanical methods. 



The attempt might be made to obtain the trajectory 

 of the extremity of the wing by a similar means. 



But the wing, moving as it does in all sorts of 

 directions round its thoracic articulation, describes a 

 spherical figure, the whole of which could not possibly 



Fig. 169. — Movements of the wing of Macroglossus of cheese rennet on the surface 

 of a smoked cylinder. 



be traced on anything else than the inner surface of a 

 sphere. The contact of the wing with the surface of 

 the cylinder could only take place to a very small 

 extent. Consequently another method must be em- 

 ployed for obtaining the trajectory described in the 

 air by the extremity of the wing. 



Trajectory of the Extremity of the Wing — Remember- 

 ing the fiery tracks left upon the retina when a 

 luminous object was waved in front of the eyes, we 

 fastened a spangle of gold-leaf to the extremity of a 

 wasp's wing. The insect was then seized with a pair 

 of forceps and held in the sun in front of a dark back- 

 ground. We then watched the luminous trajectory 



