AERIAL LOCOMOTION 247 



methods of propulsion. The scull used by the water- 

 man offers a rigid surface to the water, and the operator 

 has to impart alternate rotary movements to the scull 

 by his hand — at the same time taking care that the 

 scull strikes the water at a favourable slant. The 

 mechanism in the case of the insect's wing is far 

 simpler, the flexible membrane which constitutes the 

 anterior part of the wing presents a rigid border, 

 which enables the wing to incline itself at the most 

 favourable angle. 



The muscles only maintain the to-and-fro movement, 

 the resistance of the air does the rest, namely, effects 

 those changes in surface obliquity which determine 

 the formation of an 8-shaped trajectory by the ex- 

 tremity of the wing. 



Photography as applied to the Study of Insect 

 Flight. — The reader may, perhaps, be surprised that 

 we have not, as yet, resorted to photography as a 

 means of determining the trajectory of an insect's 

 wing, since this is the only method of recording an 

 accurate tracing. This is because the experiments 

 just mentioned were carried out long before photo- 

 graphy could be employed to study any kind of move- 

 ment. Photography was applied by Lendenfeld * for 

 determining the position of the wings of a dragon-fly. 



This author also showed how the lemniscate descrioed 

 by the extremity of the wing became displaced and 

 distorted by the animal's forward progression. The 

 experiments of the German naturalist were made on a 

 dragon-fly, which was fixed at the end of a sort of 

 balanced beam ; and although the animal could raise 

 itself to a slight degree, the conditions were not such 

 as to indicate the normal trajectory of the wing, when 

 the in>ect was free to fly where it liked. 



* Lendenfeld, Der Fluq der Libellen, Acad, der Wissenschaften. 

 Vienna, 1881, Hei't. i. p. 289. 



