FLIGHT OF INSECTS. 



187 



loops usually predominates over the other ; it is generally the 

 lower one which increases while the upper diminishes. Indeed, 

 by a still greater opening, the hgure is occasionally trans- 

 formed into an irregular ellipse, at the extremity of which we 

 can recognise a vestige of the second loop. 



Fig. 71.— Appearance of a wasp, the extremity of each of whose larger 

 wings has been gilded. The insect is supposed to be placed in a sun- 

 beam. 



We thought that we had been the first to point out the form 

 of the trajectory of the wing of the insect, but Dr. J. B. Petti- 

 grew, an English author, informs us that he had already 

 mentioned this figure of 8 appearance described by the wing, 

 and had represented it in the plates of his work.* It will 

 be seen presently that, notwithstanding this apparent agree- 

 ment, our theory and that of Dr. Pettigrew differ materially 

 from each other. 



Changes of the plane of the wing, — The luminous appearance 

 given during flight by the gilded wing of an insect, shows 



* On the Mechanical AppHances by which Flight is Maintained in the 

 Animal Kingdom. Transact, of Linnean Society, 1867, p. 233. 



