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TEXT-BOOK OF ENTOMOLOGY 



28, and the butterfly (Pier is rapes) 9. Tims the smaller the species, 



the more rapid are the movements of the wings. 



The path or trajectory 

 made by the tip of the wing 

 is like a figure 8. Marey 

 obtained this by fastening 

 a spangle of gold-leaf to 

 the extremity of a wasp's 

 wing. The insect was then 

 seized with a pair of for- 

 ceps and held in the sun 

 in front of a dark back- 

 ground, the luminous tra- 

 jectory shaping itself in 

 the form of a lemniscate 

 (Fig. 164). 



FIG. 164. Appearance of a wasp flying in the sun 

 the extremity of the wing- is gilded. After Marey. 



To determine with accuracy the direction taken by the wing at different 

 stages of the trajectory, a small piece of capillary glass tubing was blackened in 

 the smoke of a candle, so that the slightest touch on the glass was sufficient to 

 remove the black coating and show the direction of movement in each limb of 

 the lemniscate. This experiment was arranged as shown in Fig. 165. Different 

 points on the path of movement were tested by the smoked rod, and from the 

 track along which the black had been removed the direction of movement was 

 deduced. This direction is represented in the figure by means of arrows. 



Theory of insect flight " The theory of insect flight," says Marey, 



" may be completely explained from the preceding experiments. The 

 wing, in its to-and-fro move- 

 ment, is bent in various 

 directions by the resistance 

 of the air. Its action is 

 always that of an inclined 

 plane striking against a 

 fluid and utilizing that part 

 of the resistance which is 

 favorable to its onward 

 progression. 



FIG. 165. Experiment to test the direction of move- 



" illlS mechanism IS the mentof an insect's wing: a, a', b, b', different positions 



of the smoked rod. 



same as that of a water- 

 man's scull, which as it moves backwards and forwards is obliquely 

 inclined in opposite directions, each time communicating an impulse 

 to the boat." 



The mechanism in the case of the insect's wing is far simpler, 



