Vol. 1.] 



Woodivorth. — Wi7ig Veins of Insects. 



27 



This same unsymmetrical path could result from air pressure, 

 if the angle of the wing were different in the two strokes, as 

 might be produced by peculiarities of the hinge structure, in 

 which different bearing joints are brought into operation in the 

 two strokes, the wing lying free between them when at rest. 

 Another way in which the character of the curve might be 

 influenced by the hinge structure is by the development of a 

 catch which should restrain the wing at one or both ends of its 

 course while the wing is traveling in one direction, and not 

 affect it on the return stroke. The sudden release of the wing 

 from this catch would result in an immediate change in the 



FIG. 8. Diagram of the stroke of the 

 wing in the blowfly, according to Lowne. 



F, point at which there is a sudden 

 change of direction. 



FIG. 9. Diagram illustrat- 

 ing tiight oi Pnnlia rapu'. A 

 and B, two positions of wing. 

 EFGH, a phme intersecting 

 the wings at I and J. K, path 

 of motion. 



direction of motion. In this way there would be produced just 

 such an angle as is given by Lowne at point F (see Fig. 8) in 

 the path of the tip of the wing in a blowfly, at which place, 

 according to his account, "the hammulus escapes from the 

 uncinate sclerite." This would produce an unsymmetrical 

 curve, unless an exactly similar structure were developed at 

 the opposite point. This is probably never accomplished, and 

 an influence of this kind on wing motion is of only secondary 

 importance, if indeed it ever occurs. 



The three methods of modifying the stroke described above 

 may all be considered as possibly operating in particular 

 cases, but only one factor — air pressure — is invariably present. 

 A wing with a simple up and down stroke modified only by 

 the influence of air pressure may be considered as representing 



