22 University of California Publications. [Entomology 



bird's wing is different on the two sides, that of an insect pre- 

 sents the same kind of surface to the air in both phases of the 

 stroke, and finally, as pointed out by Amans ('85), the struc- 

 ture of the Hying apparatus as a whole, as w'ell as in every 

 detail of structure, is fundamentally different in the two groups. 



The path of the wing in flight is evidently correlated with 

 the nature of the articulation at the base of the wing, but 

 whether the articular structure requires the wing to pass 

 through the air in the course indicated, or is simply flexible 

 enough to permit the air resistance to force the wing out of 

 what would otherwise be a simple to-and-fro motion, is still a 

 subject of controversy. This latter theory was first pro- 

 pounded by Marey ('69), and was the result of very careful 

 observation and experiment. The opponents of this view 

 include two of the three who have made a serious study of the 

 articulation of the wing. The third, Amans ('85), does not 

 take sides with either party, but expresses himself as incom- 

 petent with only anatomical data to decide the matter. 



The observations of both von Lendenfeldt ('81) and Lowne 

 ('90-95) were confined to single insects with rather complex 

 structure, and in the case of von Lendenfeldt not with the one 

 that was studied for hinge structure. While both of these 

 authors agree that the course of the wing is determined directly 

 and entirely by the muscles of flight and the articular struc- 

 tures at the base of the wing, they differ in a matter of fact of 

 fundamental importance. The point at issue is the direction 

 taken by the wdng in passing over its characteristic path; 

 whether, for instance, the wing when passing over the part of 

 its course farthest above the body as seen from the side is 

 moving forward, as described by von Lendenfeldt, or backward, 

 in conformity with the views of Lowne and ]\Larey. The 

 method employed by von Lendenfeldt, that of photography, 

 gives with perfect accuracy a series of positions which, by 

 attention to the effects of air pressure on the different parts of 

 the wing, should give unmistakable evidence as to the direc- 

 tion in Avhich the wing is moving. We have no means, how- 

 ever, of determining, from the figures given, the correctness of 

 his interpretation of the photographs. In like manner, Marey's 

 results, though doubtless clear to him, can not be correctly 

 interpreted by any one else, because he mentions neither the 

 direction of tlie movement of the cylinder nor the position of 



