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University of California Publications. [Entomology 



described, but its direction would be reversed. Undoubtedly 

 this tendency to bagging is a factor in the flight of all insects, 

 unless the wing is so stiff as not to bend appreciably during a 

 stroke; but in a beetle it becomes of high importance, if not, 

 indeed, the controlling factor. As far as I know, the question 

 of the direction in which the wing moves' during the flight of a 

 beetle has not been investigated. 



A second force which modifies the stroke of the wing is the 

 action of the wing muscles directly attached to the base of the 

 wing, of which quite a numl)er have been descril)ed. B}^ 

 means of these muscles the wing can be pulled forward and 



backward; moreover, 

 the angle which its plane 

 makes with the frontal 

 plane of the body can be 

 varied. These muscles 

 are evidentl}^ the means 

 by which the insect varies 

 the precise nature of 

 the stroke of the wing, 

 and also doubtless in 

 most insects they are 

 the means of placing the 

 wing into most of the 

 positions of rest assumed by this organ in different insects and 

 of bringing it again into position for action. 



If the action of any one of these muscles should become 

 synchronized with either set of the muscles producing the 

 wing strokes, it would doubtless greatly modify the path of the 

 wing. The muscles which Amans denominates the preaxil- 

 laries or anteaxillaries pull the wing forward; the postaxillaries 

 pull it backward. With such a curve as occurs in Pieris a 

 preaxillary or an anteaxillary would augment the width of a 

 curve, and a postaxillary diminish or reverse it. 



Supposing that such a synchronization occurred, it is prob- 

 able that in most cases there would not be an equal association 

 of axillary muscles with both systems of primary muscles, so 

 that the probable effect would be the exaggeration in the size 

 of one loop of the curve. An exaggeration of this kind, though 

 I can not state if for this cause, is exhibited by the posterior 

 loop in a side view of the curve in Agrion (Fig. 7). 



FIG. 7. Agrion, showing figure 8 patli of wing 

 as seen from above and from the side. 

 A, position of wing when ready to fly. B, po- 

 sition of complete rest. C, position of rest with 

 expanded wings. 



