34 University of California Puhlications. [Entomology 



The action of the mechanism of the wing, as shown in Fig. 11, 

 does not resemble in the slightest degree that described and 

 figured by Graber ('77), but indicates an entirely distinct kind 

 of motion. The action of the elevators, which are the princi- 

 pal muscles of flight, results in pulling the whole dorsum of 

 the meso- and metathorax into the thoracic cavity, causing 

 the wings to assume a vertical position. When the tension is 

 released, the wing begins its descent by the expansion of the 

 compressed thoracic contents. Both of the strokes are at the 

 beginning somewhat in the nature of a recoil. The full depres- 

 sion of the wing is brought about by the action of the side 

 muscles of the thorax, which, by contracting the body cavity, 

 force the dorsum outward toward the back, elevating the inner 

 ends of the wing-roots. 



Although von Lendenfeldt's description of the structures is 

 quite full, it is very difficult to identify his parts. Amans 

 evidently experienced difficulty, and gave a new description, 

 much more simple and quite easy to follow. His figures, 

 however, possess more artistic beauty than structural accuracy. 

 Von Lendenfeldt's figures are not better, for the parts that can 

 be identified are grossly inaccurate. It can be safely said that 

 the many small cuticular wrinkles and thickenings that gave 

 occasion to von Lendenfeldt's errors, and the minute muscles 

 described by him and by Amans as attached at various posi- 

 tions in the base of the wings, are of only subordinate impor- 

 tance in flight. 



According to the account given above, the articulation in 

 the case of the wing of a dragonfly is brought about by the 

 expansion of the bases of the veins into a broad wing-root 

 corrugated to correspond with the wing itself, and presenting 

 two broad, flat areas; these become on the under side condyloid 

 cavities fitting the ends of processes developed above the pleu- 

 rites in connection with the interpleural suture. The inner 

 ends of the wing-roots connect by a rather complicated thick- 

 ening of the membrane with the deeply infolded and internally 

 expanded edge of the scutum where the elevator muscle is 

 attached. 



Let us now turn to other insects and see to what extent, if 

 at all, the articulations there found may be reduced to this 

 same type. One of the insects described and figured by Amans, 

 the common harvest fly, is quite favorable for study. One 



