^0.1331. DRAG OX-FLY WINa YENATIOX—NEEDHAM. 753 



inipid vibration in air. Botii have developed at the wing base close 

 again.st the body a broad soaring surface, an aero-plane, which in 

 rapid flight supports the weight of the body upon the resistant air. 

 [Wings of broad base and pointed apex are characteristic of other 

 finsects of rapid flight, but in most others (hawk moths, cicadas, bees, 

 etc.) the two wings are united and used as one. The })asal expanse is 

 'Secured by shortening the hind wing and directing it posteriorly. 

 Difl'erent as are the wings of birds, these also are sharply pointed in 

 the species of swiftest flight (ducks, swallows, etc.). I can not state 

 ithe aeronautic principle involved in the pointed wing, but I ask no 

 better proof of its existence than is furnished b}" the efScienc}" of 

 s,\xc\i a wing and its repeated independent development. 

 I, In the arrangement of the principal veins we have called attention 

 to the fact that the Odonata, except in the earliest stages, difl'er very 

 widely from all other insects. There is hardly a group from which 

 'they difl'er more in fundamental plan than the Ascalaphida?. The latter 



Fig. 41.— Wing of Vedali^ amoena Sei.ys. 



have the radial sector enormously developed and in its accustomed 

 place, occupying the central held of the wing, while the media is 

 greatly reduced; in the Odonata the development of these parts is 

 reversed and the radial sector is out of place. The differences at the 

 costal border of the wings is so great that I will only invite compari- 

 son of the Ascalaphid wing in Plate XXXVI, fig. 2, with the wing of 

 any dragon-fly. If now, without reference to homologies, we examine 

 this wing of Ulida, we will see in it familiar mechanical features. 

 (1) From the stigma there extends obliquel}- across the wing tip to 

 the posterior margin a vein whicli occupies the position, and probably 

 performs the function, of the vein J/j^ in the Odonata. (2) Inter- 

 secting the wing obliqueh% so as to mark ofl' a basal posterior tliird 



pied in the two cases. In the echinoderm the area is symmetrical, and new rows are 

 introduced alternately on the two sides. In the dragon-fly wing the space is uni- 

 lateral, as shown in the diagram, and the rows are introduced chiefly upon the 

 anterior, convex side. The principle is the same; ])ut we should not omit to notice 

 how different are the two things whose arrangement it controls — in the one case, 

 solid plates; in the other, a mere rim of solid matter surrounding an almost emi)ty 

 i'pace. 



