THE GENERAL FEATURES OF WINGS 



63 



in the wing in this position; in both the longitudinal margin is strength- 

 ened by vein 3dA2. 



The fibula of Corydalus differs in structure from that of Rhyacophila in 

 that it is composed in part of the axillary membrane. It is a triangular, 



backward projecting lobe of 

 the wing, along the middle of 

 which extends vein 3dAo (Fig. 

 50). That part of this fibula 

 that lies distad of this vein is 

 homologous with the jugum of 

 the Hepialidge and the fibula 

 of Rhyacophila; the part lying 

 proximad of this vein is a por- 

 evident from the. fact that it is 



Fig. 48. — Jugum of a hepialid. 



tion of the axillary membrane; this 

 margined by the axillary cord. 



The apex of this fibula, which is strengthened by the tip of vein 3dA2, 

 curves down forming a hook. In the living insect, this hook clasps a fold 

 in the hind wing, which extends from 

 the apex of the anterior tuberosity to 

 the margin of the cubito-anal sulcus. 

 In this manner the two wings are 

 clasped together. 



The relation of the fibula to the 



hind wing can be seen only rarely in 



dried insects. In the spreading of 



specimens the fibula is pulled out of its 



normal position; and in drying both 



the fibula and the fold of the hind 



wing behind which it hooks become 

 1 • 1 J it, j.j.1. ■ 111.- Fig- 49- — VihwXa. oi Rhxacophila. 



shriveled so that their normal relations ' 



are not obvious. The conclusions given above are based on a study of 



living individuals. 



The two types of fibular described above will serve as a basis for more 



extended studies of this organ. Doubtless 

 much material of taxonomic value can be 

 obtained from a study of this part of the wing. 

 But such a study docs not fall \vithin the 

 scope of this essay, the preparation of which 

 was undertaken with special reference to the 

 application of the uniform terminology of the 

 wing-veins. 

 An expanded humeral angle of the hind ivings. — In certain insects the 



humeral angle of the hind wings is greatly expanded so that it projects 



Fig. 50. — Fibula of Corydalus. 



