166 



THE WINGS OF NEUROPTERA 



Gradate veins. — In many Neuroptera one or more series of cross-veins 

 extend across the wing and form with sections of the longitudinal veins 

 that they connect a very regular zigzag line; such cross-veins are termed 

 gradate veins; there is a well-developed series of gradate veins parallel with 

 the outer margin in each of the wings of Osmylus hyalinatus (Fig. i6i), and 

 a second, less perfect series proximad of this one. 



The recurrent vein. — In many families of the Neuroptera the humeral 

 cross-vein curves back toward the base of the wing and bears branches, 



'^Snzzzi77f'////////////rA 



Fig. l6l. — Wings of Osmylus hyalinatus, showing gradate veins. 



when of this form it is designated as the recurrent vein. The statement 

 often made in descriptions of Neuroptera that there is no recurrent vein 

 does not indicate the absence of the humeral cross-vein, but merely that 

 this vein is not recurved and branched. 



The coalescence of veins So and Rj. — In many families, veins Sc and Ri 

 come together in the outer part of the wing and appear to be continued as a 

 single vein, which is designated as vein Sc+Ri. This apparent coalescence 

 of these two veins, or the lack of it, is commonly considered an important 

 characteristic, and is frequently mentioned in diagnoses of families. 



I believe, however, that in some cases, where there appears to be a 

 coalescence of these two veins, vein Sc ends upon vein Ri at the point 



