170 



THE WINGS OF NEUROPTERA 



The last mentioned feature is the one to which I wish to call especial 

 attention. The radial sector in this genus is nearly typical in form; the 

 only modification being the development of one or more marginal accessory, 

 veins upon it. These accessory veins, however, are in a quite different 

 position than that occupied by the accessory veins borne by the radial 

 sector in the Corydalinse, where a pectinately branched radial sector has 

 been developed. 



In Sialis the accessory veins are borne by vein R3, instead of vein R2 as 

 in the Corydialinas, and they extend toward the costal margin of the wing. 

 The method of specialization is in a quite different direction than that 

 which produces the pectinately branched radial sector of the Corydalinse. 



The accessory veins borne by vein R3 in Sialis have not attained a 

 permanent form ; they vary in number in different individuals of the same 

 species and in being either simple or forked; for this reason they are not 

 numbered; they are not definitive accessory veins, but are of the type 

 termed marginal accessory veins. Occasionally there are accessory veins 

 on other branches of the radial sector; there is one on vein R4 in the fore 

 wing represented in Figure 164. 



The dichotomously branched radial sector of Sialis, which closely 

 resembles the radial sector of the hypothetical primitive type of wing 

 venation, shows conclusively that the pectinately branched radial sector of 

 the allied genera and of most other Neuroptera, has been derived from the 

 dichotomously branched type. 



The wings of the Corydalinae. — The wings of the members of the sub- 

 family Corydalinse present a very different appearance from those of Sialis; 

 this is due largely to the fact that in the Corydalinae a pectinately branched 



^^^ 



Fig. 165. — Wing of a i)uixi of Chaidiodes pectinicornis (After C. & N.). 



radial sector has been developed, while in Sialis this vein lias retained the 

 dichotomoiis type of l:)ranching, modified only by the addition of a limited 

 number of marginal accessory veins. 



