148 



THE WINGS OF NEUROPTERA 



from the supporting stem of the pectinate vein; and third, by the coales- 

 cence of veins R4 and R5, which would obliterate the forking of these veins. 

 The accompanying series of diagrams (Fig. 138) illustrates these changes. 

 The first diagram (Fig. 138, i) represents the manner of branching of the 

 typical radius in which the radial sector is dichotomously branched. The 



.^j second diagram represents 



/ „ ■ — — o a radius in which the radial 



sector has become pecti- 

 nate by the splitting apart 

 of veins R4 and R5, so that 

 they arise separately from 

 the supporting stem of the 

 pectinate vein thus f oraied. 

 This represents the sim- 

 plest type of a pectinately 

 branched radial sector. 

 An illustration of this 

 simplest type is afforded 

 by the wings of Sisyra 

 (Fig. 139)- 



In comparatively few 

 cases is a pectinately 

 branched radial sector so 

 simple as that of Sisyra; 

 usvially a pectinate sector 

 bears more than four 

 branches; this is the 

 result of the development 

 of accessory veins on the 

 posterior side of vein R2. 

 The third diagram (Fig. 

 138, 3) represents a radial 

 sector in which vein R2 

 bears two accessory veins, 

 labeled R2a and Rob; this 

 condition exists in the wing 

 of ChauUodes (Fig. 140); in the wings of Polysiccchoies (Fig. 141) the 

 addition of accessory veins to vein Ro has been carried to a much greater 

 extent. 



The second method of suppression of the dichotomy of the radial 

 sector occurs in* the wings of certain insects in which there are many cross- 

 veins. In these cases the base of vein R4 has become connected with a 

 cross-vein, perhaj)S by splitting back until the cross-vein is reached, and 



Flig. 138. — Diagrams of several types of radius. 



