182 



THE WINGS OF NEUROPTERA 



It has been shown, in the preceding section of this chapter, that in the 

 Sympherobiidag the radius of the fore wings has two sectors ; but this result 

 in that family has been brousjht about in a very different way than that 



Fig. 176. — Base of hind wing of Hemerobiiis huniuli. 



just described. In the one case there is a diyision of the stem of the radial 

 sector; in the other, a suppression of this part of the sector, by its coales- 

 cence with vein Ri. 



The separate origin of one or more branches of the radial sector occurs 

 also in the wings of the Dilaridse described in the next section of this 

 chapter, and in an Australian insect recently described by Tillyard ('16 

 p. 279), under the name Ithone fulva. In both of these cases there appears 

 to have been a splitting back of the branches that arise separately, and not 

 a suppression of the stem of the radial sector. This, however, is not per- 

 fectly clear in the case of Ithone ftdva. 



An early stage in the suppression of the stem of the radial sector is 

 shown in the hind wing of Hemerohius himiidi (Fig. 175), where vein R5 has 

 split back nearly to the base of the radial sector, so that it separates from 

 the remainder of the sector, i. e. vein R2+3+4 nearly opposite the anterior 

 end of the first radio-medial cross-vein (Fig. 176). From the point of 



Fig. 177. — Trachcation of a hcmerobiid wing (After C. & N.). 



separation of veins R5 and R2+3+4, the latter extends obliquely forward 

 and anastomoses with vein Ri thus forming a small cell opposite the cell 

 closed by the first radio-medial cross-vein. The extending of the union of 

 veins Ri and R2+3+4 from ^he point where they now anastomose towards 



