180 THE WINGS OF NEUROPl ERA 



This peculiar method of speciaUzation of the radius may be termed the 

 division of the stem of the radial sector. 



The radial sector of the fore wing of Sympherobius is very similar to that 

 of Sisyra (Fig. 172), except for the switching of the base of vein R2+3- 



Fig. 174. — Fore wing of Sympherobius showing the probable primitive type 

 of radial sector, the dotted line indicates the present course of vein R2+3. 



Figure 174 is a copy of the figure of the fore wing of Sympherobius amicidiis 

 given above (Fig. 173) except that a slight change is made in the course of 

 the base of vein R2+3 and of the cross- vein associated with it the two veins 

 being brought into their probable position before the switching of vein 

 R2+3 began; with these changes in Sympherobius the radial sectors of the 

 two genera are strikingly alike. The dotted line in Figure 174 indicates 

 the present position of vein R2+3. 



In the Sympherobiidae the number of the branches of the radial sector 

 has not been increased; this vein being four-branched in both fore and hind 

 wings; but the tips of all of the branches are forked. The costal area of 

 the fore wings is broad toward the base of the wing; the humeral vein is 

 recurved and branched; and marginal dashes are present. 



{i) THE WINGS OF THE HEMEROBIID.-E 



After the separation from the Hemerobiidae of the Sisyridse, Symphero- 

 biidae, Dilaridee, and Polystoechotidas, all of which were included in this 

 family until quite recently, there remains a group of genera that is charac- 

 terized by a distinctive manner of specialization of the radius of the fore 

 wings. This feature is a coalescence of vein Ri and the stem of the pec- 

 tinately branched radial sector, which results in what may be termed the 

 suppression of the stem of the radial sector. 



In this family the migration of the base of vein R^ towards the base of 

 the wing that is seen in the two preceding families has progressed to an even 

 greater extent. The combination of this factor with the suppression of the 



