168 THE WINGS OF NEUROPTERA 



The first radio-medial cross-vein of the hind wings is longitudinal and 

 sigmoid in the subfamily Corydalinas, the genus Ithone, and in the families 



Fig. 162. — Base of hind wing of Hemerobius 



. humiill. 



Polystoechotidae, Sisyridae, Sympherobiids, Hemerobiidae, Dilaridae, and 

 Osmylidae. 



(c) THE WINGS OF THE SIALID^ 



The wings of the Sialidte form an excellent starting point for a study of 

 the methods of specialization of the wings that have been evolved in the 

 order Neuroptera. 



The most characteristic feature of the more highly specialized wings 

 found in this order is the presence of a very perfectly developed pectinately 

 branched radial sector. In one of the two subfamilies of this family the 

 Sialinffi, the modification of the typical dichotomously branched radial 

 sector into a pectinately branched one has not begun; in the other sub- 

 family, the Corydalinas, this modification has taken place; but in some 

 members of this subfamily, as Chauliodes, the modification has not pro- 

 gressed far, consisting merely in the suppression of the dichotomy and the 

 development of one or two accessory veins. 



The tracheation of the wings of nymphs of three of the genera of this 

 family was figured by Comstock and Needham and the result of our 

 studies leaves no doubt as to the homologies of the principal veins. 



The family includes two qtiite distinct subfamilies, the Sialinas and the 

 Corydalinse, which are distinguished by different types of wing-venation. 



The wings of the Sialinae. — The subfamily Sialinae includes only two 

 genera, Sialis and Protosialis. These resemble each other very closely in 

 the more general features of the venation of the wings. As we were able to 

 study the wings of pupae of Sialis infumata, this species is used to illustrate 

 the type of wing venation characteristic of the subfamily. 



Figure 163 represents the tracheation of a wing of a pupa of this species 

 which was photographed when the forming veins appeared as pale bands; 

 and Figure 164 represents the wings of an adult. 



