332 



AN INTRODUCTION TO ENTOMOLOGY 



side. Note that the figure is a ventral view, hence the paragnathus 

 is represented as passing beneath the maxilla. The paragnatha have 



Fig. 379. — The wings of a psocid. 



been known as the fur ccb maxillares. The labium {C) bears a pair of 

 one-jointed palpi. 



The venation of the wings is distinctively characteristic in this order. 

 The venation is more or less reduced; but its most characteristic 

 feature is the bracing of the wing by anastomoses of the principal 



Fig. 380. — Fore wing of a full-grown nymph of a psocid. 



veins instead of by cross-veins. This is well shown by the wings of 

 Psocus (Fig. 379). The determination of the homologies of the 

 wing-veins in this insect was accomplished by a study of the trachea- 

 tion of the wings of nymphs. Figure 380 represents the tracheation 

 of a fore wing of a full-grown nymph of Psocus. 



There are no cross-veins in the wings of Psocus; the arculus (ar) 

 in the fore wing is merely the base of media, and what appear as 



