ORDER CORRODENTIA 253 



in the same order with the termites, or with the Orthoptera. The wings, 

 when they are present, are like those of termites in form and in being 

 all alike, but they are not caducous, and they have a peculiar imperfect 

 venation. The species are found in sheltered places, under stones, on 

 bark, in wood and thatch, etc., and they spin webs for protection. 



Order CORRODENTiA : Book-lice. 

 (Lat. corrodere = to gnaw.) 



This order stands for a single family, the PsocidcB (? Gr. 

 \/f60X<'? = *^"st), which are sometimes included in the Isoptera 

 and sometimes in the Orthoptera. 



Book-lice (Fig. 115) are soft-bodied, and for the most 

 part exceedingly minute insects, so named because certain 



Fig. 115. — " Book -louse," from dried fish. 



species are commonly found in old books, eating the binding. 

 They are also frequent pests of entomological collections, 

 feeding not only upon the lining of the trays but also upon 

 the specimens, and they will sometimes attack dried 

 provisions. 



The head and eyes are (relatively) large, and the antennae 

 are long and very slender : the mouth-parts are formed for 

 biting. The thorax usually appears to consist of 2 segments. 

 Metamorphosis incomplete. In the winged species both 

 pairs of wings are membranous, the anteriov pair being the 

 larger, and the veins are sinuous and prominent, the cross- 

 veins being few. 



Many Psocids live in moss, lichen, the bark of trees, etc., 



