68 INSECT LIFE. 



queens, also occur. A mature, egg-laying queen is 

 presumably present in each nest; but this form of 

 our common species has not yet been found. Fig. 42 

 represents an egg-laying queen of an African species. 

 The name of this order is from two Greek words : 

 isos, equal, and pteron, a wing. It refers to the fact 

 that the two pairs of wings are similar in form and 

 structure. 



Order Corrodentia (Cor-ro-den'ti-a). 

 The Psocids {Psoc'ids) and. the Book-lice. 



The winged members oj this order have four m.em- 

 hranous wings, with the veins prom.inent, but with com- 

 paratively few cross-veins ; the fore wings are larger 

 than the hind wings ; and both pairs when not in use are 

 placed rooflike over the body, being almost vertical, and 

 not folded in plaits. The mouth-parts are formed for 

 biting. The metamorphosis is incomplete. 



The winged members of this order feed upon 

 lichens and are found on the trunks of trees and on 



fences ; they 



often occur in 



swarms. Fig. 



43 represents a 



common form. 



with its wings 



spread. 

 Tj,^ '^ . * .. The most fig. 44.— a book- 



FIG. 43.-A pSOCld. ^„3^ 



laminar repre- 

 sentative of the wingless forms is the book-louse 

 (Fig. 44). This is a minute insect which occurs be- 

 tween the leaves of old books and on papered walls 

 of houses. 



