CHAPTEE XVII 



NEUROPTERA CONTINUED PSOCIDAE (BOOK - LICE AND DEATH- 



WATCHES) THE FIRST FAMILY OF AMPHIBIOUS NEUROPTERA 



(PERLIDAE, STONE-FLIES). 



Fam. IV. Psocidae Book-Lice, Death- Watches. 



Minute Insects with slender, thread-like, or hair-like antennae ; 

 four delicate membranous wings, the front pair of which are 



the larger; their neuration is not 

 ^~ abundant and is irregular, so that 

 the cells are also irregularly ar- 

 ranged ; the transverse nervules are 

 only one or two in number. 1 Pro- 

 thorax very small, in the winged 



FIG. UI.-PSOCUS fascwtus,f orms 2 uite concealed between the 

 England. (After M'Lachlan.) head and the large mesothorax ; this 

 latter closely connected with, or fused 



with, the metathorax. Species quite wingless, or with wings 

 unfitted for flight, exist ; in them the prothorax is not so ex- 

 tremely small, while the mesothorax is smaller than in the 

 ivinged forms. Tarsi of two or three segments. Metamorphosis 

 slight, marked chiefly by the development of wings and ocelli. 



THE Psocidae are without exception small and soft-bodied Insects, 

 and are only known to those who are not entomologists by the 

 wingless forms that run about in uninhabited or quiet apart- 

 ments, and are called dust-lice or book-lice. They are perhaps 

 more similar to Termitidae than to any other Insects, but 

 the two families differ much in the structure of their wings, and 

 are totally dissimilar in the nature of their lives. 

 1 In some exotic species there is a dense network on a part of the anterior wing. 



