MANUAL OF NATUEAL HISTORY, 215 



loped, powerful, toothed ; antennae very short ; 

 abdomen long, cylindrical or depressed ; wings 

 long, of equal size, carried separately and 

 horizontally when at rest. Flight quick and 

 powerful. 



4. Family. — Willow-Flies (Perlidae). Head broad; 



eyes prominent, wide apart; antennae long, 

 filiform, composed of many joints ; body de- 

 pressed ; abdomen sometimes terminated by 

 two slender filaments ; wings longer than 

 abdomen, recumbent, posterior pair largest, 

 and folded when at rest. 



5. Family. — White-Ants (Termitidae). Head and 



body depressed, abdomen flat and composed 

 of narrow segments ; mandibles strong and 

 horny, toothed ; maxillae terminated by hook- 

 ed teeth ; antennae of moderate length, mo- 

 niliform ; legs rather short ; wings narrow, 

 of equal size, nearly twice the length of body, 

 not much reticulated, semi-transparent. Only 

 males and females have wings, neuters are 

 apterous, and have the head large and the 

 mandibles very long. 



6. Family. — Book-Insects (Psocidae). Size small ; 



head large ; eyes rather prominent ; antennae 

 long and setaceous ; body short, soft, ovate ; 

 anterior wings larger than posterior, which 

 are slightly folded, deflected when closed, 

 Often found among books and old papers. 



7. Family. —Thunder-Flies (Thripidae). Head ob- 



long; eyes large, distant, placed forward; 



