34t) 



ZOOLOGY. 



katydids, etc., and locusts, produce loud, shrill sounds, 

 ■which are sexual calls. They stridulate in three ways — i.e., 

 first, by rubbing the base of one wing-cover on the other 

 (crickets and green grasshoppers); second, by rubbing the 

 inner surface of the hind legs iiguinst the outer surface of 

 the fi-ont wings (some locusts): third, by rubbing together 

 the upper surface of the front edge of the hind wings and 



Fig, 320. — An African Mantis^ or soothsayer, with its egg-mass. — From Itton- 

 teiro^s Angola. * 



the under surface of the wing-covers during flight (some 

 locusts). 



Order 4. Plalyplera. — This group comprises the bird- 

 lice, Psocidae, Periidae, and white ants {Termitidm). The 

 body is flattened, the head horizontal. The pronotum is 

 usually large, broad, and square. Tlie bird-lice {Mollophaga) 

 are more nearly related to the wingless Psocidffi, such as the 

 death-tick (Atropos) than to the Hemiptcra, among which 

 they are usually placed, since their free jaws and mouth- 

 parts generally are like those of the Psocidae. They prob 



