346 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 against the outer surface of 

 the front wings (some locusts); third, by rubbing together 

 the upper surface of the front edge of the hind wings an<3 



Fig. 320. An African Mantis, or soothsayer, with its egg-mass. From Mon- 

 teiro's Angola. 



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

 locusts). 



Order 4. Platyptera. This group comprises the bird- 

 lice, Psocidae, Perlidae, and white ants (Termitidce). The 

 body is flattened, the head horizontal. The pronotum is 

 usually large, broad, and square. The bird-lice (Mallophaga) 

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

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

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

 parts generally are like those of the Psocida3. They prob- 



