346 ZOOLOGY. 
katydids, etc., and iocusts, produce loud, shrill sounds, 
which are sexual calls. They stridulate in three ways—.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 and 
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, Psocide, Perlidw, and white ants (Zermitide). 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 Psocidex, 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 Psocide. They prob- 
