34^ 



COLLEGE ZOOLOGY 



is the dog-louse, H. urius, the 

 hog-louse, and H. spinulosus, 

 the rat-louse. 



(2) Homoptera (Plant-lice, 

 Scale Insects, Cicadas, Tree 

 Hoppers, Spittle Insects, Figs. 

 276-278). The Homoptera have 

 wings, when present, similar in 

 thickness, and a jointed beak 

 which arises from the posterior, 



Fig. 276. — Order Hemiptera. . c , 11 



Grape-louse, Phylloxera vastatrix. ventral part of the head. 



a, wingless form, b, same, ventral The plant-liceoraphids (Family 



surface c winged form. (From „. ,\ r 



Sedgwick's ZoologV) Aphtdiid^, Fig. 276) are of con- 



siderable biological and economic 

 importance. They are very small (less than | inch), but ex- 

 tremely prolific. In summer certain females, called the stem 

 mothers, bring forth living 

 young which have developed 

 within their bodies from 

 unfertilized eggs. In the au- 

 tumn fertilized eggs are laid, 

 which serve to carry the 

 race through the winter. 

 Many aphids are very de- 

 structive to vegetation. The 

 grape-phylloxera , Phylloxera 

 vastatrix (Fig. 276), is the 

 most notorious; it punctures 

 the roots of grape-vines, 

 causing decay or " cancer " 

 and the formation of tuber- 

 cles. The woolly apple- 

 aphis attacks the roots and 

 twigs of apple trees ; the 



green fly" injures wheat, (After Howard.) 



Fig. 277. — Order Hemiptera. San 

 Jose scale, Aspidiotus perniciosus, on 

 pear. Above, single scale enlarged. 



