346 



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. *_ 



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



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



surface, c, winged form. (From 



Sedgwick's Zoology.) APHIDHD.E, Fig. 276) are of con- 



siderable biological and economic 



importance. They are very small (less than f 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 FIG. 277. Order HEMIPTERA. San 



twicrs of annle trees the Jos< scale ' As P idiotus perniciosus, on 



" pear. Above, single scale enlarged. 

 " green fly " injures wheat, (After Howard.) 



