260 SYSTEMATIC ZOOLOGY. 



the time the eggs are laid until the animals are ready to 

 lay another series of eggs. These eggs are laid in the 

 twigs of trees. The young when hatched from these eggs 

 drop to the ground, and, burrowing beneath its surface, 

 spend the next seventeen years * sucking the juices of 

 the roots of the trees. 



Another group of Homopterans are the 'spittle-in- 

 sects, ' small forms which, settling upon a blade of grass 

 or twig of shrub, soon surround themselves with a frothy 

 mass. They suck the juices of the plant, and after having 

 taken out what they desire eject the rest as a mass of foam. 

 Examine one of these bits of froth and you will find the 

 immature bug inside. Allied to them are the tree-hoppers 

 and leaf-hoppers, so common and so injurious to vegeta- 

 tion. 



The plant-lice, or aphides, deserve a little more atten- 

 tion. They occur on almost every kind of plant, sucking 

 its juices and reproducing as rapidly as possible. One 

 does but little damage, but the havoc wrought by thou- 

 sands is very considerable. In the summer the colonies 

 of these forms will be found to be largely wingless, and 

 these wingless forms are all females, capable of reproduc- 

 tion without males. In some species they lay eggs, in 

 others they bring forth living young. These in time 

 reproduce in the same way, and so rapidly do they in- 

 crease that one plant-louse may be the progenitor of 

 100,000,000 in five generations. At the close of the season 

 the true sexual forms appear, the males always winged. 

 These sexual forms produce eggs which last through the 

 winter. All of the plant-lice are destructive to vegeta- 

 tion, and some, like the Phylloxera of the grape, are ex- 

 tremely so. 



* In the South the period is thirteen years, in the North seventeen. 



