1 62 



AN INTRODUCTION TO ENTOMOLOGY. 



this larva moults, rapidly increases in size, and soon commences lay- 

 ing eggs. These in due time give birth to young, which soon 

 become agamic, egg-laying mothers, like the first ; and, like them, 

 always remain wingless. Five or six generations of these parthen- 



FIG. 136. Phylloxera, root-inhabiting form, a shows a healthy root ; , one on which the lice are 

 working, representing the knots and swellings caused by their punctures; <r, a root that has 

 been deserted by them, and where the rootlets have commenced to decay ; d, d, d. shows how 

 the lice are found on the larger roots ; e, female nymph, dorsal view ; f, same, ventral view ; g, 

 winged female, dorsal view ; h^ same, ventral view ; z, magnified antenna of winged insect ; /, 

 side view of the wingless female, laying eggs on roots ; k shows how the punctures of the lice 

 cause the larger roots to rot. (From Riley.) 



ogenetic, egg-bearing, wingless mothers follow each other, when 

 (about the middle of July, in the latitude of St. Louis) some of 

 the individuals begin to acquire wings. Thus is produced the second, 

 or migrating, agamic, winged form (Fig. 136). These issue from 

 the ground while yet in the pupa state ; as soon as they have ac- 



