250 INJUEIOUS IKSECT3 



is in strong contrast with the more dusky color of the 

 egg-shell, escapes in the course of two minutes. Issuing 

 from the mouth of the gall, these young'lice scatter over 

 the vine, most of them finding their way to the tender 

 terminal leaves, wliere they settle in the downy bed which 

 these leaves afEords, and commence pumping up and ap- 

 propriating the sap. The tongue-sheath is blunt and 

 heavy, but the tongue proper — consisting of three brown, 

 elastic, and wiry filaments, which, united, make so fine 

 a thread as scarcely to be visible with the strongest mi- 

 croscope — is sharp, and easily run into the leaf. Its 

 puncture causes a curious change in the tissues of the 

 leaf, the growth being so stimulated that the under side 

 bulges and thickens, while the down on the upper side 

 increases in a circle around the louse, and finally hides 

 and covers it as it recedes more and more within the 

 deepening cavity. Sometimes the lice are so crowded 

 that two occupy the same gall. If, from the premature 

 death of the louse, or other cause, the gall becomes abor- 

 tive before being completed, then the circle of thickened 

 down or fuzz enlarges with the expansion of the leaf, and 

 remains (fig. 151, c), to tell the tale of the futile effort. 

 Otherwise, in a few days the gall is formed, and the 

 inheld louse, which, while eating its way into house and 

 home, was also growing apace, begins a parthenogenetic 

 maternity by the deposition of fertile eggs, as her imme- 

 diate parent had done before. She increases in bulk 

 with pregnancy, and one egg follows another in quick 

 succession, until the gall is crowded. The mother dies 

 and shrivels, and the young, as they hatch, issue and 

 found new galls. This process continues during the 

 summer until the fifth or sixth generation. Every egg 

 brings forth a fertile female, which soon becomes wonder- 

 fully prolific. The number of eggs found in a single gall 

 averages about two hundred; 3'et it will sometimes reach 

 as many as five hundred. Even supposing there are but 



