E BE RH ARTS OUTLINES OF 



make so fine a thread as scarcely to be visible with the 

 strongest microscope — is sharp, and easily run into a 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 abortive before being completed, 

 then the circle of thickened down or fuzz enlarges with the 

 expansion of the leaf, and remains 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, is also growing apace, begins a parthenoge- 

 netic maternity by the deposition of fertile eggs, as her im- 

 mediate parent had done before. She increases in bulk 

 with pregnancy, and one egg follows another in quick suc- 

 cession 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 wonderfully prolific. The 

 number of eggs found in a single gall averages about two 

 hundred; yet it will sometimes reach as many as five hun- 

 dred. Even supposing there are but five generations during 

 the year, and taking the lowest of the above figures, ••he 

 immense prolificacy of the species becomes manifest. As 

 summer advances, they frequently become prodigiously multi- 

 plied, completely covering the leaves with their galls. The lice 

 also settle on the tendrils, leaf-stalks and tender branches, 

 where they also form knots and rounded excrescences much 



