GALL-FLIES. 545 



hatched, the little grubs, proceeding therefrom, find them- 

 selves comfortably bedded within the pulpy tumors, and 

 plentifully supplied with food on every side. They feed 

 on the vegetable substance immediately around them, come 

 to their growth in due time, cast their skins, and appear 

 first in the chrysalis and then in the winged form, and 

 finally gnaw their way through the hard shell of the galls, 

 and come out into the open air. There are a few of the 

 grubs, however, that leave the galls when fully grown, and 

 finish their transformations in the ground. 



The grubs or young of the gall-flies are of a whitish 

 color, and somewhat resemble maggots, but are shorter 

 and thicker, and have a small, distinct head. They are 

 without proper legs, and move only by means of the swollen 

 edges of their rings, with the aid, it is said, of certain little 

 contractile warts on their bodies, that serve them instead 

 of feet. There are almost as many kinds of galls as there 

 are species of gall-flies ; and each species confines its 

 attacks to some one sort of plant, and to some particular 

 part thereof. It is wonderful that there should be such a 

 diversity in the forms and texture of the galls of insects 

 so nearly resembling each other in form and structure; 

 and, on the other hand, that each species of gall-fly should 

 invariably produce galls of the same kind. Many galls are 

 very irregular and uneven, others are round and resemble 

 fruits ; some are smooth, others are beset with prickles, 

 or covered with a woolly substance; some hang by little 

 stems, others are perfectly flat, and adhere closely to the 

 surface of leaves. At first they are soft or spongy within, 

 but after some time they become hard, and almost or quite 

 woody. The eggs of some gall-flies do not hatch till the 

 galls begin to grow hard on the outside; this is the rea- 

 son why we do not find any insects within certain kinds 

 of galls, so long as they remain soft and unripe. 



The round and hard Aleppo galls, or nutgalls of com- 

 merce, used in the making of ink, in coloring, and in med- 

 69 



