432 INSECTS INJURIOUS TO VEGETATION. 



plants, are followed by swellings of the wounded parts, which 

 increase rapidly in size, and become spongy or pulpy within. 

 The thin-skinned eggs, dropped into the punctures, grow 

 awhile, by absorbing the sap around them, and, when at length 

 they are hatched, the little grubs, proceeding therefrom, find 

 themselves 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 trans- 

 formations 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-fiies; 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 tifl the gafls 

 begin to grow hard on the outside ; this is the reason why we 

 do not find any insects within certain kinds of gaUs, so long 

 as they remain soft and unripe. The round and hard Aleppo 

 galls, or nutgalls of commerce, used in the making of ink, in 

 coloring, and in medicine, are caused by the punctures of the 



