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, wdtli 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- 
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