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473 
develops on the leaf, but which after reaching full growth falls off, when the 
Fig. 665.—The giant gall of the California white oak, produced by Andricus californicus; 
at right a gall cut open to show inside structure. (After Jordan and Kellogg; one- 
half natural size.) 
wriggling of the still active larva within causes it to roll about or even spring 
a quarter of an inch or more into the air. 
Of the rose-galls Comstock mentions 
the mossy rose-gall, produced by Rhodites 
rosce, as a very common one on the sweet- 
brier. It consists of a large number of 
hard kernels surrounding the branch and 
covered with reddish or green mossy 
filaments. In each kernel is a larva. 
The pith blackberry - gall, Diastrophus 
nebulosus, is a common, many-chambered, 
large, woody gall that occurs on black¬ 
berry - canes. It attains a length of 3 
inches and a width of 1 inch to i| inches. 
Regarding the wonderful instinct of 
the gall-fly, I quote the following from 
Stratton, an English student of galls: 
■ “It is impossible that intelligence or 
memory can be of any use in guiding the 
Cynipidae; no Cynips ever sees its young, 
and none ever pricks buds a second season, 
or lives to know the results that follow 
the act. Natural selection alone has pre¬ 
served an impulse which is released by 
seasonally recurring feelings, sights, or 
smells, and by the simultaneous ripening of the eggs within the fly. 
Fig. 666 .—Jumping galls of the oak 
produced by Cynips quercus-sal - 
tatrix. (Galls on leaf of natural 
size; at left a single gall much 
enlarged.) 
