620 
THE STUDY OF INSECTS . 
States is a bullet-like gall, which is attached to the small 
twigs, and which measures from one half to two thirds inch 
in diameter. In this gall the central kernel is surrounded 
by a hard, woody substance. 
The Giant Oak-gall, Andricus californicus (An'dri-cus 
cal-i-for'ni-cus.—This is the most common oak-gall of the 
Pacific coast. It is very abundant on the twigs and branches 
of the California white oak, and during the winter, when the 
trees are bare, it is a very conspicuous object. It differs 
from the preceding galls in being of the type termed poly- 
thalamous; that is, instead of containing a single cell, there 
are several cells within it, in each of which a gall-fly is devel¬ 
oped. This gall varies greatly in form and size ; some of the 
larger ones measure ten or twelve inches in their greatest 
circumference. The outer surface of the gall is white, and 
usually smooth. 
The Pithy Blackberry-gall, Diastrophus nebulosus (Di-as'- 
tro-phus neb- 
u-lo'sus), is 
another exam¬ 
ple of a poly- 
thalamous gall. 
It is a large 
woody growth, 
which occurs 
on the stems 
of blackberry. 
It is sometimes 
three inches in 
length and one 
and one-half 
inches in diam¬ 
eter. It varies 
in shape, but 
Fig, 747.— The Mossy Rose-gall, Rhodites rosee . there are al¬ 
ways several wrinkled ridges along the stem. 
