Packard.] 
INSECTS AS ARCHITECTS. 
311 
the exception of the Termites, present such evidences of 
mechanical skill as the bees and wasps and ants. The 
Hymenoptera, of which they are the most familiar examples, 
were among the latest insects to appear on the surface of 
the earth. The lower forms, so far as the scanty records 
show, appeared first in the Jurassic rocks, while the ants are 
first found in the amber of the Tertiary period, so that the 
ants and wasps and bees were in all probability among the 
latest insect creations. This inference is borne out by 
the fact that the individuals and species are very abundant. 
Did they belong to an ancient stock their numbers would 
have been thinned out. 
The lowest hymenopterous insect which lives in a house 
of its own, not, however, made with its own hands, is a kind 
of saw-fly (Euura), which constructs a gall. The female 
lays an egg in the bud of a willow ; the presence of the egg 
sets up an irritation, causes an unnatural enlargement of the 
bud-leaves, until a round swelling or tumor is formed, in 
which the false-caterpillar lives and feeds on the walls of its 
house, which grows with its growth. Mr. Walsh has studied 
these gall saw-flies. The gall in which Euura orbitalis lives 
is at first a bud which is enlarged two or three times its 
natural size before it unfolds in spring. In the autumn it 
bores through the walls of its dwelling, and descends to the 
ground, burrowing an inch deep below the surface. Here it 
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