ENTOMOLOGY. 
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hairs assume a lanceolate shape, and spring like small 
leaflets from each side of the longitudinal nervures. 
In assuming this form, they make an approach to the 
scales of the Lepidoptera. These hairs, doubtless, 
serve the purpose of preserving the wings from the 
lacerations to which they would be exposed from the 
nature of the places which the insects frequent for 
food ; and, particularly, in the case of many of them, 
when constructing tlieir nests. In addition to this 
use, M. Chabricr is of opinion that they may likewise 
contribute to fix the atmospheric fluid on the wings 
during flight, and thereby increase their buoyancy. 
The ribs alluded to, ramifying over the surface of 
the wing, are properly called nervures . They are 
horny tubes, whose office it is to support and give 
tension to the membrane. A transverse section 
shews that they contain a soft parenchyma, and a 
large spiral vessel, accompanied by a fine nerve. 
This spiral vessel is a genuine trachea, emanating 
from the cavity of the thorax, and therefore adapted 
for conveying air throughout the wing. The nervures 
are usually uninterrupted, but in some instances, 
particularly among the Hymenoptera, (especially such 
as have a petiolated abdomen,) tlieir continuity is 
frequently broken. This takes place chiefly at the 
points where they anastomose with each other, and 
the place where it occurs presents the appearance of 
a small transparent spot, resembling an air bubble, 
which led Jurine, who first noticed it, to call it a 
bulla. The nervures there lose their tubular form, 
rnd become scattered in the shape of very fine 
H 
