208 
SYSTEMATIC ARRANGEMENT. 
the inner edges approximate when dosed, hut the 
one usually overlaps the other. Although, for the 
most part semi-membranous, they vary considerably 
in consistency in different tribes. In certain species 
of Mantis, for example, they nearly assume the 
appearance of transparent reticulated wings, while 
among the convex-backed Blattce they approach 
to the rigidity of elytra. They are generally re- 
ticulated by a series of strong nervures, radiating 
from the base to the summit, and crossed by a 
multitude of smaller ones, resembling fine lace. 
Sometimes, however, these nervures are visible only 
at the apex of the tegmina, but their existence is 
always obvious on the under side. Among the 
GryUi, the males of which are provided with a musical 
apparatus, situated at the base of the abdomen, some 
of the nervures are much more prominent than others, 
and instead of being longitudinal, are curved in a 
variety of ways; it iB by rubbing these against the 
apparatus mentioned, that these insects produce the 
peculiar noise for which they are remarkable. 
The under w r ings being adapted solely for flight, 
are of a much more delicate texture than the superior 
pair. They are traversed by a scries of pretty strong 
parallel nervures, diverging from the base, and are 
folded up and expanded nearly in the same manner 
as a fan. From this cause they cannot be packed 
in so small a compass as in beetles, the wings of 
which are folded transversely upon themselves ; ac- 
cordingly, they are not always quite covered by the 
tegmina when at rest, and in some instances they 
