614 EXTERNAL ANATOMY OF INSECTS. 
and in Aradus depressus the corium,—divided, however, 
though indistinctly, into the three areas,—is driven to 
the base of the wing: two ends are answered by this 
structure—as this insect lives under bark, its thin he- 
melytra take less room ; and as it flies, though it has only 
rudiments of wings, they are more fit to supply their 
place: the part we are speaking of usually runs obliquely 
from the vertex of the Anal Area to the base of the 
Costal. 
4. As to their position, and folding in repose, He- 
melytra are usually nearly or altogether horizontal ; but 
in Notonecta and Plea they are deflexed and cover the 
sides of the body; and the apical area of one wing pre- 
cisely covers that of the other; where. the scutellum 
does not intervene, as in Scutellera, Pentatoma, &c., the 
vertical angles of the Anal Area meet in the middle of 
the back, so as to exhibit the appearance of a cross, In 
Notonecta, in which the hemelytra are deflexed, at the 
apex of the membrana is a fissure which permits the two 
sides to form an angle with each other, and to apply 
exactly to the body. In Plea, in which there is no api- 
cal area, the posterior margins of the ¢egmina, as they 
ought rather to be termed, unite, but do not lap over 
each other. With regard to the appearance of some- 
thing like a phialum, if you examine the hemelytra of 
most species of bugs on the underside, you will see that 
the costal nervure at the base is inflexed and covers a 
kind of channel; if you next take one of Belostoma 
grandis, where the structure is most conspicuous, or 
even the common Nepa, cinerea, you will find in the 
same situation, adjacent to the inflexed costal nervure, 
a hollow tube running from the base of the wing, and 
