616 EXTERNAL ANATOMY OF INSECTS. 



runs obliquely from the vertex of the Anal Area to the 

 base of the Costal. 



4. As to xhew position and folding in repose, Hemelytra 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 precisely 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 apical area, the posterior 

 margins of the tegmina, as they ought rather to be term- 

 ed, unite, but do not lap over each other. With regard 

 to the appearance of something like a phialum, if you ex- 

 amine the hemelytra of most species of bugs on the un- 

 derside, 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 con- 

 spicuous, or even the common Nepa cinerea, you will find 

 in the same situation, adjacent to the inflexed costal ner- 

 vure, a hollow tube running from the base of the wing, 

 and terminating, after proceeding about one-fourth of its 

 length, in a hollow cavity, which, as it is covered by a 

 membrane, appears to me to be a collapsed pouch. This 

 circumstance is worthy of further and more general in- 

 vestigation. 



5. In their shape, with few exceptions, hemelytra more or 

 less represent a wedge, being wider at their apex, where 



