THE THORAX. 9f> 



elytra or hemelytra ; for sometimes they are shorter than the body, 

 broad, ovate (Gryllotalpa) ; sometimes as long, with parallel sides, 

 rounded (Blatta) ; sometimes longer, very slender, acute, and narrowed 

 at the base ( Gryllus, Fabr.) ; and sometimes very wide, large, and ellip- 

 tical (Mantis'). By means of the veins originating from a main stem, 

 which furcate from the very base, they are divided into three prin- 

 cipal areas; the first of which, seated upon the exterior margin (PI. XV. 

 f. 2, A), is in general the narrowest, and towards the apex of the 

 tegmina contracts gradually to a point ; it is also usually of a harder 

 substance than the following. This second piece (PI. XV. f. 2, B) 

 lies contiguous to the former, and is separated from it by the before- 

 mentioned chief vein ; it is the largest of the three areas, embraces the 

 majority of the ramifications of the veins, becomes gradually wider 

 towards the apex of the wing, and consists of a softer membrane than 

 the marginal area. The third, or sutural area (PI. XV. f. 2, c), lies 

 inwardly beyond the second, and it is also harder than the central area ; 

 in many families it forms the superior dorsal covering, while the two 

 other areas fall down upon the sides of the body (Gryllodea, Locusturia) . 

 It varies considerably in figure ; it, like the marginal area, is sometimes 

 a very pointed isosceles triangle (Gryllodca); sometimes, as in the hem- 

 elytra, a space surrounding the scutellum (Achetaria) ; it also some- 

 times appears to be wanting, or not distinctly separated from the cen- 

 tral area (Mantodea). 



There seems likewise to be some difference in the ramification of the 

 horny veins throughout these three areas ; in the marginal one they are 

 small, broad, multitudinously divided veins, which appear to spread 

 from two or three radiating main branches. In the central area, the 

 large stems spread more parallelly from the inner side of the chief stem, 

 which separates them ; the transverse veins also run parallel, and thus 

 divide the whole area into small squares. In the inner area, lastly, the 

 veins are most delicate, and ramify variously on all sides, whereby an 

 irregular reticulation is formed. 



80. 



The mere membranous wings (/) distinctly differ from the pre- 

 ceding organs by their transparency, and purely membranous nature. 

 In respect to their situation and general function, they perfectly agree 

 with the former ; but the wings are exclusively organs of flight, while 



