EXTERNAL ANATOMY OF INSECTS. 581 
cuous in Coleoptera. It is usually in them a vertical 
piece, resembling the prophragm in substance, but twice 
its height, of a quadrangular shape with a notch in the 
middle; it fills the sinus of the postdorsolum, the sides 
of which sometimes descend below it. In this Order 
the chamber that it forms with the prophragm is very 
small’, the motions of the elytra requiring no powerful 
apparatus of muscles; but that which it forms with the 
metaphragm, which is appropriated to the muscles 
moving the wings, is very large*. In the Orthoptera 
the anterior chamber is larger than in the preceding 
Order, which proves that ¢egmina are more moved in 
flight than elytra. In the Heteropterous Hemiptera a 
remarkable variation takes place—the anterior being 
larger than the posterior chamber; which last, in fact, 
consists of two, one for each wing: in these the meso- 
phragm towards the abdomen forms an angle, which in 
Pentatoma, &c., is acute; in Belostoma a right angle, 
and in Notonecta an obtuse one. In the two first the 
angle of the mesophragm sends two short diverging 
ridges to the metaphragm; and in the last only a single 
one: in this also the posterior chambers together are 
nearly as large as the anterior. From this structure it 
should seem that in flight the Hemelytra are more im- 
portant than the wings. In the Homopterous section 
the anterior chamber is the smallest, at least in Fulgora 
candelaria ; and the mesophragm is lofty and bipartite. 
In the Lepidoptera the anterior chamber is the largest, 
and the part in question conspicuous’. In the Lvbellu- 
* Prats XXII. Fic. 9. a a. b Tbid. Fic. 11. a. 
© Tbid. b. ¢ Prats IX. Fic, 2. 5’, 
