626 EXTERNAL ANATOMY OF INSECTS. 
faces; it is thus capable of greater tension and relaxation, 
and more flexile.© The stigma or carpus*, though most 
conspicuous in the Hymenoptera Order, may be traced in 
some Coleoptera, Heteropterous Hemiptera, the Libel- 
lulina, &c.; but it has no representative in the Ortho- 
ptera, Lepidoptera, Trichoptera, &c. The mediastinal is 
usually a very slender nervure, placed between the costa 
and postcosta, sometimes terminating in the former, and 
at others in the latter ©: inthe Orthoptera, Lepidoptera, 
&c., however, and some others, it is a very conspicuous 
and principal one‘; in the Hymenoptera it is obsolete, 
merging in thosenervures*. The Postcosta is the prin- 
cipal nervure of the wing in Scuéellera, but in Staphylinus 
it is wanting; in Chalcis sispes it is the only true nervure 
of that organ, the others being represented by spurious 
ones*. The externomedial and internomedial are some- 
times distinct at their origin, but more frequently are 
branches from a common stem. 
Having made these general remarks, I shall now con- 
sider particularly the neuration of the wings in the dif- 
ferent Orders, beginning with the Coleoptera. The first 
thing that strikes the physiologist in surveying a wing 
belonging to an insect of this Order, is the general 
arrangement of the nervures ‘; which are so placed that 
the required degree of tension may be given to every 
part of this organ: thus some are nearly straight & ; 
others run in a serpentine direction"; others are forked 
with one branch recurrent and another proceeding on- 
* Prate X. Fie. 4, 11, m’”’. > Ibid. Fie. 14. k. 
* Ibid. Fic. 12. 4. 4 Ibid. Fic. 8, 9. 
© Jurine Hymenopt. t. v. Gen. 47. f Prate X. Fic. 4. 
© Ibid. a. :, 0°. h bid. m”. 
