EXTERNAL ANATOMY OF INSECTS. 639 
gate the apical margin. In the Vespid@ the upper wings 
are folded longitudinally into three nearly equal portions, 
but in the wnder ones the Anal Area only forms the fold. 
In the Diptera Order, as to their position when at rest, 
the wings are mostly incumbent one on the other ; but in 
Psychoda they are deflexed, so as to form a kind of pent- 
house. With regard to their plication, in some, Tipula 
oleracea, &c., a slight oblique semifold runs from the 
stigma to the apical margin, and the Anal Area has two, 
as it has in many Muscidae, itself forming nearly a right 
angle with the rest of the wing; besides these it is cor- 
rugated with minute transverse semifolds, which are ob- 
servable also in several other Dipterous insects; in many 
Stratyomideé they are oblique, and run from the disk to 
the posterior margin; and in Asilus, Bombylius, &c., 
they are wavy. 
5. We are next to say something upon the shape of 
wings: this, though apparently extremely various in the 
different Orders and tribes, may I think be traced in 
every wing to one original prototype, a triangle with the 
largest angle rounded and subtended by the anterior or 
costal margin: in some, as the Coleoptera, Orthoptera, 
&c., this type of formation is a right-angled triangle ? ; 
and in others, as in the Hymenoptera, Diptera, &c., the 
majority of the Neuroptera, &c., it is an obtusangled one?; 
it may be further observed, that in receding from these 
forms wings very often assume that of the half or qua- 
drant of some regular figure, as we shall see when we 
consider those of the different Orders. Another general 
observation I shall first mention,—that these organs are 
* Prate X. Fic. 4, 5. and XXVIIL Fic. 21, 22. 
> PrateE X, Fic. 6—14, 
