EXTERNAL ANATOMY OF INSECTS. 641 



stigma to the apical margin, and the Anal Areahastwo, as it 

 has in many Muscidcc, itself forming nearly a right angle 

 with the rest of the wing; besides these it is corrugated 

 with minute transverse semifolds, whichare observable also 

 in several other Dipterous insects; in many Stratyomidte 

 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 a ; and in others, as in 

 the Hymenoptej-a, Diptera, &c, the majority of the Neuro- 

 ptera, &c, it is an obtusangled one b ; it may be further 

 observed, that in receding from these forms wings very 

 often assume that of the half or quadrant of some regular 

 figure, as we shall see when we consider those of the diffe- 

 rent Orders. Anoth er general observation I shall first men- 

 tion, — that these organs are universally narrowest at their 

 base and widest at the apex, provided we consider as the 

 apex the termination outwards of the three Areas ; otherwise 

 we might say that wings in the Coleoptera, Orthoptera, 

 &c, were wider at the base than at the apex c . The wings 

 in the former Order, and in several of the Heteropterous 

 Hemiptera, as Gerris, Velia, &c, may in general, as to 

 their shape, be termed semicordate or semiovate d ; in the 

 Dermaptera they incline to an oval figure e ; in the Stre- 



1 Plate X. Fig. 4, 5. and XXVIII. Fig. 21,22. 

 b Plate X. Fig. tl— 14. L " Ibid. Fig. 4, 5. and XXVIII. 



Fig. 21, 22. A Plate X. Fig. 4. e Ibid. Fig. 5. 



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