EXTERNAL ANATOMY OF INSECTS. 621 



and of an irregular shape % but in the Hymenoptera are 

 smaller and semicircular b . 



2. Wings, with regard to their substance, may generally 

 be termed membranous ; but they vary in this respect, some 

 being much thicker than others, either partially or total- 

 ly: in spotted wings, as in those of many Libellulina, 

 Tettigonice F., &c, the dark opaque parts are denser than 

 those that are transparent : in several Orthopterous in- 

 sects, as in Phasma, some Mantes, &c, the Costal Area 

 or covering part of the wing is of a substance equally 

 firm with that of the tegmen. This is a compensating 

 contrivance, that where the latter is shorter and smaller 

 than the former, its membranous part, when folded, may 

 be protected from injury. Another similar contrivance 

 of Divine Wisdom is exhibited by those Pterophyllce 

 K. [Locusta F.) whose tegmina resemble the leaves of 

 plants (Pt. laurifolia, &c); in these the tip of the wings 

 when folded being longer, is not covered by the tegmina, 

 and therefore exposed to injury ; to prevent which this 

 small piece, while the whole wing, as far as covered by 

 those organs, is membranous, is of the same substance 

 with them c . The wings of most Coleoptera, Orthoptera, 

 Hemiptera, and Thereva coleoptrata, in the Diptera, &c, 

 are of a firmer substance than those of the other Orders; 

 in many Locustce Leach, Fulgorce, &c, they are nearly as 

 firm as the tegmina-, and in Ascalaphus italicus, except 

 at their base, the secondary wings are less membranous 

 than the primary. M. Chabrier has observed d that the 

 wine's of insects in general diminish in thickness from their 



» Plate IX. Fig. 5. b Ibid. Fig. 11. 12. g". 



« Stoll Sauterelles a Sabr. t. iv./. 12. t. vi. f. 21. &c. 

 «' Sur le Vol des Ins. c. i. 424. 



