280 PTILOTA: IMAGO EXTERNAL ANATOMY. 



ing good generic characters, has ordinarily been given to 

 Jurine, a celebrated Swiss entomologist, who arranged the 

 Hymenoptera in accordance therewith. Frisch, however, a 

 German, and Harris, an English author, had long previously 

 made use of the same characters. 



In general, membranous wings remain expanded at all 

 times to their full extent : but this is by no means a con- 

 stant character. Thus in the Hymenopterous family of the 

 wasps (Vespida), and the species of the genus Leucnsjiix, 

 they are folded throughout their whole length when unem- 

 ployed. In the Lepidoptera the same occurs in the family 

 of the plume moths, already mentioned. The second wings 

 of orthopterous and homopterous insects are also longi- 

 tudinally folded beneath the wing-covers; and the wings of 

 coleopterous insects are folded both longitudinally and trans- 

 versely when unemployed. The posterior wings of the ear- 

 wig are similarly folded, the nervures, when the wings are 

 extended, forming a most beautiful object. The position 

 of the wings when shut afforded to Linnanis the chief 

 character by which he divided the moths into various sections. 

 Thus they were said to be depressed, deflexed, horizontal, 

 extended, divaricate, &c. 



Some lepidopterous insects appear to have six wings, and 

 have hence been specifically named Hexapterata, &c., form- 

 ing the genus Lobophora of Curtis ; a name indicative of the 

 real character of the wings, of which the posterior pair are 

 furnished with a large membranous lobe. 



It still remains for me to mention a small membranous 

 appendage connected with the base of the wings in the ma- 

 jority of dipterous insects, to which the name of alula, or 

 winglet, is generally given, consisting of two concave and 

 convex membranes united together, and surrounded by a 

 fine fringe, which fold over each other like the valves of a 





