166 PHYSIOLOGY OF INSECTS. 



assistance of a second similar pair ; a portion at the base 

 of membranaceous wings is called the winglet or alula: 

 they are called crustaceous or criistaceiB when composed 

 of a hard, brittle substance, incapable of being bent or 

 folded without injury ; incapable also of being used in 

 flight, and serving only as a protecting cover to the more 

 delicate hind wings ; the fore wings possess this character 

 in all beetles, and in descriptions are usually called wing- 

 cases or elytra : they are called leathery or coriacece when 

 composed of a tough, leathery substance, which will bend 

 readily without breaking, but which never folds naturally ; 

 such wings are seldom of much service in flight, yet are 

 occasionally used for that purpose ; they have this charac- 

 ter in the locust : they are said to be half-leathery or semi- 

 coriace(B when they have the basal portion composed of 

 the leathery substance just described, and the apical por- 

 tion membranaceous and transparent ; plant-bugs have 

 this kind of fore wings : and lastly, reticulated or reticii- 

 lat(B is the term employed when they are covered by an 

 infinity of nervures crossing each other in every direction ; 

 these nervures give the wings the appearance of beautiful 

 net- work ; dragon-flies have wings of this character. 



The hind wings or metal(B possess the characters of 

 being scaly, membranaceous, or reticulated, the same as 

 the fore wings ; but they are never crustaceous, leathery, 

 or half-leathery. The hind wings rise from the sides of 

 the metaihorax, one behind each of the fore wings; they 

 occasionally possess characters which the fore wings have 

 not : they are said to be petiolated or stalked when they 

 have ceased to bear the appearance of wings, and have 

 become mere knobs, placed at the extremity of a short 

 foot-stalk; in this form they are usually termed poisers or 

 halteres, and are possessed by all flies and gnats: and 

 setaceous or sefiformes when they have ceased to bear the 



