1^ POFULAE ENTOMOLOGY. 



according to the sex; in Lepidojptera and some otliers they 

 are much more numerous. A great diversity also often 

 exists in the structure of these organs in the opposite sexes 

 of the same species. 



The elytra, or wing-cases^ are the hard coverings which 

 conceal the wings of the order Coleoptera and others ; they 

 open longitudinally, and the difference in their form affords 

 generic and specific characters. The alcBj or wings, are the 

 organs of flight : insects possess either two or four, when 

 not entirely wanting ; where there are only two, they are of 

 a uniform size and appearance ; when four, they most fre- 

 quently differ, the first or anterior pair being larger than 

 the other. These appendages are membranous, elastic, ge- 

 nerally transparent, attached to the upper side of the thorax, 

 and intersected with nerves, which sometimes form a kind 

 of net-work. In Wasps and Bees the wings are naked and 

 transparent; in Butterflies they are covered with minute 

 scales, embellished with the liveliest colours ; in the Caddice 

 riies they are clothed with fine hairs, whence the name of 

 the order TricJwptera. Halteres, or poisers, are two short 

 moveable appendages placed near the origin of each wing ; 

 this organ is peculiar to the two-winged insects. 



The aculeus, or sting, is the instrument by which insects 



