12 MODERN CLASSIFICATION OF INSECTS. 



naceous wings, halteres or pseudo-halteres. In the Coleoptera the 

 uj)per pair of wings is transformed into "a pair of corneous cases 

 (elytra), generally extending to the extremity of the body, and, 

 when unemployed, shutting closely together by a straight suture 

 down the back. Thus united, they become a shield of great strength, 

 defending the posterior pair of wings, which, when at rest, are 

 transversely folded up beneath them, and which, when the insect is 

 on the wing, are its only effective organs of flight. This lower pair 

 of wings is membranous, and traversed by various corneous veins. 

 In the orders Orthoptera and Homoptera the anterior wings (teg- 

 mina), when at rest, form a roof-like shield to the posterior wings, 

 although much less effective than that of the beetles, since they are 

 of a much more coriaceous texture. The posterior wings themselves 

 are membranous, of a large size, and, when at rest, they are longitu- 

 dinally folded. During flight, both pairs assist in locomotion. In 

 theHeteroptera, the anterior wings (/lemeli/tra) are coriaceous through- 

 out their basal half, and membranous throughout their apical portion ; 

 the posterior wings are of moderate size, membranous, folded lon- 

 gitudinally at rest, and defended by the hemelytra, which shut hori- 

 zontally, the membranous portion of the one folding upon the same 

 part in the other. In the Neuroptera the wings are generally of equal 

 size : they are of a membranous texture, and the posterior are seldom 

 defended when at rest by the anterior, and they are consequently 

 not folded up : whilst in the Hymenoptera and Lepidoptera the ante- 

 rior wings are larger than the posterior, which are likewise never 

 folded up. We thus see, that where the posterior wings take a large 

 share in the act of flight, it is necessary that, being of a larger size, 

 they should be folded up and defended by more or less powerful 

 wing-cases while unemployed; when, on the other hand, the anterior 

 wings take the largest share of action during flight, the poste- 

 rior are so much reduced as to require no defence ; in other words, 

 where we find large and strong wing-cases or shields, the active 

 organs of flight are membranous, large, and folded up. The veins, 

 which I have already noticed, are extremely variable in their number: 

 thus, whilst the wings of the Dragon-fly are covered with cells or meshes 

 formed by the conjunction of these veins, the wings of some Hymeno- 

 ptera are almost destitute of them. The numberand position of 

 these veins and cells are of great use in determining the genera, 

 especially of Hymenopterous and Dipterous insects. The wings of 



