58 ENTOMOLOGY 



Modifications of Wings. Being commonly more or less 

 triangular, a wing presents three margins: front (costal), 

 outer (apical) and inner (anal). Various modifications occur 

 in the front wings, which are in many orders more useful for 

 protection than for flight. Thus, in Orthoptera, they are 

 leathery, and are known as tegmina; in Coleoptera they are 

 usually horny, and are termed elytra; in Heteroptera, the base 

 of the front wing is thickened and the apex remains mem- 

 branous, forming a hemelytron. Diptera have, in place of the 

 hind wings, a pair of clubbed threads, known as balancers, or 

 halteres, and male Coccidge have on each side a bristle that 

 hooks into a pocket on the wing and serves to support the lat- 

 ter. In many muscid flies a doubly lobed membranous squama 

 occurs at the base of the wing. 



In Hymenoptera the front and hind wings of the same side 

 are held together by a row of hooks (hamuli) ; these are situ- 

 ated on the costal margin of the hind wing and clutch a rod- 

 like fold of the fore wing. In very many moths, the two 

 wings are enabled to act as one by means of a frenulum, con- 

 sisting of a spine or a bunch of bristles near the base of the 

 hind wing, which, in some forms, engage a membranous loop 

 on the fore wing. 



Venation, or Neuration. A wing is divided by its veins, 

 or nervures, into spaces, or cells. The distribution of the 

 veins is of great systematic importance but, unfortunately, the 

 homologies of the veins in the different orders of insects have 

 not been fixed, until recently, so that no little confusion has 

 existed upon the subject. For example, the term discal cell, 

 used in descriptions of Lepidoptera, Diptera, Trichoptera and 

 Psocidse, has in no two of these groups been applied to the 

 same cell. The admirable work of Comstock and Needham, 

 however, seems to settle this disputed subject. By a study of 

 the tracheae which precede and, in a broad way, determine the 

 positions of the veins, these authors have arrived at a primi- 

 tive type of tracheation (Fig. 67) to which the more complex 

 types of tracheation and venation may be referred. 



