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 fegmina; 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 Coccidze 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 wveiis, 
or mervures, 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. [or example, the term discal cell, 
used in descriptions of Lepidoptera, Diptera, Trichoptera and 
Psocidze, 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 tracheze 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. 
