There is no ovipositor, and the wings are either without nervures or have only a single degraded longitudinal nervure which does not reach to the tip. While the Terebrantia are (After H.
Tower (1903), of nervures similar to those of the hind-wing, and by the proof that the small membranous structures present beneath the elytra of certain beetles, believed by Meinert to represent the whole of the true fore-wings, are in reality only the alulae.
There are several curved median and cubital nervures and a single anal, but few cross nervures or areolets.
Both lengthwise and transversely, and doubled up beneath the elytron; to permit the transverse folding, the longitudinal nervures are interrupted.
Close to a transverse fold near the base of the wing, the median nervure divides into branches which extend to the wing-margin; there is a second transverse fold near the tip of the wing, and cross nervures are altogether wanting.
A wing is an outgrowth from the dorsal and pleural regions of the thoracic segment that bears it, and microscopic examination shows it to consist of a double layer of cuticularized skin, the two layers being in contact except where they are thickened and folded to form the firm tubular nervures, which serve as a supporting framework for the wing membrane, enclose air-tubes, and convey blood.
These nervures consist of a series of trunks radiating from the wing-base and usually branching as they approach the wing-margins, the branches being often connected by short transverse nervures, so that the wing-area is marked off into a number of " cells " or areolets.
The wings are carried erect: the anterior pair large, with numerous longitudinal nervures, and usually abundant transverse reticulation; the posterior pair very much smaller, often lanceolate, and frequently wanting absolutely.
The hind wings, on the contrary, are for the most part membranous and, when extended, of large size; each consists of two portions, the distal of which, in virtue of the arrangement and jointing of its nervures, is capable of being both doubled up and folded fanwise beneath the proximal, which is partly horny when the wing is tucked away under the front wing-case of the same side.
Nervures; d, basal nervures; Io.
E, f, recurrent nervures; st, i 1.
The wings in the Hymenoptera show a marked reduction in the number of nervures as compared with more primitive insects.
The main median nervure, and usually also the sub-costal become united with the radial, while the branches of radial, median and cubital nervures pursuing a transverse or recurrent course across the wing, divide its area into a number of areolets or " cells," that are of importance in classification.
In the hind-wings - on account of their reduced size - the nervures are even more reduced than in the fore-wings.
The ten thousand known species included in this group agree with the Cynipoidea and Chalcidoidea in the position of the ovipositor and in the jointed trochanters, but are distinguished by the fore-wing possessing a distinct stigma and usually a typical series of nervures and areolets (figs.
The eyes are well developed, with numerous facets; the antennae minal one shaped like that of the are transparent, with few nervures, flight.
The feelers are long and simple, and the wings are very narrow, each with a sub-costal, a radial, a median and a cubital nervure; the branches of the median and the cubital, however, as well as the anal nervures, are vestigial, and there are a few short cross-bars between After Marlatt, Ent.
These nervures taper towards the extremity of the wing, and are strongest towards its root and anterior margin, where they supply the place of the arm in birds and bats.
On the anterior margin the extended nervures make it rigid, while behind it is fine and flexible.