Needham the wing-neuration in this order is the most primitive to be found in the Hexapoda.
When wings are present the front pair are much larger than the hind pair, and the neuration is remarkable for the concresence of the median with the After Marlatt, Bull.
On the other hand, the reduced feelers, the numerous Malpighian tubes (40), the large complex eyes, the vestigial condition of the jaws, the excessive size of the fore-wings as compared with the hind-wings and their complex neuration with an enormous number of crossnervules are all specializations.
All the wings are of firm, glassy texture, and very complex in their neuration; a remarkable and unique feature is that a branch of the radius (the radial sector) crosses the median nervure, while, by the development of multitudinous cross-nervules, the wing-area becomes divided into an immense number of small areolets.
They may be distinguished from the Neuroptera by the elongation of the head into a beak, the small prothorax, the narrow, elongate wings with predominantly longitudinal neuration, the presence of abdominal cerci and the cruciform larva.