1. Thysanura (Bristle-tails): with ten abdominal segments; number of abdominal appendages variable. Cerci prominent. Developed tracheal system.
2. Collembola (Spring-tails): with six abdominal segments; appendages of the first forming an adherent ventral tube, those of the third a minute “catch,” those of the fourth (fused basally) a “spring.” Tracheal system reduced or absent.
Sub-class: Exopterygota.
Hexapoda mostly with wings, the wingless forms clearly degraded. Maxillulae rarely distinct. No locomotor abdominal appendages. The wing-rudiments develop visibly outside the cuticle. Young like or unlike parents.
Order: Dermaptera.
Biting mandibles; minute but distinct-maxillulae; second maxillae incompletely fused. When wings are present, the fore-wings are small firm elytra, beneath which the delicate hind-wings are complexly folded. Many forms wingless. Genital ducts entirely mesodermal. Cerci always present; usually modified into unjointed forceps. Numerous (30 or more) Malpighian tubes. Young resembling parents.
Includes two families—the Forficulidae or earwigs (q.v.) and the Hemimeridae.
Order: Orthoptera.
Biting mandibles; vestigial maxillulae; second maxillae incompletely fused. Wings usually well developed, net-veined; the fore-wings of firmer texture than the hind-wings, whose anal area folds fanwise beneath them. Jointed cerci always present; ovipositor well developed. Malpighian tubes numerous (100-150). Young resemble parents.
Includes stick and leaf insects, cockroaches, mantids, grasshoppers, locusts and crickets (see [Orthoptera]).