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). Order: _Plecoptera_. Biting mandibles; second maxillae incompletely fused. Fore-wings similar in texture to hind-wings, whose anal area folds fanwise. Jointed, often elongate, cerci. Numerous (50-60) Malpighian tubes. Young resembling parents, but aquatic in habit, breathing dissolved air by thoracic tracheal gills. Includes the single family of the _Perlidae_ (Stone-flies), formerly grouped with the Neuroptera. Order: _Isoptera_. Biting mandibles; second maxillae incompletely fused. Fore-wings similar in shape and texture to hind-wings, which do not fold. In most species the majority of individuals are wingless. Short, jointed cerci. Six or eight Malpighian tubes. Young resembling adults; terrestrial throughout life. Includes two families, formerly reckoned among the Neuroptera--the _Embiidae_ and the _Termitidae_ or "White Ants" (see TERMITE). Order: _Corrodentia_. Biting mandibles; second maxillae incompletely fused; maxillulae often distinct. Cerci absent. Four Malpighian tubes. Includes two sub-orders, formerly regarded as Neuroptera:-- 1. _Copeognatha_: Corrodentia with delicate cuticle. Wings usually developed; the fore-wings much larger than the hind-wings. One family, the _Psocidae_ (Book-lice). These minute insects are found amongst old books and furniture. 2. _Mallophaga_: Parasitic wingless Corrodentia (Bird-lice). Order: _Ephemeroptera_. Jaws vestigial. Fore-wings much larger than hind-wings. Elongate, jointed cerci. Genital ducts paired and entirely mesodermal. Malpighian tubes numerous (40). Aquatic larvae with distinct maxillulae, breathing dissolved air by abdominal tracheal gills. Penultimate instar a flying sub-imago. [Includes the single family of the _Ephemeridae_ or may-flies. See also NEUROPTERA, in which this order was formerly comprised.] Order: _Odonata_. Biting mandibles. Wings of both pairs closely alike; firm and glassy in texture. Prominent, unjointed cerci, male with genital armature on second abdominal segment. Malpighian tubes numerous (50-60). Aquatic larvae with caudal leaf-gills or with rectal tracheal system. Includes the three families of dragon-flies. Formerly comprised among the Neuroptera. Order: _Thysanoptera_.