Includes the single family of _Panorpidae_ (scorpion-flies), often comprised among the Neuroptera. Order: _Trichoptera_. Mandibles present in pupa, vestigial in imago; maxillae suctorial without specialization; first maxillae with lacinia, galea and palp. Prothorax small. Two pairs of membranous, hair-covered wings, with predominantly longitudinal neuration. Larvae aquatic and eruciform. Pupa free. Six Malpighian tubes. Cerci absent. Includes the caddis-flies. See NEUROPTERA, among which these insects were formerly comprised. Order: _Lepidoptera_. Mandibles absent in imago, very exceptionally present in pupa; first maxillae nearly always without laciniae and often without palps, or only with vestigial palps, their galeae elongated and grooved inwardly so as to form a sucking trunk. Prothorax small. Wings with predominantly longitudinal neuration, covered with flattened scales. Fore-wings larger than hind-wings. Cerci absent. Four (rarely 6 or 8) Malpighian tubes. Larvae eruciform, with rarely more than five pairs of abdominal prolegs. Pupa free in the lowest families, in most cases incompletely or completely obtect. Includes the moths and butterflies. See LEPIDOPTERA. Order: _Diptera_. Mandibles rarely present, adapted for piercing; first maxillae with palps; second maxillae forming with hypopharynx a suctorial proboscis. Prothorax small, intimately united to mesothorax. Fore-wings well developed; hind-wings reduced to stalked knobs ("halteres"). Cerci present but usually reduced. Four Malpighian tubes. Larvae eruciform without thoracic legs, or vermiform without head-capsule. Pupa incompletely obtect or free, and enclosed in the hardened cuticle of the last larval instar (puparium). Includes the two-winged flies (see DIPTERA), which may be divided into two sub-orders:-- 1. _Orthorrhapha_: Larva eruciform. Cuticle of pupa or puparium splitting longitudinally down the back, to allow escape of imago. Comprises the midges, gnats, crane-flies, gad-flies, &c. 2. _Cyclorrhapha_: Larva vermiform (no head-capsule). Puparium opening by an anterior "lid." Comprises the hover-flies, flesh-flies, bot-flies, &c. Order: _Siphonaptera_. Mandibles fused into a piercer; first maxillae developed as piercers; palps of both pairs of maxillae present; hypopharynx wanting. Prothorax large. Wings absent or vestigial. Larva eruciform, limbless. Includes the fleas. Order: _Hymenoptera_.