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_.
Piercing mandibles, retracted within the head-capsule. First maxillae
also modified as piercers; maxillae of both pairs with distinct palps.
Both pairs of wings similar, narrow and fringed. Four Malpighian
tubes. Cerci absent. Ovipositor usually present. Young resembling
parents, but penultimate instar passive and enclosed in a filmy
pellicle.
Includes three families of Thrips (see THYSANOPTERA).
Order: _Hemiptera_.
Mandibles and first maxillae modified as piercers; second maxillae
fused to form a jointed, grooved rostrum. Wings usually present. Four
Malpighian tubes. Cerci absent. Ovipositor developed.