Anus: the end of the digestive tract, through which the food remnants are passed: the posterior part of the individual: specifically, in Coccidae, a more or less circular opening on the dorsal surface of the pygidium, varying in location as regards the circumgenital gland orifices: = anal orifice.
Aorta: the anterior, narrow part of the heart, opening into the head.
Apex: that part of any joint or segment opposite the base by which it is attached; that point of a wing furthest removed from base or at the end of the costal area.
Aphaniptera: indistinctly winged; see Siphonaptera.
Aphideine: see aphidilutein.
Aphidilutein: a yellowish fluid found in plant lice, changed to a rich violet by alkaline reagents.
Apical: at, near or pertaining to the apex; usually of a wing.
Apical area: see petiolar area.
Apical areas: apical cells in some Homoptera.
Apical cell: a cell near or at the apex of a wing; in Hymenoptera (Norton) = medial (Comst.); outer apical cell = 2d medial 2 (Comst.); inner apical cell = medial 3 (Comst.).