The Wings of Insect and Wing Venation
The wings are outgrowths of the body wall. It is flattened double layered expansion of body wall with dorsal and ventral laminate having the same structure as the integument. Both layers grow, meet and fuse except along certain lines. These channels serve for passage of tracheae, nerves and blood vessels, which nourishes the wing. Later the walls of these channels become thickened to form veins. They serve to strengthen the wing and give it rigidity.
The arrangement of veins on the wing is called venation, which is very important for insect classification. The principal longitudinal, veins in order from the anterior margin are Costa (C), Subcosta (Sc), Radius (R), Media (M), Cubitus (Cu) and Anal veins (A). Small veins often found inter connecting the longitudinal veins are called cross veins. Due to the presence of longitudinal veins and cross veins, the wing surface gets divided into of longitudinal veins and cross veins, the wing surface gets divided into number of enclosed spaces termed cells. Positive (+) and negative (-) veins indicate convex and concave veins, respectively.
The wing is triangular in shape and therefore has three sides and three angles. The anterior margin called costal margin, the outer margin called apical margin and the posterior margin is called anal margin. The angle by which the wing is attached to the thorax is called humeral angle. The angle between the costal and apical margin is called apical angle. The anterior area of the wing supported by veins is usually called remigium. The flexible posterior area is termed vannus. The proximal part of vannus is called jugum. Each wing is hinged to two processes of notum, the anterior notal process and posterior notal process.