in distal side of has characteristic cuticular depression External cuticular depression. The surface of the cuticle in insects is the entire surface of an organism, and it is composed of flat, concave and convex regions. Concavities sometimes correspons with invaginations of the cuticle and the underlaying sinlge layer epidermis, somtimes correspond to a decreased cuticular thickness. The region of the cuticle that corresponds to a concave surface. insect region of cuticle independent continuant concave