The procuticle

Procuticle is composed almost entirely of protein and chitin. The latter is a nitrogenous polysaccharide consisting primarily of N-acetyl-D-glucosamine residues together with a small amount of glucosamine linked in a β1,4 configuration.

The procuticle (= fibrous cuticle) forms the bulk of the cuticle and in most species is differentiated into two zones:

1. endocuticle
2. exocuticle

The border between the two zones is not clear and an intermediate area, the mesocuticle, is visible

The endocuticle:

• composed of lamellae (is made up of a mass of microfibers arranged in a succession of planes, all fibers in a plane being parallel to each other).

The exocuticle:

• The region of procuticle adjacent to the epicuticle that is so stabilized that it is not attacked by the molting fluid and is left behind with the exuvium at molting
• Exocuticle is absent from areas of the integument where flexibility is required, for example, at joints and intersegmental membranes, and along the ecdysial line. In many soft-bodied endopterygote larvae the exocuticle is extremely thin and frequently cannot be distinguished from the epicuticle and cuticulin envelope