The integument

The integument is the outer covering of arthropods and consists of a single layer of epidermal cells (often called the hypodermis) which rests on a basement membrane and secretes the cuticle. The cuticle covers the outer surface of the animal and lines the invaginations that arise from it such as the fore- and hind-guts, the tracheae, the lower parts of the genital ducts and the ducts of the epidermal glands.

The centipede cuticle appears to consist of three main layers: an outer, thin, refractile membrane usually about 1 μm in thickness called the epicuticle; a rigid, usually amber-coloured exocuticle and an inner thick elastic layer, the endocuticle, which is colourless and lamellated. The varying terminologies that have been used for these layers by different authors are shown in Table 1. The layers below the epicuticle are sometimes termed the procuticle. The outer part of the procuticle becomes tanned and sclerotised to form the exocuticle, the remaining undifferentiated part being the endocuticle. Between the exocuticle and the endocuticle there may be a region of hardened but not fully darkened cuticle which is fuchsinophil and lamellate like the endocuticle. This layer is termed the mesocuticle. The exocuticle and endocuticle show a variety of staining reactions and Blower (1951) regarded the optical appearance of the two layers as the only criterion which constantly differentiated them.