ABSTRACT
The histology of the cuticle and epidermis of certain chilopods and diplopods is described. Two principal layers of the cuticle are recognized, an outer homogeneous and refractile exocuticle which is usually but not invariably pigmented and an inner endocuticle.
The endocuticle and the exocuticle both contain chitin. The exocuticle is considered as a modification of the outer part of the chitinous matrix by an impregnating substance.
Certain properties of the impregnating substance are described. It appears to be a substance rich in phenolic groups, perhaps a protein, which has a stability and resistance to acids in its own right irrespective of the presence of pigment or aromatic cross-links. Pro-sclerotin is suggested as a name for this substance. Chemical tests show that it is present in regions not optically definable as exocuticle.
The epidermis is virtually an epithelium of gland cells which appear to secrete lipoid material. The lipoid passes on to the surface of the cuticle by means of ducts passing through the cuticle. Here it appears to form a superficial layer and to impregnate the sclerotin and pro-sclerotin.
There appears to be an intimate association of lipoid with the aromatic groups of the pro-sclerotin and sclerotin. Destruction of the aromatic groups by means of an oxidizing agent appears to intensify the colouring of the lipoid by Sudan.
The myriapod cuticle is shown to have many features in common with that of other arthropods. The main difficulty in the way of extensive homology with other arthropod types is the absence in myriapods of an outer non-chitinous and resistant layer.
