A study of the cuticle of Ricinoides sjostedti, Ricinoides afzelii and Cryptocellus lampeli has been carried out using staining and histochemical tests in an attempt to determine its chemical composition and to relate it to other arthropod cuticles. The examination has revealed that the cuticle of ricinulids differs in several ways from other arthropods studied and shows most similarity to the spider and king crab cuticle. Histochemical tests failed to reveal the presence of sulphur, an element occurring in the cuticle of other arachnids. Insufficient material prevented the use of strong oxidizing methods to determine whether or not sulphur does occur in the cuticle. A description is given of the pore canals in the ricinulid cuticle. The structure and pattern of the pore canals is different from that seen in any other arthropod so far described.