The elucidation of the ultrastructure, cytochemistry and reactivity of cutaneous recep­ tors is of particular importance in the unsolved biological problem of sensory transduc­ tion. Topographically and with regard to evolution, cutaneous receptors are the most widespread primary sense organs. Because of their simple structure they are particular­ ly useful in the study of the functional morphology of receptor end-organs. Research into receptor structures in classic neuromorphology revealed magnificent patterns and pictures of receptors, showing their great diversity and their presence in all human and animal systems. Since the end of the sixties, ultrastructural studies have led to the discovery of a large amount of new information. The findings concerning the cellular organization of the inner core (pease and Quilliam, 1957), axon terminals (Cauna and Ross, 1960) and capsule cells (Polacek and Mazanek, 1966) of encapsulated receptors have opened up new possibilities for a revaluation of receptor cell units and their relationships.