Contribution to ontogenesis of Merkel cells.

Merkel cells appear in the epidermis of planum nasale of the rat fetuses from the 16th day of i. u. development, namely in the 2nd-3rd layer of epidermal cells. Nerve fibres appear in the subepidermal connective tissue from the 20th day of i.u. development. Long cytoplasmic processes filled in with specific dense core vesicles grow from Merkel cells against them. Intraepidermally, nerve fibres appear in postnatal period (from 3rd day after birth). Granular vesicles of Merkel cells probably have the leading role in the formation and maintenance of contacts between Merkel cell and the nerve ending. The results of studying ontogenetic development of Merkel cells in the rat are favour of hypothesis about the differentiation of Merkel cells in the epidermis, however, the possibility of secondary equipment of epidermis with Merkel cells independently on the development of nerve fibres is not eliminated.