[Determination of "functional units" of rat epidermis during its histogenesis].

Sheets and cryocut sections of embryonic, newborn and aged rats have been analyzed. The epidermis of aged rats was confirmed to consist of "functional units", each of them corresponds to the square of one scale and has a hexagonal shape. In the epidermis of 19, 20, 21 day old rat embryos these structures were not observed 4-5 days after birth single hexagonal cells appeared in the granular layer whose formation completed by day 6. Non-organized cornified cells were substituted by hexagonal scales in 10-12 day old neonatal rats.