28 rabbits were irradiated with the collective spectrum of a mercury ultraviolet lamp. The corneae were examined under the scanning electron microscope. On the basis of the results, the hypothesis is propounded that the different cells with various surface structures are transition stages of the same cells, i.e. for the time being, the cells only show part of their surface. These are the small light cells with the greatest number of cytoplasmatic processes. While the cells are being carried to the surface, the number of microplicae diminishes and ‘craters’ are formed, probably accomplishing a metabolic function. In the last stage, the ‘craters’ disappear again; the same applies to most of the microplicae. The cells become circular and dark, and show the greatest expansion shortly before ascending.