Centen-nary of the Cell Theory Address. In a modern view, cells are characterized by physiological individuality rather than morphological discreteness. The egg has the properties of a cell plus those of an organism. During development the former are passed on to the individual cells arising from successive divisions, while the latter continue into the supracellular field activities of the embryo which are manifestations not of individual cells but of collectives of cells. Thus, ontogeny is characterized by the counterplay between cellular individuals and cellular collectives.