This chapter explains some simple dynamical models representing the global evolution of a cell, and discusses what extent these models can account for known phenomena. The most primitive animals, coelenterates in particular, compensate for their histological simplicity by a highly developed infracellular differentiation. A morphological theory for the structures seems easier; they are already much more labile and respond rapidly to biochemical variations of the local cytoplasm. The least explicable part of such a model is the adaptation of the chromosome to the permeability properties of the membrane. Only the fiber space of internal variables has been considered in the preceding, whereas a complete model needs spatial coordinates. Almost every elementary phenomenon of duplication that has been observed in biology, particularly at the level of subcellular organelles, is a budding phenomenon. One of the basic questions connected with nuclear material is whether a mutation arises from a chemical or a geometrical modification in the structure of DNA.