  The evolving galaxy is considered as a system of baryonic fragments embedded
into the static dark nonbaryonic (DH) and baryonic (BH) halo and subjected to
gravitational and viscous interactions. Though the chemical evolution of each
fragment is treated in the frame of one -- zone model with instantaneous
recycling, the local gas density and, therefore, its star formation (SF)
activity is influenced by other interacting fragments. In spite of its
simplicity the model provides a realistic description of the process of galaxy
formation and evolution over the Hubble timescale.
