A series of numerical models is presented describing the dynamical evolution of globular clusters with a mass spectrum, based on integration of the Fokker-Planck equation. Three-body binary heating and a steady galactic tidal field are included in the models. A wide range of initial mass functions is adopted and the evolution of the mass function is examined. The mass function begins to change appreciably during the post-collapse expansion phase due to the selective evaporation of low-mass stars through the tidal boundary. One signature of highly evolved clusters is thus the significant flattening of the mass function. The age (in units of the half-mass relaxation time) increases very rapidly beyond about 100 signifying the final stage of cluster disruption. This appears to be consistent with the sharp cut-off of half-mass relaxation times at near 10 exp 8 years for the Galactic globular clusters.