Evolution in time of a halo with virial mass M_vir = 10¹²  M_⊙ and formation epoch a_c = 0.15 (for a cosmology with h = 0.7, Ω_m = 0.28, and Ω_Λ = 0.72) using the Wechsler model. The left panel shows that the mass growth rate reaches a minimum for all shells between t = 1 and t = 7 Gyr, and is negative for the innermost shells, which implies they decrease in mass. The central panel shows the mass history for all shells. The shells show a temporary stall in their growth, or even a decrease in mass, between t = 1 and t = 7 Gyr, before resuming growth again at later times. The right panel shows the mass profile at different epochs.