First column: m=2 Fourier amplitudes, A₂, as a function of time (color bar) for our model galaxies. Columns 2–3: edge-on view for each disc and bulge (separately) for earlier and later times of their evolution, as indicated in each panel. Columns 4–5: scale-heights, h, at  ~2.5 disc scale-lengths. The dotted red line shows a single exponential fit. Note that in 3–4 Gyr of evolution with strong perturbation from bars and spirals, h only doubles despite the efficient stellar radial migration.