Nebular excitations, E, vs. 5007 Å velocities, V_exp = 0.911V_FWHM, for Magellanic Clouds PNe (Dopita et al. 1985, 1988) and our hydrodynamical simulations. Observed objects and models are broken down into the same M(5007) brightness classes, as indicated by the symbol sizes: the larger the symbol, the brighter the object or model, respectively. The approximate brightness range covers 4 mag. The top abscissa is labelled in terms of V_HWHM for easier comparison with previous figures. Left panel: LMC and SMC PNe additionally broken down into classes of different oxygen abundances (from Dopita & Meatheringham 1991a,b), visualised by various grey shades. The darkest grey corresponds to  ≥ Z_GD/2, the lightest grey to  ≤ Z_GD/5. The vertical arrow indicates the oxygen abundance corresponding to Z_GD/3. Middle panel: comparison of observations with the model sequences as indicated. The gaps seen in the model sequences are artefacts due to the definition of E combined with the lower oxygen abundance of the Clouds (Eqs. (5), see text there). Note that the spacings of the models within a sequence does by no means reflect the speed of evolution. Right panel: a 0.625 M_⊙ model sequence (α = 2, Z = Z_GD/3) with different initial parameters, Ṁ_agb = 0.5  ×  10^-4 M_⊙ yr^-1 and V_agb = 7.5 km s^-1 (filled triangles), compared with the 0.625 M_⊙Z_GD/3 sequence from the middle panel and a metal richer (Z = Z_GD) 0.625 M_⊙ sequence (see legend).