Early evolution of the magnetic field in model 75. Models (a), (b), (c) (first row) at approximate time 0.078,0.78,2.34 Gyr respectively; models (d), (e) (second row) at times 3.9,7.8 Gyr. The continuous contours delineate the regions (“arms”) where field is injected; these rotate rigidly, with pattern speed such that the corotation radius is at fractional radius r ≈ 0.7. As time proceeds, the large-scale organization of the field increases – see also the first column of Fig. 1.