Top panel: mean volume density in dependence of radius for (i) the whole stellar component (vertical sequence of red circles at R = 6 pc); and (ii) the associated embedded cluster (decreasing sequence of blue circles on the left). The open circle size scales with the logarithm of the stellar mass. The embedded cluster refers to the part of the star-forming region seen above the stellar background against which it is seen projected (Σ_bck = 40   M_⊙   pc^-2, solid red line). As a result of the applied surface density cut-off, the predicted embedded-cluster sequence has a constant mean surface density. Also, it does not differ much from the observed embedded-cluster sequence defined by Pfalzner (2011) (dashed green line; see text for details). The times and stellar masses are given along the plotted sequences. Middle panel: mass in stars against radius, for the whole star-forming region (red vertical track to the right) and for the developing embedded cluster (blue track to the left). Quoted to the left of the sequences are the times elapsed since the onset of star-formation (in Myr). Bottom panel: same as the middle panel but for the mass-vs-time space.