Spatial distribution of Class II (red dots, left panels) and Class III (blue dots, right panels) NGC 2264 members in four age groups. The gray, red and blue contours highlight the cluster subregions shown in Fig. 10. The empty square identifies the O-type binary star S Mon; the crosses mark the positions of other massive, B-type stars in the NGC 2264 region (from Dahm 2008, Table 2). The black contour delimits the area within 1 pc from S Mon.