Model for tergite – sternite/leg pair correlation in millipedes based on morphological evidence from adult ring-forming millipedes. The model is based on the way the tergites and sternites are fused into rings in ring-forming millipede species. Tergites are denoted with roman numbers (I–VI), sternites and leg pairs are denoted with Arabic numbers (1–8). For explanatory reasons, the post-maxillary segment is drawn between the head and the first trunk segment; in fact this segment is the last segment of the head. The way the tergites and sternites fuse into rings in ring-forming species as indicated by same shade of blue for one ring in panel B. This fusion into rings is used in this model to correlate tergites with sternites/leg pairs. The hypothetical extrapolation for the tergite – sternite/leg pair correlation in non-ring-forming species is depicted in panel A. For details, see text.