Different lineage, same fate. (a1-f2) Three-dimensional models of embryonic cell nuclei. In early Plectus embryos, five S1 descendants are contacted by S3 (white and blue arrows). Two of these are contacted in addition by P3 (red arrows). The three S1 blastomeres contacted exclusively by S3 (white arrows) generate descendants that occupy posterior dorsal and posterior lateral positions (b1, c1). These cells (light orange; remainder of S1, black) contribute to hypodermis (a2-c2) and later express retarded cell cycles (c3). In cleavage types M1L, R and L, different sets of three S1 cells are exclusively contacted by S3 (not shown). Nevertheless, they all occupy the same positions as those in type M2L (d1-f1), contribute to posterior hypodermis (d2-f2) and express retarded cell cycles (d3-f3). For nomenclature of spatial variants, see Figure 4.