Fig. 1. Cell lineage arrangement in the germinal band of a stage 7/8 leech embryo. Each of the five teloblasts produces a column or `bandlet' of primary blast cells, shown here in cross-section. The four ectodermal bandlets (white) lie in parallel above a single mesodermal (m) bandlet (cyan), and are overlaid by a provisional integument composed of micromere-derived epithelial cells (yellow). The n and q bandlets are located respectively on the future ventral and dorsal sides of the germinal band. The o and p bandlets are initially equipotent, and are committed to distinct O and P developmental pathways during normal development on the basis of positional cues encountered in the germinal band (Shankland and Weisblat, 1984; Huang and Weisblat, 1996).