Cell lineage and pattern formation in the earthworm embryo

ABSTRACT The pattern of segmental contribution of teloblasts in the earthworm embryo was examined by injection of the lineage tracer HRP and by studying the timing and symmetry of the first few divisions in each teloblast bandlet . The changing spatial relationship of the ectoteloblasts during development was also used to assess segmental contributions. A mathematical method for determining the cell cycle time of each teloblast is presented. The teloblasts and their immediate progeny, the blast cells, were found to undergo unique and highly stereotyped patterns of division which lead to equally stereotyped patterns of contribution in the segments apparent in the later embryo.