The effects of ectoteloblast ablation in the earthworm embryo

The effects of ablating individual earthworm embryo ectoteloblasts were studied in terms of the morphology of the ventral nerve cord (VNC) and a discrete population of histochemically identified cells normally present in each segment of the worm. The activity of ectoderm cells in the vicinity of the ablated teloblast was assessed by observing the pattern of cells undergoing DNA synthesis for up to 72 h after an ablation. While examination of the morphology of the VNC in whole mounts suggests that a reconstitutive process is elicited by ectoteloblast ablation, this is not borne out in sections and at the level of individual, histochemically identified cells, which up to the hatchling stage appeared to be missing following ablation of particular ectoteloblasts. A proliferative response to ablation by the ectoderm cells in the vicinity of the ablated teloblast, however, suggests that some reconstitutive process(es) operate in this annelid, even if they do not result in a completely normal nerve cord at the hatchling stage.