Epimorphic regeneration of the distal part of the planarian pharynx

The totipotent stem cells called neoblasts seem to be concerned with the re markable regeneration ability of planarians. However, the pharynx is able t o regenerate after the amputation of its distal part, in spite of a lack of neoblasts in the pharynx. The process of regen eration has been referred t o as morphallaxis based on conventional histochemical observations. We exam ined it again immuno-histochemically using anti-Dugesia japonica proliferat ing cell nuclear antigen (DjPCNA) antibody for neoblasts and anti-D. japoni ca myosin heavy chain-A (DjMHC-A) antibody for pharynx muscle fibers. This immuno-histochemical study, together with observations of the regeneration process of planarians irradiated with X-rays in particular regions, reveale d that after the amputation, neoblasts from outside the pharynx entered tha t organ, moved through the mesenchyme of the pharynx to the wounded area, a nd differentiated into the cells that had been lost there. We show here tha t the regeneration after amputation of the distal part of the pharynx is an 'epimorphic' process.