Abstract: Background and Objective: Regeneration is characterized by the restoration of tissue components identical to those removed. The purpose of this study is to describe the origin of the totipotent cells and how they act as progenitors. Follow up the trans-differentiation cells to new cell types. Materials and Methods: Specimens of Platynereis dumerilii were collected at 1-3 m depth from the Mediterranean Sea of Alexandria, Egypt in 2017. The posterior five segments with the pygidium are cut from clam worms with healthy body segments. The amputated worms are studied through light microscopy and TEM, starting at 12-24 hrs intervals to 2 weeks. Results: The hemocytes agglutinate and form a pseudo-clot at the wound site. The endoblast forms from the internal endoderm. The dedifferentiated cells form the true blastema during the first 5-6 days of post-amputation. The subsequent regenerating five segments are formed at front of the pygidium. After fifteen days of post-amputation, the transverse musculature thickens. The dermis is formed by the cells furthest from the longitudinal axis. Conclusion: If physicians could activate the human quiescent and permanent cells to follow the result of this study, limb regeneration could be possible. It is still an open question. This study provides a detailed description to help scientists extend researches on human regeneration.