Cell death was observed in the nematocyte differentiation pathway in Hydra during head and foot
regeneration. This death occurs throughout the regenerating piece, is transient in nature and is
selective for committed stenotele and desmoneme precursors. Proliferating nematoblasts are unaffected.
Cell death appears to be caused by release of a toxic factor rather than loss of a hormone
required for differentiation, since regenerating pieces released a factor that inactivated differentiating
nematocytes, and injured animals that had intact head and foot tissue also lost differentiating
nematocytes. The inactivated nematocytes are removed by phagocytosis by epitheliomuscular cells
