blastema

https://doi.org/10.1351/goldbook.10460
Mass of cells from which an organ or a body part develops, either in normal development or in the regeneration of a lost body part.
Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 730 [Terms] [Paper]