Regeneration of Hydra from reaggregated cells

The process of reaggregation and regeneration of cells of H. attenuata is described. Cell differentiation can be assayed by the mixing of labelled cells of various origins and pretreatments into aggregates. It is shown that differentiated nerve cells are incorporated into regenerating aggregates and the cells introduced into aggregates as precursors subsequently differentiate to nerve cells at the stage of tentacle formation. Those components, which determine tissue polarity were found to survive disaggregation and reaggregation, and the stability of tissue polarity is shown to be due to the graded composition of cell types or cellular constituents, and not to their orientation.