Practice question

Morphallaxis describes regeneration achieved through repatterning existing tissues with minimal new growth, contrasting epimorphosis which builds blastema. Hydra fragment or posterior planaria regenerates entire animal by reorganizing remaining cells, altering positional values via Wnt gradients, rescaling pattern to smaller size. Cell number roughly constant, tissue mass declines, transdifferentiation and migration restore polarity without extensive proliferation. No blastema forms, proliferation limited. This mode emphasizes plasticity of differentiated cells re-specifying fate according to new positional information rather than generating new cells extensively, typical of cnidarians and some flatworms.