Morphallaxis

Morphallaxis is the regeneration of specific tissuein a variety of organismsdue to loss or death of the existing tissue. The word comes from the Greekallakt, which means to exchange. The classical example of morphallaxis is that of the Cnidarianhydra, where when the animal is severed in two (by actively cutting it with, for example, a surgical knife) the remaining severed sections form two fully fuctional and indepedent hydra. The notable feature of morphallaxis is that a large majority of regenerated tissue comes from already-present tissue in the organism. That is, the one severed section of the hydra forms into a smaller version of the original hydra, approximately the same size as the severed section. Hence, there is an "exchange" of tissue. Morphallaxis is often contrasted with epimorphosis, which is characterized by a much greater relative degree of cellular proliferation. Although cellular differentiationis active in both processes, in morphallaxis the majority of the regeneration comes from reorganization or exchange, while in epimorphosis the majority of the regeneration comes from cellular differentiation. Thus, the two may be distinguished as a measure of degree.

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It uses material from the http://en.wikipedia.org/wiki/Morphallaxis Wikipedia article Morphallaxis.