Platyhelminthes (Flatworms) - Regeneration in Invertebrates
Between flatworms the turbellarians, (mostly fresh water species and fresh water and terrestrial triclads) routinely again generate asexually by fragmentation; and most of them have considerable power of regeneration. Their regenerative capability has been investigated by numerous workers specifically in several species of the planarians (fresh water triclads) such as Dugesia. As per to some recent studies dedifferentiated cells are apparently the main source for regeneration of new tissues. But it has been held from the past that there is a reserve of undifferentiated cells, neoblasts that are the main source of cells for regeneration. The procedure of regeneration seems to be a combination of morphallaxis and epimorphosis. A different physiological gradient exists in the flat worms so that the body is polarized, the anterior (head end ) presenting one pole and the posterior (tail end) representing the other. Regeneration is correlated along with this polarity. So in an excized piece the anterior cut surface regenerates the head and the posterior cut surface regenerates a new tail.