Protozoans - Regeneration in Invertebrates

Most single celled animals such as protists, i.e. protozoans, regenerate very well. If part of the cytoplasm is removed from the amoeba it is readily replaced. An identical process takes place in flagellates and ciliates. In each instance, though, regeneration occurs only from that fragment of the animal (cell) which consists of the nucleus. A protozoan in which regeneration has been extensively studied is Stentor. It is a large ciliate organism where regeneration takes place only if both the cortical cytoplasm and nuclear genome (which is a large beaded macronucleus) are present in the pan that is to regenerate.

It regenerates in the same way as it reproduces. For reproduction it first divides transversely and after that each half reforms an entire animal. Likewise when Stentor is cut transversely into two halves, then the wound at each cut end heals. The anterior part reconstitutes first by regenerating its posterior end. After this the posterior cut end regenerates its anterior portion. So two animals are formed each complete with cortical cytoplasm and nuclear genome.