User:Lizalutter/sandbox

History
The word comes from the Greek allazein, which means to exchange. The biological process was first discovered in hydra by Abraham Trembley, who was considered the father of environmental zoology. Abraham Trembley was doing a research on a sample pond water and examined the lifestyle of hydra. He couldn’t decide if they belong to the animal or plant kingdom, so he cut them in half and planned to see whether they die, like animals would, or re-pattern, as plants. Even though the halves and smaller pieces gave rise to new individuals, he still believed that hydra is an animal, since all their features, like movements or feeding behavior matched with animals’. Trembley came to the conclusion, that some animals have the ability to regenerate.

The process and mechanism of planarian regeneration was eventually renamed to 'Morphallaxis' by Thomas Hunt Morgan, the father of experimental genetics.

Types of Regeneration
There are three types of regenerations. One of them is Epimorphosis, which appears in Salamander limbs. This type of regeneration includes the formation of a new part, which is called the blastemal*. The amputation is sensed by a large number of somatic stem cells, that migrate to the wound meanwhile they increase their division rate. At the wound blastemal (a white region) forms and the blastemal cells proliferate to re-generate the lost tissues. There is no significant re-patterning of the remaining tissue.

Another type of regeneration is Morphallaxis, which is usually observed in Hydras. The main difference between the two types is that morphallatic regeneration does not include the formation of blastemal and there is no proliferation. Instead the existing tissue undergoes re-arrangement and it is transformed into the new organ.

The third type occurs for example in planarians. It was discovered once regeneration was observed in a cellular level. For very long biologists believed that planarians undergo epimorphosis, because regeneration on a trunk piece shows new tissue formation from a blastemal. However, on a tail piece next to the formation of a blastemal (which serves as a signaling center in this case), pharynx was re-arranged from a pre-existing tissue. The conclusion is that planarian regeneration cannot be listed neither to Epimorphosis or Morphallaxis.