ABSTRACT
In this chapter, the authors look at regeneration as it occurs as a natural process across the animal kingdom, ranging from the complete rebuilding of the body of some invertebrates through to limb, heart, and skin regeneration in some vertebrates. They pay particular attention to the extent to which stem cells play a role in the regenerative processes. Many of animals that are able to regenerate have need to do so due to the process of autotomy, which literally means self-amputation, usually as way to evade predation. The experimental organism that has provided some of the deepest insight into regeneration and the evolution of stem cells is the pretty unassuming flatworm, which belongs to the genus Planaria that includes species living in freshwater, seawater, or on land. The ancient origins of the neoblast stem cell regulatory mechanisms seen in planarians have been strengthened by recent findings in acoel worms, combined with a reassessment of their place in the evolutionary tree.
