Regeneration

Regeneration–the ability of animals to replace lost body parts–was first studied by scientists in the 18th century. In 1712, Rene’ Antoine Ferchault de Reaumur [French: 1683-1757] presented a beautifully illustrated paper in which he described the ability of crayfish to regenerate missing limbs.

In 1740, Abraham Trembley [Swiss: 1710-1784] discovered a tiny green animal with a cylindrical body and flexible tentacles around a mouth at the top. When Trembley cut the animal in half horizontally both halves survived; the top half grew a new bottom and the bottom half grew a new top. Trembley continued to experiment, making all sorts of cuts. For example, with a series of vertical cuts in the head region he created a creature with seven heads. He compared his creation to Hydra, the many-headed monster slain by Hercules.

Carolus Linnaeus thought Trembley’s comparison was appropriate and in his classification scheme gave the name Hydra to the little green animals.

In 1768, Lazzaro Spallanzani described regeneration in earthworms, snails, salamanders, and frogs. Another organism whose regenerative powers have been investigated in great detail, beginning in the early 1800s, is the planarian, a small flatworm.

Among mammals, regeneration is limited. No mammals can regenerate lost limbs or tails, but some regeneration of internal tissues is possible. For example, if part of a human liver is lost to desease or surgery, the rest of the liver grows larger to handle the functions of the lost part. Much research is currently being conducted on regeneration of human tissue, with the hope that in the future it will be possible to return damaged eyes, spinal cords, and other organs to their proper function.