Overview

The hydra is a small organism, often less than an inch (2.5 cm) long, that became the focus of much attention and debate during the eighteenth century. Abraham Trembley (1710-1784), along with a number of others, used the hydra to investigate basic issues concerning development, regeneration after damage, and the differences between plants and animals. Because of this and related work, by the end of the century the extents of both the plant and animal kingdoms were more clearly defined and how development occurs was more fully understood.

Background

Trembley, who was born in Geneva, Switzerland, was working as a tutor in Holland when he first encountered a green hydra called Chlorohydra viridissima in a sample of pond water. It was clinging to a plant, and at first he thought it was itself a plant because of its green color...