Trembley regarded the freshwater hydra (then called a polyp) as an animal rather than a plant because of its feeding behavior. The polyp captures food with its tentacles and actively delivers the prey to its interior cavity for digestion. Moreover, the polyp reacts to touch, and transports itself from place to place, responding to agitation and moving toward light and warmth.

When Trembley cut a polyp into two pieces, believing that only a plant could regrow, he was surprised to discover that both parts regenerated to form two living polyps! He documented that entire polyps regrow from various parts regardless of how they are divided. 

Leeuwenhoek had previously described the polyp, but had not reported this ability to regenerate. Regeneration seemed to challenge preformationism. Preformationism met its ultimate demise with the 19th-century development of cell theory.

This copy is inscribed and annotated by George Sarton (1884-1956), a founder of the professional field of history of science in America.