280 THE SCHOOL OF R]fiAUMUR 



plant or an animal ? Its form and colour were those 

 of a plant, and sensitive plants were known, which droop 

 when touched or shaken. But when he found that the 

 supposed plant could move from place to place, he was 

 inclined to change his first opinion. It then occurred 

 to him to cut the stalk in two, and see whether the 

 halves would live when separated ; if they did, the 

 natural inference would be that it was a plant. The 

 halves gave at first no signs of life beyond movements 

 of contraction or expansion, but on the ninth day small 

 prominences were found to have formed on the cut end 

 of the basal half; these gradually grew into new ten- 

 tacles. Trembley had now two complete organisms in 

 place of one ; each was able to extend or contract its 

 body, and to move about. 



Hydra was therefore capable of increase by artificial 

 fission ; in other words, it could be multiplied by 

 cuttings, like a plant. Leeuwenhoek^ had proved in 

 1702 that Hydra also buds spontaneously, a fact which 

 Trembley abundantly confirmed. These points of re- 

 semblance between Hydra and a plant were however 

 balanced by the discovery that Hydra fed upon small 

 aquatic animals, capturing and devouring live water- 

 fleas (Daphnia) with avidity. No wonder that Trembley 

 wavered in opinion, regarding this puzzling object now 

 as a plant, then as an animal, and again as neither 

 plant nor animal, but something intermediate. When 

 the water was warm and " pucerons " (Daphnia) abun- 

 dant, the polyps formed colonies of great size, each 

 consisting of countless attached animals. 



Trembley found the ovary of the Hydra, and observed 

 the liberation of the ovum. He suspected that a small 

 polyp which afterwards appeared had proceeded from 



' Supra, p. 216. 



