THE LOWER FORMS OF LIFE. 73 



end. After a time the youngster separates from its respected 

 parent and starts a hydra life of its own. They also increase 

 by fissiperation or division, as we have seen done by the Infusoria, 

 and also by the union of the sexes. 



Trembley, by whom the true nature of the fresh-water Hydra was 

 first determined, performed, many most interesting experiments with 

 them, which have been fully verified by later inquirers. Among other 

 things, he tells us that upon one occasion two Hydrse had seized 

 upon the same worm, and, after a short struggle, the strongest being 

 unable to get the worm away, swallowed it with rts brother polyp at 

 the same time. But he was no nearer the winner of the battle by 

 this manoBuvre, for digestion having gone on equally in the stomachs 

 of the two Hydrae, the swallowed one was ejected, none the worse for 

 its adventure in the belly of the polyp. On another occasion he 

 turned a Hydra inside out by means of a fine wire ; thus the stomach 

 was outside. But this process did not at all inconvenience the 

 creature, which went on catching animalculse and digesting them 

 with what had been his outer skin, just as though nothing had 

 happened. 



To vary his experiment he cut one into two parts, and was 

 surprised to find that in a short time each developed itself into a 

 perfect polyp. He then cut off a small piece with the same result, 

 and even divided one into fifty parts, with the effect of causing fifty 

 new Hydrse to rise up. He then grafted one upon another, and even 

 two of different species, and they grew firmly united, like the 

 Siamese twins. It is remarked that when a Hydra is cut into two 

 that the head portion develops a tail part more quickly than the tail 

 part will form a head and tentacles. 



The history of the fresh-water polyp, or Hydra, is a very important 

 and interesting one in science. The celebrated Reaumer was a firm 

 believer in the floral or vegetative character of Corals, Madrepores, 

 &c. ; and when Peysonnel, a French naval surgeon, addressed a 

 memoir to the French Academy in 1727, maintaining their animal 

 nature, he was strongly opposed by Eeaumer. Peysonnel, being 

 quite sure that he was right, published, in 1751, a paper in the 

 " Philosophical Transactions " of our Royal Society, and Trembley's 

 discovery of the Hydra came most opportunely to the assistance of 

 truth. The French Academy appointed a commission of inquiry, 

 which confirmed all Peysonnel' s statements. Eeaumer was convinced, 

 retracted his former opinions, and wrote in favour of the new 

 doctrine. Strange to say, however, the scientific world was not 

 convinced. Dr. Parsons analysed and combated Peysonnel' s views 

 in a paper read before the Eoyal Society in May, 1752, and he 

 seems to have carried the majority with him. About this time. 



