THE BUDDING-OUT OF NEW ANIMALS 59 



Daphnia or water-flea. When it was well nourished it 

 branched spontaneously again and again, forming 1 a 

 compound mass made up of scores or even hundreds 

 of polyps, all connected with a single base. The power 

 of locomotion and the power of devouring prey were 

 held to settle the animal nature of Hydra, a decision to 

 which zoologists have ever since adhered. Lyonet 

 went on to try the effect of division upon some common 

 freshwater worms, and found that each part grew into 

 a complete worm. Artificial division is not indispens- 

 able ; in the worm called Nais division takes place 

 spontaneously at certain seasons, one segment dividing 

 repeatedly, so as to form the segments of a complete 

 new individual. The process may be repeated until a 

 chain of worms is produced, which at length breaks 

 up. 1 



A nail was thus driven in a sure place. The concep- 

 tion of an animal was enlarged, for it was shown that 

 an animal may branch and multiply in a way hitherto 

 supposed to be peculiar to plants. The old connecting 

 links between animals and plants (zoophytes, sponges, 

 etc.) had never been really investigated ; no one knew 

 what sort of organisms formed or inhabited their plant- 

 like skeletons. But Hydra, thanks to Trembley's 

 description, furnished a clear example of an animal 

 which possessed some of the attributes of a plant. 

 Forms more ambiguous than Hydra, such as Volvox 

 and Euglaena, were ultimately to make the distinction 

 between animal and plant very uncertain and shadowy. 

 It was Hydra that gave the first clue to the structure of 



1 This discovery is usually attributed to Bonnet, but the testi- 

 mony of Reaumur (Hist, des Jnsecfes, Vol. VI., p. Ivi.) and of 

 Trembley (Hist, des Polypes d'eau douce, p. 323) is decisive in 

 favour of Lyonet. 



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