EXPERIMENTS ON HYDR^. 137 



the phial containing the Hydrse, I observed it thrice caught 

 by three different IIydra3 ; it did not " sham dead," but tore 

 itself away without visible hurt. Nay, I also observed one 

 of those animalcules known as " paste-eels " for some time 

 in contact with the tentacle of a Hydra, on the stage of the 

 microscope, but, in spite of its having no shell to protect it 

 from the poison, it was unhurt by the contact. Not having 

 a Nais, I could not test what Siebold says of it ; but what 

 has already been mentioned must, I think, suffice to convince 

 the reader that the current opinion is an error, founded on 

 Observation unverified by Experiment. It was only by veri- 

 fication, according to the demands of inductive scepticism, that 

 the error became obvious.* 



Had Trembley's celebrated work on the fresh- water Polyi^es 

 been read by one in a hundred of those who cite it, the 

 error just noticed would never have gained currency ; the 

 observations of that very accurate observer would have 

 suggested a fallacy in the interpretation. " J'ai vu souvent 

 des Piicerons (water-fleas) qui parvenoient a se mettre en 

 liberte. II m'a paru qu'ils le pouvoient plus facilement que 



* The day this was written I could not rest till I had dredged a favourite 

 pond, and brought home a supply of Na'ids, with whicli, on the following morn- 

 ing, I tested Siebold's statement. First, I placed a Xuis fiUformis in a glass 

 cell with a Hydra viridis; but although its wrigghng constantly brought it into 

 contact with the tentacles, it was never grasped. I then placed a Nals in the 

 phial containing many Ilydnc ; it was instantly caught by one, and held for 

 some time till it struggled itself free. Not only was it apparently unhurt by 

 this contact, but to-day it is as lively as it was three days ago, just before the 

 experiment. With two other Naids the same result was obsci-ved. This com- 

 pletes the overthrow of the current opinion respecting the Hydra's paralysing 



power. 



M 



