EXPERIMENTS ON HYDR^. 143 



the Hydra ; and, intently watching them, I saw them 

 at last swim away again as lively as before. I removed 

 a Hydra from the phial, in a little water, and placing 

 it on a slip of glass, allowed it to settle and expand 

 there for two hours, when I added several water-fleas 

 {CypyHdce) to the little pond, and patiently watched 

 them swimming to and fro. Eepeatedly they touched 

 the tentacles in their course, but were not hurt, were 

 even not arrested. At length one was caught, and 

 held for some seconds ; it then fell to the bottom, and 

 remained motionless for at least two minutes, after 

 which it started up, and was off" as if its course had 

 never been arrested. This certainly had very much 

 the appearance of a case of slight paralysis ; the 

 animal seemed arrested by some benumbing influence, 

 which for two minutes rendered it powerless ; at the 

 expiration of that time it seemed to have sufficiently 

 recovered itself to swim away. If Observation alone 

 sufficed, in questions so complex as those of Biology, 

 this observation would have confirmed the statements 

 of Siebold, Corda, and Owen. But observation alone 

 does not suffice. I bethought me of a simple experi- 

 ment. With a needle I gently arrested one of these 

 water-fleas ; it suddenly sank motionless, remained thus 

 for more than a minute, and then darted off" again. 

 Thrice I repeated this act, and each time with similar 

 result. Will any one say the needle had a paralysing 

 power, or a benumbing poison which was secreted, 

 when the animal came in contact with it ? And does 

 not the reader at once recognise in this sudden motion- 



