EXPEKIMENTS ON HYDR^. 135 



tion to what was reported of the fresh-water Polypes. Read 

 this passage from the last edition of Owen's Lectures, bear- 

 ing the date 1855 : " That the tentacula have the power of 

 communicating some benumbing or noxious influence to the 

 living animals which constitute the food of the hydra, is 

 evident from the eflfect produced, for example, upon an ento- 

 mostracan, which may have been touched, but not seized, by 

 one of these organs. The little active crustacean is arrested 

 in the midst of its rapid darting motion, and sinks apparently 

 lifeless for some distance ; then slowly recovers itself, and 

 resumes its ordinary movement. Siebold states, that when 

 a Nais, a Daphnia, or the larva of a Cheironomus have been 

 wounded by the darts, they do not recover, but die. These 

 and other active inhabitants of fresh waters, whose powers 

 should be equivalent to rend asunder the delicate gelatin- 

 ous arms of their low-organised captor, seem paralysed 

 almost immediately after they have been seized, and so 

 countenance the opinion of Corda, that the secretion of a 

 poison enters the wounds." Such statements can only be 

 set aside by direct Experiment ; and the superiority of 

 Experiment over mere Observation needs no argument. 



As a matter of observation, I too had been struck with the 

 fact noticed by Owen. I saw the tiny Water-fleas drop ap- 

 parently lifeless to the bottom of the phial, after being some 

 time held by the tentacle of the Hydra ; and, intently watch- 

 ing 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 {Cy- 



