THE HYDR.E, OR POLYPES. 17 



with fluid, their substance being a congeries of cells and 

 granules like the rest of the body, of which, indeed, they 

 are only prolongations. The arms have rows of minute 

 eminences or nodules spirally arranged, which can be 

 exserted and drawn in at pleasure. Tliis structure may 

 account for the security with which the living prey is 

 retained in spite of its struggles, but will in nowise 

 enable us to explain how instruments so dehcate can 

 resist the violent contortions of worms and other rela- 

 tively powerful animals. I have seen a polype seize 

 two large worms at the same instant; and, to reach them, 

 the arms were extended to such a degree of tenuity, as 

 scarcely to be perceptible without the aid of a lens ; and 

 the worms, though very lively, and struggling violently, 

 were unable to break asunder these delicate instruments 

 and escape, but in an instant were struck motionless. 

 This phenomenon strikingly resembles the effect pro- 

 duced by the Gymnotus, or electrical eel ; and it is not 

 improbable, that the Hydra, like that fish, kills its prey 

 by an electric shock. 



