hyd'ras. 167 



arranged the arms or tentacles. These tentacles are 

 themselves hollow, and communicate with the cavity 

 of" the stomach. 



The food consists of small worms, water-fleas or 

 other Entomostraca (Chapter X.),or even of little 

 pieces of raw beef, if the observer chooses to feed 

 them. They seize the living victim as it is swimming 

 past, by twining a tentacle around it and drawing the 

 struggling creature down to the mouth, through which 

 it is thrust into the stomach. The act of seizure takes 

 place so rapidly that the eye can seldom follow it. The 

 observer can usually only know that the prey is caught 

 and is slowly approaching the oral aperture. Often 

 when the captured object is too large or strong for one 

 arm to hold, several tentacles bend over and twine 

 around it. A creature once caught rarely escapes. 

 When a gathering of aquatic plants is brought home, 

 the Hydras soon make their way to the lightest side of 

 the aquarium or bottle and attach themselves to the 

 glass. At such times I have often amused myself, and 

 doubtless pleased the Hydras, by feeding them with 

 small larvae or with aquatic worms. Take in the for- 

 ceps a small aquatic worm by one end, and present the 

 wriggling thing to a Hydra's arm. No second invita- 

 tion is needed. The worm is embraced as quick as a 

 flash, and, if too long to be swallowed all at once, part 

 of it will hang out of the mouth until t+ie other end is 

 partly digested, but the tentacles in the meanwhile, 

 will not cease to fish for more. It is said that if the 

 Hydra and the worm .are placed together in a deep cell 

 under the microscope, the performance can be watched 

 through' a low-power objective. I have never suc- 

 ceeded in doing this, but there is no trouble in feed- 



