HYDRAS. 157 



The food consists of small worms, water-fleas, or other 

 Entomostraca (Chapter X.), or even little pieces of raw 

 beef, if the observer chooses to feed them. They seize 

 the 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 approach- 

 ing the mouth. 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 quantity of aquatic plants is 

 brought home, the Hydras soon make their way to the 

 lightest side of the -aquarium or bottle and attach them- 

 selves to the glass. At such times I have often amused 

 myself, and doubtless pleased the Hydras, by feeding 

 them with small larvse or aquatic worms. Take with 

 the forceps a small aquatic worm by one end, and pre- 

 sent the wriggling thing to a Hydra's arm. No second 

 invitation 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 the other 

 end is partially digested, but the tentacles will not cease 

 to fish for more. It is said that if the Hydra and the 

 worm are placed in a very deep cell under the micro- 

 scope, the performance can be watched through a low- 

 power objective. I have never succeeded in doing this, 

 but there is no trouble in feeding them in an aquarium. 



