72 The Animal Mind 



ble and inedible substances when very hungry (291). Sagar- 

 tia davisi will also swallow inedible substances if hungry 

 enough (403). Stoiachactis helianthus will give either a 

 positive or a negative reaction to food according to its condi- 

 tion of hunger or satiety (207). The reaction of Metridium 

 to food may vary decidedly with the degree of hunger (3) ; 

 although it will continue taking food as long as the process is 

 mechanically possible (211). Fatigue has also been shown 

 to affect the food responses of Metridium and other sea- 

 anemones ; specimens that have been fed meat and filter paper 

 alternately will after a time refuse to take filter paper (207, 

 291, 303). This behavior was thought by Nagel to indicate 

 that the animal had discovered the deception practiced upon 

 it ; but apparently the real cause is fatigue ; showing itself first 

 T with reference to the weaker of the two stimuli (3). 



As regards the localization of the sensitive elements, au- 

 thorities, and probably species, differ. Nagel finds the ten- 

 tacles most sensitive (291) ; Loeb observed that the stump of 

 the animal has discriminative reactions (237), while Fleure 

 and Walton state that in the species tested by them the mouth- 

 region is most responsive to chemical stimulation (127). 



A certain amount of discrimination between mechanical 

 stimuli is asserted of these animals by Romanes. "I have 

 observed," he says, " that if a sea- anemone is placed in an 

 aquarium tank and allowed to fasten upon one side of the 

 tank near the surface of the water, and if a jet of sea water 

 is made to play continuously and forcibly upon the anemone 

 from above, the result of course is that the animal becomes 

 surrounded with a turmoil of water and air bubbles. Yet 

 after a short time it becomes so accustomed to this turmoil 

 that it will expand its tentacles in search of food, just as it does 

 when placed in calm water. If now one of the expanded ten- 

 tacles is gently touched with a solid body, all the others close 



