Modffiability in Behavior. 455 



by feeding meat alone than by feeding the two alternately, or 

 than even by feeding filter paper alone. Thus, two specimens of 

 Aiptasia No. 2, which we will call A and B, living side by side, 

 were both found to take plain filter paper readily. Then A was 

 fed alternately meat and filter paper, while B was fed successive 

 pieces of meat. After eight pieces had thus been fed to each, 

 A still took filter paper (though slowly), while B refused it abso- 

 lutely — though B would still slowly take a piece of meat. Thus 

 B, through satisfying its hunger with meat, had come to reject 

 filter paper, while A still accepted it after devouring several 

 pieces. Apparently meat is more satisfying to sea anemones 

 than is filter paper! 



In another case a specimen of the same species was fed filter 

 paper alone. It swallowed ten pieces in succession, till the body 

 was puffed out with them, meanwhile ejecting some of the pieces 

 already swallowed, in the intervals between the taking of new ones. 



In Aiptasia annulata similar relations were found. The animal 

 could be caused to reject filter paper soaked in crab juice much 

 more readily by feeding it meat alone than by feeding soaked 

 paper alone, or by feeding the two in alternation. A large number 

 of comparative experiments were tried, showing this result to be 

 general. It is therefore clear that the state of hunger or satiety 

 is the essential factor in this behavior, in Aiptasia. 



The experiments showed further that it is not the mere mechani- 

 cal fulness of the digestive cavity that determines acceptance or 

 rejection, but some change in the metabolic processes themselves. 

 Filling the digestive cavity with filter paper does not have the 

 same eff'ect in producing rejection as does filling it with meat. 

 Even when the cavity is so filled that pieces of paper are repeatedly 

 disgorged, new pieces are readily taken. In Aiptasia No. 2, a 

 piece of paper that has been disgorged after remaining some time 

 in the cavity, is usually swallowed again immediately, if it is 

 returned to the disk. 



As the animal becomes less hungry the details of the behavior 

 toward food bodies change greatly. In a hungry specimen, as 

 we have seen, the food reaction is rapid, often requiring but ten 

 to fifteen seconds. After several pieces of meat have been ingested 

 the reaction of all parts becomes much slower and less precise. 

 The tentacles touched by the food may not react at all for several 

 seconds; then they bend in a rather languid way toward the 



