INFLUENCE OF INTERNAL FACTORS 151 



but eventually become weaker and may later be replaced by 

 movements of rejection. That it is not the mere filling of the 

 digestive cavity alone that determines the change of be- 

 havior is shown in an experiment of Jennings on Aiptasia, 

 in which the digestive cavity was filled with filter-paper. 

 When so filled that pieces of paper were repeatedly disgorged 

 the anemones continued to take in new pieces. The meta- 

 bolic conditions of the organism are therefore a determining 

 factor in its behavior toward food. 



To a certain extent though, the food taking is influenced 

 by the previous local stimulations of particular parts of the 

 body. Nagel and Parker have found in Adamsia and 

 Metridium that the tentacles of a certain part of the body 

 after being stimulated several times with filter-paper soaked 

 in meat juice will refuse to carry it toward the mouth. If 

 now the soaked paper is offered to other tentacles they give 

 the usual food taking reaction. Similar behavior was ob- 

 served by Jennings in Aiptasia, who found also that if one set 

 of tentacles had carried several pieces of meat to the mouth 

 until they refused to carry it longer, the other tentacles, 

 while they might still carry the meat, would cease to respond 

 much sooner than they would if the animal had not already 

 received food. The animal according to Jennings "is a 

 unit so far as hunger and satiety are concerned." 



The effects of hunger and satiety on the behavior of higher 

 forms are so general and so familiar that we need not pursue 

 the subject further. As regards food animals hi general are 

 self regulating mechanisms, and if under certain conditions 

 an injurious quantity of food is devoured, or material which 

 is unwholesome is selected, the exceptional behavior only 

 serves to emphasize the rule that the food taking of animals 

 is on the whole pretty adequately adjusted to their needs. 

 In higher forms this function is conscious and voluntary, 



