150 MODIFICATIONS OF BEHAVIOR 



therefore no occasion for wonder if the organism responds in 

 different ways to a given stimulus. The wonder would be 

 if it always responded in the same way. 



INFLUENCE OF INTERNAL FACTORS ON BEHAVIOR 



That behavior of organisms in general should be greatly 

 influenced by their internal condition is obvious. Hunger 

 and repletion influence the activity of animals, even hi the 

 lowest forms. Even the white blood corpuscles when they 

 have ingested a number of bacteria refuse to take in any 

 more. Paramoecium, while it may not reject food swept 

 into its gullet, behaves differently when well fed, and Stentor, 

 as we have seen in a previous chapter, takes in objects 

 when it is hungry which at other times are rejected. Hy- 

 dras when hungry eagerly take in food, but they are quite 

 indifferent to it when well fed. If starved for some time 

 they become more active, extend and contract the tentacles 

 and body, and move about in various directions as if to 

 increase their chances of coming in contact with food. The 

 jelly-fish Gonionemus when hungry swims about actively, 

 frequently coming to the surface and settling slowly through 

 the water, with its tentacles extended to catch its food. After 

 a hearty meal the jelly-fish is more frequently at rest and has 

 its tentacles contracted. 



The effect of hunger on the movements of sea anemones 

 is very striking. When starving, anemones will often take 

 in such things as filter-paper and stones which they reject 

 under ordinary conditions, as is well shown in the experiments 

 of Torrey on Sagartia. Weak food stimuli produced by 

 giving the anemones filter-paper soaked with dilute crab 

 juice produce at first the food reaction, but in a little while 

 the animal no longer responds (Nagel, Parker). If meat 

 is offered the food taking activities continue for a long time. 



