364 Appendix 



reacts negatively toward a falling but not toward a rising 

 temperature. We see also that Euglena in a moderate 

 light reacts negatively toward a decrease but not toward 

 an increase in the intensity of light, whereas in a stronger 

 light the reaction is exactly reversed. 3 



The tendency of organisms to maintain their physio- 

 logical state unaltered consequently resolves itself into a 

 tendency to invariability in their external and internal 

 environments. Thus for instance, oysters and actinians 

 close when exposed to the air; that is, they behave so as 

 to keep the standard of moisture unaltered within them- 

 selves and in their immediate surroundings. 4 



To the tendency toward invariability of environment 

 is due also the position which the organism takes with 

 relation to the direction of the various forces to which 

 it is exposed, especially gravity. Hence the tendency to 

 preserve or restore its normal position. Thus, for in- 

 stance, the amoeba draws in its pseudopodia when they 

 come in contact with solid non-edible bodies; but if it is 

 lifted off the bottom of the aquarium and is suspended 

 in the water it stretches out its pseudopodia in all direc- 

 tions. As soon as one of these touches a solid object, 

 the amoeba takes hold of it, draws its body over to it, and 

 again resumes its original position. Likewise a starfish 

 when inverted tries to turn, over, that is, to return to 

 its normal environmental conditions with relation to 

 gravity. 5 



All "needs"to throw off substances which have been 

 produced by the general metabolism and which the or- 



3 Jennings, Behavior of Lower Organisms, pp. 294-295. 



4 H. Pieron, Uevolution de la memoire, pp. 29, 74. Paris, Flam- 

 marion, 1910. 



5 K. C. Schneider, Vorlesungen iiber Tier psychologic, pp. 5, 57. 

 Leipsic, Engelmann, 1909. 



