ACTIVITY AND ENVIRONMENT 27 



the same living substances into different special organs would of necessity 

 give different organisms different properties. 



Different chemical substances often behave differently under a given 

 condition of temperature, pressure, or light, etc. Likewise, if a cockroach 

 and a house fly are liberated in the center of a room, the fly goes to a 

 window and the cockroach into a shadow; furthermore, a cold night will 

 kill the house fly, while to dispose of the cockroach the proverbial two 

 wooden blocks are necessary. Both differences in physiological char- 

 acter (behavior) are due to differences in the organisms. Different 

 organisms often behave differently in the same intensity of the same 

 physical factor, for example, the same temperature or light, just as the 

 different chemical substances do. Different chemical substances often 

 undergo different changes with variations in temperature, pressure, or 

 light. Each has its characteristic reactions. Still whole groups may be- 

 have quite similarly. Changes in conditions affect organisms. We have 

 all noted the effect of a cool day upon the activity of animals such as the 

 insects. Different organisms usually behave differently in some respects, 

 while whole communities may behave quite similarly in other respects. 



a) The organism as unaffected by the environment. — When all of the 

 external conditions continue approximately the same, the activities of 

 the organism are called spontaneous (35, p. 347). As has been stated, 

 the organism is naturally active. Accordingly, movements may possibly 

 take place as a manifestation of the released energy inside the animal, 

 or of disturbances and changes in the organism which are not directly 

 initiated by the environment. Probably animals often move without 

 any external stimulation (44, chap. xvi). One who has observed the 

 wonderful Japanese dancing mice knows that their constant movement 

 may not be the result of the external conditions, but of the energy which 

 is expended within the organism. 



Jennings (44) stated that these spontaneous movements must be 

 recognized in the study of behavior, and that many errors have arisen 

 from their neglect. If we see an animal moving, we should not assume 

 that it is moving because of some external condition acting on it at the 

 time. It may be due to previous stimulation or it may be the result 

 of internal conditions. Growth, maturity, reproduction, and death are 

 accompanied by changes in behavior, structure, etc. All may take place 

 without great change in environment. 



b) The organism as affected by the environment. — Many organisms are 

 not sensitive to slight changes in the external environment. Having 



