318 BEHAVIOR OF THE LOWER ORGANISMS 



of complexity in structure. Differentiation of structure and of physio- 

 logical states must go hand in hand. It is not our province to attempt 

 to account for structural differentiations. The problem is the general 

 problem of evolution. 



(4) Progress in behavior may take place through increased variety 

 and precision of the movements brought about by stimulation. Certain 

 kinds of movements are much better adapted to relieving an organism 

 from an unfavorable stimulation or securing it a favorable one than are 

 others. This is illustrated by a comparison of the reactions of Amoeba 

 and Paramecium, or of the reaction of Bursaria to heat with that 

 of Paramecium, as set forth on page 305. Owing to the difference in 

 the effectiveness of their movements, if an area containing equal num- 

 bers of Paramecia and Bursaria is heated at one end, many of the 

 Bursariae are killed, while all the Paramecia escape. 



New and better adapted methods of movement may be acquired 

 through the selection of varied movements, in conjunction with the 

 law of the resolution of physiological states. Under strong stimula- 

 tion the organism, as it passes from one physiological state to another, 

 tries successively all the movements of which it is capable. One of 

 these movements (the spiral course, in the case of Bursaria) finally 

 removes the organism from the stimulating agent. This happens every 

 time the organism is stimulated in this manner. The result is that each . 

 physiological state is resolved into the succeeding one, until that one is 

 reached in which the organism responds by the effectual movement. 

 After a number of repetitions, this resolution takes place immediately, 

 in accordance with the law that after repeated resolutions of one physio- 

 logical state into another, this resolution takes place spontaneously and 

 rapidly. Thus the organism responds at once with the effectual move- 

 ment, and escapes. 



In the same way the use of new organs might be acquired. Suppose 

 that an Amoeba sends forth, as sometimes happens, a long, slender pseu- 

 dopodium, which may vibrate back and forth, like a flagellum. When 

 stimulated, the overproduced movements of the organism, as it passes 

 from one physiological state to another, include the vibration of this 

 pseudopodium. Suppose that by this vibration the Amoeba is at once 

 moved away from the stimulating agent the pseudopodium acting as 

 does the flagellum in Euglena. If this is repeated, the physiological state 

 inducing other movements will always be resolved finally into that induc- 

 ing this one, and in time this resolution will take place so rapidly that 

 only this movement will come to actuality. The Amoeba will have ac- 

 quired the habit when stimulated of swimming by means of a flagellum. 



Thus the behavior of organisms is of such a character as to pro- 



