EN GRAPHIC RECORDS 463 



his highly organised nervous and muscular systems, is able to 

 adapt himself readily and, therefore, reigns supreme. 



In the previous chapter we referred to some experiments in which 

 planarians were subjected to two stimuli — geotropic and photo- 

 tropic — and stated that the movements of the animal were 

 governed by the angle of incidence and relative intensities of the 

 effective stimuli falling on it. Crozier and Wolf found on carrying 

 out repeated experiments on the same animals that adaptation 

 to light gradually took place. This adaptation occurs according 

 to a definite mathematical formula, so that one could predict, for 

 any intensity of light, how soon the animal would cease to be 

 influenced by it and follow undisturbed its geotropic path. Some 

 change had, therefore, occurred in the protoplasm of the animalcvde 

 which rendered it insensitive to light. 



A somewhat different type of experiment leads us to the same 

 conclusion. If we arrange the stage of a microscope so that a 

 tiny strongly illuminated square appears in the field, and observe 

 the movements of an amoeba near the square, we will find that, by 

 chance, a pseudopod will enter the illuminated part for about 

 1 or 2 microns. Protoplasmic flow in the pseudopod will stop for 

 a moment, then begin again, but in the reverse direction. Finally, 

 the pseudopod will withdraw from the illuminated area. Later, 

 another pseudopod will be advanced towards the square, thrust in, 

 and the above process repeated, and so on. " After the animalcule 

 had repeated this process several times, thrusting one pseudopod 

 after another into the square, a general change in the course of 

 action took place. Pseudopods were no longer formed on that side 

 of the organism. It was noted that the number of attempts to 

 enter the square decreased with every succeeding pseudopod 

 formed, till wdth the last pseudopod thrust out in that direction a 

 single attempt sufficed and the square was barely entered. 

 Repeated experiments with the same specimen of amoeba proteus 

 led to such a change in the protoplasm that after ten or fifteen 

 experiments the moment the organism touched the square it 

 withdrew that pseudopod and, thrusting one out in the opposite 

 direction, moved away from the light''' (Mast). 



McClendon, in a modification of Mast's experiment, tapped the 

 amoeba with a glass rod, and found that the strength of the stimu- 

 lus, the number of shocks and their frequency, all influence the 

 response. That is, the amoeba can profit by experience and be 

 taught just like the higher animals. 



Careful examination of the proto])lasm during these lessons 

 shows that a different mass of protoplasm is thrust into the square 

 each time in any one experiment. That is, the shock leaves some 



