70 LIBBIE H. HYMAN 



is that it is only partially determined by the localization of the 

 stimulus and the part of the body on which the stimulus acts 

 and that internal differentiation plays an important role in de- 

 termining the direction of the subsequent movement. To quote 

 directly: 



But the localization of the external stimulus is not the only factor 

 in determining the direction of locomotion After stimu- 

 lation at one side or end, the new pseuclopodium is as a rule not sent 

 out in a direction exactly opposite that from which the stimulation 

 comes. It usually appears, as we have seen, on some part of the 

 original anterior end of the body, and at first alters the course only 



slightly If the new direction still leaves the anterior 



part of the body exposed to the action of the stimulus, then a new 

 pseudopodium is sent out in the same way, still further altering the 



course From these facts it is clear that the direction of 



movement in a negative reaction is not determined entirely by the 

 position of the stimulating agent or the part of the body on which it 

 acts. The moving amoeba is temporarily differentiated, having two 

 ends of opposite character, while the two sides differ from the ends. 

 These internal factors play a. large part in determining the direction of 

 movement; the present action of amoeba, even when responding to 

 stimuli, depends, as a result of these temporary differentiations, partly 



on its past action In amoeba we see in the simplest way 



the effects of past stimuli and past reactions in determining present 

 behavior (Jennings, '06, pp. 21 and 22). 



These remarks of Jennings refer to -weak or moderate stimula- 

 tion. In regard to strong stimulation, Jennings makes the 

 following statements : 



But if all of one side or one end if strongly stimulated, then a pseudo- 

 podium may be sent out on the side opposite so that the animal turns 

 almost directly away from the stimulated region (Jennings, '06, p. 6). 



If the stimulus is very strong the contraction which takes place at the 

 region stimulated may be very marked, resulting in the formation of 

 strong folds in this region. 8 The contraction may include the entire 

 anterior end of the Amoeba. Such a contraction destroys the attach- 

 ment to the substratum, and the new pseudopodium now bursts out 

 in some part of what was the posterior end of the bod}'. The new 

 course followed may then be at right angles to the old one, or at any 

 greater angle or the course may be exactly reversed, the new pseudo- 

 podium being formed at the posterior end (Jennings, '04, p. 183). 



8 Jennings is here speaking of stimulation applied to the anterior end. He 

 does not discuss the effect of strong stimulation when locally applied to other 

 parts of the body. 



