ORGANIC MOVEMENTS 23 



Jennings has spoken of the method of " trial and error ): 

 in these cases as well as in others to be studied hereafter. 

 I should like to avoid this term, for, besides its psychological 

 aspect, which seems to be out of place here, the word " trial ' 

 seems to me to imply some sort of so-called " experience." 

 But here in the simple fact of movement at random there 

 is nothing of that sort as far as we know ; it only might 

 be, that the true random-motions might offer the material 

 for " experience," as will be seen on a later occasion. 



Contingency thus is the leading characteristic of the 

 performance of all these most elemental single motor acts, 

 as well as of their being stopped. 



But there are cases where something more definite 

 may be said about the factors that determine the type of 

 each single motion. Typical interior states not only 

 quite generally conceived ones may change the type of 

 reaction as well as stop motion altogether in spite of 

 the external stimulus being still present. Thus it is well 

 known, especially from the studies of Coelenterata, that a 

 hungry animal reacts otherwise or not at all, if compared 

 with a fed one, with regard to the same stimulus, and there 

 are also differences of reaction corresponding to the different 

 embryonic stage or the age of an organism. 



And moreover we find that a competition among 

 various external stimuli may determine the type of 

 reaction. The effect of a second external stimulus may 

 be either that there is no longer any reaction to the 

 original stimulus, or that a sort of resultant reaction 

 goes on, or that the type of the original reaction is other- 

 wise changed. Here we must recall attention to the 

 so-called reversal of the " sense " of the reaction, as 



