vi PREFACE 



is an innate tendency in all organisms that move which compels 

 them, when free from stimulation, to move in definite predictable 

 paths. This thesis is discussed at some length in Chapters XII 

 and XIII. 



In view of the fact that ameboid movement has been considered 

 largely as a theoretical question heretofore, I wish to state at 

 once that my discussion of this subject is based directly on ob- 

 servation and experiment. I have no new theory of ameboid 

 movement to offer ; the list of theories is already extensive enough. 

 I am, on the other hand, strongly of the opinion that this funda- 

 mental question, if it is to be solved at all, can be solved only 

 by persistent observation and experiment on the ameba and re- 

 lated organisms themselves. "All knowledge is vain and erron- 

 eous excepting that brought into the world by sense perception, 

 the mother of all certainty" (Leonardo). 



