But in addition to presenting an account of the main facts concerned in the movement of the ameba from the various points of view mentioned above, this book has a second object which is scarcely subsidiary to the main one. This second object is to present the thesis that moving organisms in which orienting organs are absent or not functioning, always move in orderly paths, i. e., in helical or true spiral paths. The movements of the ameba under controlled conditions, which, as the following pages will show, take the form of a helical spiral projected on a plane surface, therefore serve as an introductory study to the movements of organisms generally. For the presumption is strong that there 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 observation 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 fundamental question, if it is to be solved at all, can be solved only by persistent observation and experiment on the ameba and related organisms themselves. “All knowledge is vain and erroneous excepting that brought into the world by sense perception, the mother of all certainty” (Leonardo). CONTENTS PAGE CHAPTER I Introduction 1 CHAPTER II Historical Sketch 3 CHAPTER III The General Features of Endoplasmic Streaming 8 CHAPTER IV The Transformation of Endoplasm into Ectoplasm 18 CHAPTER V Pseudopods and the Nature of the Ectoplasm 25 CHAPTER VI The Species Question 41 CHAPTER VII Experiments on the Surface Layer of the Ameba 48 CHAPTER VIII On the Nature of the Surface Layer 63 CHAPTER IX The Surface Layer and Theories of Ameboid Movement 76 CHAPTER X Streaming, Contractility and Ameboid Movement 92 CHAPTER XI The Surface Layer as a Locomotor Organ 105 CHAPTER XII The Wavy Path of the Ameba 109 CHAPTER XIII The Wavy Path of the Ameba and the Spiral Paths of Ciliates and Other Organisms 126 CHAPTER XIV Conclusions 142