144 AMEBOID MOVEMENT 



some spirally swimming organisms are not asymmetrical enough 

 to make swimming in spirals necessary. It is also unlikely that 

 so many thousands of species of animals and plants of widely 

 different groups would hit upon the same complex habit to solve 

 widely different problems ; for it is not equally important that all 

 animals should swim in straight paths. It also necessitates sup- 

 posing that the ancestors of our present ciliates, flagellates, roti- 

 fers, swarm spores, zoospores, etc., were symmetrical and swam 

 without revolving on the long axis and without forming spirals. 

 Such an assumption is too formidable and makes the explanation 

 top-heavy. 



Spiral swimming is supposed to be due to an automatic regulat- 

 ing mechanism which is present in all moving organisms. It is 

 held to be a spatial aspect of the physical processes originating 

 and controlling movement. The property of moving automatically 

 in an orderly path is inherent in organisms in the same way, 

 e. g., as the property of growth is. A spiral path will be followed 

 whenever an organism is free to move, that is, when not dis- 

 turbed by sensory stimulation. Slight stimulation is often without 

 effect. The justification of supposing that probably all moving 

 organisms are within the grip of the spiral urge is found in the 

 fact that the amebas, ciliates, flagellates, swarm spores, zoospores, 

 Oscillatoria, diatoms, rotifers, larvae of worms, molluscs and 

 echinoderms, oligochaets, copepods, as well as man, all move in 

 regular smooth spirals of one kind or another when free from 

 strong stimulation, and that no organism that is free to move as 

 these are, moves in a straight or irregular path. 



The observations indicate that the same type of mechanism that 

 controls the direction of the path of an organism also unifies and 

 coordinates the streaming of the protoplasm of the ameba, the 

 action of the cilia of the paramecium, or the contraction of the 

 muscles of man, as the case may be. Why the automatic mechan- 

 ism controlling the direction of movement should produce a 

 helical spiral in paramecium, a wavy path or flattened spiral in 

 ameba, and a series of spirals in man, is not yet subject to profit- 

 able discussion, except of course to point out that paramecium 

 is not restricted to two dimensions of space as is ameba and man. 

 In the nature of the case there can be no question but that the 



