AMEBOID MOVEMENT 141 



similar nature in all organisms, as is indicated by the tendency 

 to spiralize the path. This mechanism, being automatic, abso- 

 lutely controls the direction of the path so long as outside inter- 

 ferences permit; but when sensory stimulation occurs, or when 

 changes in temperature, etc. occur, the mechanism is no longer 

 able to operate automatically or smoothly. The direction of the 

 path then depends upon the nature and direction from which 

 stimulation was received, and upon the degree and direction of 

 change of temperature, etc. 



The importance of this conception of movement lies in the 

 fact that it enables us to look at a large mass of otherwise un- 

 related data from a single point of view. Secondly, it permits 

 of a mathematical treatment of the whole subject of movement 

 in organisms. And third, it replaces a teleological explanation of 

 spiral movement ki unicellulars, swarm spores, rotifers, etc., with 

 a purely mechanistic explanation. 



