PATTEN— COOPERATION AS A FACTOR IN EVOLUTION. 513 



external lines of force acting upon it; (2) to determine its own 

 direction of movement, and thereby determine its distribution in 

 space; (3) to establish definite internal lines of conveyance, unlike 



Fig. I. A-E. Diagrams indicating the lines of exchange in a hypo- 

 thetical growing body suspended in a nutrient fluid, and the form and 

 structure it would assume if growth followed the lines of easiest convey- 

 ance and its products accumulated along the lines of least resistance. 



F-I. Diagrams to illustrate how local inequalities in radial growth would 

 be obliterated and the original asymmetry restored by the tendency of the 

 other parts to grow along the paths of least resistance. 



J-L. Diagrams to illustrate the conversion of radial growth into the 

 apico-bilateral growth, the body of the radiate type, /, becoming the head 

 of the bilateral type, L. The new cylindrical body supplants the old spher- 

 ical one owing to the greater economic advantages and creative power of 

 linear and bilateral distribution over radial distribution. 



