3 o INDIVIDUALITY IN ORGANISMS 



the action of factors external to the mass acted upon, 

 whether part of a cell or a cell mass. A simple schematic 

 consideration will serve to make these points clear. 

 Let us assume a spherical mass of living protoplasm 

 (Fig. i) which is morphologically and physiologically 

 homogeneous except as regards the essential features of 

 protoplasm or cells. Such a mass, whether consisting 

 of a single or of many cells, possesses no axis, is undiffer- 



FIG. i. Diagram illustrating the origin of a single axial gradient in 

 protoplasm: a, the point of action of the external factor. 



entiated, and is not a physiological individual. Now let 

 us suppose some external factor which increases meta- 

 bolic rate, a " stimulus," to act on this mass in the region 

 a of its surface. The first result of such action is an 

 increase in the rate of metabolic or of certain metabolic 

 reactions in the region a. This is followed by a spread- 

 ing or irradiation of a dynamic change, either over the 

 surface of the mass or through it from the region a. 



