46 BIOLOGICAL LECTURES. 



effect of this factor in both the plant and animal worlds, as 

 a modifier of form, we are obliged to consider it as an agent 

 of the first importance in the possible development of the 

 future science of exact dynamical morphology. Its action is 

 so constant an accompaniment of development that the forces 

 of the latter may be divided into the kinetogenetic, or those 

 that develop movement, and the statogenetic, or those that 

 develop rest or equilibria amongst the parts of the germ. The 

 kinetogenetic forces are the consequences of metabolism, but 

 the statogenetic forces, though dependent upon metabolism, 

 are produced as a consequence rather of the interaction of the 

 surface layers of the plasma of the cells, contemplated as if 

 they were small cohering masses of viscous dead matter. These 

 masses are separated, in the organism or germ, by interfacial 

 planes, free and interfacial curved surfaces that are the results 

 of segmentation and growth, and the extent of the areas of 

 which obey a law first pointed out in relation to soap-bubbles 

 by the blind physicist Plateau, who showed that such bubbles 

 tended to form interfacial films and surfaces wherever in con- 

 tact with each other, of an area that was. the minimal consistent 

 with their statical equilibrium. ^ In this connection it may 

 also be remarked that, inasmuch as the cells of a germ or 

 organism are always in statical equilibrium, their surface layers 

 of molecules also always represent complex systems of equi- 

 potential surfaces, no matter how intricate the form of the 

 organism may be. Since the equilibria between the molecules 

 of the surface layers of cells can normally be disturbed only 

 by the metabolism incident to physiological activity, it is evi- 

 dent that the figure of the organism must ultimately be ascribed 

 to the action of metabolism or to the functions of the organism 

 as affecting the physical properties of its plasma. 



A statical equilibrium in a living cell may be one in which 

 it is not in contact with others at any point on its surface, as 

 in the case of blood-corpuscles or disks. Or a cell may be 

 greatly extended in one direction, as in the case of the axis- 



1 Some interesting applications of the geometrical theory of radical axes and 

 centers also apply here that have never been studied in connection with the phe- 

 nomena of segmentation. 



