238 DEVELOPMENT AND HEREDITV. 



of the stimuli applied to the organism. Remember- 

 ing that by stimuli we mean all of the forces acting 

 on the organism, we must believe that every change 

 in the stimuli necessitates a change in the organ- 

 ism, — or else we are left to suppose that the pro- 

 cesses of development transcend the law of the 

 conservation of energy. We have seen how unnec- 

 essary and erroneous it is to suppose that the 

 germ is a complex mechanism of molecules so 

 charged with potential energy that it will unfold 

 and evolve itself into a predetermined adult form, 

 without regard to the stimuli of its surroundings. 

 All such suppositions fall short of explaining the 

 real nature of developmental change. They do 

 not touch the fundamental nature of the property 

 which makes development possible, nor explain how 

 the complexity of development has originated in 

 the course of evolution. From the manner in which 

 this property of development is exhibited in or- 

 ganisms, from its retention of latent potentialities, 

 from its ability to survive division and commingling 

 of the protoplasm, and from its power of reacting 

 to stimuli, we must conclude that it is a fundamental 

 property of living protoplasm. When we consider 

 the protoplasm's responsiveness to stimuli, and to 

 the effects of repetition or practice, with the intricate 

 co-ordinations that may thereby be effected, also 



