496 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



These two forms of motion have been coextensive 

 with the existence of life, neither one preceding the 

 other in time. Statogenesis is the expression of a form 

 of energy which characterizes inorganic matter, while 

 bathmogenesis is entirely peculiar to living things. 

 Kinetogenesis is the fundamental principle in organic 

 evolution, since it determines the amount and kind 

 of physiogenesis, because it creates the environment 

 which furnishes the conditions of physiogenesis. Pro- 

 gressive organic evolution may, then, be described as 

 due to kinetogenesis corrected by natural selection. 

 At the basis, however, molar organic motion, i. e., con- 

 traction of protoplasm, is probably molecular, but it is 

 distinguished from other forms of molecular motion in 

 the vast aggregate of molecules which move simultan- 

 eously in one direction, as in an amoeba or a muscle, 

 thus effecting a change in the position of all or a part 

 of an organism. Hence the distinction is a real one. 

 Molar motion being, then, of such fundamental im- 

 portance as a factor in evolution, the cause of such 

 motion is also a capital question. Contraction of 

 protoplasm is caused by stimuli, such as currents of 

 electricity and chemical reagents ; but such stimuli are 

 not those which ordinarily produce the contractions to 

 which the molar movements of living animals are due. 

 In those animals which possess a nervous system it 

 has been shown that contractions only follow stimuli 

 which are conveyed to the contractile elements by 

 nervous threads, and the internal energy which repre- 

 sents the external stimulus, is called nervous energy 

 or neurism. In animals without a nervous system, and 

 in plants, external stimuli must be justly supposed to 

 be converted into the same form of energy, which in 

 such organisms has a general circulation throughout 



