5 I2 PRIMARY FACTORS OF ORGANIC EVOLUTION. 



lief from the oppression of too great bulk. With the 

 increasing specialization of form, this process would 

 become necessarily localized in the body, and growth 

 would repeat such resulting structure in descent, as 

 readily as any of the other structural peculiarities. No 

 function of the higher animals bears the mark of con- 

 scious origin more than this one, as consciousness is 

 still one of the conditions of its performance. While 

 less completely " voluntary" than muscular action, it 

 is more dependent on stimulus for its initial move- 

 ments, and does not in these display the unconscious 

 automatism characteristic of many other functions. 



There remain, however, some phenomena which do 

 not yield so readily to this analysis. First, we have the 

 conversion of inorganic substances into protoplasm by 

 plants. It is also well known that living animal or- 

 ganisms act as producers, by conversion, of various 

 kinds of inorganic energy, as heat, light, sound, electri- 

 city, motion, etc. It is the uses to which these forces are 

 put by the animal organism, the evident design in the 

 occasion of their production, that gives them the stamp 

 of organic life. We recognize the specific utility of the 

 secretions of the glands, the appropriate distribution of 

 the products of digestion and adaptation of muscular 

 motion to many uses. The increase of heat to protect 

 against depression of temperature ; the light to direct 

 the sexes to each other ; the electricity as a defence 

 against enemies display unmistakably the same util- 

 ity. We must not only believe that these functions 

 of animals were originally used by them under stimu- 

 lus, for their benefit, but, if life preceded organism, 

 that the mechanism which does the work has devel- 

 oped as the result of the animal's exertions under stim- 

 uli. This will especially apply to the mechanism for 



