THE KINETIC SYSTEM 159 



etc., may be regarded as aiding materially, though 

 indirectly, in the function of the kinetic system. 



Adaptive Variation in Amount of Energy Stored in 

 Different Animals 



In considering the evolution of such a system in the 

 human organism two points demand special attention : 

 the amount of potential, transformable energy which is 

 stored in the animal body in excess of the needs of the 

 moment ; and the variation in rates of speed at which 

 this store must be expended in accordance with the 

 dictates of any specific adaptive reaction. In general, 

 the amount of available, convertible energy resident 

 in living organisms appears to be proportional to the 

 dependence of the organism upon motor activity for 

 survival. That is, as we ascend the life scale from the 

 stationary species and animals protected by such me- 

 chanical contrivances as shells and barbs, poisons, 

 odors and emanations, and approach animals which 

 depend entirely upon power and speed for survival, 

 we find an increasing need for the storage of energy 

 in great excess of the needs of the moment and for 

 discharging that energy and overcoming the consequent 

 acid by-products at varying rates. 



It is conceivable that plants and polyps, which make 

 little change in their position throughout life, have no 

 need for an elaborate kinetic system. The snail, the 

 turtle and Crustacea generally, protected by their 

 shells, are proverbially slow of motion, and it is diffi- 

 cult to exhaust the small supply of convertible energy 

 which is all that is required for their sluggish routine 

 reactions. The horse and the deer, on the other hand, 



