OTHER POSSIBLE GUIDING FACTORS 429 



dividual development, each step of which seems to be in preparation 

 for the next, as though taken in anticipation of it. 



The reader may well revolt against the introduction of speculations 

 of this sort into a treatment of the mechanism of evolution; but if 

 such a concept as elan vital does nothing more than to serve as a con- 

 trast with the more tangible and verifiable mechanisms of evolution 

 we have previously dealt with, it will have justified the space given 

 to it. 



