OTHER THEORIES OF SPECIES-FORMLNG 283 



4. The tetrakinelic theory of'H. F. Osborn: This is a recent restate- 

 ment in energistic terms, of the causo-mechanical basis of evolution. 

 It is placed in the next chapter, but cannot fully be understood until 

 the subject of genetics has been presented. 



It is almost impossible satisfactorily to pursue a further study of 

 the causal factors of evolution without encroaching upon the field that 

 is now called genetics, and so we shall pass without further explana- 

 tions to a consideration of this field of experimental and analytical 

 evolution. 



