324 GENERAL BIOLOGY 



each is but a part of a true explanation, the complete 

 key to which will be discovered only by subsequent 

 researches. The painstaking and brilliant work of 

 Darwin can never be set aside in spite of the fact that 

 we may be compelled to doubt the universality of 

 his theory of Natural Selection. Instead of his 

 fluctuating variations, however, it may be that the 

 basis for selection is something like Johanssen's 

 " genes," or those vague units of organization that 

 reveal themselves to us as Mendelian unit-char- 

 acters. But we must have a far deeper insight into 

 the physics and chemistry of the organism than 

 is now available before we can begin to formulate 

 an hypothesis as to the real nature of these units. 



