640 MUTATION THEORY OF PROFESSOR DE VRIF.S. 



the assumed extreme antiquity of the habitable condition of the earth 

 has been drawn from the theory of the origination of organic forms 

 by the slow process of natural selection. Indeed such extreme antiq- 

 uity has been assumed expressly to meet the demands of that theory. 

 A general acceptance of the mutation theory will remove that question 

 from such discussions, and geological science would probably not sutler 

 by the loss. 



The great master, Darwin, in one of his aphorismic utterances, says 

 that in "scientific investigations it is permitted to invent any hypoth- 

 esis, and if it explains various large and independent classes of facts 

 it rises to the rank of a well-grounded theory." One can not doubt 

 that if he were now living he would be among the first to give the 

 mutation theory respectful consideration. 



Whatever the final verdict of biologists may be concerning the theory 

 that Professor de Yries has so elaborately proposed, the subject is so 

 important and the presentation is so carefully made that no student of 

 any branch of biology can afford to ignore it. 



