DE VRIES' "MUTATION" 87 



contributed its quota to the solution of that 

 riddle of the universe which^ until it is solved, 

 will always command a paramount position in 

 the thoughts of men. 



DeVries discourages the notion that muta- 

 tions are always occurring everywhere, which 

 might seem to be one of the inferences from 

 his theory, and his twenty-fourth lecture of 

 the series, delivered before the University of 

 California is entitled "The Hypothesis of Pe- 

 riodic Mutations." The common primrose, he 

 says, seems to be Immutable at present, and 

 argues that it must have had a mutatory pe- 

 riod sometime in the past, when, perhaps, the 

 evening primrose was not mutating. He says : 

 "All the facts point to the conclusion that 

 these periods, of stability and mutability, al- 

 ternate more or less regularly with one an- 

 other." 



He deals the Neo-Lamarckians a heavy 

 blow by his denial of "direct" adaptation, and 

 he greatly strengthens their opponents when 

 he asserts that mutation takes place, not only 

 in useful directions, but in all directions, leav- 

 ing natural selection to destroy the unfit. This 

 is a restatement of Darwin's conception, fol- 

 lowed by Weismann, of "fortuitous" varia- 

 tions, and is contrary to the notion of Spencer 

 and Haeckel, that variations are mainly in the 



