PHENOMENA OF INHERITANCE 211 



of evolution, but that the case is quite different 

 with "sports." 



More recently the entire biological world 

 has been greatly influenced by the "Mutation 

 Theory" of deVries, which has placed a new 

 emphasis upon the importance of sudden vari- 

 ations in the process of evolution. At first 

 deVries was inclined to emphasize the degree 

 of difference between discontinuous and con- 

 tinuous variations, but in later works this dis- 

 tinction is given a minor place as compared 

 with the distinction between inherited and 

 non-inherited variations. Inherited variations, 

 whether large or small, are called by deVries 

 "mutations," whereas non-inherited variations 

 are known as "fluctuations." The former are 

 caused by changes in germinal constitution, 

 the latter by alterations in environmental con- 

 ditions; the former represent changes in he- 

 redity, the latter changes in development. 



3. Mutations and Fluctuations. This clear 

 cut distinction between mutations and fluctu- 

 ations marks one of the most important ad- 

 vances ever made in the study of development 

 and evolution. Thousands of fluctuations oc- 



