158 THE THEORY OF MUTATION 



out that it is usually very difficult to form a judgment 

 as to the real usefulness or otherwise of organs. 



[NOTE. A most remarkable series of mutations has 

 been obtained by Prof. T. H. Morgan, of New York, in 

 the little Fruit Fly Drosophila. A description of many 

 of them, and of the manner of their inheritance, will be 

 found in his books ' A Critique of the Theory of Evolu- 

 tion,' Princeton University Press, 1916, and ' The 

 Physical Basis of Heredity,' 1919.] 



BIBLIOGRAPHY. 



BATESON, W. : Materials for the Study of Variation, 1894. 

 VRIES, H. DE : Die Mutationstheorie, 1901. 



,, Species and Varieties, their Origin by Mutation, 



1905. 

 MACDOUGAL, D. T. : Various papers published by Carnegie 



Institution. 

 TOWER, W. L. : An Investigation of Evolution in Chrysomelid 



Beetles of the Genus Leptinotarsa, 1906. 

 GATES, R. R. : The Mutation Factor in Evolution, 1915- 



