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. 
BIBLIOGRAPHY. 
Bateson, W.: Materials for the Study of Variation, 1894. 
Vries, H. bE: Die Mutationstheorie, 1901. 
J Species and Varieties, their Origin by Mutation, 
IQ05. 
MacDoucaL, D. T.: Various papers published by Carnegie 
Institution. 
Tower, W.L.: An Investigation of Evolution in Chrysomelid 
Beetles of the Genus Leptinotarsa, 1906. 
