CONTENTS* 



Page 

 Observed changes in hereditary characters in relation to evolution. Prof. 



H. S. Jennings, Johns Hopkins University, Baltimore, Maryland ^81 



The control of the sex ratio. Dr. Oscar Riddle, Department of Experimen- 

 tal Evolution, Cold Spring Harbor, New York. ! 319 



The role of selection in evolution. Prof. W. E. Castle, Harvard University, 

 Cambridge, Massachusetts 369 



1 The lectures are reprinted from the Journal of the Washington Academy of 

 Sciences, Vol. 7, 1917. 



