PREFACE TO SECOND EDITION 



The interest of the public and the kindness of the publishers 

 have made possible a revised edition of this book within a year 

 after its first publication. This has permitted the rewriting of 

 certain passages which were not well expressed and the introduc- 

 tion of considerable new material which will serve, it is hoped, to 

 further elucidate some of the questions discussed, as well as to 

 give results of more recent work. In particular Figs. 4, 5, 9, 10, 

 1 8, 19 have been added and besides minor corrections and addi- 

 tions to all the chapters considerable changes have been made in 

 Chapter III, section on Maternal Inheritance, Chapter IV, sec- 

 tion on Inheritance or Non-Inheritance of Acquired Characters, 

 and Chapter V, sections on Artificial Selection, Origin of Muta- 

 tions, Past Evolution of Man, and Eugenics. 



January, 1916. 



PUBLISHER'S NOTE. In the second edition, second printing, August, 1917, 

 the text was corrected by the author so as to embody some of the results 

 of the latest investigations in this subject. 



