PREFACE TO SECOND EDITION 



IN this second edition a few slight modifications of the 

 text have been made for the sake of greater clearness, several 

 inadvertent errors have been rectified, and mistakes have 

 been corrected in two of the plates (76 and 77) which 

 were borrowed without sufficient scrutiny. The author de- 

 sires to acknowledge with most cordial appreciation the 

 kindness of Professor E. B. Poulton, who pointed out the 

 errors in these plates. In a few instances proper credit was 

 not given for borrowed figures. These omissions have now 

 been supplied. Also a few titles have been added to the list 

 of books in the Appendix. 



In the first edition of this book, the author suggested 

 very briefly that there might be inherent tendencies in 

 organisms, leading them to evolve in certain directions rather 

 than in others. In Appendix I to this edition, some further 

 evidence for this view has been given, and Weismann's sug- 

 gestion as to a possible explanation of these tendencies has 

 been briefly treated. It has seemed best, also, in Appendix I, 

 to discuss a little further the influence of individual plasticity 

 upon evolution. 



For all the kindly comments, and especially for criticism, 

 upon this book, the author feels very grateful. He was at 

 first doubtful if the published lectures would be useful, and it 

 is a satisfaction to know that they have found a place and are 

 apparently proving helpful. 



