PREFACE vii 



Where I am indebted to other writers, I believe I have 

 in all cases acknowledged my indebtedness. I had prac- 

 tically finished this book before I came across Professor 

 Mackintosh's work, From Comte to Benjamin Kidd. Hence 

 there is very little in the way of direct reference to it. 

 However, the difficulties he raises with regard to evolu- 

 tion on Neo-Darwinian lines are not new to me, and I 

 have dealt with them to the best of my ability. 



It only remains for me to acknowledge gratefully 

 my obligations to friends. Fig. 10 is from an original 

 drawing by Mr C. G. C. King, and several of the other 

 illustrations are copies by him from the originals. Fig. 

 1 1 is from a photograph by Mr E. T. D. Francis. Mr 

 M. D. Hill has read the manuscript of Chapter I. Mr 

 E. L. Gowlland has read the proofs from end to end. 

 If I make no formal acknowledgment of the kindness of 

 friends who have always been ready to discuss the pro- 

 blems I have attempted to grapple with, it is not because 

 I forget how much I owe to them. 



F. W. HEADLEY. 



HAILEYBURY, Aug. izt/i, 1900. 



