vffi PREFACE 



given to three kinds of conclusions those reached by microscopic 

 study of the germ-cells, those reached by the application of 

 statistical methods, and those reached through experiment. 

 There is equal justification for these three ways of attacking 

 the mysterious problems, and the results which have been 

 reached in a few years by a relatively small number of resolute 

 investigators, deserve the attention of all thoughtful men and 

 women. The new facts are of especial interest to medical 

 practitioners, to educationists, including clergymen, to social 

 reformers, and to actual or prospective parents. 



I have, throughout, acknowledged my indebtedness to autho- 

 rities, and the bibliography (which is merely representative) 

 shows how many fields there are from which to glean. In 

 particular, I have been indebted to the works of Galton, Weis- 

 mann, Pearson, Bateson, and De Vries. 



I have to thank my friends Mr. E. S. Russell and Dr. John 

 Rennie for going over the proofs of the first edition, and saving 

 the pages from many mistakes. Dr. Leslie Mackenzie was kind 

 enough to read the chapter on Heredity and Disease, and some 

 of his helpful suggestions have been incorporated. I have to 

 thank Professor C. Correns and Professor H. E. Ziegler for 

 generously allowing me to copy four admirable diagrams ; also 

 Mr. Young Pentland and the Walter Scott Publishing Company 

 for allowing me the use of a number of figures which have done 

 duty in other books of mine. My thanks are also due to Mr. 

 Murray, who has encouraged me in a work which I was often 

 attempted to abandon, whose good-humoured patience over 

 many delays I should long since have exhausted had he been 

 as many men are. 



demand for a third edition has given me the opportunity 



