vi PREFACE 



invaluable book, ''The Ceil in Development and Inherit- 

 ance." Hundreds of persons have voluntarily contributed 

 the data upon which the conclusions that have been drawn 

 are based. My friend and colleague, Mr. H. H. Laughlin, 

 Superintendent of the Eugenics Record Office, has assisted 

 in many points and has contributed the frontispiece. My 

 wife has, as usual, revised the manuscript and prepared it 

 for the printer. The Trustees of the Carnegie Institution 

 have granted me exceptional opportunities for the prosecu- 

 tion of the work. Last, but by no means least, this work 

 and the collection of data out of which it has grown have 

 been made possible by the financial assistance and by the 

 personal stimulus and advice given by the lady to whom, 

 in insufficient recognition, this book is, with her permis- 

 sion, dedicated. To all those who have so kindly assisted 

 me I return thanks. I trust the book will be useful to hu- 

 manity, so as to justify them for the pains they have taken 

 to bring it to pass. 



C. B. D. 



Carnegie Institution of Washington 

 Station for Experimental Evolution 

 Cold Spring Harbor, N. Y. 



I I I 1 1 



