[** Transcriber's Note: Underscores "_" before and after a word or phrase indicate ITALICS in the original text. Hyphenation was used inconsistently by the author and has been left as in the original text. ] THE SILLIMAN FOUNDATION In the year 1883 a legacy of about eighty-five thousand dollars was left to the President and Fellows of Yale College in the city of New Haven, to be held in trust, as a gift from her children, in memory of their beloved and honored mother, Mrs. Hepsa Ely Silliman. On this foundation Yale College was requested and directed to establish an annual course of lectures designed to illustrate the presence and providence, the wisdom and goodness of God, as manifested in the natural and moral world. These were to be designated as the Mrs. Hepsa Ely Silliman Memorial Lectures. It was the belief of the testator that any orderly presentation of the facts of nature or history contributed to the end of this foundation more effectively than any attempt to emphasize the elements of doctrine or of creed; and he therefore provided that lectures on dogmatic or polemical theology should be excluded from the scope of this foundation, and that the subjects should be selected rather from the domains of natural science and history, giving special prominence to astronomy, chemistry, geology, and anatomy. It was further directed that each annual course should be made the basis of a volume to form part of a series constituting a memorial to Mrs. Silliman. The memorial fund came into the possession of the Corporation of Yale University in the year 1901; and the present volume constitutes the fifth of the series of memorial lectures. PREFACE This book gives the substance of a series of lectures delivered in Yale University, where I had the privilege of holding the office of Silliman Lecturer in 1907. The delay in publication was brought about by a variety of causes. Inasmuch as the purpose of the lectures is to discuss some of the wider problems of biology in the light of knowledge acquired by Mendelian methods of analysis, it was essential that a fairly full account of the conclusions established by them should first be undertaken and I therefore postponed the present work till a book on Mendel's Principles had been completed.