PREFATORY NOTE.

THE present volume is made up of popular essays or addresses on the general subject of Organic Evolution. These were originally given as oral lectures before University Extension societies in California, having been condensed and written out in their present form after delivery. Three of these papers have already appeared in Appletons' Popular Science Monthly, and three in The Arena. To the editors of these periodicals I am indebted for the privilege of reprinting them.

Besides the twelve essays of my own, it is my good fortune to enhance the value of the volume by the insertion of three papers of special importance, setting forth the present state of knowledge concerning the method of evolution and the method of heredity. The first of these, on the Factors of Organic Evolution as displayed in the Process of Development, is by Professor Edwin Grant Conklin, of the University of Pennsylvania; the second, on the Physical Basis of Heredity, is by Professor Frank Mace McFarland, of Leland Stanford Jr. University; the third, on the Testimony from Paleontology, is by Professor James Perrin Smith, of

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