PREFATORY NOTE. 
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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 in- 
sertion 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 Pennsyl- 
vania; the second, on the Physical Basis of Heredity, 
is by Professor Frank Mace McFarland, of Leland Stan- 
ford Jr. University ; the third, on the Testimony from 
Paleontology, is by Professor James Perrin Smith, of 
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