Preface. vii 



naturalists of America on the English scientist. My 

 acknowledgments are also given to Professor True, 

 of the Smithsonian Institution, for the loan of a rare 

 and excellent likeness of Darwin, and important 

 papers ; and to my wife, whose aid and cooperation 

 have been invaluable. 



C. F. H. 

 Pasadena, Cal., November i, 1890. 



