PREFACE xi 



to those who have helped us in the matter of illus- 

 trations. The portraits of Dr. Asa Gray, Mr. Huxley, 

 Sir Charles Lyell, Mr. Romanes, are from their 

 respective Biographies, and for permission to make 

 use of them we have to thank Mrs. Gray, Mr. L. 

 Huxley, Mrs. Lyell, and Mrs. Romanes, as well as 

 the publishers of the books in question. For the 

 reproduction of the early portrait of Mr. Darwin we 

 are indebted to Miss Wedgwood ; for the interesting 

 portraits of Hugh Falconer and Edward Forbes we 

 have to thank Mr. Irvine Smith, who obtained for us 

 the negatives ; these being of paper, and nearly sixty 

 years old, rendered their reproduction a work of some 

 difficulty. We also thank Messrs. Elliott & Fry 

 for very kindly placing at our disposal a negative, of 

 the fine portrait, which forms the frontispiece to 

 Vol. II. For the opportunity of making facsimiles 

 of diagrams in certain of the letters, we are once 

 more indebted to Sir Joseph Hooker, who has most 

 generously given the original letters to Mr. Darwin's 

 family. 



Cambridge, October, 1902. 



