PEEFACE vii 



interpretations that have sprung from the theory 

 of Natural Selection. The subject, ' the Value of 

 Colour in the Struggle for Life,' is treated histori- 

 cally. Darwin's own hypotheses and discoveries 

 in this line, and his keen interest in the 

 hypotheses and discoveries of others are especially 

 considered here and also in part of the seventh 

 Section. 



The sixth Section deals with Mimicry, the 

 most arresting of aU the uses which colour may 

 subserve in the struggle for existence. It is 

 maintained that this complicated subject is best 

 approached by the study of North American 

 examples, and attention is directed to the number 

 of inspiring problems which await a thorough and 

 systematic attack by American naturalists. 



Darwin's hitherto unpublished letters to Mr. 

 Eoland Trimen, F.RS., form the subject of the 

 seventh Section. An interesting account of 

 Mr. Trimen's first meeting with the illustrious 

 naturaUst fifty years ago is also included. In 

 addition to the eighteen letters in Section VII, 

 four written by Darwin to other correspondents 

 are published in this volume — one in Section I, 

 two in Section V, and one in Section VI. I 

 desire to thank my friends for generously 

 lending me these twenty-two deeply interesting 

 letters, and Mr. Francis Darwin for kindly 

 permitting their publication. 



