PREFACE vii 



fore contain much that was omitted from want of time and 

 the interruption caused by the exhibition of numerous 

 illustrations. The last and longest essay has been written 

 for the present volume. Its title, The Place of Mimicry 

 in a Scheme of Defensive Coloration, formed the subject 

 of a lecture delivered seventeen years ago. I have now 

 attempted to discuss the same question, replacing the 

 standpoint of 1890 by that of 1907, and directing special 

 attention to the advance which has been made in the 

 interval between these two dates. 



Mendelism and Mutation, which occupy so large a share 

 of public attention at the present moment, are not directly 

 discussed in any of the essays. The relation of these 

 interesting modern researches and speculations to older 

 theories of evolution is briefly considered in an intro- 

 ductory chapter, in which it is maintained that the 

 conclusions supported in the present volume are incon- 

 sistent with a theory of evolution by Mutation, inconsistent 

 with the views often expressed by Mendelians, but not 

 inconsistent with the discoveries of Mendel himself. 



A full reference to the original source of publication will 

 be found in the introductory note to those essays which 

 have already appeared. I desire to thank the administra- 

 tive bodies of scientific societies and the proprietors of 

 journals for permission to reprint from the publications 

 under their control. 



Much invaluable assistance has been rendered by kind 

 friends in the preparation of this volume or of the original 

 addresses. A large part of the first essay on the age of 

 the earth could never have been written without the help 

 of Professor Perry, F.R.S., who has now kindly contri- 

 buted a note (p. 15) on the bearing of the discover) of 



