viii PREFACE 



Radium upon the argument founded on the life of the 

 sun. The hiatus in my argument caused by the want of 

 any reference to the evolution of land -plants has now 

 been to some extent filled by a brief summary of the main 

 conclusions, prepared for me by my kind friend Dr. D. H. 

 Scott, F.R.S. ; also by a quotation from an address by 

 Professor A. C. Seward, F.R.S. I well remember how 

 much I owed to the kind help of my friend Sir Ray 

 Lankester, F.R.S., in the difficult task of summing up 

 in a few words the chief conclusions as to the origin and 

 history of each of the main branches of the animal 

 kingdom. And essential parts of the second and fifth 

 essays are due to his published writings, or have sprung 

 from the memory of discussions with him. 



In rewriting large parts of the fourth essay I owe a 

 great debt to Dr. J. W. Jenkinson for valuable sugges- 

 tions and criticism. Without the help of one who is 

 devoting his life to the subject, I should have shrunk 

 from the attempt to display in a few pages the main con- 

 clusions of the modern embryologist as to the potentiali- 

 ties latent in the germ, and their gradual emergence 

 into actuality during the developmental history of the 

 individual. 



It is unnecessary to speak here individually of all the 

 numerous friends who have rendered the kindest assist- 

 ance in the preparation of this volume, and especially of 

 essays VII-X, dealing with Protective Resemblance and 

 Mimicry. All such help is fully acknowledged in the 

 pages of the work. I wish, however, especially to thank 

 my friends Dr. F. A. Dixey and Mr. Guy A. K. Marshall. 

 Not only do their researches contribute a most important 

 element to this volume, but I also owe them a deep debt 



