PREFACE. 



The subject wliicli is treated in this book has occu- 

 pied my thoughts for ten years or more, but I have re- 

 frained from publishing my views, as I hope that I 

 may some time be able to submit them to tlie test of 

 experiment. 



Many experiments have suggested tiiemselyes to me, 

 but as most of them involve the cultivation and hybrid- 

 ization, for many generations, of such animals and plants 

 as will thrive and multiply in confinement, they can only 

 be carried out by some one who has the means for ex- 

 perimental researches, and who has also a permanent 

 home in the country, where organisms of many kinds 

 may be kept under observation for years, and where 

 many specimens of hybrids between various wild and 

 domesticated species can be reared to maturity. 



My own studies have been in a different province of 

 natural science, and it has therefore seemed best to 

 publish this volume in order to call renewed attention 

 to this most fascinating subject. 



I have little hope that my views will be permanently 

 accepted in the form in which they are here presented, 

 but I do hope that they may serve to bind together and 



