vi PREFACE 



this one, though purely biological in scope, is the opposite 

 of a specialist's book. It is hoped that if it comes into 

 the hands of a taxonomist, a Mendelian, a pathologist, or 

 an alienist, that he will take it as offered, not as an attempt 

 to teach him his particular subject, but as an assortment 

 of opinions which may be of suggestive value. 



It is necessary to warn the reader, who may be inex- 

 perienced in biological matters, that the book is not in the 

 least a review of the present position of biology, but an 

 assortment of personal opinions, most of which are 

 borrowed from well-known sources. 



It may seem to the experienced reader that the main 

 idea expressed in the last chapter is taken from M. Henri 

 Bergson's " Creative Evolution," but most of the last 

 chapter, including the attempted illustration of things 

 varying in all directions, was written in 1910 before I 

 made my first acquaintance with M. Bergson's enlighten- 

 ing philosophy. I wrote the passage " Variation is chaotic 

 or ' in all directions.' Is it possible to know whether 

 it is so or not ? What does the phrase mean ? " before 

 reading the words of Bergson, " It is unquestionable that, 

 when ordinarily we speak of disorder, we are thinking 

 of something. But of what ? " The matter is of little 

 importance, but it must be referred to here, in men- 

 tioning the sources from which I have drawn. 



My thanks are due to Mr. W. L. Tower of Chicago for 

 permission to reproduce the illustrations on Plate II. It 

 may seem that I have abused this kindness, by suggesting 

 that his judgment of his own work cannot be considered 

 final. It was, however, necessary for me to take this 

 step, for if there is no evidence of the efficacy of mutants 

 in the facts collected by Mr. Tower, there is less than none 



