xii AUTHOR'S PREFACE 



contrary, as may easily be imagined, it often encountered 

 severe, if kindly, criticism, from which I derived the greatest 

 benefit, even though it did not in some cases wholly convince 

 me. Last of all, but assuredly not least, I must thank 

 Professor Arthur Keith, whose almost unequalled general 

 knowledge has ever been at the service of all interested in 

 science, while his openness of mind and his readiness to 

 consider fresh views, whether orthodox or the reverse, are 

 as well known as they are remarkable and exemplary. 



MORLEY ROBERTS. 



