PREFACE TO THE SECOND EDITION. 



During the seven years which have elapsed since the pub- 

 lication in 1868 of the first edition of this Work, I have 

 continued to attend to the same subjects, as far as lay in my 

 power ; and I have thus accumulated a large body of addi- 

 tional facts, chiefly through, the kindness of many corre- 

 spondents. Of these facts I have been able here to use only 

 those which seemed to me the more important. I have 

 omitted some statements, and corrected some errors, the dis- 

 covery of which I owe to my reviewers. Many additional 

 references have been given. The eleventh chapter, and that 

 on Pangenesis, are those which have been most altered, parts 

 having been re-modelled; but I will give a list of the more 

 important alterations for the sake of those who may possess 

 the first edition of this book. 



