INTRODUCTION 5 



It is now twenty years since the theory first came into my mind, 

 and the work of those twenty years has convinced me more and more 

 of its truth, and yet during the whole time it has heen ignored by 

 the morphological world as a whole rather than criticized. Whatever 

 may have been the causes for such absence of criticism, it is clear 

 that the serial character of its publication is a hindrance to criticism 

 of the theory as a whole, and I hope, therefore, that the publication 

 of the whole of the twenty years' work in book-form will induce 

 those who differ from my conclusions to come forward and show me 

 where I am wrong, and why my theory is untenable. Any one 

 who has been thinking over any one problem for so long a time 

 becomes obsessed with the infallibility of his own views, and is not 

 capable of criticizing his own work as thoroughly as others would 

 do. I have been told that it is impossible for one man to consider 

 so vast a subject with that thoroughness which is necessary, before 

 any theory can be accepted as the true solution of the problem. I 

 acknowledge the vastness of the task, and feel keenly enough my 

 own shortcomings. For all that, I do feel that it can only be of 

 advantage to scientific progress and a help to the solution of this 

 great problem, to bring together in one book all the facts which I 

 have been able to collect, which appeal to me as having an important 

 bearing on this solution. 



In this work I have been helped throughout by Miss R. Alcock. 

 It is not too much to say that without the assistance she has given 

 me, many an important link in the chain of evidence would have 

 been missing. With extraordinary patience she has followed, section 

 by section, the smallest nerves to their destination, and has largely 

 helped to free the transformation process in the lamprey from the 

 mystery which has hitherto enveloped it. She has drawn for me 

 very many of the illustrations scattered through the pages in this 

 book, and I feel that her aid has been so valuable and so continuous, 

 lasting as it does over the whole period of the work, that her name 

 ought fittingly to be associated with mine, if perchance the theory of 

 the Origin of Vertebrates, advocated in the pages of this book, gains 

 acceptance. 



I am also indebted to Mr. J. Stanley Gardiner and to Dr. A. 

 Sheridan Lea for valuable assistance in preparing this book for the 

 press. I desire to express my grateful thanks to the former for 

 valuable criticism of the scientific evidence which I have brought 



