viii PREFACE 



problems cannot be satisfactorily solved without the 

 assistance of morphology, and conversely that the larger 

 morphological problems, such as those concerned with 

 evolution, must take into account the facts of physiology. 

 It is this guiding principle which is responsible on the one 

 hand for the "Origin of Vertebrates" and on the other 

 for the present treatise. 



W. H. GASKELL. 



DURING the two months before my father's death, I was 

 engaged with him in revising the various chapters of the 

 present work. 



This revision was completed a few days before his 

 death ; only one or two paragraphs here and there not 

 having been satisfactorily written. He then told me that 

 on the whole he was satisfied with the form of the book, 

 and that it represented fairly accurately his views on 

 problems to which he had devoted his life. 



He had not, however, fully collected and arranged the 

 many references : I have thought it better to leave un- 

 altered certain quotations and references from books, later 

 editions of which had been published than the one quoted. 

 There are also certain passages about which he talked to 

 me, with which he was not entirely satisfied, but I have 

 thought it better to leave them as written, rather than to 

 attempt to modify them. The diagrams had also been 

 approved by him, though no actual descriptions of them 

 had been written out ; for these descriptions I am re- 

 sponsible. I desire to express my thanks to Mrs. Thacker 

 for help with the author's index and references, and to 

 Miss Alcock for the subject index. 



J. F. GASKELL. 



THE UPLANDS, 

 GREAT SHELKORD, September, 1915. 



