PREFACE ix 



facilities which I have enjoyed in the Department of Zoology 

 and Comparative Anatomy of the Oxford University Museum. 



On occasion, I have had the privilege of discussing certain 

 matters with Professor G. Elliot Smith, F.R.S., Professor C, 

 Judson Herrick, Professor J. P. Hill, F.R.S., Professor Sir 

 Charles Sherrington, O.M., F.R.S., Professor W. J. Sollas, 

 F.R.S., Professor A. Thomson, and Professor D. M. S. Watson, 

 F.R.S. To all of them I wish to make due acknowledgment 

 for the help which their information and advice have afforded 

 me. To my friend and colleague Mr. B. W. Tucker I am 

 especially indebted for reading the MS., and for making 

 several valuable and helpful suggestions. I take great pleasure 

 in recording my thanks to Professor Julian Huxley, without 

 whose suggestion, interest, and persistent encouragement this 

 book would have remained unwritten. It goes without saying 

 that these gentlemen are not responsible for the errors which 

 this book contains. 



I have thought it inadvisable to burden the text with 

 references. Instead, a short list of works is appended at the 

 end of most of the chapters. I may mention here certain easily 

 accessible works of great general utility in the study of 

 vertebrates : 



Abel, O. Die Stamme der Wirbeltiere. Berlin and 

 Leipzig. 1 9 19. 



Brachet, A. Traite d'Embryologie des Vertebres. Paris. 

 1921. 



Graham Kerr, J. Text-Book of Embryology. Vol. II. 

 London. 1919. 



Hyman, L. H. A Laboratory Manual for Comparative 

 Vertebrate Anatomy. Chicago. 1925. 



Ihle, j. E. W., and others. Vergleichende Anatomie der 

 Wirbeltiere. Berlin. 1927. 



Jenkinson, J. W. Vertebrate Embryology. Oxford. 



!9i3- 



Kellicott, W. E. Chordate Development. New York. 



Kingsley, J. S. Comparative Anatomy of Vertebrates. 

 London, 1927. 



G 2 



