x PREFACE TO FIRST EDITION 



the length of a single book. Mammalian structure, function, and 

 development will therefore be dealt with in a separate volume, which 

 will also include a survey of comparative embryology. 



The original plan was that the palaeontological parts of the book 

 would be written by J. A. Moy-Thomas. Had he lived this aspect of 

 the work would have been very much better, and his common sense 

 and laughter would have lightened the whole. I have tried to give 

 some compensation at least by the speculation that is possible from a 

 single point of view. To protect the reader against the limitations of 

 my ignorance I have consulted specialists on every part of the work, 

 and my deepest thanks are due to those who have helped in this way. 

 They have done wonders in correcting mistakes, but, of course, are 

 not responsible for any that remain, or for views expressed. Among 

 those who have helped in this way with particular parts are Professor 

 G. R. de Beer, Mr. R. B. Freeman, the late Professor W. Garstang, 

 Dr. A. Graham, Professor J. B. S. Haldane, Professor W. Holling- 

 worth, Dr. W. Holmes, Dr. J. S. Huxley, Dr. D. Lack, Mr. Maynard 

 Smith, Dr. F. S. Russell, Dr. Tyndell Hopwood, Mr. H. G. Vevers, 

 Professor D. M. S. Watson, and Professor S. Westoll. They have been 

 patient and severe critics, and the reader and I owe them very much. 



One of the main problems of such a work is its illustration, and here 

 I have been extraordinarily fortunate in having the help of Miss E. R. 

 Turlington, who has not only provided brilliantly clear and beautiful 

 pictures, but has taken extremes of care to ensure their accuracy by 

 drawing from live animals, from dissections, and from skeletons, as 

 well as by research into the illustrations of others. Miss J. de Vere 

 has also given much help with drawing. We have borrowed good 

 pictures unhesitatingly and should like to thank those who have given 

 permission for their reproduction. 



I should also like to thank particularly my secretary, Miss P. Codlin, 

 who has played a large part in making the book possible, and my 

 daughter Cordelia for help with the index. 



Finally, I have to thank the Secretary and members of Oxford 

 University Press for the care with which the book has been produced, 

 and for their friendly co-operation, which has made the work a 

 pleasure. 



J. Z. Y. 



1950 



