vi PREFACE TO SECOND EDITION 



control system works by examining hundreds of different variants of 

 it. The more one thinks of it the more surprising it is that biology 

 has made so little use of the experiments that have been done for us 

 by nature. Surely soon someone will come along with sufficient know- 

 ledge and logical and mathematical ingenuity to show us how to study 

 vertebrate organization. 



Besides those mentioned below who have assisted in the revision of 

 particular sections, I should like to thank the many people, including 

 teachers and students, who have written about particular points, and 

 especially Professor J. Lever of Amsterdam for his many detailed 

 comments. My grateful thanks are also due to Mrs. J. Astafiev, who 

 has redrawn many of the figures, Mr. C. Marmoy for assistance with 

 the Bibliography, Mr. P. N. Dilly, who has helped throughout, also 

 my secretaries and especially Miss S. Thistleton and Miss J. Everard, 

 for continuous help with the manuscript. It is also a pleasure to thank 

 the members of the Clarendon Press and in particular Miss M. Gregory 

 for the help with the revision. 



J. Z. Y. 



February 1962 



