PREFACE TO 

 THE SECOND EDITION 



For this edition every part of the book has been revised and corrected, 

 but the basic plan and balance of interests have not been altered. 

 Changes of arrangement and emphasis might have suited some types 

 of reader but I have thought it better that the book should continue 

 to show the idiosyncracies and interests of the author. One of the 

 dangers of a textbook is, surely, that unsophisticated readers may sup- 

 pose that they are getting the authentic and complete treatment of the 

 subject. Some obvious imbalances may, therefore, even be an advan- 

 tage as reminders of the relativity of all statements. 



Nevertheless, I have attempted to make the treatment rather more 

 complete and systematic than before. For example, the descriptions 

 of the parts of the body are now arranged more nearly similarly for all 

 groups. With the help of many friends mistakes have been removed 

 and accounts of recent work added. The anatomy of Mammals is not 

 dealt with in the same detail as that of other groups, being covered 

 separately in The Life of Mammals (Clarendon Press, 1957), where 

 also there is a fuller account of the comparative embryology of 

 vertebrates. 



During the revision I have become even more conscious of the 

 defects of the work, both in general form and detailed treatment. It is 

 still not possible to see more than the vaguest outlines of a proper 

 science of comparative biology. We are faced with a great series of 

 wonderful systems, differing slightly from each other and maintaining 

 themselves in slightly different surroundings. But we have no proper 

 scientific words with which to talk about them. For example, it is 

 absurd that this book contains so little reference to genetics, bio- 

 chemistry, or control theory. No doubt this is partly my fault, but the 

 fact is that these more exact sciences have yet to show us how to treat 

 the organization of a whole creature. 



Fortunately, the animals remain as fascinating as ever, indeed the 

 search for exact ways of describing makes them even more so. Those 

 of us who have revised the book will be well rewarded for our trouble 

 if others arc helped to look and think for themselves. If they do they 

 will find a really astonishing array of experiments made by natural 

 selection with every part of the vertebrate organization. To take one 

 example, we are offered the opportunity to learn how the endocrine 



