PREFACE TO FIRST EDITION ix 



that there is no work that attempts to define the organization of the 

 whole life and its evolution in all its aspects. Indeed, none of these 

 works defines what is being studied or tries to alter the direction of 

 investigation — all authors seem prepared to agree that biological study 

 is adequately expressed through the familiar disciplines of anatomy, 

 physiology, palaeontology, embryology, or natural history. In passing, 

 we may note the extraordinary fact that there are no detailed works on 

 the comparative histology or biochemistry of vertebrates — surely most 

 fascinating fields for the future, as is, indeed, hinted by the attempts 

 that have been made in older works, such as that of Ranvier (1878), 

 and the newer ones of Baldwin (1937 and 1945). 



The present book has gradually grown into an attempt to define 

 what is meant by the life of vertebrates and by the evolution of that 

 life. Put in a more old-fashioned way, this represents an attempt to 

 give a combined account of the embryology, anatomy, physiology, 

 biochemistry, palaeontology, and ecology of all vertebrates. One of 

 the results of the work has been to convince me more than ever that 

 these divisions are not acceptable. All of their separate studies are 

 concerned with the central fact of biology, that life goes on, and I 

 have tried to combine their results into a single work on the way in 

 which this continuity is maintained. 



A glance through the book will show that I have not been successful 

 in producing anything very novel — others will certainly be able to 

 go much farther, and in particular to introduce to a greater extent facts 

 about the evolution of the chemical and energy interchanges of verte- 

 brates, here almost omitted! However, I have very much enjoyed the 

 attempt, which has provided the stimulus to try to find out many 

 things that I have always wanted to know. 



For any one person to cover such a wide field is bound to lead to 

 inexactness and error in many places. I have tried to verify from 

 nature as often as possible, but a large amount has been copied, no 

 doubt often wrongly. Throughout, the aim has been to provide 

 wherever possible an idea of the actual observations that have been 

 made, as well as the interpretations placed upon them. A proper 

 appraisal of general theories can only be reached if there is first a 

 knowledge of the actual materials, which is the characteristic feature 

 of scientific observation. A book such as the present has value only 

 in so far as it leads the reader to make his own observations and helps 

 him to know the world for himself. 



Mammalian organization requires more detailed treatment than 

 that of other groups, and in providing this the work grew to beyond 



