PREFACE xxi 



evolution of energy in living matter, I enjoyed the cooperation 

 of Doctor I. J. Kligler, formerly of the American Museum of 

 Natural History, and now at the Rockefeller Institute for 

 Medical Research. 



In the botanical section I am especially indebted to Pro- 

 fessor T. H. Goodspeed, of the University of California, and tO' 

 Doctor Marshall Avery Howe, of the Botanical Gardens, for 

 many valuable notes and suggestions, as well as for certain 

 illustrations. In the early zoological section I am indebted 

 to my colleagues at Columbia University, Professor Edmund 

 B. Wilson and Professor Gary N. Calkins. Especial thanks 

 are due to Mr. Roy W. Miner, of the American Museum, for his 

 careful comparisons of recent forms of marine life with the Cam- 

 brian forms discovered by Doctor Charles Walcott, who sup- 

 plied me with the beautiful photographs shown in Chapter IV. 



In preparing the chapters on the evolution of the verte- 

 brates, I have turned to my colleague Professor W. K. Gregory, 

 of the American Museum and Columbia University, who has 

 aided both with notes and suggestions, and in the supervision 

 of various illustrations relating to the evolution of vertebrate 

 form. The illustrations are chiefly from the collections of the 

 American Museum of Natural History, as portrayed in original 

 drawings by Charles R. Knight, Erwin S, Christman, and 

 Richard Deckert. The entire work has been faithfully collated 

 and put through the press by my research assistant. Miss 

 Christina D. Matthew. 



It affords me great pleasure to dedicate this work to the 

 astronomer friend whose enthusiasm for my own field of work 

 in biology and palaeontology has always been a source of en- 

 couragement and inspiration. 



Henry Fairtield Osborn. 



American Museum of Natural History, 

 February 26, 191 7. 



