PREFACE TO THE SECOND EDITION 



Nine years' use has shown many needs for revision of the original text, 

 and we are grateful to the numerous teachers who have pointed out errors 

 or omissions of details and suggested changes in emphasis, arrangement, 

 and treatment. The discussions of mitosis and meiosis and the whole 

 section on evolution have been completely rewritten and brought up to 

 date. The portions dealing with the structure and functioning of the 

 human body and of the plant have been considerably revised in the light 

 of recent studies, particularly as concerns hormones, vitamins, and 

 physiology of blood, photosynthesis, and the transport of water and 

 solutes in plants. There has been some rearrangement of chapters to 

 present a more unified treatment of reproduction, and a short summary 

 chapter has been added. 



Our thanks are extended to all the numerous persons who have aided 

 us in the task of revision. We are especially indebted to the following: 

 Profs. Edwin B. Mains and Alexander H. Smith for contributing 

 many photographs of plants; Prof. Wm. Randolph Taylor for advice 

 on botanical matters; and Profs. Robert J. Braidwood, Emerson F. 

 Greenman, Volney H. Jones, and Leslie A. White for reading and 

 criticizing the chapters dealing with prehistoric man and the biological 

 significance of culture. 



The chief merit of the new edition, we feel, lies in the carefully planned 

 and skillfully drawn illustrations by William L. Brudon. We believe that 

 these not only make the book far more attractive as a volume, but con- 

 tribute much to the hoped-for clarity of presentation and integration of 

 subject matter. Many of the illustrations are original; acknowledgment 

 of source is made in the captions of the others. Gray's Anatomy of the 

 Human Body and Spalteholz's Atlas of Human Anatomy served as refer- 

 ence works to ensure accuracy in representation of the human body. 



We have not changed the over-all plan of the book. Its treatment is 

 still frankly selective, aiming at a one-course presentation of biological 

 principles that seem to us both pertinent to the student's basic education 

 and capable of being presented as a related whole. 



J. Speed Rogers 

 Theodore H. Hubbell 

 C. Francis Byers 



Ann Arbor, Mich. 



Gainesville, Fla. 

 June, 1952 



