vi PREFACE 



Built upon this foundation concerning the nature of animals and their 

 environments, Part IV traces the long evolutionary sequence from one-celled 

 forms to man. Here animals are described both morphologically and physiologi- 

 cally, with special emphasis upon their origins. The full weight of the evolu- 

 tionary idea is given to the chordates in Chapter 13, concluding with a brief 

 history of early man. 



With this background the student is ready for a rather careful study of the 

 organ systems of man, to which Part V is devoted. Each chapter is introduced 

 by a brief resume of the organ system under scrutiny as it appears in the 

 various animal groups. This is done to fix firmly the origin of the various sys- 

 tems and to demonstrate that they are not peculiar to man. Because of the 

 importance of the human species, considerable attention has been devoted to 

 this section which, in some respects, will be the most valuable to students. 



The continuity of life is taken up in Part VI, beginning with the reproduction 

 of cells and carrying on through the continuity of the individual and of the 

 race. Considerable attention is given to modern concepts in both embryology 

 and genetics. 



The book concludes in Part VII with a return to the discussion of organic 

 evolution — its meaning, theories, and mechanisms. A word of speculation about 

 the future of mankind seems a fitting finale for a work of tliis kind. 



The material presented in these pages is derived from many sources, not only 

 from published books and research papers but from first-hand observation in 

 many instances. Wherever possible, living or preserved materials have been 

 used in making the drawings. 



I am indebted not only to those who have received specific recognition in the 

 list of Acknowledgments in the back of the book, but also to former teachers 

 and associates who have influenced my thinking regarding many topics con- 

 tained in this book. I should like particularly to mention Professor D. E. Min- 

 . nich, who has gone over the entire book critically and has given advice and 

 suggestions of inestimable value. Professors Norman E. Kemp, Paul A. Wright, 

 Drs. Frank Hooper, James F. Hogg, and Stanley P. Wyatt have examined sev- 

 eral chapters and have made many helpful suggestions. The attractiveness of 

 the drawings is due to the skill of Doris Stirratt Garlock, whose patience in 

 interpreting my ideas knew no bounds. Some of the drawings, taken from my 

 Atlas in General Zoology, were originally done by Ohvia Jensen IngersoU. The 

 chapter headings and some of the plates were done by Raymond Jansma. Much 

 of the beauty of the photographs is due to the expert ability and many hours of 

 hard labor by Herbert Weinert, who gave unstintingly of his time to obtain the 

 best possible pictures. To him and Fred Anderegg, director of the Photographic 

 Services of the University of Michigan, I express my sincere appreciation. 



