Vlll 



find suggestions for helpful class discus- 

 sions and for experiments that will either 

 add to the information contained in the 

 text or make the text discussions more 

 clear. These suggestions are grouped at 

 the end of each Problem and are called 

 Exercises. At the most appropriate places 

 in each Problem these Exercises are re- 

 ferred to. You cannot possibly do all of 

 them; the authors hope you will find 

 time to do many of them. Each of these 

 Exercises has been chosen with great care 

 to help you understand some part of bi- 

 ology, to help you to learn how a biolo- 

 gist works (the scientific method), or to 

 help you to find out something new. 



The Questions at the ends of the Prob- 

 lems are designed for your use in re- 

 viewing what you learn in studying the 

 Problem. If you can answer all the Ques- 

 tions, you can feel pretty sure that you 

 have done a good job on that section of 

 the text. 



If you are one of those who like biol- 

 ogy very much, you will want to try 

 some of the Further Activities in Biology 

 that are listed at the end of each Prob- 

 lem. You may also wish to read some of 

 the many books and articles that are 

 listed at the end of the book, just before 

 the Index. 



Since this book was designed to fit the 

 courses of study in schools throughout 



Preface 



the United States, it may contain some 

 topics that are not required in your 

 school. Therefore your teacher may pre- 

 fer not to assign certain sections of it. 

 Some sections are marked "Optional." 

 These may be omitted, if your teacher 

 so desires, without interfering with your 

 understanding of the parts that follow. 



All the authors' long experience in 

 teaching, directing other teachers, and 

 writing for students has been applied to 

 the writing of this text, which is a suc- 

 cessor to Adve?inires with Livmg Things. 

 To insure accuracy, the authors have 

 asked a number of people to read por- 

 tions of this book. In addition to the 

 large number of specialists who critically 

 read many portions of the authors' earlier 

 text, they wish now to thank: Mr. 

 Aiaurice Bleifeld, Chairman, Department 

 of Biology, Newtown High School, 

 Queens, N. Y.; Professor A. L. Kroeber, 

 Emeritus, University of California; Pro- 

 fessor Laurence H. Snyder, Dean, The 

 Graduate College, University of Okla- 

 homa; and Dr. Charles Tanzer, DeWitt 

 Clinton High School, New York Citv. 

 The authors thank also Airs. Charlotte O. 

 Wolff for assistance in preparing the 

 Index. 



Elsbeth Kroeber 

 Walter H. Wolff 



