Xll 



are many devices in this book designed 

 to help you to learn biology readily. Of 

 these, the Unit headings, Problem ques- 

 tions, and paragraph titles are the most 

 important, because they tell you what 

 you are supposed to learn. From the 

 very beginning of any study period you 

 should know what you are trying to 

 learn. After reading a paragraph title, 

 think over the meaning of the title and 

 ask yourself what, you already know 

 about that subject. When vou have 

 thought through and organized your 

 previous knowledge, you will be better 

 equipped to grasp the additional infor- 

 mation that is supplied by the book. You 

 will find it helpful to do the Exercises 

 referred to throughout the text as vou 

 are studying the section those Exercises 

 are intended to supplement. Perhaps the 

 class as a whole can plan with the teacher 

 how to do some of the Exercises. This is 

 more interesting than following direc- 

 tions laid down by others. 



If, at first reading of the text, you do 

 not understand a sentence, finish the par- 

 agraph to find out if your questions are 

 answered. Then go back and re-read the 

 sentence as it stands in relation to the 

 rest of the paragraph. If you still have 

 questions, make a note of them and have 

 them explained in class. If it is a word 

 that vou do not understand, look it up. 

 If that is not possible, make a note of the 



How to Use This Book 



word so that you can learn its meaning 

 in class. The field of biology makes use 

 of many special words that you will 

 need to learn. These words are printed in 

 italics and defined when they first ap- 

 pear. If you do not recall the meaning of 

 a word when it is used later in the book, 

 look it up in the Index to find where it 

 was used first. A good way to learn the 

 special vocabulary of biology is to pre- 

 pare a glossary for yourself in your note- 

 book. A glossary is simply a special dic- 

 tionary. You can list the new terms you 

 learn and write their definitions in your 

 own words. As a basis on which to build 

 your o\\ n more complete list of words 

 you will find a glossary prepared by the 

 authors beginning on page 583. 



There are many illustrations in this 

 book. Every one has been chosen to add 

 to your understanding and information. 

 It will be useful for you to look at them 

 carefully and to study the legends. 



Both the printed text and the illustra- 

 tions will undoubtedly raise questions in 

 your mind. These are the most precious 

 results of study because they lead to 

 interesting class discussions and, later, to 

 a more complete understanding of the 

 subject. Such questions will also empha- 

 size to you that in biology, as in other 

 sciences, there is much that remains to be 

 learned. 



