PREFACE 



The field of Zoology, along with all of the biological sciences, has 

 grown enormously in the last few decades. To deal with this vast array of 

 knowledge some courses are based upon a thorough examination of 

 certain representative animals. Other courses are centered around dis- 

 cussions of broad biological principles. Each of these has obvious merits 

 and we have tried in writing this text to blend the two. Neither method 

 can be carried to extreme, for one cannot hope to teach principles without 

 concrete examples, nor can one teach animal types without the synthesis 

 provided by an understanding of principles. 



The special task of anyone writing a textbook is to select with care 

 the topics to be discussed so as to present a clear picture of the subject 

 without giving an overwhelming mass of detail. This text probably in- 

 cludes some material that the instructor will have neither the time nor 

 the inclination to consider in his course. Each instructor, of course, em- 

 phasizes those topics he considers most important; the text provides the 

 interested student with an opportunity to read about subjects which may 

 be omitted or considered only briefly in the lectures and laboratory 

 exercises. In discussing the many subjects which comprise modern zoology 

 we have tried to distinguish between fact and theory and to cite some of 

 the problems that remain for future zoologists to solve. The conclusions 

 presented and the inferences drawn represent, to the best of our knowl- 

 edge and ability, the current interpretation of the relevant observations 

 and experiments. 



The introductory chapter describes Zoology and its sub-sciences, 

 scientific method, and the sources of scientific knowledge. The general 

 concepts basic to a study of the form and function of both vertebrate and 

 invertebrate animals are presented in Part One. Chapters 2 and 3 provide 

 some of the chemical and physical background for an understanding of 

 protoplasm, cells and tissues. The chemistry and physics are not discussed 

 separately but are introduced as needed to understand the biological 

 material being presented. The nature of enzymes and their role in 

 cellular physiology is discussed in Chapter 4. Vertebrate and invertebrate 

 animals have had to solve the same major problems in order to survive, 

 and an examination of their physiological mechanisms shows that they 

 have much in common. The principles of nutrition, digestion, circulation, 

 respiration, excretion, protection, sensation, locomotion, irritability, and 

 integration are discussed in Chapter 5 to provide a general background 

 for the discussions of the animal types which follow. The principles of 



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