PREFACE 



many extremely significant aspects of zoology cannot be adequately presented 

 without reference to biochemical concepts. Chief among these are the mech- 

 anisms whereby foods are utilized in the body and the pathways through 

 which energy is obtained, transformed, and utilized in cells. In no area of 

 biological science have more rapid advances been made during the past 

 decade than in the elucidation of the complicated enzyme systems of cellular 

 metabolism. To discuss these phenomena in the vague terms customary in 

 introductory textbooks is to skirt around the central fact of life itself. The 

 presentation provided in this book is as simple and straightforward as it can 

 be made and is supplemented by a diagram showing the interrelations of the 

 various enzyme systems. The subject is no more difficult to understand than, 

 for example, the sequence of events in digestion or the life cycles of many 

 parasites. Perhaps only a few students will become aware of the deeper 

 implications of this study, but all should acquire more than just a vague idea 

 of the pathways of energy utilization in cells. The mechanisms of cellular 

 metabolism will undoubtedly become a standard feature of introductory 

 zoology, just as all achievements of advanced research are eventually re- 

 flected in introductory teaching. 



Although many areas of zoology are developing so rapidly that no textbook 

 can be expected to remain completely up to date for more than a few months, 

 we have incorporated the recent discoveries that have come to our attention. 

 Thus, in the section describing the morphology of cells, full use has been made 

 of the results obtained by thin-sectioning techniques and electron microscopy. 

 A surprisingly we 11 -developed nerve net has been reported in sponges, suggest- 

 ing the necessity of revising the classical concept of coordination in these 

 primitive metazoans. The discoveries relating to hormonal integration in 

 arthropods have been incorporated at several points. But beginning students 

 are often stimulated to eager interest by realizing that much is yet to be 

 discovered in zoology; accordingly, we have consistently noted significant gaps 

 in knowledge of structure, function, and life cycles in animals. 



For the most part, new illustrations have been prepared for this book. 

 Some excellent figures from the fourth edition of the Curtis and Guthrie text 

 have been retained, usually after redrawing and modification. Aside from 

 original drawings and photographs, there can be no better source for textbook 

 illustrations than figures appearing in the original scientific articles, hand- 

 books, or monographs in which a discovery is reported or some special feature 

 of an animal described. Therefore, many of our illustrations have been taken 

 from such sources, modified as necessary for our purposes. In each case a full 

 reference to the source is given following the legend so that the teacher or 

 the interested student may consult the original article. The large majority 

 of line drawings were prepared by Bente Starcke King, to whom we are much 

 indebted for her faithful and talented services. Additional drawings were 

 made by Mary Guerriere Loomis and Evelyn J. Erickson; preliminary letter- 

 ing in some charts was the work of Asad Isaf. To all of these contributors 

 we express our appreciation. 



