VI 



PREFACE 



Despite all the reasons given for the se- 

 quence of material in this book, some ex- 

 cellent teachers of zoology prefer the 

 method in which the frog and most of the 

 basic principles are studied before consider- 

 ing representative types in phylogenetic or- 

 der. Doubtless different paths may be used 

 to reach the same goal. If this approach is 

 preferred, the order of chapters should be: 

 1, 23, 2, 8, 31, 32, 33, 34, 35, 36, 37; then 

 these should be followed by the phylo- 

 genetic studies starting with Chapter 3. 

 This text is designed to be so flexible that 

 the arrangement of the chapters can be al- 

 tered in any way to suit the teaching phi- 

 losophy of the instructor. 



Most teachers of zoology agree that the 

 students who take the introductor)^ course 

 in college zoolog\' may be divided into three 

 groups: (1) those who will major in this 

 field; (2) those who wish to do further work 

 to prepare themselves for teaching in high 

 schools, or for the medical sciences; and 

 (3) those for whom this is a terminal course 

 as a part of their general education. A con- 

 scious attempt has been made to develop a 

 textbook that will satisfactorily serve all 

 three groups. 



The introductory course in zoology should 

 give the student a knowledge of animals 

 that will add greatly to his interest in life; 

 it should present the various subjects in 

 such a way that he can apply the principles 

 of zoologv' to man so as to obtain a better 

 understanding of man's place in nature; and 

 it should furnish a good idea of the many 

 more or less direct relations between man 

 and the other animals. In College Zoology 

 a definite effort has been made to meet these 

 requirements. Reference is made in various 

 chapters to human anatomy and physiology, 

 especially in Chapters 31 to 34. At the end 

 of most chapters, the direct relations of the 

 animals under consideration to man are 

 presented. 



The discussion of the animal phyla has 

 purposely been made more comprehensive 

 than is customary to enable each instructor 



to make a choice of representatives of the 

 groups; he can select those that best imple- 

 ment his own educational philosophy. Ad- 

 mittedly, it would be difficult for the aver- 

 age student to master the material for all 

 forms treated. 



All chapters have been revised to clarify 

 the presentation and improve the read- 

 abilitv. A few of the more conspicuous new 

 features are as follows: hundreds of superior 

 drawings by one artist possess a style de- 

 signed for clarity, to attract the student's at- 

 tention, stimulate his imagination, and im- 

 press his memory. The labels have been 

 printed, and the margins are in a straight 

 line. Also many new photographs have been 

 added, including electron micrographs and 

 a color photograph of a tidepool com- 

 munity. Wherever possible, the drawings 

 were based on actual dissection, and the 

 photographs are those of living animals. 

 Decorative headpieces for the 38 chapters 

 suggest the themes of the respective chap- 

 ters and also contribute something of in- 

 structional value. This edition with over 

 1400 illustrations, grouped in 467 figures, 

 tries to tell the story of zoolog}' by means 

 of the graphic arts. Many legends for the 

 illustrations were rewritten and are more 

 descriptive than in the previous edi- 

 tions. 



The chapters on the invertebrate ph\'la 

 do not merely form a survey of these groups, 

 but they illustrate the progression of levels 

 of organization through evolution. This edi- 

 tion contains more material of human inter- 

 est and emphasizes the socially significant 

 application of zoologv. 



A photograph and line drawing with full 

 discussion of the newly discovered deep-sea 

 mollusk, Neopilina, is included. This is con- 

 sidered to be a more incredible discovery 

 than Latimeria, the living coelacanth. The 

 explanation of osmosis is in keeping with 

 present-day thinking. The newest concepts 

 on animal beha\ior have been included. 

 Recent advances in organic evolution have 

 been incorporated. Consideration is also 



