PREFACE 



VH 



given to some of the problems of human 

 flight into outer space. 



There is much more emphasis on the 

 ecology of communities and populations, 

 natural histor\', parasitology, and the scien- 

 tific method. The physiologic content has 

 been increased, and there is much more 

 emphasis on biological principles. New 

 material has been added on experimental 

 embryology. There is somewhat more em- 

 phasis on economic zoology. New sections 

 have been added on the enzymes, vitamins, 

 hormones, gene action and genetic effect of 

 fallout, and many other subjects. A constant 

 effort has been made to achieve better in- 

 tegration of subject matter throughout the 

 text. 



The problem of revising classification is 

 always one of the most difficult encountered, 

 for the specialists themselves are not in 

 agreement. In the matter of classification of 

 animals, an author cannot be all things to 

 all people. Even a beginning zoology stu- 

 dent should learn that there is no such thing 

 as a definitive classification of animals. 

 However, the classification of each major 

 group in this text was checked by an au- 

 thority. 



All phylogenetic trees (dendograms) have 

 been redrawn to bring them into harmony 

 with the newest concepts of animal phy- 

 logeny. The number of species in the various 

 groups is based mostly on information ob- 

 tained by correspondence with authorities. 

 If the numbers seem large, it is because 

 taxonomists are continually making studies 

 that result in an increase in the numbers 

 of new species described. 



The references at the ends of the chapters 

 give the student a ready entrance to the 

 literature; these have been greatly increased 

 in number. 



The glossar}' has been made much more 

 comprehensive than those usually found in 

 introductory texts, because vocabulary stud- 

 ies provide evidence that words are of great 

 importance in the learning process. We 

 keep an object in mind by means of a word 



or symbol; in fact, languages have developed 

 from such simple beginnings. A single word 

 recalls an experience, as well as a complex 

 of ideas associated with it. Therefore, a 

 glossary enables the student to learn the 

 present meaning of the scientific term as 

 well as its origin. By the inclusion of syl- 

 labification and accent marks, the student 

 is helped in the pronunciation of these 

 terms as well. 



A very complete index is also provided so 

 that the reader can easily find the informa- 

 tion he wishes. 



In an effort to achieve the highest degree 

 of authenticity in a subject as broad as gen- 

 eral zoology, a specialist in a given field can 

 best exercise the critical judgment necessar}' 

 for the evaluation of facts in a particulai 

 field. Such help was sought and received in 

 great measure, as the acknowledgments be- 

 low testify. 



ACKNOWLEDGMENTS 



The excellent spirit of cooperation shown 

 by the writer's colleagues was a heart-warm- 

 ing experience. The friendly and generous 

 help of many eminent specialists proves 

 that they are interested in improving the 

 teaching of general zoology. Their contribu- 

 tion guarantees a higher degree of authen- 

 ticity than would othenvise have been pos- 

 sible. In a very real sense this book has been 

 a team effort. 



Above all I am appreciative of the many 

 hours of conscientious effort spent by my 

 wife, Nettie R. Stiles, in the exacting work 

 of editing, proofreading, and indexing. Mrs. 

 Olivia Jensen Ingersoll has not only con- 

 tributed her outstanding talent as an artist 

 in the preparation of all the drawings, but 

 as a zoologist she has shown a consistent 

 interest in her work which has made for 

 clarity in the illustrations. 



Helpful suggestions and critical com- 

 ments were made by the following persons 



