xii PREFACE TO THE FIRST EDITION 



class room text and reference work at the same time. An 

 introductory course in college zoology is assumed as a prerequisite 

 to a course for which this book is designed as a text. 



More material has been included than could ordinarily be 

 covered in a single semester. This offers the instructor greater 

 opportunity of selection in organizing his work than is possible 

 when only the materials for a specific course are presented. 



In zoological textbooks, it is frequently the custom to give 

 a detailed description of a representative of each of the major 

 groups. The writer has had a firm conviction that specific 

 information of this nature is more readily grasped by students 

 when they approach it through laboratory study of type forms 

 with a mind unbiased by minute textbook descriptions. 



When a highly characteristic representative of a group is 

 described in full detail in the text, the instructor has the alter- 

 native of choosing some less characteristic or less easily available 

 species for laboratory study or of permitting his laboratory 

 instruction to become largely routine verification of statements 

 set forth in the text. 



By avoiding duplication in the text of materials indented for 

 laboratory approach, it has been possible to place greater emphasis 

 upon biological principles and generalizations in the treatment 

 of each group. 



A considerable number of my colleagues, and especially those 

 in the University of Illinois, have rendered valuable assistance in 

 reading and criticising portions of the manuscript and in offering 

 suggestions during its preparation. It is a pleasure to acknowl- 

 edge the very able assistance of Bernice F. Van Cleave whose 

 criticisms of the early drafts of the manuscript and aid in reading 

 the proofs have been of very great value. 



Various publishers have granted the use of cuts or the per- 

 mission to reproduce illustrations. Henry Holt and Co. and P. 

 Blakiston's Son and Co. have supplied cuts for a considerable 

 number of illustrations. The John Wiley and Sons, The Com- 

 stock Publishing Co., Gustav Fischer, and the MacMillan Co. 

 have granted permission to redraw illustrations and in some few 

 instances have furnished cuts. Acknowledgment of these 

 courtesies is further made in the legends accompanying the 



^"^^-^S"^^^- H. J. Van Cleave. 



Urbana, Illinois, 

 November, 1923. 



