X PREFACE 



ing; but we take it or leave it all our lives, and perhaps the prin- 

 cipal trouble with college teaching is that we do not make our 

 students feel that college work is a serious enterprise. 



As it stands, the present volume represents a temporary crys- 

 talUzation of the course in General Zoology as developed in the 

 University of Missouri, although it contains more than the authors 

 are able to offer in a course extending through but one semester. 

 In the Laboratory Directions,^ designed to accompany the present 

 volume, it was possible to include work upon flatworms, molluscs, 

 and echinoderms. These have been omitted from the text, since 

 it is obviously impossible to deal so largely with principles and at 

 the same time present types of all the phyla. A chapter upon the 

 History of Zoology has been omitted in favor of the inclusion 

 of historical references in connection with special topics, since it 

 is the authors' experience that historical chapters are not very 

 effective with students. 



In general, the aim has been to include the substantial body 

 of well-estabUshed facts concerning the structure and functions 

 of the animals described and to avoid undue inclusion of veiy 

 recent details, however interesting. The authors hope that the 

 book is not out of date in regard to recent biological investiga- 

 tion, but they have not tried to make it so "up to the minute" 

 that it would soon be found to contain premature conclusions 

 from very recent work. Such details are always better left to the 

 teacher as a means of vivifying his instruction. For example, it 

 is well to explain in a text the saUent facts of "endocrine secre- 

 tion," but not to include very recent extensions that have not been 

 verified. It has been assumed throughout that the laboratory 

 work of the course should be definitely related to lectures and 

 text, and not given as though it were a separate course, as is done 

 in some institutions. The authors' view of laboratory study has 

 been discussed at some length in the Remarks to Instructors as 

 printed in the Laboratory Directions. It is the behef of the 

 authors that a textbook should contain a fundamental body of 

 subject-matter that is correlated with the laboratory work and 

 that may be extended by lectures at the discretion of the teacher. 

 If laboratory work means anything, it should mean some measure 

 of first-hand contact with the facts. On this foundation the text 



2 Curtis, W. C, and Guthrie.. M. J., "Laboraton^ Directions in General 

 Zoology." 



