PREFACE TO THE THIRD EDITION x 



2. Each chapter of the general part contains the following 

 elements: (i) the general statement of principles or facts; 

 (2) interspersed with this are such practical exercises for labo- 

 ratory, field, or library, as have been found practicable for 

 elementary classes. These are intended to compensate for the 

 enforced brevity and abstractness of definitions and description, 

 by causing the student to find concrete illustration of the princi- 

 ples; (3) an analytic summary of the most important general 

 truths of the chapter in outline, at the close of the chapter; 

 and finally (4), a list of supplementary topics for individual 

 laboratory or library investigation and report. These supple- 

 ment and illustrate the text, and enrich the review by introduc- 

 ing a new viewpoint and new matter. It is not intended that 

 all of these topics shall be demanded of the whole class. The 

 writer has got best results in interest and knowledge by allow- 

 ing each member of the class to select some topic in which he is 

 interested and to make a brief report of his investigation before 

 the whole group. 



3. In the chapters of the special part each phylum is intro- 

 duced by field and laboratory work on some representatives 

 taken as types. This is purposely made brief and suggestive 

 in order to stimulate the teacher and class to build up their 

 own detailed program. This is followed, corrected, and en- 

 larged by a brief discussion of the typical condition of the organs 

 and functions in the group as a whole. This serves to unify the 

 isolated and local observations of the student. Next follows 

 a brief statement of the most important facts of classification, 

 together with ecological and economic suggestions. Finally, 

 each chapter concludes with a list of supplementary questions 

 calling for field, laboratory, and library work in review, and as 

 a brief view of new material. 



4. The figures are carefully selected, the majority of them 

 being specially made for this book. With each figure of special 

 moment is a brief list of queries designed to assist the student 

 in the study of the figure. It is a common complaint among 

 teachers that it is difficult to get students to appreciate and to 

 use illustrations intelligently, and to relate them to the text. 

 A sane emphasis on these questions will solve this problem. 



