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PREFACE TO FOURTH EDITION 



Numerous changes have been made throughout this revision. Mate- 

 rial has been rearranged for better organization and presentation, and 

 additions and deletions have been made in the light of the needs in 

 various courses as presented. A wide selection of material is given so 

 that a proper balance can be secured in the various courses. Many of 

 the benefits of a course in biology are to be derived from a laboratory 

 or field study of the phenomena of living organisms. Consequently, it 

 seems that a textbook in such a science should make available those per- 

 tinent facts which will assist the instructor to help the student to help 

 himself to understand these phenomena better and to develop the many 

 attributes of scientific study, including the scientific method. The 

 instructor must attempt to initiate and maintain in the student a curi- 

 osity and fundamental interest in the phenomena of the living world. 

 Through proper techniques and constant practice, the student should 

 develop a method of working and thinking whereby he is able to formu- 

 late logical conclusions from scientifically observed and recorded data. 

 He should become familiar with the technique of proving important 

 principles for himself rather than merely reading about them or being 

 told about them. The student should ascertain the facts, and with «a 

 minimum of help from the instructor, he should formulate his own con- 

 clusions and prove the more important principles based on the scientific 

 interpretation of his collected facts and data. 



A textbook is not intended to be a book of entertainment, and illus- 

 trations are not included necessarily for beauty or esthetic purposes but 

 to assist the student to gather and evaluate facts scientifically. The joy 

 and entertainment come from scientific discovery of new facts and 

 phenomena with which he may not have been familiar. The joy and 

 satisfaction of learning anything new is an essential basis upon which 

 profitable educational progress is built. 



Pronunciations and derivations of terms are more widely considered 

 than in previous editions in order that the student may understand bio- 

 logic terminology better and increase his command of the English lan- 



3 



