PREFACE. 



THE principal change from the earlier edition consists in the 

 addition of directions for field study and for the laboratory 

 study of the live animals. In the nature of the work these 

 directions must be somewhat general, and should be modified 

 by the teacher to suit local conditions and the requirements of 

 the class. Because of the fact that conditions greatly vary in 

 different localities, it is not to be supposed that each teacher 

 can accomplish all the work here outlined. It is hoped that 

 there is variety enough to suit most localities. Other types 

 may often serve the purpose better than these here presented. 

 The work must also be adapted to the age and experience of 

 the students and to the time allotted to the subject. The 

 author's reasons for the order of study here presented are given 

 in the preface of the descriptive part of the book. 



For convenience, the practical part follows the descriptive 

 text, but, of course, the actual study of the types should precede 

 any assigned lesson or reading in reference books. 



The " Suggestions to the Student " have been entirely re- 

 written. 



Ihe " Suggestions to the Teacher " have become so extended 

 that they are no longer included in the book, but are printed in 

 a separate pamphlet, which can be obtained of the publishers. 

 In this pamphlet are hints as to laboratory equipment, class- 

 room management, notes and drawings, supervision of dissec- 

 tion, collecting outfit, field work, preservation of material, etc. 



A full-page cut of the microscope has been introduced to 

 accompany the directions for its manipulation. The author 

 takes this occasion to thank the firm of Bausch and Lomb for 



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