PREFACE vii 



technique has no part in this course. Facts are neither 

 better nor worse for educational purposes because of 

 technical difficulties that may or may not stand in the way 

 of their acquisition; and therefore, other things being equal 

 I have given preference to such observations as are most 

 likely to be continued after the work of the college course is 

 ended. 



The purpose of the introduction given for each subject is 

 to orient the student for the work assigned — not to replace 

 the lecture or the recitation. I have tried to tell what he 

 should know in order to outline what he should do; and I 

 have tried so to shape the conclusion of his work as to invite 

 a little thinking. During the past seven years I have been 

 seeking methods that would facilitate the handling of bodies 

 of facts sufficiently large for satisfactory illustration of 

 general biological principles and phenomena. Many new 

 exercises have been tried by my classes in field and labora- 

 tory; the ones that have proved most serviceable are 

 included in the following pages. Herein are detailed the 

 methods I have found most available. The materials used 

 are of less consequence. I have used whatever lay nearest 

 at hand, only seeking to draw my materials from a wide 

 range of groups, in order to extend the acquaintance of the 

 student with the face of nature. In so far as it has been 

 necessary to touch upon theoretical questions, it has been 

 my purpose, not to advance any biological theories but to 

 bring the student into practical contact with the facts under- 

 lying all the theories. 



The field of biology is so vast that no one can claim expert 

 knowledge in any considerable portion of it. It is very 

 probable, therefore, that in covering so much ground in even 

 so elementary a manner, I have made some mistakes. I 

 can only hope that they may not be of such nature as to 

 seriously mislead or confuse the student and that I may 



