PREFACE TO THE FOURTH EDITION. 



" YES," said my eminent friend to whom I had con- 

 fided the general plan of this book, then in the original 

 manuscript, " and who will read such a book as that?" 



The question astonished me, but the manner in which 

 it was asked clearly intimated that it was a method of 

 expressing his conviction that no one would do so. 



My friend is a distinguished educator, occupies an im- 

 portant chair in one of the most prominent American 

 institutions, and should have known; but apparently did 

 not. Time has shown him to have been mistaken. Stu- 

 dents were anxious for a writing that would connect the 

 Botany and Zoology they had learned in college with the 

 Anatomy and Physiology they were learning in the Med- 

 ical College, and those subjects with the world of living 

 things in which they moved. 



I still am unable to answer the original question, " who 

 will read it?" All that- I can say, as the result of three 

 editions completely exhausted, is that thousands are reading 

 it, and for me that is enough to justify the long period 

 spent in its preparation. 



JOSEPH McFARLAND. 

 PHILADELPHIA, PA., 

 March, 1920. 



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