PREFACE vii 



sketch which does not pretend to give a complete history of 

 biological thought. The story has been developed almost 

 entirely from the side of animal life; not that the botanical 

 side has been underestimated, but that the story can be told 

 from either side, and my first-hand acquaintance with botan- 

 ical investigation is not sufficient to justify an attempt to es- 

 timate its particular achievements. 



The writer is keenly aware of the many imperfections in 

 the book. It is inevitable that biologists with interests in 

 special fields will miss familiar names and the mention of 

 special pieces of notable work, but I am drawn to think that 

 such omissions will be viewed leniently, by the consideration 



J ' r 



that those best able to judge the shortcomings of this sketch 

 will also best understand the difficulties involved. 



The author wishes to acknowledge his indebtedness to 

 several publishing houses and to individuals for permission 

 to copy cuts and for assistance in obtaining portraits. He 

 takes this opportunity to express his best thanks for these 

 courtesies. The parties referred to are the director of the 

 American Museum of Natural History; D. Appleton & Co.; 

 P. Blakiston's Sons & Co.; The Macmillan Company; 

 The Open Court Publishing Company; the editor of the 

 Popular Science Monthly; Charles Scribner's Sons; Pro- 

 fessors Bateson, of Cambridge, England; Conklin, of Phila- 

 delphia; Joubin, of Rennes, France; Nierstrasz, of Utrecht, 

 Holland ; Newcombe, of Ann Arbor, Michigan ; Wheeler and 

 E. B. Wilson, of New York City. The editor of the Popu- 

 lar Science Monthly has also given permission to reprint the 

 substance of Chapters IV and X, which originally ap- 

 peared in that publication. 



W. A. L. 



NORTHWESTERN UNIVERSITY, 

 Evanston, 111., April, 1908. 



