PREFACE vu 
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 
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, Ill, April, 1908. 
