vi Preface 



over, their consideration would have demanded too much 

 space to be included with the present matter in a single 

 volume. The fascinating study of the psychical side of living 

 phenomena also belongs to the province of experimental 

 biology, especially comparative psychology; but this subject 

 has quite recently been fully dealt with by Loeb and by 

 Jennings, who have themselves been largely instrumental in 

 developing the subject, so that further treatment would be 

 more than superfluous. 



The excellent summaries and reviews of some of the topics 

 discussed here, that have been published in recent years, 

 have greatly facihtated my work. I need only mention 

 Roux's and Driesch's analysis of the experimental method, 

 Grafin v. Linden's summary of the experiments on butter- 

 flies, Herbst's excellent treatment of the subjects of "For- 

 mative Reiz," PhilHps's very full review and literature on sex 

 determination, and Cuenot's, Lenhossek's, and O. Schultze's 

 treatment of the same subject. I need scarcely add that, 

 while using these and other reviews, I have made my own 

 compilation almost exclusively from the original sources. 



Covering as extensive a field as I have attempted to cover, 

 it is probable that the different subjects have received un- 

 equal treatment, and I fear that some omissions may have 

 been made. I trust, however, that no serious oversights or 

 mistakes will be found. 



It gives me great pleasure to express here my appreciation 

 of the generous assistance in the correction of the manuscript 

 and proof rendered by my wife, by Professor E. B. Wilson, 

 by Professor C. B. Davenport, and by Professor C. E. Castle. 



