XVlll PREFACE 



during two winter sessions. My hearty thanks are also due 

 to my friends and colleagues Professors Baumann, Liiroth, 

 Wiedersheim, and Ziegler, as well as to Professor Goebel, of 

 Munich, for information of various kinds ; and I am no less 

 indebted to Miss Else Diestel, who, in addition to much 

 help of a technical nature, has also been at the great pains 

 of preparing an alphabetical index. 



I thus venture to bring into the light of day a work which 

 is the fruit of many years labour and of many doubts ; and 

 even though but few of my results should remain unmodi- 

 fied, I hope nevertheless that my work has not been in 

 vain ; for even error, if it originate in correct deductions, 

 must become a step towards truth. 



AUGUST WEISMANN. 



Freiburg, i/Br., 

 May igth 1892. 



