ON HEREDITY. 



PREFACE. 



The following essay was my inaugural lecture as Pro-Rector 

 ot the University of Freiburg, and was delivered publicly in 

 the hall of the University, on June 21, 1883 ; it first appeared 

 in print in the following August. Only a few copies of the first 

 edition were available for the public, and it is therefore now 

 reprinted as a second edition, which only differs from the 

 first in a few not unimportant improvements and additions. 



The title which I have chosen requires some explanation. 

 I do not propose to treat of the whole problem of heredity, but 

 only of a certain aspect of it — the transmission of acquired 

 characters which has been hitherto assumed to occur. In 

 taking this course I may say that it was impossible to avoid 

 going back to the foundation of all the phenomena of heredity, 

 and to determine the substance with which they must be 

 connected. In my opinion this can only be the substance of 

 the germ-cells ; and this substance transfers its hereditary 

 tendencies from generation to generation, at first unchanged, 

 and always uninfluenced in any corresponding manner, by 

 that which happens during the life of the individual which 

 bears it. If these views, which are indicated rather than 

 elaborated in this paper, be correct, all our ideas upon the 

 transformation of species require thorough modification, for 

 the whole principle of evolution by means of exercise (use and 

 disuse), as proposed by Lamarck, and accepted in some cases 

 by Darwin, entirely collapses. 



The nature of the present paper — which is a lecture and not 

 an elaborate treatise — necessitates that only suggestions and 



