ON HEREDITY. 



PREFACE. 



THE following- essay was my inaugural lecture as Pro-Rector of 

 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 sub-^ 

 stance transfers its hereditary tendencies from generation to ge- 

 neration, at first unchanged, and always uninfluenced in any corre- 

 sponding 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 not 



