SIGNIFICANCE OF SEXUAL REPRODUCTION, ETC. 



PREFACE. 



THE greater part of the present essay was delivered at the first 

 general meeting of the Association of German Naturalists, at 

 Strassburg, on September i8th, 1885, and is printed in the Pro- 

 ceedings of the fifty-eighth meeting of that Society. 



The form of a lecture has been retained in the present publica- 

 tion, but its contents have been extended in many ways. Besides 

 many small and a few large additions to the text, I have added 

 six appendices in order to treat of certain subjects more fully than 

 was possible in the lecture itself, in which I was often obliged to be 

 content with mere hints and suggestions. This appears to be all 

 the more necessary because it is impossible to suppose that many 

 views and ideas upon which the lecture was based would be well 

 known to all readers, although they have been described in my 

 former papers. It was above all necessary to deal with the class of 

 acquired characters, which, as it seems to me, is easily confounded, 

 especially by the medical profession, with the much broader class of 

 new characters generally. Only those new characters can be called 

 'acquired' which owe their origin to external influences, and the 

 term 'acquired' must be denied to those which depend upon the 

 mysterious relationship between the different hereditary tendencies 

 which meet in the fertilized ovum. These latter are not ' acquired ' 

 but inherited, although the ancestors did not possess them as such, 

 but only as it were the elements of which they are composed. 

 Such new characters as these do not at present admit of an exact 

 analysis : we have to be satisfied with the undoubted fact of their 

 occurrence. The transmission or non-transmission of acquired cha- 

 racters must be of the highest importance for a theory of heredity, 

 and therefore for the true appreciation of the causes which lead 

 to the transformation of species. Any one who believes, as I do, 

 that acquired characters are not transmitted, will be compelled to 



