AUTHOR'S INTRODUCTION 



In the year 1868, in the second volume of his cele- 

 brated work, ''The variation of animals and plants under 

 domestication," Darwin formulated the provisional hypo- 

 thesis of pangenesis. The discussion of this hypothesis 

 is preceded by a masterly survey of the phenomena to be 

 explained. Owing to this, as well as to his clear concep- 

 tion of the whole problem, this part of his book has at- 

 tracted universal attention. We find it mentioned in 

 almost all works which deal with general biological ques- 

 tions. While, however, the general part of the chapter 

 has until now remained the basis for all scientific consid- 

 erations of the nature of heredity, the hypothesis itself 

 has not enjoyed such general appreciation. 



Darwin assumes (Variation 2: 369) that the cells, 

 as is generally accepted, multiply by division, and that in 

 so doing they preserve essentially the same nature. He 

 considers that this rule forms the basis of heredity. By 

 it, however, not all of the groups of phenomena brought 

 together by Darwin may be explained. Especially does 

 it not explain the effects of use and disuse, the direct ac- 

 tion of the male element on the female, and the nature of 

 graft-hybrids. In order to take Into account these phe- 

 nomena, Darwin assumes that there exists, in addition to 

 cell division, yet another means of transfer of hereditary 

 qualities. Each unit of the body, according to his theory, 



