REDUCTION OF VARIABILITY. 



From a Biomechanical standpoint heredity is the transmis- 

 sion of genes, which under certain circumstances can influence 

 developmental processes and in this way final qualities of the 

 organisms. This conception of heredity is fundamentally dif- 

 ferent from the de Vries — Weismann conception of the pro- 

 cess as a transmission of pangens, determinants, which would 

 each directly call into being, directly determine a correspond- 

 ing organ or quality. This last conception brought with it the 

 necessity of assuming, that such determinants could exist in a 

 definite latent, dormant state, namely in all those instances 

 where we knew a certain inherited thing to be present without 

 the corresponding quality with which it was commonly found 

 associated, showing itself. 



If we look upon genes simply as upon substances, which by 

 their presence act upon the course of definite developmental 

 processes, growth-processes, we need not assume that they are 

 dormant or latent in those instances in which the process they 

 can influence does not take place. 



If we take this view of inheritance, we can understand how 

 in a species of plants or animals large numbers of genes may be 

 common property of all the cells, which genes in organisms of 

 this particular biotype do not actively participate in the devel- 

 opment. 



In rats we know a gene, which, when present in coloured 

 animals, makes otherwise black animals agouti. In albino 

 rats, this same gene, though it has no influence upon the col- 

 our, is nevertheless transmitted in the same way as in famil- 

 ies of animals in whose development it plays an active role. 

 It is regularly distributed over one half of the number of germ- 

 cells produced by individuals impure for it, as can be readily 



