10 HEREDITY. 



cell-nucleus, or even in a particular "locus" of a chromosome, 

 all the hypotheses which see the inherited as "determinants" 

 of characters or of organs, must have this in common, that 

 they have to assume that these determinants are sometimes 

 "latent" or inactive, namely in those instances, in which an 

 individual which does not show a certain peculiarity that his 

 parents have, nevertheless transmits it to some of its offspring. 



With the growth of Biomechanics, the science of the factors 

 of development and fimction, a quite different conception of 

 heredity begins. 



Wilhelm Roux distinguishes two fundamentally different sets 

 of factors in the development of the organisms, determination- 

 factors and realization-factors, the former constituting the ' 

 "inherited" and the latter the environment. On different occa- 

 sions we have tried to show that Genetics is essentially a 

 branch of Biomechanics, concerning itself with a study of those 

 factors in the development of an organism which are inherited, 

 and we are still convinced that little progress can result from 

 a conception of Genetics as a mere statistics of cross-breeding 

 experiences. 



The question whether the inherited is simple or multiple, has 

 been long a point of discursive argument, and not the least 

 benefit derived from Mendel's discovery has been, that his 

 question has been definitely solved. 



Those authors who take a Biomecljanical view of inheritance 

 'instead of a morphological or a statistical one, believe, that 

 numerous things are transmitted from parent to offspring, 

 which each, by their presence in the cells, tend to influence one 

 or more definite steps, processes in the development, whenever 

 these steps are taken or those processes undergone. From a 

 biomechanical standpoint it is clear that no special states, no 

 latency or semi-latency or in'activity need be ascribed to those 

 inherited things, which in a certain individual are not factors 

 in the development and which nevertheless are transmitted 

 by it to some of its children. ; 



In every instance ih. which we investigate such "Latency", 



