308 THE GERM-PLASM 



holds good as regards the crossing of the different human races. 

 According to this law, the intermingling of a racial character 

 is uniform in the first generation, but subsequently becomes 

 quite irregular when recrossing with one of the original races 

 occurs. The skin of mulattoes, which are a cross between 

 white races and negroes, is never quite white, its colour being 

 as a rule an approximate mean between that of the two parents. 

 When mulattoes and white races are recrossed, the skin does 

 not regularly become less black, but the descendants of the 

 third and fourth generations are sometimes white and sometimes 

 fairly dark : this fact indicates the absence of uniformity in the 

 process of 'reducing division.' 



2. Reversion to Individual Characters in Man. 



The essential difference between the process of reversion in 

 plant-hybrids and in Man, consists in the fact that the former is 

 concerned with the intermingling and subsequent separation of 

 specific or racial characters, while in the case of the reproduc- 

 tion of human beings of the same race individual characters 

 only are intermingled. As regards hybrid-plants, the idants of 

 each parent might be assumed to be similar, — although this may 

 not be strictly true in all instances, as will be seen later on, — but 

 in the case of individual differences the idants of each parent 

 cannot be regarded as similar. Each of these idants consists 

 of a number of separate ids, which may differ in many respects. 

 In all of them the determinants are as similar as the retention 

 of the specific character renders necessary : that is to say, all 

 the determinants of the same ontogenetic stage are homologous, 

 though at the same time they are never all homodynamous, 

 but differ in many respects owing to slight individual devia- 

 tions. Hence different ids may contain different variations 

 of any particular homologous determinant. In the following 

 examples, each homologous determinant is indicated by a letter, 

 and variants of a determinant are distinguished by dashes after 

 each letter. Thus id i. of the germ-plasm might, for instance, 

 contain the determinants a, b, c, d, e, n ; id ii., the deter- 

 minants a, b', c, d', e, n' ; id iii., a', b'^ c', d'", e', n, 



and so on. The total effect of the idants is decided by the 

 struggle of the ids ; the laws which regulate this struggle 

 cannot at present be determined more precisely, and until we 

 know more about them, we may suppose that those variants 



