THE GENERAL SIGNIFICANCE OF AMPHIMIXIS 205 



cliildren of a pair are often dissimilar. And while the ' Schiller ' 

 cannot be separated again into red wine and white, this hap23ens often 

 in sexual reproduction, and sometimes to such an extent that the 

 grandchild exactly resembles one or other of the grand-parents, as is 

 most clearly proved in the case of plant-hybrids. 



There is thus a deep-seated difference, depending on the fact 

 that what is mingled in amphigony is not sim^^le but composite, not 

 a simple uniform developmental tendency associated with a simple 

 and definite substance, but a combination of several or many 

 developmental tendencies, associated with several equivalent but dif- 

 ferent material units. These units are the ids or ancestral plasms, and 

 we have seen how they are not only halved by reducing division, 

 but are also arranged in new combinations in amphimixis. 



These ids differ very little within the same germ-plasm ; in species 

 which have long been established the majority probably only differ 

 in correspondence to the individual differences of the fully-formed 

 organisms, but the}' are only absolutely alike in the case of two ids 

 which have been formed by the division of a mother-id. Let us dis- 

 regard this for the moment, and assume that all the ids of a gerju-plasm 

 are different: the germ-plasm of a father, A, will be composed of ids 

 A i-ioo, that of the mother, B, of the ids B i-ioo. But in each 

 mature germ-cell of these two parents only fifty ids are contained, 

 and if we assume that the mingling of the ids is controlled solely by 

 chance, then in the various germ-cells A x B the most diverse com- 

 binations of ids maybe contained; for instance, A i, 3, 5, 7, 9, 11, 

 . . .to 99, or A i-io and 20-30, and 40-50, and so on, and similarly 

 in the germ-cells B. If all germ-cells produced by A and l)y B 

 attained to development, or even if all the ova succeeded, the thousand 

 or hundred thousand children of this pair would necessarily exhibit 

 every possible mingling of their characters, and each in the same 

 number according to the rules of probability calculations. But it is well 

 known that this does not happen: of the thousands of human ova, for 

 instance, which come to maturity in the course of the life of a female 

 individual more than ten rarely develop, and more than thirty never, 

 and these are determined solely by chance and quite independently of 

 the mixture of ids which they contain. It is thus purely a matter of 

 chance which of the complexes of primary constituents contained in 

 the germ-plasm of an individual are transmitted to descendants, and 

 it is also purely a matter of chance which combination of ids comes 

 to be developed. Therefore we may say that no regular neutralizing 

 of contrasts, either in the primary constituents of the parents or as 

 regards the differences in their characters, can occur. In one case there is 



