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 they are only absolutely alike in the case of two ids which have been formed by the division of a mother-id. Let us disregard this for the moment, and assume that all the ids of a germ-plasm are different: the germ-plasm of a father, _A_, will be composed of ids _A_ 1-100, that of the mother, _B_, of the ids _B_ 1-100. 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_ × _B_ the most diverse combinations of ids may be contained; for instance, _A_ 1, 3, 5, 7, 9, 11, ...to 99, or _A_ 1-10 and 20-30, and 40-50, and so on, and similarly in the germ-cells _B_. If all germ-cells produced by _A_ and by _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 a blended inheritance; in another the child takes after the father or after the mother; in a third, and this probably occurs most frequently, the child resembles the father in some characters and the mother in others. But how then does Galton's curve of frequency of variations come about? Why does the mean of any character occur by far the most frequently, and why does the frequency of a variation diminish regularly in proportion to its approximation to either extreme? To this it is answered: Because the process of mingling through amphigony goes on through numerous generations, and thus an elimination of chance, and the establishment of an average, must be brought about.