90 NATURAL INHERITANCE. (C1IAP.
of Like Parents ; (b) those who are the progeny of Unlike Parents. Next we write the statures of the individuals in each Fraternity under the form of M + (:D) (see page 51), where M is the mean stature of the Fraternity, and D is the deviation of any one of its members from M. Then we marshal all the values of D that belong to the group a, into one Scheme of deviations, and all those that belong to the group b into another Scheme, and we find the Q of each. If it should be the same, then there is no greater diversity in the a Group than there is in the b Group, and such proves to be the case. I applied the test (see Table 10) to a total of 525 children, and found that they were no more diverse in the one case than in the other. I therefore conclude that we have only to look to the Stature of the Mid-Parent, and need not care whether the Parents are or are not unlike one another.
The advantages of Stature as a subject from which the simple laws of heredity may be studied, will now be well appreciated. It is nearly constant in the same adult, it is frequently measured and recorded ; its discussion need not be entangled with considerations of marriage selection. It is sufficient to consider the Stature of the Mid-Parent and not those of the two Parents separately. Its variability is Normal, so that much use may be made of the curious properties of the law of Frequency of Error in cross-testing the several conclusions, and I may add that in all cases they have borne the test successfully.