the heredity of physical abnormalities or defects. TABLE IV. _Symbols used in Pedigrees. As adopted by the Galton Eugenics Laboratory._ [Symbol] Male and female respectively, not possessing the trait under consideration. [Symbol] Male and female possessing the trait under consideration. [Symbol] Unknown sex--normal or affected. [Symbol] Trait incompletely developed. [Symbol] Neither presence nor absence of trait can be affirmed. [Symbol] With a deformity or disease of special character which may possibly be associated with that under consideration. [Symbol] Twins. [Symbol] Indicates number of children. [Symbol] Marriage. [Symbol] Number of children unknown. [Symbol] Number and character of children unknown. _S. P._ _Sine prole._ (No offspring.) Fig. 13 illustrates a family history where brachydactylism (an abnormality of the digits commonly called shortfingeredness, due to the lack of one joint in each digit) is present and frequently associated with dwarfism. We may describe this case rather fully because it illustrates nicely the heredity of a trait according to the Mendelian formula. The parentage of the affected female (II, 1) who started this line is uncertain. The marriage was with a normal male whose parentage is unknown but evidently normal. This pair produced 11 children, the character of 8 of whom is known; 4 were affected, 4 unaffected, a Mendelian ratio resulting from the mating of a normal with a hybrid individual, the observed character dominating (i. e., the abnormality appearing in the hybrid individuals). According to Mendelian laws, the normal offspring of affected hybrids when mated with normals should produce all normal offspring; this result is shown clearly through generations IV-VI, where no affected individuals are produced by two normal parents, although one or two of the grandparents were affected. Marriage of a normal person with one affected parent is fit because this individual is wholly without germinal determiners for this character. Marriage between a normal and an affected person is unfit (or it would be if the observed character were a serious defect) because approximately one half their offspring will be affected like the one parent. Thus in IV, 7-21, we see 12 children from one such marriage, 7 of whom are affected, 5 unaffected. All of the 11 children of the 5 unaffected are normal, while of the 16 children of the affected persons, all of whom that married at all married normal individuals, 9 were affected, 7 unaffected. Similar relations are found in generation VI, where the 9 affected persons in V married normals, producing 33 children, 15 of whom were affected, 18 unaffected. Taking all the offspring of marriages between unaffected and affected (hybrid) persons through the four generations III-VI, we find 35 affected and 33 unaffected, with the condition of 3 unknown.