=Digital Malformations.--=An interesting and easily followed defect is a condition known as _brachydactylism_, in which the digits are shortened because of the absence or rudimentary condition of one segment. The fingers, therefore, appear to be only two-jointed like the thumb. Several families showing this defect have been charted and it appears to behave as a typical dominant. In looking over such a chart (Fig. 21, p. 106) one is struck by the fact that only half of the children from most of the matings show the defect, but when we recall that the affected parent, after the first generation, probably carried the condition in only the simplex form and married a normal individual, such a result is just what would be expected (see formula 2). _Polydactylism_ (Figs. 22, 23, pp. 109, 110) is a condition in which there are extra digits on hands or feet. The character, with apparently slight exceptions in a few records, behaves as a typical dominant. Among other digital defects which are inherited as a dominant is a condition known as _syndactylism_ (Fig. 24, p. 111), in which two or more digits are fused side by side. For an example of syndactyly which seems to be in the class of sex-linked characters, see Fig. 15, p. 65. =Eye Defects.--=_Congenital cataract_ is another not uncommon defect in man which is transmitted as a dominant (Fig. 25, p. 112) with occasional irregularities. It is a condition of opacity of the lens of the eye which produces partial or total blindness. In a paper on _Hereditary Blindness and Its Prevention_, Clarence Loeb (1909) mentions 304 families of which pedigrees have been published. Of the 1,012 children in these families 589, or 58 per cent., were affected. It is obvious that this is near the expected percentage in the case of a dominant trait where matings of affected with normal individuals prevailed. An unfortunate circumstance about this malady from the eugenic standpoint is the fact that it is frequently of the presenile form which comes on late in life so that it is usually impossible to predict whether an individual of marriageable age is immune or will later become affected. [Illustration: FIG. 22 Radiograph (Courtesy of Dr. W. B. Helm) showing polydactyly in a child's hand. For genealogy of this see Fig. 23, p. 110.] [Illustration: FIG. 23 Chart showing a history of polydactylism through five generations in the B---- family. The individual whose hand is pictured in Fig. 22, p. 109, is of the fifth generation. Squares represent males, circles females.]