Another defect of the eye following the course of a dominant in heredity is a pigmentary degeneration of the retina known as _retinitis pigmentosa_. Atrophy of the optic nerve is also involved and the final result is blindness. Still another example frequently cited is that of hereditary night blindness (_hemeralopia_), a disease in which the affected person can not see by any but the brightest light. In most affected families the final outcome is usually total blindness. One of the most remarkable pedigrees of defects in man ever collected is one of this disease published by Nettleship. He succeeded in tracing the defect through nine generations, back to the seventeenth century. The genealogy includes 2,116 persons. The character behaves as a single dominant in males, but frequently, though not always, females may be carriers of the defect in transmissible form though not exhibiting it themselves. That is, males in which the condition is simplex (Aa) develop the defect but females of similar simplex constitution (Aa) frequently do not. It follows, therefore, that normal males of such strains will have normal offspring but normal females may have affected children. [Illustration: FIG. 24 Radiograph (Courtesy of Dr. W. B. Helm) showing a partial syndactyly in each hand of an individual. Some degree of webbing between the more distal portions of the affected parts is usual.] [Illustration: FIG. 25 Pedigree of a family with presenile cataract (black symbols); numbers in circles indicate unaffected individuals (after Davenport).] =Other Defects Inherited as Dominants.--=Not to go into details other defects which behave as dominants or modified dominants in human inheritance may be mentioned. The following list is not complete and it must be understood that in some cases the statistics are insufficient to justify us in making anything but a tentative decision. We may thus enumerate as dominant over normality: _Achondroplasy_ (abnormally short limbs with normal head and body); _Keratosis_ (thickening of epidermis); _Epidermolysis_ (excessive formation of blisters); _Hypotrichosis_ (hairless, toothless condition); _Diabetes insipidus_; _Diabetes mellitus_; ordinary (not Gower's) _muscular atrophy_; _Glaucoma_ (internal swelling and pressure of eye-ball); displaced lens; _Coloboma_ (open suture in iris); spottedness of hair-coat; and corneal opacity.