+-------------+-----+-----------------------------+--------------+ | | | Expectation. | Realization. | | Nature of | +--------------+--------------+--------------+ | mating. | f | Dominants + | Pure | | | | |heterozygotes.| dominants. | Syndactyls. | +-------------+-----+--------------+--------------+--------------+ | | | _P. ct._ | _P. ct._ | _P. ct._ | | DD × DD | 41 | 100.0 | 100.0 | 56.1 | | DD × DR | 132 | 100.0 | 50.0 | 26.5 | | DR × DR | 277 | 75.0 | 25.0 | 10.1 | | RR × DR | 16 | 50.0 | 0.0 | 0.0 | | RR × RR | 119 | 0.0 | 0.0 | 0.0 | +-------------+-----+--------------+--------------+--------------+ These studies on syndactylism in poultry may be used for a critical examination of the recent work of Lewis and Embleton (1908) on syndactylism in man. The cases described by them follow the types I have just described in poultry. Their fig. 18 corresponds to my types _a_ and α; figs. 10 and 11 to my type β. The "crossbones" referred to by the authors correspond to bones of the "curved toe." The facts presented by the authors support the idea that syndactylism is dominant rather than recessive, but they deny the application of Mendelian principles to this case. Actually, the foot deformities described by Lewis and Embleton are inherited much like syndactylism in poultry. No extracted normal (recessive) extremity produces the abnormal condition. Heterozygotes show much variation, from very abnormal to slightly abnormal (possibly perfectly normal?) appendages. Dominance is, indeed, much more potent than in poultry. The authors' denial of the application of Mendelism to this case seems to be based on an all too superficial consideration of the hereditary behavior of the character and a tendency to "mass" statistics--a procedure that tends to obscure the interpretation of the data of heredity. As to the inheritance of type, my statistics are not extensive enough to give a final answer, but if all types be grouped into those with straight and those with curved toes, then in crosses of straight-toed syndactyl and normal 33 per cent of the offspring were of the curved type, whereas in crosses of curved-toed syndactyls and normal 45 per cent were of the curved type. These averages depend on 22 and 15 individuals, respectively. They lead us to look for an inheritance of type when more extensive data shall be available.