loo HEREDITY AND EUGENICS 



third toes, and is sometimes even there so slight as 

 to be scarcely noticeable. It is not found in the 

 hands at all. The condition is found in the grand- 

 father, in his onl}^ child (a son), and in three out of 

 six of the F2 generation in accordance with Mendelian 

 expectation. There is no doubt that innumerable 

 slight abnormalities of this kind occur in man and 

 are inherited in the Mendelian manner, as has been 

 shown to be the case with many similar mutations 

 in Drosophila. 



Schultz (1922) adopts Weidenreich's term zygo- 

 dactyly for true webbing, confining the term syn- 

 dactyly to those cases where a union or fusion of 

 bones is involved. Zygodactyly is found in many 

 mammals. In a Sumatran ape Siamanga syndactyla 

 (see Wallace, Malay Archipelago, p. 134), the two first 

 digits of the feet are joined together nearly to the 

 end. In an early stage of development of the human 

 foot the toes are all webbed, and the webbing extends 

 slightly further between the second and third toes 

 than between any others. Webbing or zygodactyly 

 is, therefore, a case of arrested development. It is 

 also found that when certain toes are webbed the 

 corresponding tendons are joined for a greater dis- 

 tance. Schultz cites the observations of Schurmeier, 

 who examined 20,000 men in the American army 

 and found 8 cases of zygodactyly, always between 

 toes II and III. This condition was combined 

 in some cases with webbing of fingers III and IV, 

 or I and II and III and IV, or all fingers. In a 

 family described by Sommer, the webbing of toes 

 II and III was only on the right foot in all members, 

 the pedigree extending through five generations. 

 It was inherited by both sexes, probably as a simple 

 dominant. In Schofield's (1922) family the webbing 

 is always longer on the right foot and is transmitted 

 only from male to male, appearing in all the sons 



