96 HEREDITY AND EUGENICS 



(with four toes on one foot and five on the other) 

 varied somewhat according to whether the male or 

 female belonged to the five-toed breed, and also in 

 Fj as compared with F^. In a total of 402 birds, 172 

 had four toes on both feet , and 3 8 were heterodact^dous . 

 Of the latter, 34 had the extra digit on the left side 

 and only 4 on the right. In 2 birds rudiments of 

 six toes appeared, suggesting that the character for 

 extra toe is not stable. Bateson and Punnett also 

 found that among 89 asymmetric birds from various 

 matings, the extra digit was on the left side in y2 

 cases, and on the right in 17. In 49 other birds the 

 extra toe was larger on one side than on the other, 

 being larger on the left side in 34 of these cases, and 

 smaller in 15. Barfurth, in similar matings between 

 normal and h^^perdact^dous fowls, obtained 556 

 four-toed and 475 hyperdact3dous. Of the latter, 

 6s were asymmetrical, 35 having the extra toe on 

 the left and 30 on the right. In another list 12 birds 

 were left-sided and 6 right-sided. Castle (1906) 

 in guinea-pigs also found a slight tendency for 

 the extra toe to appear on the left side. Out of 

 1,219 individuals, 630 had the extra digit on the 

 left and 582 on the right. The explanation is not 

 clear. 



Bonnevie (191 9) describes a type of postaxial 

 Polydactyly in man, which is usualty stronger on the 

 right side of the body. The extra finger arises from 

 the base of the little finger, the metacarpal bones being 

 normal. There is much variation in this abnormality, 

 and families showing it are now distributed all over 

 Norway, but they are all probably descended from 

 the same ancestor about 300 3^ears ago. Boas (191 7) 

 assigns two causes for polydact3dy in horses : 

 (i) Atavism, " Hipparion-toes "; (2) doubling of 

 certain digital parts of the foot. The case of Caesar's 

 horse, which belonged to the former class, is well 



