Experiments with other Mammals 1 1 9 



given by Struthers.^ A normal man married a woman who had 

 six fingers on the left hand. There were 18 children, only one 

 of whom was abnormal. In this case the polydactyhsm was 

 not dominant except in one case ; but among the normal chil- 

 dren in the third generation one polydactyl individual is re- 

 corded, indicating that polydactyhsm was in the strain. The 

 failure of the polydactyl condition to dominate in this case, 

 except in one instance, shows how unsafe it is to argue from a 

 few cases to all others. The same character may be a dominant 

 one in certain strains and not in others.^ 



The preceding records and observations are made much clearer 

 by Castle's recent experiments with polydactylous guinea pigs. 

 There was born of normal parents a male guinea pig with an 

 extra toe on the left hind foot. The toe bore a claw, which was not 

 connected to the foot by appropriate muscular and tendinous 

 connections.^ From the polydactylous male were obtained 15 

 individuals with extra toes out of a total of 77 offspring. In sub- 

 sequent generations, partly inbred, the number of extra-toed 

 offspring varied. When the male w^as paired with females from 

 families in which polydactyhsm was not know^n, there were pro- 

 duced about 6.25 per cent extra-toed young. Females, de- 

 scended from the original father, that gave the first polydactylous 

 male, gave 25 per cent extra-toed offspring. Females, them- 

 selves polydactylous, gave 44 per cent polydactylous young. 



Many of the young of the first male had extra toes on both 

 hind feet, and in several cases they were better developed than 

 in the original male. The extra toes were supplied with all the 

 muscles characteristic of functional toes. Castle has traced the 

 descent of this race through five generations, and has obtained 

 some important data regarding the inheritance of the anomaly. 

 He finds that the "potency" of certain individuals is a more im- 

 portant factor in the transmission of their characters than is their 



^ Edinburgh New Philosophical Journal, 1863. 



^ Several other cases of inherited polydactyhsm are given by Gregg Wilson. 

 ^ The same father that produced this "sport" subsequently produced also 

 five others out of 147 offspring. 



