Experiments with other Mammals 119 
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 polydactylism 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 polydactylism 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 toeon the left hind foot. The toe bore a claw, which was not 
connected to the foot by appropriate muscular and tendinous 
connections.2 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 was paired with females from 
families in which polydactylism was not known, 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 
1 Edinburgh New Philosophical Journal, 1863. 
2 Several other cases of inherited polydactylism are given by Gregg Wilson. 
3'The same father that produced this “sport” subsequently produced also 
five others out of 147 offspring. 
