120 Experimental Zoology 
ancestry. If the various sires are arranged ‘‘in the order of the 
respective amounts of polydactylous ancestry which they possess, 
we see at once that this is not the order of their potencies, for 
those having the same amount of polydactylous ancestry often 
differ much in the potency with which they transmit the poly- 
dactyl character.” 
When polydactylous individuals were mated with normal ones, 
the results were far from being uniform. Some of the offspring 
have the extra toes greatly weakened; in other cases there is no 
toe at all, while in still other cases the extra toe may be fairly 
well developed. ‘The inheritance is neither sharply alterna- 
tive (Mendelian) nor completely blending.” It is clear that in 
its inheritance the extra toe of these guinea pigs does not follow 
Mendel’s law. Castle concludes that the extra toe is inherited 
in a manner intermediate between blending and alternative in- 
heritance. The gametes, he thinks, only partially blend in the 
zygote, producing a variable result. “If the inheritance were 
sharply alternative, we should expect to get, not a series of gradu- 
ated forms, but two or at most three sharply distinct groups, 
but this is not the result observed. If, on the other hand, the 
inheritance were fully blending, all the offspring of two pure par- 
ents, or of two cross-bred parents should be alike, but this is not 
the result observed. We are forced to conclude, therefore, that 
there occurs a partial blending of gametes [characters] in the 
zygote, and a partial segregation as the zygote gives off 
gametes.” 
Castle points out, further, that partial blending is the more 
common result of hybridizing, since both sharply alternative 
inheritance and complete blending are rare. By selection the 
breeder is able to produce an almost pure race by picking out the 
more potent individuals in each generation. It is interesting to 
note that the potency of the male is a germinal variation, tend- 
ing toward determinate inheritance, and not simply an extreme 
fluctuating variation due to external conditions. Hence, in 
selecting prepotent individuals the process involves the choice of 
certain individuals that transmit certain qualities in a high degree, 
