24 ORIGIN OF A POLYDACTYLOUS RACE OF GUINEA-PIGS. 



often an intermediate condition. The gametes formed by the cross-breds 

 are not homogeneous, as would be the case if complete blending occurred 

 in the zygote, but are highly variable as regards the extra-toe. If the inher- 

 itance were sharply alternative, we should expect to get, not a series of 

 graduated forms, but two or at most three sharply distinct groups, but this 

 is not the observed result. If, on the other hand, inheritance were fully 

 blending, all the offspring of two pure parents, or of two cross-bred parents, 

 should be alike, but this is not the observed result. We are forced to 

 conclude, therefore, that there occurs a partial blending of gametes in the 

 zygote, and a partial segregation as the zygote gives off gametes. 



Not improbably more characters fall in this category than in any other. 

 Sharp alternative inheritance is comparatively rare, so is fully blending 

 inheritance ; most characters appear from generation to generation in a more 

 or less well developed condition, not always strictly intermediate between 

 the conditions found in the respective parents, nor always corresponding 

 closely either with the condition found in one parent or with that found in 

 the other. In dealing with such characters, selection must be the breeder's 

 method of working. If he wishes either to eliminate or to " fix " a par- 

 tially blending character he must make an appropriate choice of parents, 

 not once nor twice, but many times over until the undesired condition ceases 

 wholly to reappear. 



It would be interesting to know in what condition characters like the 

 extra-toe exist in the germ. It can not be in a state of simple recessiveness, 

 for in that case the character should reappear in a Mendelian proportion 

 of the offspring formed, but this, as we have seen, is not the case. More 

 probably the character is present, active or inactive, in every gamete, but 

 the conditions under which it may become active are too complex for present 

 analysis. On the other hand, it is possible that nothing in the germ of a 

 normal guinea-pig stands for the character, extra-toe, and that when this 

 character is formed, it is formed de novo. But if so, we must account 

 for the appearance of a new digit in the precise position of a lost one, 

 and with all the appropriate nervous and muscular connections. This 

 it seems quite as hard to do as to suppose an antecedent state of latency or 

 inactivity of the character throughout certain generations of ancestors. 

 Moreover, we have strong reasons for believing that, in color inheritance, 

 specific pigments and specific color patterns may be transmitted unseen in 

 a latent condition, often through long series of generations. If color char- 

 acters are subject to transmission in a latent condition, it seems reasonable 

 to suppose that other characters also may be transmitted in the same way. 



