Nos. 620-621] INHERITANCE IN PEBOMTSCUS 



449 



stripe appears in its full size and intensity. 31 Neverthe- 

 less, the stripe itself was shown in the preceding pages 

 to vary from race to race and from one individual to 

 another. And these variations, both racial and individ- 

 ual, were found to be hereditary. 



The case, of course, is parallel to that of Castle's 

 hooded rats. Since "lroodedness" is recessive to "self- 

 color" and reappears in one fourth of the F 2 generation, 

 Castle argues that it is dependent upon a single unit fac- 

 tor. Nevertheless, this factor itself presents hereditary 

 variations in "potency," since it can be modified indefi- 

 nitely by selection. The Mendelian counter-argument is 

 that "hoodedness" behaves as a unit character in certain 

 crosses merely because there is some one factor without 

 which it can not manifest itself at all, The variability in 

 its degree of manifestation is due to the fact that the 

 ^hooded pattern is modified by the action of a number of 

 independent cumulative factors. The argument seems a 

 bit scholastic, but we must admit that it is logical and 

 consistent. 



Take another instance. Here I admit that my evidence 

 is to some extent inferential at present. I have given 

 good grounds for believing that the pigmentless con- 

 dition of the snout in certain strains of rubidus is a 

 simple recessive trait, dependent upon a single factor (or 

 its absence). By this I mean that the pigmentless con- 

 dition is probably allelomorphic to any degree of pig- 

 mentation uhatever. 



Now we find, in examining a series of mice, all grada- 

 tions from those with heavily pigmented snouts to those 

 in which no pigment is to be discovered with the aid of a 

 hand lens. Indeed, there are a few "borderland" cases, 

 which can be only doubtfully distinguished as pigmented 

 or unpigmented. Unfortunately, I have no data showing 

 whether or not these various gradations are- hereditary. 

 Analogy with the case of the tail-stripe would make it 

 probable that they are. Moreover, we do know that those 



