104 



INHERITANCE IN GUINEA-PIGS. 



4 toe 

 stock 



leas, on the other hand, behaved like the wild cavies in reducing the 

 roughness. 



PROBLEMS. 



The following figures show the kinds of roughs which have appeared 

 in the experiments with the four principal stocks and the nature of 

 the variability in the rough character, the inheritance of which it is 

 desired to analyze. All roughs are included, but only such smooths 

 as had at least one rough parent. 



Inspection of figure 7 at once shows striking differences in the 

 variability of the rough character in the different stocks. In the 4-toe 

 stock there is a wide gap between the lowest rough and the smooths 

 which come from the same parents. Only one individual in the 4-toe 



stock was graded rough B and this 



A CDC Sm 



was close to rough A (lacked only 

 groin and hip rosettes). Most of 

 the individuals were strong rough 

 A. In the Luna stock most of 

 the individuals which were rough 

 at all were rough B or a weak 

 rough A, but 5 were rough C or D. 

 Among the tricolor and cutleri 

 hybrids a continuous series can 

 be formed passing from the best 

 roughs to the smooths. Both 

 show a distinctly bimodal distri- 

 bution of the roughs, the modes 

 being at rough A and rough C. 

 Such a distribution would of 

 course be purely artificial if rough 

 B were a more limited category 

 than rough A or rough C, but the 



FIG. 7. Distribution of grades of roughness of the definitions show that TOUgh B in- 

 fur in four stocks of guinea-pigs. ^^ perhaps the ^^ range 



of possible variation. Further, the large number of rough B's in the 

 Lima stock shows that this class may be practically as numerous as 

 rough A under the right hereditary conditions. Thus there are strong 

 intimations that in the tricolor and cutleri stocks, rough A and rough 

 C differ by a unit hereditary difference. 



The problem of the inheritance of the variations in the rough char- 

 acter thus seems to resolve itself into three phases: (1) The inheritance 

 of roughness of any sort as opposed to smoothness; (2) the inheritance 

 of a more or less full-rough type averaging about rough A as opposed 

 to a partial-rough type averaging between rough C and D; (3) the 

 inheritance of the variations within the full-rough and partial-rough 

 types. 



Tricolor 

 stock 



Lima 

 stock 



Cutleri 

 hybrids 



