100 INHERITANCE IN GUINEA-PIGS. 



especially black, in the BB and BW races, the feebler development in 

 the 4-toe race, and the much feebler development in the wild species. 

 If this is correct, the resemblance of light-bellied rufescens to light- 

 bellied agoutis, like that of the pale color of C. cutleri to dilute guinea- 

 pigs, is secondary. In both cases the wild species possess a different 

 allelomorph from the guinea-pig in the principal series of factors 

 involved, but owing to different residual heredity, have a superficial 

 resemblance. 



THE INHERITANCE OF THE AGOUTI OF CAVIA CUTLERI. 



The writer has had the opportunity of working with the agouti of 

 Cavia cutleri. Repeated crosses have been made with blacks of the 

 BW race of guinea-pigs to see whether a ticked-bellied agouti could be 

 obtained. While some ventral ticking has been observed in some cases, 

 the f-blood cutleri hybrids are still on the whole good light-bellied 

 agoutis. The cutleri agouti is unquestionably more resistant to dark- 

 ening influences than was rufescens agouti. No results have been 

 obtained yet which serve to differentiate it from the guinea-pig agouti. 

 This is additional evidence that C. cutleri was ancestral to porcellus. 

 The experimental results are given in crosses 68 to 78. 



Only one cross has been made between a cutleri and ticked-bellied 

 rufescens hybrids. Male K56, a black f cutleri (f 4-toe), was crossed 

 with two ticked-bellied agoutis, which of course had some rufescens 

 ancestry. There were 6 young (3 blacks and 3 ticked-bellies) of which 

 one was quite light and one was black, except for a few ticked hairs on 

 the chest and whiskers. There was thus no very conspicuous tendency 

 toward light-belly introduced by the cutleri hybrid. It seems safe to 

 assume that C. cutleri has a different member of the agouti series of 

 allelomorphs from C. rufescens, but the same or nearly the same as 

 C. porcellus. 



Wild species of the same genus seldom differ as much superficially 

 in any one character as do many varieties of domesticated animals. 

 Yet while very large variations in the latter have been shown in many 

 cases to behave as simple Mendelian units in inheritance, the char- 

 acters by which wild species differ usually seem to be highly complex 

 in heredity. Few well-defined Mendelian factors are recorded in the 

 literature of hybridization. It is, therefore, interesting to find that the 

 darker agouti of Cavia rufescens differs from the lighter agouti of C. 

 cutleri by a clear-cut Mendelian factor. 



INHERITANCE OF ROUGH FUR. 



In the wild species of cavy, and in the ordinary smooth guinea-pigs, 

 the hair shows a definite direction of growth, which is always away 

 from the snout on the body and toward the toes on the legs. This is at 

 least the general tendency of the hair in most mammals, and it is 



