ROUGH FUR. 



107 



As has been mentioned before, Nehring (1894) crossed a rough male 

 guinea-pig with Cavia aperea of Argentina. He described the young as 

 smooth at first, but developing a mane along the back later. This 

 was evidently the dorsal crest of rough D. The reversal of hair direc- 

 tion on the hind toes might easily have been overlooked. Detlefsen 

 (1914) described crosses of C. rufescens of Brazil with full-rough guinea- 

 pigs. His rufescens was undoubtedly a different species from the aperea 

 used by Nehring, since the latter found complete fertility among the 

 hybrids of both sexes, whereas Detlefsen found sterility among all the 

 male hybrids. The rough young were rough D. The skin of one of 

 them (A10) shows roughness on all the toes and a very slight dorsal 

 crest. The writer has crossed rough A guinea-pigs with C. cutleri of 

 Peru with similar results. Nine rough young have been obtained, of 

 which 3 show good side rosettes and are rough C, while the others 

 merely show a dorsal crest (and rough toes) and are rough D. A male 

 of pure lea stock, which being from feral stock probably had consider- 

 able wild ancestry, was tested by crosses with full roughs and also 

 gave only partial-roughs — 5 all rough C. Castle (1905) obtained 

 partial-roughs, C or D, on crossing full-roughs with smooths of tri- 

 color stock. The writer has made further crosses of this kind with 

 similar results. One smooth guinea-pig of the Lima stock, L24, had 

 some partial-rough young when crossed with full-roughs of her stock. 



The results given in table 47 show that in partial-roughs from a great 

 variety of sources, the low grade of the roughness is not due to a vari- 

 ation of the rough factor, i. e., to an allelomorph, nor is it due to an inde- 

 pendent duplicate rough factor which produces somewhat similar 

 effects to the factor of full-roughs. These partial-roughs have the 

 identical rough factor present in full-roughs derived directly from the 

 latter. 



(3) When a wild cavy is crossed with a partial-rough guinea-pig, 

 rough young of the lowest grade (rough E) are produced. 



