102 



INHERITANCE IN GUINEA-PIGS. 



Reversal of hair direction on the hind toes is the most constant 

 feature of the roughness of series I and has been found in all rough 

 guinea-pigs of series I without exception. Following is the usual order 

 of succession of the additional rosettes and irregularities found in pass- 

 ing from a smooth to a full-rough: 



Hind toes K 



Front toes J 



Dorsal crest e 



Side rosettes, crest between ears E,C 



Forehead, hip, ventral rosettes. . . A,F,H,I,L 



Eye rosettes B 



Groin, shoulder, second side ro- 

 settes G,D,E 2 



There is seldom more than a slight amount of asymmetry. As a 

 rule the paired rosettes are present or absent as pairs. The most 

 common exception is in the side rosettes in low-grade partial-roughs. 

 Among these it is not uncommon to find a good rosette on one side and 

 merely a slight change in hair direction on the other. In classifying, 

 six of the most distinct sets of rosettes have been used as the principal 

 criteria, viz, forehead, eyes, sides, hips, front toes, and hind toes. 



CLASSIFICATION. 



Rough A. The forehead and five critical pairs of rosettes must be 

 well developed. In addition, there is always some ventral roughness 

 and a crest between the ears. 



Rough B. This includes various conditions intermediate between 

 rough A and rough C. 



Rough C. There is only one pair (or half pair) of well-developed 

 rosettes, usually the side rosettes. There is always, in addition, rough- 

 ness on at least the hind toes and usually a crest between the ears. 



Rough D. A mid-dorsal crest is present and roughness of at least 

 the hind toes, but no well-marked rosettes. 



Rough E. Roughness is confined exclusively to the toes, usually to 

 the hind toes. 



The following list shows the variations which have been met with in 

 each grade; the letters represent the rosettes: 



Rough A. ABcEFHIJK to ABCDEiE2FGHIJKL. 



Rough B. AcEJK, AcEHJK, abFGJK, ABcFHIJKl, ABcDEHIJKl. 



Rough C. EK, EJK, cEK, cEJK. 



Rough D. eK, cK, eJK, cJK. 



Rough E. K, JK. 



PREVIOUS WORK. 



Nehring (1894) made crosses between rough guinea-pigs and the 

 wild species Cavia aperea. He described the young as smooth, but 

 noted that a mane developed along the middle line of the back. Castle 

 (1905) demonstrated that rough fur behaves as a Mendelian unit 



