ROUGH FUR. 101 



obviously the most advantageous; the hair lying thus is not ruffled or 

 caught by obstacles when the animal is moving. This direction is not 

 directly imposed on the hair by outside agencies, as might be supposed, 

 but is due to the direction of growth of the hair follicles (Wilder, 1909). 



Certain fancy varieties among guinea-pigs, as the long-haired rough 

 "Peruvians " and the short-haired rough " Abyssinians," show a striking 

 deviation from the normal hair direction. In these varieties the coat 

 can be divided into a number of areas, within each of which all hair 

 directions radiate from a definite center. The boundaries of these 

 areas, where contrary hair-currents meet, are marked by crests. The 

 centers with their radiating hair-currents are called rosettes. Many 

 mammals, including man, naturally show rosettes, crests, or other 

 peculiarities of hair direction, but less conspicuously than the rough 

 guinea-pigs. (See plate 7.) 



The positions in which rosettes may occur in guinea-pigs are quite 

 definite. Following are the rosettes and irregularities given by Castle 

 (1905), with the addition of L, irregular roughness on the chest. 



A. Forehead, unpaired. E. Sides, between shoulder and hip. I. Navel, unpaired. 



B. Eyes. F. Hips. J. Front toes. 



C. Ears. G. Above the groin. K. Hind toes. 



D. Shoulders. H. Mammae. L. Irregular roughness of chest. 



In the grading of the young guinea-pigs, large letters, as above, have 

 been used for well-defined rosettes and small letters for feeble rosettes 

 or slight deviations from normal hair direction in an area, indicated 

 only by crests at a boundary. Thus a mid-dorsal crest or mane (e) 

 without any side or hip rosettes is characteristic of a certain grade of 

 partial roughs. The ear rosettes (C) are usually only revealed by a 

 crest between the ears. The shoulder rosettes are seldom well developed. 

 The side rosettes are sometimes doubled in the roughest animals (E,E2). 



The number of rosettes present varies from the full set described 

 above, through a continuous series of intermediate grades, to one pair. 

 The variations are not merely haphazard, but may easily be classified. 

 In the first place, it is necessary to distinguish two series. A slight 

 roughness found in certain stocks (the BW, lea, and Arequipa stocks) 

 does not fit into the usual series of variations and will be discussed 

 separately as series II. The roughness of the remaining stocks and 

 also of the fanciers' "Peruvians" and "Abyssinians" we may call 

 series I. In series I all the variations found may be arranged with con- 

 siderable accuracy in a single linear series. Thus Castle (1905) used 

 six grades, passing from rough A with the maximum number of rosettes 

 to rough F, smooth except for the hind toes. These grades will be 

 used in this discussion, with the exception that it has been found con- 

 venient to combine grades C and D, leaving five grades, A to E. These 

 letters used for grades must not be confused with those used to name 

 the rosettes. 



