COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



ment potentialities, which by unequal cell multiplication come to cover 

 areas which may or may not be symmetrical in arrangement. 



Sometimes one or both of a pair of patches is wanting altogether; 

 in other cases a patch apparently gets displaced from its normal posi- 

 tion, so that it lies across the median plane ; frequently when a right 

 or left patch is wanting, its mate extends somewhat beyond the median 

 plane (fig. 3). Nevertheless, when one examines a number of spotted 

 animals it is clear that there is a strong tendency for the pigmented 

 areas to occur in the general body regions indicated, each of the ten 

 recognizable patches being a unit in the composition of the coat. 



FIG. 3. Coat pattern of ^ 1358, a son of Cj 973 

 (fig. i). The right cheek patch is black, 

 the left one red. There is a left side 

 patch of black, but no right side patch. 

 The fused rump patches are red. 



FIG. 4. Coat pattern of J* 1360, a son of ^ 97; 

 (fig. i). There are cheek patches of red. 

 and a right neck (ear) patch of black, 

 No others of the typical patches arc 

 present. 



This unity may be obscured if it happens that two pigments, as black 

 and red for example, are both present in the same patch. Neverthe- 

 less, in such cases one can often still identify the typical patches either 

 by the occurrence of unpigmented areas between them, or by the 

 occurrence of mixed pigments in one patch and of unmixed pigments 

 in adjacent patches. 



At one time I thought that I had obtained an explanation of the 

 difference in behavior of the centrifugal and centripetal types of pigmen- 

 tation. It seemed that the centrifugal pigmentation was of dermal 

 origin, the centripetal of epidermal origin ; but more careful examina- 

 tion of sections of the skin indicates that both sorts of pigmentation are 

 similar in origin, arising within cells of the epidermis. 



