IO 



COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



ter. It is possible that we should recognize as a sixth distinct center 

 the retina of the eye. These same centers are recognizable with great 

 clearness in the guinea-pig, for in many cases adjacent patches, when 

 not separated by unpigmented areas, contain elementary pigments whose 

 limits are marked by sharp color contrasts/} Thus a cheek patch may 

 btTbTack and the adjacent shoulder patch red (fig. 5) ; * or the side patch 

 black and the sacral patch red, or vice versa (figs, i and 3) ; or again, the 

 right patch of a pair black, the left red, or vice versa (figs. 3 and 6). 

 As compared with the mouse, the guinea-pig shows slight differences 

 in the location and extent of the pigment patches, as one might expect 



FIG. i. Diagram showing the coat pattern of Q FIG. 2. Coat pattern of Q 2166, a daughter of Q 



973. Cheek, side, and rump patches are 973 (fig. i). Cheek and rump patches 



present, though much reduced in extent. are present, but no shoulder or side 



Each pair is of a different color. patches. 



in forms structurally so different. The side patch of the guinea-pig lies 

 chiefly posterior to the middle of the body and frequently extends well 

 back, covering the greater part of the hip and hind leg, while the 

 sacral patches maybe so small and closely approximated that they seem 

 to form an unpaired area at the extreme posterior end of the body (figs. 

 i, 5, and 7). The pigment patches are apparently not correlated with 

 internal structures, such as the distribution of blood vessels or nerves. 

 They are epidermal in origin and subject to more or less apparent asym- 

 metry and mutual displacement, as if they were derived from distinct 

 groups of ectodermal cells endowed in many cases with distinct pig- 



* In figs. i-S, solid black indicates black coat; black stipple, red coat; white 

 stipple on black ground, red and black hairs interspersed. 



