482 THE AMERICAN NATURALIST [Vol. XLYIII 



The side patches are rather small and seem to center, 

 as in Fig. 51, near the groin on either side. They pig- 

 ment the belly back of the breast area included by the 

 shoulder patches, and extend on to the hind legs as well. 

 In a specimen before me, the shoulder patches pigment 

 the bases of the wings and the entire breast correspond- 

 ing roughly to the length of the sternum, and tend to be 

 separated by encroaching white feathers midventrally. 

 The side patches are much more reduced, and are con- 

 fined to a small area at the top of each thigh. The re- 

 mainder of the patches has heroine inactive, so that a 

 completely white belly and back result. A very common 

 occurrence is the white rump patch due to the restriction 

 of the side patches, so that a break occurs between them 

 and the tail patches. The rump patches in birds are 

 situated far back, as in mammals, and pigment the tail 

 coverts and the rectrices as in Figs. 49-51. The bilater- 

 ality of the two patches is often indicated in pigeons by 

 the occurrence of a few pure white rectrices in the center 

 of the tail. Other birds show pure white feathers at 

 either side of the tail, with a tendency to bilateral sym- 

 metry, a most important fact, since it indicates restriction 

 at the outer extremes of these centers. In the restriction 

 of pigment formation, the rectrices are the first to be- 

 come white, as one would expect, since they are situated 

 at the extremity of the body and farthest from the center 

 of the patch. In Fig. 52 these centers are seen to be at 

 the base of the tail above, and include the upper tail 

 coverts. They are still joined medially, but that of the 

 left side is more extensive than the patch on the right side. 

 The approximate boundaries of the several pigment 

 patches are indicated in Fig. 53 by dotted lines ; 1 is the 

 crown patch, 2 the ear patch, 3 the neck patch, 4 the 

 shoulder patch, 5 the side, and 6 the rump patch, as they 

 appear in a dorsal view. Ventrally the neck patch runs 

 forward to the symphysis of the mandibles. 



In a flock of domesticated mallard ducks which I 

 studied, the same patches were found indicated, and 



