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THE AMERICAN NATURALIST [Vol. XLVHl 



nite white markings in the patterns of many mammals 

 and birds. Magazines of natural history abound with 

 instances of total or of partial albinism among mammals 

 and birds, either of domesticated or of wild species. 

 Some writers have even recognized the fact that such 

 white markings tend to occur in certain parts of the 

 body, as at the tip of the tail or on the forehead. Darwin 

 speaks of the white forehead spot or star, and the white 

 feet so common among horses, and implies that such 

 markings must be of some significance. His statement 

 on hearsay that white-marked horses are more suscep- 

 tible to poisoning from noxious herbs is, however, un- 

 corroborated. In 1882, W. H. Brewer gathered a number 

 of statistics as to the presence of white marks in horses 

 and cows, but reached no conclusion. He could find no 

 necessary correlation between the presence or absence 

 of white spots in forehead and feet, though it appeared 

 that white marks might be more frequent on one side of 

 the body than the other. But the tentative conclusion 

 that such animals habitually reclined on the side showing 

 the more white, is begging the question. 



As briefly stated in my paper of 1904, the important 

 thing is not that white tends to appear at certain places, 

 but the converse, that pigment production is more intense 

 at certain definite centers on the body and the occurrence 

 of white or pigmentless areas is due to the restriction of 

 pigment formation at the periphery of these centers, so 

 that white occurs at their extremities or as breaks be- 

 tween contiguous color patches. 



In mammals and birds these centers are typically five 

 on each side of the body, and a median one on the fore- 

 head. They appear to be homologous in both groups, 

 though in different species they show varying degrees of 

 modification in their behavior and development. When 

 a reduction of the pigment areas occurs, the appearance 

 is as it were a shrinking of the particular color patch 

 toward its definite center. The reduction may vary to 

 any degree, from that condition in which the break 



