EVOLUTION OF THE COLORS OF BIRDS. 175 



metrical. Then the question is are the divisions lateral 

 or transverse? This is determined in the main by the 

 position of the patch. If the feathers in question occur 

 on the side of a patch they are ordinarily divided later- 

 ally. Thus the white streak down the back of the downy 

 woodpecker (Dryobates pubescens) is defined along its 

 sides by feathers which are, in 'general, white on the 

 inner side of the shaft and black on the outer. So also 

 with the streaks on the head of the meadow lark (Stur- 

 nella magna), the boundaries of which are fixed by 

 feathers which are white on one side and brown on the 

 other. Examples of tranverse symmetrical hybrids have 

 already been given, no better case being known than 

 such as the dividing line between the white and red 

 across the head of the Californian woodpecker (Melanerpes 

 formicivorus bairdi). 



When a band occurs, as for instance, across the head 

 or breast, cutting some uniform ground color into two 

 areas, the line of demarcation is generally made by 

 hybrid feathers on one side only. Thus the breast of 

 the belted kingfisher (Ceryle alcyon)is white, but crossed 

 by a broad, well-defined band of blue. The white feath- 

 ers along the upper border of this blue strip are edged 

 with blue, and both the blue and white in a single 

 feather are visible. Accordingly the line separating the 

 white from the blue along this edge is not made by the 

 tips of feathers of one color overlapping another, but 

 cuts right through the center of the visible part of the 

 feather. The blue feathers along the lower edge of the 

 blue patch, on the contrary, were not, in the specimens 

 examined, edged with white. In other words, the lower 

 border of the blue patch is marked off simply by the 

 tips of the blue feathers overlapping the white feathers. 

 This state of affairs is due to the fact that in all the 

 feathers of the breast the relative position of the colors 



