176 CALIFORNIA ACADEMY OF SCIENCES. 



is constant, that is, if there be two colors, the white will 

 occupy the base of the feather and the blue the tip. 

 This is probably due to the fact that the breast of this 

 species was white, and that the blue pigment which 

 came into these white feathers, in following out a gen- 

 eral law of pigment distribution, sought the tip of the 

 feather in every case. Or the converse may be true, 

 that the breast was blue, and that in becoming white 

 the base of the feather was uniformly affected first. 



The black crescent on the breast of the red-shafted 

 flicker (Colaptes caferj has already been mentioned as a 

 case where the relative position of the colors on the 

 hybrid feathers is interchangeable. In other words, 

 both the upper and the lower border of the black patch 

 is defined by hybrid feathers the upper border by 

 light feathers with black edgings, the lower border by 

 black feathers with light edgings. 



We come next to the asymmetrical hybrids. It 

 would be wrong to suppose that there is a sharp 

 distinction between these two classes. Hybrids which 

 are not asymmetrical are really quite the excep- 

 tion. The distinction is made to express the difference 

 between hybrids where a definite plan is followed to 

 produce the effect,. as by the cutting of the feather in 

 two, more or less regularly either transversely or lateral- 

 ly, and hybrids where no regularity is observed, but the 

 two colors distributed on the feather more or less at 

 random. Many of the hybrid feathers on the throat of 

 the rose-breasted grosbeak (Habia ludoviciana) are of this 

 asymmetrical type. So also are they on the back of the 

 neck of the golden-crowned sparrow (Zonotrichia coro- 

 nata) where the black, white and brown are all mingled, 

 but the area of each color sharply defined. 



Asymmetrical hybrids are sometimes not sharply de- 

 fined as in the preceding instances, but the two colors 



