150 CALIFORNIA ACADEMY OF SCIENCES. 



black, while the female has the under parts gray and 

 white. Among the blackbirds, the females frequently 

 have the under parts lighter than the back. This is 

 noticeable in Scolecophagus and extremely pronounced 

 in Agelaius. In Xanthocephalus, the breast of the 

 female is mixed with white. In the hawks it is fre- 

 quently the case that a melanistic phase will occur in 

 which the bird is dark above and below, whereas, in the 

 normal phase the breast is light colored. Such is the 

 case, for example, with Biiteo borealis and B. sivainsoni. 



Some of the tanagers (Piranga crythromclas, for in- 

 stance), present a rather unusual localization of black, 

 the wings and tail alone being shaded thus. In the 

 Louisiana tanager (Piranga ludoviciana) the back as well 

 as the wings and tail is black. P. erythroinelas un- 

 doubtedly represents a more advanced stage, in which 

 the black has become restricted to these regions. 



Perhaps the most instructive example of the way the 

 black spreads from the breast, as a center of pigmenta- 

 tion, is the female of Williamson's sapsucker ( Si^hyrapi- 

 ^cus thyroideus). The final color of the male is an almost 

 uniform black, varied on the breast by only one patch 

 of red on the throat. Every stage may be traced from 

 the young female with white under parts, through the 

 adult female with a black patch upon the breast, and 

 the different stages of its extension in the young males 

 to the final plumage of the adult. 



The most complete example with which I am ac- 

 quainted of the spreading of black upon the back is the 

 green-backed goldfinch and its allies (Plate VII). Spinus 

 psaltria has a black cap upon the top of its head, and 

 the shoulders are usually dark. In S. psaltria arizonce 

 both of these areas of color have become more extended 

 and the dark on the shoulders is a more pronounced and 

 uniform black. In addition to this, black feathers are 



