EVOLUTION OF THE COLORS OF BIRDS. 335 



black, and yellow being present and also the bluish 

 gray. Phyllopseustes has not progressed beyond the 

 generalized stage of the warblers, no conspicuous sexual 

 ornaments having been added, but the crown patch of 

 Eegulus is a highly developed character. In R. calen- 

 dula the yellow has been completely intensified into 

 scarlet, but in R.satrapa the intensification is less com- 

 plete. This species exhibits the pure yellow and its in- 

 tensification into orange in different parts of the crown. 

 The bluish or black crown patch of Polioptila is prob- 

 ably the result of sexual selection, as it is confined to 

 the male. A remarkably fine illustration of discrimi- 

 native marks is shown in the outer tail feathers of P. 

 plumbea and P. calif ornica, the outer web being white 

 in the former and black in the latter species. 



FAMILY TURDID^. The Thrushes, Solitaires, 

 Stonechats, Bluebirds, etc. 



(8) Adult male usually more conspicuously colored 

 than female; young with a peculiar first plumage, or (2) 

 male like female; young like some ancestral stage of 

 adult. 



Prevailing colors, black, white, brown, rufous, plum- 

 beous, bluish gray, blue. 



The ancestral form from which this family arose was 

 a brown spotted or mottled bird, as shown by the young 

 of to-day. The different genera have diverged very 

 widely in point of color, however, but may all be ex- 

 plained in accordance with the law of the assortment 

 of pigments. If the primitive pigments were blue and 

 reddish brown their combination would produce Mya- 

 destes, the brown alone would serve for Turdus, while 

 the blue deepened would produce the color of the back 

 of Merula and Hesperocichla, in combination with 

 brown, the back of Cyanecula and Saxicola, and inten- 



