EVOLUTION OF THE COLORS OF BIRDS. 309 



istic marks. It is specialized beyond the streaked plum- 

 age, and the head has distinctive although very dull 

 marks. The only conspicuous character which has per- 

 sisted is the yellow edge of the wing, which is apparently 

 either a sexual or recognition marking, developed upon 

 this conspicuous place (see ante, p. 184). 



Genus Pipilo. The Towhees. 



(2) Adult male like female, or (8) more conspicu- 

 ously colored than female ; young like some ancestral 

 stage of the adult. 



Prevailing colors, black, white, brown, rufous, olive 

 green. 



This genus is of particular interest in the study of the 

 evolution' of color. In the first place, the relation of 

 the sexes in such very closely allied species as P. ery- 

 throphthalmiis and P. maculatus, changes in regard to 

 the correspondence of color. Again, there are three 

 groups of species in the genus, and they seem at first 

 glance to be hopelessly different in point of color origin. 

 An examination discloses the interesting fact, however, 

 that there are more points of similarity than would at 

 first appear. The first group includes P. erythrophtlud- 

 mus, P. maculatus, etc., the second P. chlorurus, and the 

 third P. fuscus. The differences between the first and 

 second are peculiarly striking, yet it will be noticed that 

 the color of the flanks of the first is the same as the 

 crown of the head of the second, and accordingly might 

 be explained in accordance with the law of assortment 

 of pigments, the color being distributed to different 

 parts of the body in different species. P. maculatus has 

 the feathers of the throat subterminally marked with 

 with white, showing that it formerly had a white throat, 

 such as P. chlorurus has at present. The only part about 

 which there appears to be some difficulty of exj^lanation 

 is the olive green color of the back in P. chlorurus. The 



