306 CALIFORNIA ACADEMY OF SCIENCES. 



The birds of this genus, like the preceding, have de- 

 veloped from a form streaked above and below, this style 

 being preserved in the young of all the living forms 

 except S. atrigidaris , in which the streaks are but very 

 faintly indicated. The only specialization has been the 

 loss of the streaks on the breast, which has become uni- 

 form whitish, and the acquisition of a chestnut colored 

 cap in some species, and a black throat-patch in S. atri- 

 gularis. S. pallida has the head striped in brown, black 

 and gray, while 8. hrevjeri seems to be without any form 

 of recognition marking. Recognition markings, when 

 present, are rather discriminative than directive in their 

 nature, the habits of the birds rendering the latter un- 

 necessary. 



Genus Junco. The Juncos. 



(2) Adult male like female; young like some ances- 

 tral stage of the adult. 



Prevailing colors, dark slate, gray, rufous, white. 



Although plainly enough deriving their origin from 

 the same stock as the other sparrows, the significance of 

 the colors of this genus seems peculiarly difficult to de- 

 termine. The white tail feathers form an excellent 

 directive mark, while the wing bands of J. aiheni may 

 well be discriminative marks, but why some species 

 should have the breast white and some vinaceous pink, 

 or why the back should be gray in some species and 

 reddish brown in others, I do not feel able to give an 

 opinion. The general distribution of markings in the 

 genus may be due to the working of laws of wide appli- 

 cation — especially to the effect of light in controlling 

 the deposition of pigment, as previously suggested (see 

 ante, p. 230). 



