172 CALIFORNIA ACADEMY OF SCIENCES. 



tlie wing feathers is that it is not due to selection or any 

 external force, but rather to some unknown principle of 

 repetition or correlation. 



Thus far the discussion has been confined to black and 

 white, or brown and white markings. As soon as 

 colored feathers are brought into consideration the 

 factor of selection immediately becomes more prominent. 

 It is a noteworthy fact that along the line of division of 

 (wo patches of color the feathers are not uniformly 

 colored, some the one shade and others the other, on 

 the contrary the two colors in a large number of cases 

 appear on the same feather. It will be found con- 

 venient to designate these as Hybrid Feathers. Take 

 for instance the rose-breasted grosbeak where the black, 

 white and rose color come together on the breast and 

 sides of the head. Some of the feathers are colored 

 black and white, the shaft dividing the two, and each 

 color contiguous to the general patch of that color. 

 Others are colored rose and white, the rose generally at 

 the base of the feather and adjacent to the rose patch, 

 the white at the tip of the feather and helping to cut the 

 white line of the breast from the rose of the throat. 

 Many rose and black feathers are to be found, the shaft 

 generally dividing the two colors, although sometimes 

 there is merely a black spot at the tip. The point to 

 be noticed is that the colors are not as a rule distributed 

 in accordance with any law of growth force, but in any 

 way which will produce the general effect of a rose 

 coloi'ed patch with moderately sharply marked limita- 

 tions, bordered with black on the sides and white below. 

 l)ccasionally a very interesting feather is found which 

 lieautifuUy illustrates the interplay of internal and ex- 

 ternal effects. Such a one, for instance, was marked 

 according to the ideal mode of pigment deposition with 

 a dark tip and border, but only on the side nearest the 



