180 CALIFORNIA ACADEMY OF SCIENCES. 



point downward to the tail in tolerably uniform succes- 

 sion. The Louisiana tanager {Pirwuga ludoviciana), is 

 doubtless colored somewhat after the fashion of the 

 primitive color of the scarlet tanager (P. erythromelas) , 

 which had a yellow ancestor; and here the specialized 

 color, the scarlet, first asserts itself upon the anterior 

 part of the head and throat, spreading thence down the 

 back and breast, to a greater or less degree depending 

 upon the perfection of plumage of the bird. 



Many of the conclusions concerning the feather 

 patterns will apply also to the pattern of the bird 

 as a whole. Thus, just as the streaked feather is the 

 most primitive so also is the streaked plumage. This 

 is exemplified by the young of a large number of birds. 

 Thus the breast in many of the sparrows, such as Zono- 

 trichia,Chondestes, Spizella, Junco, Amphispiza,Peuc£ea, 

 and Pipilo, which is pure white or buffy in the adult is 

 streaked in the young, and in many instances the back 

 also is streaked. The ])h\e siskin {Sj)i'iius pinus), seems 

 to have preserved this primitive plumage with very little 

 variation, in its adult state. Again, just as the accumu- 

 lation of pigment at the point or on the edge of the 

 feather is an early stage, so do we find many young 

 birds with a mottled plumage such as would be produced 

 in this manner. 



Looking at birds broadly, the endless modification of 

 pattern and infinite variety in the form and position of 

 color areas is simply bewildering. Out of this chaos, 

 however, it is possible to bring some semblance of order 

 by showing what forms of marking never or seldom 

 occur and what forms are most often repeated. 



In the first place there are no birds marked with an 

 asymmetrical pattern. It seems hardly fair to explain 

 this fact wholly by the law of bilateral symmetry, for 

 this law does not apply in the least to individual 



