EVOLUTION OF THE COLORS OF BIRDS. 187 



black among North American land birds. Nearly all 

 the characteristic head patterns are produced by the 

 black and white combinations here figured. There are 

 five general types of markings, all more or less simple 

 and rudimentary. They are all lateral, and it seems 

 probable that all transverse markings have been derived 

 from them. I have attempted in this diagram to show 

 how all the head patterns of North American birds are 

 related to these five types. Of course the relations be- 

 tween the widely different forms here associated are not 

 supposed to be genetic, but the diagram is merely in- 

 tended to show, by means of the arrows, how the various 

 patterns may have been derived by the modification of 

 the types. It is not difficult to see why these five pat- 

 terns should be the simplest and earliest developed. In 

 the first place they follow the general trend of the 

 feathers, which would be more natural than to cross it. 

 Then they follow pterylographical areas more or less. 

 It is easy to see how types 1 and 2 might be bounded 

 by the eyes and upper edge of the ear coverts, while 

 type 3 includes little besides the ear coverts. Types 4 

 and 5 occupy definite feather tracts sej)arated by bare 

 spaces, and their origin is accordingly not far to seek. 

 Poliopiila plumbea is figured as a representative of type 

 7, which includes also such species as Dendroica striata, 

 Sitta carolinensis and Galeo&coptes carolinensis. It is a 

 simple black cap. Type 2, the superciliary stripe or 

 band is illustrated by Zonotrichia coronata, Seiurus auri- 

 capiUus and Reguhts satrapa belonging in the same cate- 

 gory. The line through the ear coverts, type 3, is the 

 commonest form existing among North American birds. 

 The figure represents Saxicola^ cenanihe , but the class in- 

 cludes also the following: Psalirij)ariis melanotls , Dendroica 

 coronata, Dendroica olivacea, Oporornis formosa, Lanius, 

 Passerina cyanea, besides numerous species where 



