EVOLUTION OF THE COLORS OF BIRDS. 285 



throat, in the form of a coronet and gorget of the most 

 beautiful iridescent hues conceivable. Why, it may be 

 asked, have not the general laws of growth placed some 

 of these colors on the abdomen and sides, leaving the 

 throat and head some plain, dull hue? If Mr. Wallace 

 can suggest any single law of growth which can throw 

 even a glimmer of light upon the reason for the produc- 

 tion of not merely the greatest amount of pigment, but 

 rather the most beautiful modulations of color, depend- 

 ent more on the structure of the feather than on pig- 

 mentation, upon the most conspicuous parts of the body, 

 and upon no other part if he can indicate even a pos- 

 sible line of investigation of any law of growth explain- 

 ing this, it will be time enough to concede that it is an 

 open question whether or not sexual selection has been 

 the agent. It the meantime, it may be remarked that 

 recognition markings cannot be resorted to as an ex- 

 planation, because the metallic colors are only visible 

 when the bird is facing the observer, and recognition 

 markings could never be more useful from being invis- 

 ible from all but one point of view. 



FAMILY TYRANNID^E. THE TYRANT FLYCATCHERS. 



So far as the significance of its colors is concerned, 

 this family may be divided into two divisions the one in 

 which the red or orange crown patch is present and that 

 in which it is wanting. As has already been shown (see 

 ante, p. 199), this crown patch is unquestionably a form 

 of alluring color (pseudepisematic) in certain species, 

 and in all probability this is its function in all forms, as 

 it is present in both sexes, although generally slightly 

 restricted in the female. The genera in which it is 

 present are Milvulus, Tyrannus, Pitangus and Myiody- 

 nastes. The colors of these forms can be explained, it 

 seems to me, by the application of two principles al- 



