222 SEXUAL SELECTION: BIRDS. [Paut II. 



nouuccd tints. But if we could look still further back- 

 Avanl in time to the still earlier progenitors of these two 

 species, we should probably see the adults dark-colored. 

 I infer that this would be the case, from the analogy of 

 many other birds, which are dark while young, and when 

 adult are white ; and more especially from the case of the 

 Ardea gularts, the colors of whicli are the reverse of those 

 of A. as/ia, for the young are dark-colored and the adults 

 white, the young having retained a former state of plu- 

 mage. It appears, therefore, that the progenitors in their 

 adult condition of the Ardea asha, the Jiiq)hus, and of 

 some allies, have undergone, during a long line of descent, 

 the following changes of color: firstly a dark shade, sec- 

 ondly pure white, and thirdly, owing to another change 

 of fashion (if I may so express myself), their present slaty, 

 reddish, or golden-biiff tints. These successive changes 

 are intelligible only on the principle of novelty having 

 been admired by birds for the sake of novelty. 



JSummary of the Mwr Chapters on Birds. — Most male 

 birds are highly pugnacious during the breeding-season, 

 and some possess weapons especially adapted for fighting 

 with their rivals. But the most pugnacious and the best- 

 armed males rarely or never depend for success solely on 

 their power to di'ive away or kill their rivals, but have 

 special means for charming the female. With some it is 

 the power of song, or of emitting strange cries, or of pro- 

 ducing instrumental music, and the males in consequence 

 difier from the females in their vocal organs, or in the 

 structure of certain feathers. From the curiously-diversi- 

 fied means for producing various sounds we gain a high 

 idea of the importance of this means of courtship. Many 

 birds endeavor to charm the females by love-dances or 

 antics, performed on the ground or in the air, and some- 

 times at prepared places. But ornaments of many kinds, 



