56 



SEXUAL SELECTION: BIRDS. 



[Part II. 



by dark-blue plumes, which it can elevate into a great 

 dome ro less than five inches in diameter, covering the 

 whole head. This bird has on its neck a long, thin, cylin- 

 drical, fleshy appendage, which is thickly clothed with 





Fig. 40.— The Umbrella-Bird, or Cephalopterus ornatus (male, from Brehm). 



scale-like blue feathers. It probably serves in part as an 

 ornament, but likewise as a resounding apparatus, for Mr. 

 Bates found that it is connected " with an unusual de- 

 velopment of the trachea and vocal organs." It is di- 

 lated when the bird utters its singularly deep, loud, and 



