146 SEXUAL DIMORPHISM 



bird owes its name to its large top-knot, formed of bare quills, 

 ending in dark blue plumes. It likewise has a long cylindrical 

 fleshy appendage, not on the bill but on the throat, covered 

 with a pad of glossy steel-blue feathers. The bird utters a 

 deep, loud, prolonged note. The head-crest, and throat- 

 caruncle are rudimentary in the female. 



Darwin considered that the caruncle here was partly 

 ornamental and partly a resonator to the voice, and states 

 that it is dilated when the bird utters its note. Bates, in his 

 Naturalist on the Amazons, states that the appendage is " con- 

 nected with an unusual development of the trachea and vocal 

 organs, to which the bird doubtless owes its deep, loud, long- 

 sustained, fluty note." He also observed it in the act of 

 " performing." " It drew itself up on its perch, spread widely 

 the umbrella-formed crest, dilated and waved its glossy 

 breast-lappet, and then in giving vent to its loud, piping note 

 bowed its head slowly forward." 



Mr. Fraser, however, 1 was unable to inflate the lappet in 

 another species by blowing into the mouth or nostrils, and 

 there is nothing in Bates's words denoting that the appen- 

 dage contains a cavity communicating with that of the 

 trachea. It seems more probable that, as in Ghasmorhynchus, 

 the appendage is only erected by distension of the blood- 

 vessels. 



The performance described by Bates is apparently of 

 the nature of a challenge to other males, as well as a call to 

 the female. The erection of the crest and distension of the 

 breast-lappet, constitute mechanical stimulations such as I 

 am endeavouring to indicate in every case, but probably more 

 external stimulations than these come into play. As sug- 

 gested in the case of Chasmorhynchus, the males may fight 

 with one another, each seizing the other by the breast- 

 lappet. 



1 Proc. Zool. Soc, 1859, p. 143. 



