346 ON THE GENUS PTILOPUS. 



protuberances ; it gives a new point of view with respect to the question 

 of their origin. 



" In Gallinaceous birds markings on the head are more common than in 

 Pigeons — nay, even than in any other family of birds. They are formed in 

 the most diversified manner — as tufts of feathers, as developments of certain 

 parts of the skin more or less capable of erection and filled with pigment 

 and blood-vessels, or, finally, as protuberances which belong to the bony 

 system. All these phenomena have the same cause and the same efi^ect. . . . 



" Thus, in the genus Crax^ the species C. alberti, C. rufa, C. alector, and 

 others have on the whole upper head, beginning from the base of the bill, a 

 stately tuft, consisting of peculiar curled feathers, more hardened and glossy 

 than the other plumage. In C carunculata, besides this tuft, occurs, on the 

 base of the black bill, a red, rather strongly thickened cere, which has this 

 eff^ect, that the end of the upper mandible appears to be considerably height- 

 ened. In C glohicera this cere is yellow, and it has a bony support in the 

 region situated on the ridge of the bill. . . . C mitua shows a larger similar 

 prominence of the processus frontales of the intermaxillaria, as C glohicera, 

 which prominence, however, does not serve as support to a swelling of the 

 cere. This has disappeared ; and at the same time the tuft of feathers has 

 become smaller, while the protuberance has got stronger. The excess of 

 such a bony swelling is to be found in C. pauxi. . . . 



" Similar phenomena to what the species of Crax show appear in the 

 species of the genus Numida. Two have a tuft of feathers on the head, viz. 

 N. plumifera and N. cristata ; in other species at the same spot a high bony 

 protuberance is to be found, mostly covered with a skin of a vivid red colour, 

 in both sexes. In addition to the fact that all species of the genus look very 

 much alike, they are all black or dark greyish with white drops. The pro- 

 tuberance gets its greatest strength in Numida mitrata, ... In every 

 species ... it is formed by parts of the frontalia, which are closely blended 

 together, and is spongy within. 



