BIRDS. 435 



lappet on the throat and into two horns, one on each side 

 of the splendid top-knot; and these are then colored of the 

 most intense blue which I have ever beheld. * The African 

 hornbill {Bucorax abyssinicus) inflates the scarlet bladder- 

 like wattle on its neck, and with its wings drooping and 

 tail expanded "makes quite a grand appearance/ "f Even 

 the iris of the eye is sometimes more brightly colored in 

 the male than in the female; and this is frequently the 

 case with the beak, for instance, in our common blackbird. 

 In Buceros corrugatiis the whole beak and immense casque 

 are colored more conspicuously in the male than in the 

 female; and '^ the oblique grooves upon the sides of the 

 lower mandible are peculiar to the male sex.^^| 



The head, again, often supports fleshy appendages, fila- 

 ments, and solid protuberances. These, if not common to 

 both sexes, are always confined to the males. The solid 

 protuberances have been described in detail by Dr. W. 

 Marshall, who shows that they are formed either of can- 

 cellated bone coated with skin, or of dermal and other 

 tissues. With mammals true horns are always supported 

 on the frontal bones, but with birds various bones have 

 been modified for this purpose; and in species of the same 

 group the protuberances may have cores of bone, or be 

 quite destitute of them, with intermediate gradations con- 

 necting these two extremes. Hence, as Dr. Marshall 

 justly remarks, variations of the most different kinds have 

 served for the development through sexual selection of 

 these ornamental appendages. Elongated feathers or 

 plumes spring from almost every part of the body. The 

 feathers on the throat and breast are sometimes developed 

 into beautiful ruffs and collars. The tail-feathers are fre- 

 quently increased in length; as we see in the tail-coverts of 

 the peacock, and in the tail itself of the Argus pheasant. 

 With the peacock even the bones of the tail have been 

 modified to support the heavy tail-coverts. || The body of 



*See Dr. Marie's account with colored figures in **Proc. Zoolog. 

 Soc.,"1872, p. 730. 



fMr. Monteiro, "Ibis," vol. iv., 1862, p. 339. 



X " Land and Water," 1868, p. 217. 



" Ueber die ScLadelbocker," etc., " Niederlfindischen Archiv. 

 fur Zoologie," B. I., Heft. 2, 1872. 



I Dr. W. Marshall, " Ueber den Vogelschwanz," ibid, B. I., Heft, 

 2, 1872. 



