418 THE DESCENT OF MAN. 



two or three races or varieties, wliicli differ from each other in 

 the coloring of the tail — "aome having the whole of the feathers 

 "blue, while others have the eight central ones tipped with beau- 

 "tiful green." It does not appear that intermediate gradations 

 have been observed in this or the following cases. In the males 

 alone of one of the Australian parrakeets, "the thighs in some are 

 "scarlet, in others grass-green." In another parrakeet of the 

 same country "some individuals have the band across the wing- 

 "coverts bright-yellow, while in others the same part is tinged 

 "with red."" In the United States some few of the males of the 

 Scarlet Tanager (Tanagra rubra) have "a beautiful transverse 

 "band of glowing red on the smaller wing-coverts ;"^» but this 

 variation seems to be somewhat rare, so that its preservation 

 through sexual selection would follow only under unusually favor- 

 able circumstances. In Bengal the Honey buzzard (Pernis cris- 

 tata) has either a small rudimental crest on its head, or none at 

 all: so slight a difference, however, would not have been worth 

 notice, had not this same species possessed in Southern India "a 

 "well-marked occipital crest formed of several graduated feath- 

 "ers."™ 



The following case is in some respects more interesting. A 

 pied variety of the raven, with the head, breast, abdomen, and 

 parts of the wings and tail-feathers white, is confined to the 

 Feroe Islands. It is not very rare there, for Graba saw during 

 his visit from eight to ten living specimens. Although the char- 

 acters of this variety are not quite constant, yet it has been named 

 by several distinguished ornithologists as a distinct species. The 

 fact of the pied birds being pursued and persecuted with much 

 clamor by the other ravens of the island was the chief cause 

 which led Briinnich to conclude that they were specifically dis- 

 tinct; but this is now known to be an error." This case seems 

 analogous to that lately given of albino birds not pairing from 

 being rejected by their comrades. 



In various parts of the northern seas a remarkable variety of 

 the common Guillemot (Uria troile) is found; and in Feroe one 

 out of every five birds, according to Graba's estimation, presents 

 this variation. It is characterized" by a pure white ring round 

 the eye, with a curved narrow white line, an inch and a half in 

 length, extending back from the ring. This conspicuous charac- 



" Gould, 'Handbook to Birds of Australia,' vol. li. pp. 32 and 68. 



™ Audubon, 'Ornitholog. Biography,' 1838, vol. iv. p. 389. 



'» Jerdon, 'Birds of India,' vol. i. p. 108; and Mr. Blyth, in 'Land and 

 Water,' 186S, p. 381. 



*° Graba, 'Tagebuch, Reise nach Faro,' 1S30, s. 51-54. Macgillivray, 

 'Hist. British Birds,' vol. iii. p. 745. 'Ibis,' vol. v. 1863, p. 469. 



" Graba, ibid. s. 54, Macgillivray, ibid. vol. v. p. 327. 



