^24 The Descent of Man. Part II. 



" yellow, while ill others the same part is tinged with red." 3 ' 

 In the United States some few of the males of the Scarlet Tanagei 

 ( Tunagra rubra) have " a beautiful transverse band of glowing 

 " red on the smaller wing-coverts ; " 38 but this variation seems 

 to be somewhat rare, so that its preservation through sexual 

 selection would follow only under unusually favourable circum- 

 stances. In Bengal the Honey buzzard (Pernis cristata) 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 feathers." 59 



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 

 characters 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 clamour by the other ravens of the island was the 

 chief cause which led Brimnich to conclude that they were 

 specifically distinct; but this is now known to be an error. 40 

 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 characterised 41 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 cha- 

 racter has caused the bird to be ranked by several ornithologists 

 as a distinct species under the name of U. lacrymans, but it is 

 now known to be merely a variety. It often pairs with the 

 common kind, yet intermediate gradations have never been seen ; 

 nor is this surprising, for variations which appear suddenly, are 

 often, as I have elsewhere shewn, 42 transmitted either unaltered 

 or not at all. We thus see that two distinct forms of the same 

 species may co-exist in the same district, and we cannot doubt 



37 Gould, « Handbook to Birds of Faro,' 1830, s. 51-54. Macgillivray, 

 Australia,' vol. ii. pp. 32 and 68. ' Hist. British Birds,' vol. iii. p. 



38 Audubon, ' Ornitholog. Bio- 745. ' Ibis,' vol. v. 1863, p. 469. 

 graphy,' 1838, vol. iv. p. 389. 41 Graba, ibid. s. 54. MacgiL 



3S Jerdon, ' Birds of India,' vol. i livray, ibid. vol. v. p. 327. 

 p. 108; and Mr. Blyth, in ' Lau 1 42 'Variation of Animals and 



ind Water,' 1868, p. 381. Plants under Domestication,' vol. ii 



10 Graba, ' Tagebu<:h, Reise uach p. 92. 



