Chap. XIV. VARTABILITY. 127 



persecuted with mucli clamour by the other ravens of 

 the ishxnd was the chief cause which led Briinnich to 

 conclude that it was specifically distinct ; but this is 

 now known to be an error.^^ 



In various parts of the northern seas a remarkable 

 variety of the common Guillemot (Uria iroile) is found; 

 and in Feroe, one out of every five birds, according to 

 Graba's estimation, consists of this variety. It is cha- 

 racterised^^ 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 conspicu- 

 ous character has caused the bird to be ranked bv 

 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,^^ 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 that if the one had 

 possessed any great advantage over the other, it would 

 soon have been multiplied to the exclusion of the latter. 

 If, for instance, the male pied ravens, instead of being 

 persecuted and driven away by their comrades, had 

 been highly attractive, like the pied peacock before 

 mentioned, to the common black females, their numbers 

 would have rapidly increased. And this would have 

 been a case of sexual selection. 



37 Graba. 'Tagebuch, Eeise uach Faro,' 1830, s. 51-51. j^Tacgil- 

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

 469. 



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



^J ' Variation of Animals and Plants under Domestication,' vol. ii. 

 p. 92. 



