Chap. XIV. 
VARIABILITY. 
127 
persecuted with much clamour by the other ravens of 
the island was the chief cause which led Brunnich 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 troile) 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 by 
several ornithologists as a distinct species under the 
name of Z7. 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 w^ould have 
been a case of sexual selection. 
Graba, ‘Tagebucli, Reise nach Faro/ 1830, s. 51-54. Macgil- 
livray, ‘Hist. British Birds,’ yoI. iii. p. 745. ‘Ibis/ vol. v. 1863, p. 
469. 
Graba, ibid. s. 54. Macgillivray, ibid. vol. v. p. 327. 
‘ Variation of Animals and Plants under Domestication/ vol, ii. 
p. 92. 
