VARIABILITY. 
127 
J ‘U P . 
Xiv. 
P^Secnf l . 
the ; i C6Cl W1 ^ much clamour by the other ravens of 
Cot >e] Was ^ le ohfof cause which led Briinnich to 
ti 0 \v e ^' a * it was specifically distinct; but this is 
In v°l- n t0 be an error . 37 
v^^ous parts of the northern seas a remarkable 
ftficl ; ' ^ tbe common Guillemot ( Uria troile) is found; 
- ui p e 
Q taljr ‘ Cer °e, one out of every five birds, according to 
ll ''f , d Js jjy a p Ure -wBite ring round the eye, with 
ra et, 
l>ed 
s estimation, consists of this variety. It is elm- 
narrow white line, an inch and a half in 
% e j’ ^tending back from the ring. This conspicu- 
S| ' v ti'‘ i ) Uac ^ ei ' bas caused the bird to be ranked by 
Hp 0rTli tliologists as a distinct species under the 
^ v Ul .- ' luerymans, but it is now known to be merely 
It often pairs with the common kind, yet 
fills s f la ^ e gradations have never been seen; nor is 
for variations which appear suddenly 
-ifiipj, en > as I have elsewhere shewn , 39 transmitted 
S«2f red . or not at all. We thus see that two 
a- °!' ms of the same species may co-exist in the 
Pos Se s n ct, and we cannot doubt that if the one had 
an y great advantage over the oilier, it would 
^ f 0r ave be en multiplied to the exclusion of the latter. 
ln 8 ta Bce, the male pied ravens, instead of being 
' 1 and driven away by their comrades, had 
^tii/"’ ^ attractive, like the pied peacock before 
h J ii] ( [ p c > f° the common black females, their numbers 
Je ea a ave rapidly increased. And this would have 
Case °f sexual selection. 
W h * Hie* a Setmch, Tieisc nach Faro,' 
'!■ Britisli It;,.. I , > .,,.1 „ -7,1 
1830, s. 51-54. Macgil- 
745. ‘ Ibis,’ vol. v. 1863, p. 
British Birds,’ vol. iii. p, 
t. go y^riatio^' S ’ ^ ac &Blivray, ibid. vol. v. p. 327. 
Of A TUmolo And T)l-,ntA nndAM l l/i m aaXi/1 
°f Animals and Plants under Domestication,’ vol. ii. 
