No. 573] 



553 



is afforded by the common guillemot (Una troille) of the 

 northern Atlantic. The ether related species of the genus 

 have the head and neck uniformly pigmented, but in U. 

 troille a considerable proportion of specimens show a 

 narrow white eyebrow and a postorbital line, in exactly 

 the situation of the stripe in the albino robin previously 

 noted, though not so broad nor so extended. Birds so 

 marked were formerly considered a distinct species — the 

 ringed murre (Uria " ring via") — or perhaps a plumage 

 of r. troille, and much effort has been made to determine 

 their exact status. Both plumages are found in the same 

 colonies and the two sorts of birds are known to have 

 mated together (Miiller, 1862). Verrill estimated that 

 about 40 per cent, of the nesting birds he saw on the 

 Labrador coast were of this variety, but this is probably 

 a rather high estimate. I am convinced that the true 

 explanation of this nuzzling variation is that incipient 

 albinism has gained a foothold, of such nature that areal 

 restriction of the ear or crown patches is developing, so 

 that a white line results between them. In the crested 

 auklet (sEthia) a member of the same family, of the 

 Pacific Coast, such a line lias become fixed so that it 

 now forms a characteristic mark of the species. In the 

 case of the "ringed murre," I should expect to see the 

 eye stripe in the young as well as in the adult stage of 

 those individuals which are to have the mark — in other 

 words it is a permanent trait. No doubt the heredity of 

 this white stripe is of some definite ^ort, and if a reces- 



mon to an increasing number of birds, as this is a 

 colonial species and the possibility of inbreeding is thus 

 increased. 



The Neck Patches.— In birds the neck patches extend 

 forward from the breast to meet the crown patch at the 

 occiput and the ear patches at the sides of the head, 

 thence ventrally to include the throat and chin. A study 

 of albinistic pigeons, as previously noted, indicates that 

 the neck patches are two separate areas of pigmentation. 



