254 PROCEEDINGS OF SOCIETIES. 



of the specific difference between the two species. The eye in this 

 Guillemot (Urialachrymans) has been noticed by John Gatcombe, Esq., 

 ofWyndham-place, Plymouth, a very exact and accurate ornithologist, as 

 mentioned in a letter to me, as being considerably larger than that in the 

 other. It is encircled by a narrow white band or rim, from which the 

 white line extends backwards and downwards for about an inch and 

 a half. This line, from which the bird derives its name, in the Latin, 

 French, and English languages, is the chief apparent mark of difference, 

 the main feature on which its specific distinction has been contended for. 

 It has never, I believe, been imagined to be a characteristic of either 

 sex of the common species, but, on the cdntrary, is seen in the male as 

 well as the female, in both old and young birds, and that in spring, 

 summer, autumn, and winter. 



The question then is, is this a real specific distinction, or is it merely 

 an occasional though perpetually recurring variety, — a variety whose 

 range would appear to be defined, the chief station of the bird bearing 

 it being Spitzbergen ; while, as regards the British coasts, individuals 

 have occurred in every, or almost every, place where the Uria troile is 

 commonly seen. 



Now, with regard to colour, it will, I believe, be found that, as 

 already briefly mentioned, this species is specifically darker, that is, in 

 old and mature specimens, than Uria troile. Old birds of the latter 

 species would seem to become lighter than the young ones ; while with 

 the present species, so to call it, the case is reversed, old birds becoming 

 almost black. 



Again, the white circle round the eye, and the line of extension 

 from it, has nothing to do with age, for, as remarked in a letter to me 

 from Mr. Gatcombe, the white line is quite distinct in a young bird of 

 the year, in its first winter plumage. Now, in the first place, I do not 

 think that in the case of birds, varieties occur in perpetuity with such 

 exactitude as in the present case, or as they certainly do in insects. 

 Prima facie, if the mark at the back of the head may be spoken of, it is 

 naturally to be judged that the two birds, the one with it, the other 

 without it, are distinct. In some species every possible variation of colour 

 and marking exists, as for instance in the Buzzard and the Crossbill, 

 the Ruff and others. Great, too, are the differences in very many spe- 

 cies in the summer and the winter plumage ; manifold also the shades of 

 pied varieties, from the perfect albino down to the unfortunate bird, 

 sure to be shot, that shows a single " white feather." But I repeat, 

 such variations are of a totally different character from that of the case 

 before us. Here we have a permanent, distinctive, and always uniform 

 mark of difference — " Quod semper, quod ubique, quod in omnibus," — 

 " semper idem." And, to come to the point to which I have already 

 briefly adverted, we have instances of a precisely similar kind in other 

 species where no possible doubt is or can be, at least none is, entertained. 

 One of these, that to which I have already more particularly alluded, 

 as having occurred to me, is that of the Crow ( Corvus corone), and the 

 Hooded Crow {Corvus cornix), which two birds are so exactly or so 



