AND BLACK-BILLED AUK. 
19 
for this circumstance, that they are uniformly found in 
Zetland a month or six weeks before any other Arctic birds 
make their appearance ? Many of them are also then in a 
state of moulting, and incapable of flying; others have 
their osseous system almost cartilaginous, — their sexual or- 
gans imperfect, proving them to be young birds, and there- 
fore also equally incapable of flying. All this could not 
have happened if they had had so distant and stormy a 
migration to have effected. 
There are no Lesser Guillemots or Black-billed Auks to 
be found in Zetland in summer. Those met with in winter 
are regarded by the fishermen as the same species as the 
others. Their habits are said to be difl*erent. It is men- 
tioned that the Lesser Guillemots and Black-billed Auks 
are found in great numbers on the coast of Scotland during 
the winter, while very few are found on the coast of Eng- 
land; and in neither country a single individual of the 
other two species is to be found, though vast numbers 
breed in England. To migrate northward in winter is 
conceived to be unnatural and inconsistent, and, it is pre- 
sumed equally so, to suppose the young birds to be dif- 
ferent in their habits from the parent birds. If the old and 
young present the same plumage in winter, then there is 
no necessity for supposing that the former migrate ; and 
the objection of distinction of habits does not exist : but, 
besides, diff'erence of habits is not a specific mark in many 
instances ; it of course constitutes an important feature in 
specific distinction ; but then it is permanent diflerence, not 
that of season or age, or insulated from other circumstances. 
Many birds of the same species are very different both in 
plumage and habits in the young and adult state, and many 
species modify their habits according to locality. 
The Black-backed Gull, for instance, feeds on fish and 
carrion alone in some countries ; in others, he mimics the 
ii9. 
