B^i MR MACGILLIVRAY ON THE 
From positive, certain, fixed, determinate organs, they 
cannot, in the true meaning of the words, be said to be 
taken, inasmuch as it is merely a quality or circumstance 
of such organs that they express. But let this pass; and 
let the question be. Is the circumstance from which they 
are taken possessed of those qualifications ? It is not neces- 
Sary, as I shall afterwards shew, that the quality or circum- 
stance should be common to all the -varieties of a species; 
but is colour certain, fixed, and determinate in the male 
birds of a species, from which the distinctive characters are 
Usually taken ? That it is not, every one at all acquainted 
with even a very limited number of the species of birds, 
knows and laments. The colours of the same species vary 
in different stages of life (not reckoning those which pre- 
cede maturity), in different states of plumage, at different 
seasons, and in different climates. This assertion cannot 
be disputed ; it is acknowledged by all : nevertheless, that 
nothing which I advance as fact may seem to be deficient 
in authenticity, I shall adduce examples. 
Colour differing in the same species, beyond maturity, is 
seen in the Faico Albicilla, which, from a light-brown, be- 
comes much paler, the head tinged with cinereous, and the 
tail at length altogether white. FaIco Buteo, varies from a 
deep chocolate-brown^ through paler shades of the same 
colour, to white. 
In different states of plumage, and at different seasons, 
almost all birds vary in some degree : witness in particular 
the Ptarmigan, the Uria Grylle^ Cliaradtius plumalis^ 
Tringa variabilis, Temm. 
Climate operates like season : birds, in general, become 
whiter in arctic countries; as. Stria; Bubo, Corvus Coraa?, 
That colours are liable to misinterpretation, surely no 
one will think of denying. From the very nature of colours^ 
