THE ZOOLOGIST. 
THIRD SERIES. 
Vou. IX.] FEBRUARY, 1885. [No. 98. 
ON A SINGULAR VARIETY OF THE BLACK GROUSE, 
TETRAO TETRIX, Livy. 
By tae Epiror. 
An interesting but difficult subject for investigation is the 
cause of variation in the plumage of birds, and the laws (if any 
such can be formulated) which by their operation result in the 
production of albinism, melanism, and other abnormalities. 
I do not here refer to permanent varieties, such as occur chiefly 
in the case of domesticated species, and whose existence has been 
to some extent accounted for and explained by Darwin,* but to 
individual variation which may or may not prove to be the first 
stage in the formation of some permanent variety or race ; for 
while in some cases peculiarities of colour as well as structure 
are transmitted by inheritance, we frequently meet with varieties 
which apparently are never perpetuated. An instance of the 
latter kind is furnished in a specimen of the Black Grouse 
(Tetrao tetriz, Linn.) now before me, and of which a figure 
carefully drawn by Mr. R. Holding is here given (frontispiece). 
This bird, received in a consignment of Black-game from Norway 
in December last, was very kindly forwarded in the flesh for my 
inspection by Mr. Castang, of Leadenhall Market, who stated 
that in his lifelong experience as a game-dealer he had never 
met with a similar example. 
The feathers of the head, neck, and breast are of the usual 
glossy black, but those of the upper portion of the back, scapulars, 
* ‘Variation of Animals and Plants under Domestication.’ Vol. ii., 
chap. xxii. Causes of Variability. 
ZOOLOGIST.—FEB. 1885. 
