IN THE SHETLANDS 21 
different forms is properly brought out. Without 
my seeking it, the list includes the two extreme 
forms, as I believe them to be, of dark and light ; the 
former represented by a uniformly dark-brown bird, 
the latter by one having the whole under surface of 
the body, as well as the sides and nape of the neck, 
of a beautiful cream colour, by virtue of which, and 
of the salient contrast exhibited between this and the 
dusky upper surface, it is extremely handsome, not to 
say beautiful—one of the handsomest of all our birds 
in my opinion. Both the extreme forms are un- 
common, but only, I think, as compared with all the 
intermediate shades, not with any one of them. 
Also the extreme light, or handsome, form seems to 
me to be commoner than the extreme plain one. 
Should not a bird like this be described as multi- 
morphic rather than as dimorphic? I believe that 
there exists as perfect as series between the two 
extreme forms as between the least eye-like and the 
most perfect eye-feather in the tail of the peacock— 
to take the well-known illustration given by Darwin 
to enforce his arguments in favour of sexual selection. 
The eye, however, insensibly masses the less saliently 
distinguished individuals together, so that those in 
whose plumage the light colour is more en évidence 
than the dark, go down as the light form, and vice 
versa. Moreover, the more prononcé a bird is, in one 
or another direction, the more it is remarked; so 
that, perhaps, the intermediate shadings are forgotten, 
on the same principle as that by which extreme 
