154 THE STRUCTURE AND LIFE OF BIRDS cuHap. 
the feathers. By far the most remarkable of such 
movements are connected with flight. 
It is interesting to put side by side some of the most 
wonderful forms of feathers, bearing in mind the like 
origin of all: for instance, an Ostrich’s plume, a 
Penguin’s tiny scale-like wing-feather, one of an 
Albatross’s mighty remiges, a Cassowary’s plume with 
its equal shafts, a hackle from the neck of a Barndoor 
cock, a plume from a Bird of Paradise, a Lyre-bird’s 
tail feather, a spur from a Cassowary’s wing (a great 
wing feather that has lost its barbs so that the shaft 
alone is left), one of the Motmot’s two extraordinary 
tail feathers, one of the grandest from a Peacock’s 
train, and, to complete the collection, one of the 
stumpy business-like set with which a Woodpecker 
props himself as he climbs. 
Feather Tracts. 
Except in the Penguin the feathers do not cover 
the whole of the body, but only certain feather tracts. 
The bare regions are called Apteria, and are some- 
times devoid even of down—for instance, in the Wood- 
pecker and the Sparrow-hawk. 
Our common birds have most of them a bare tract 
down the breast, which is very convenient when you 
wish to skin them. In most sea-birds you have to 
work through a thick, almost impervious, mass of 
feathers before you can begin operations. Feather 
tracts, especially down the neck and back, have been 
found very useful for purposes of classification. 
