290 Animal Life 
of hair, would break up, instead of reflecting, 
the light, and thus intensify the effect of the 
dark upper and light lower surfaces. Hence 
the explanation of the duck-puzzle, and hence, 
too, the reason for a type of colouring very 
prevalent among aninals. 
An excellent example of this type of 
coloration is presented among mammals by 
the Asiatic wild ass, or kiang, which has a 
chestnut-coloured coat with a narrow dark 
stripe running down the middle of the back, 
and the under-parts pure white. Probably 
the dark dorsal stripe does not add much to 
the effect, as 1t would be invisible to animals 
of the same or smaller dimensions; but the 
whole of the middle of the back is distinctly 
darker than the rest of the body. The same 
type of colouring is likewise presented by the 
eazelles, although in this group there is 
generally no very decidedly marked narrow 
dark stripe down the back. ‘Sonie species, 
however, like the handsome Grant’s gazelle 
of Kast Africa, have a broad band along the 
middle of the back of a darker fawn than 
the rest of the coat. Frequently there may 
also be a dark-brown longitudinal band 
immediately above the white of the under-— 
parts, possibly for the purpose of intensifying 
the effect of the latter. In addition to the white under-parts for protective coloration, 
many gazelles have a large white patch on the rump which serves as a “recognition- 
mark” to aid the members of a herd to follow them leader when in flight. The 
yellow patch on the rump of the red deer is for the same purpose, as is the white 
under surface of the tail in the rabbit and the American white-tailed deer, in both of 
which animals the tail is raised when in flight so as to expose the white under surface. 
The under-mentioned Peking deer and its allies have also a white patch on the rump. 
Another well-known animal displaying the above type of coloration is the prongbuck 
of the prairies of western North America. In this species, however, the lightening of the 
under-parts has been carried one step further, for there are three white gorgets on 
the lower surface of the neck, obviously for the purpose of counteracting the effect of the 
dark shade naturally belonging to this part. 
This type of coloration is in the main characteristic of animals imhabiting open 
and frequently desert tracts, for it is obvious that only in a strong light is such a 
shadow thrown on the under surface as to vender necessary the adoption of special 
means of lightening this aspect of the body. Lions, it will be noted, lack white on the 
under-parts; but these animals, when in pursuit of prey (at which time alone it is 
necessary that they should be inconspicuous), slink along with their bellies almost 
touching the ground. Consequently there is no dark shade cast on the under surface 
of the body, which need not therefore be white. 2 
When we come to rufous or fawn-coloured animals, like the Indian swamp-deer 
and the smaller representatives of the African group of waterbucks, which inhabit more 
or less jungly country, we notice that the under surface of the body is yellowish or 
Photograph by W. P. Danio, IM, 
ASIATIC WILD ASS, OR KIANG. 
