50 MIMICRY, AND OTHER PROTECTIVE 
The desert birds are still more remarkably pro- 
tected by their assimilative hues. The stonechats, the 
larks, the quails,. the goatsuckers and the grouse, 
which abound in the North African and Asiatic 
deserts, are all tinted and mottled so as to resemble 
with wonderful accuracy the average colour and as- 
pect of the soil in the district they inhabit. The 
Rev. H. Tristram, in his account of the ornithology 
of North Africa in the Ist volume of the “ Ibis,” 
says: “In the desert, where neither trees, brush- 
wood, nor even undulation of the surface afford the 
slightest protection to its foes, a modification of colour 
which shall be assimilated to that of the surround- 
ing country, is absolutely necessary. Hence without 
exception the upper plumage of every bird, whether 
lark, chat, sylvain, or sand-grouse, and also the fur 
of all the s.raller mammals, and the skin of all the 
snakes and lizards, is of one uniform isabelline or 
sand colour.” After the testimony of so able an 
observer it is unnecessary to adduce further exam- 
ples of the protective colours of desert animals. 
Almost equally striking are the cases of arctic 
animals possessing the white colour that best con- 
ceals them upon snowfields and icebergs. The polar 
bear is the only bear that is white, and it lives 
constantly among snow and ice. The arctic fox, the 
ermine and the alpine hare change to white in 
winter only, because in summer white would be 
more conspicuous than any other colour, and there- 
fore a danger rather than a protection; but the 
