CLAIMS OF OOLOGY TO BE AN EXACT SCIENCE, 247 
the earth’s surface—the Alpine pastures blue with gentians, 
the Mediterranean lying beneath us like an irregular lake, 
with Syria, and Greece, and Italy, and Spain all sleeping in 
the sun. Northward, the orient colours fading away into a 
broad belt of rainy green, and northwards still, into mountain 
rock and purple moor, and bleak islands of stormy seas, till 
at last the wall of ice sets, death-like, its white teeth against 
us out of the polar twilight—and the same variations 
repeated with manifold diversity southward, from the glow 
and glories of the broad tropical girdle of the globe down to 
where the volcanoes of the Antarctic continent darken the 
- awful desolation with their grim canopy of smoke, ever south- 
ward to the unknown latitudes where the ruddy southern 
lights encarnadine the solitudes of everlasting snow.” But 
Weismann has argued that evolution by natural selection 
tends to the ultimate preservation of uniformity of colouring ; 
and Mr Russel Wallace, the English exponent of his views, 
has declared, as the result of his valuable experience, that the 
greater variety of colouring in the fauna and flora of the 
Tropics as contrasted with that of northern latitudes is by 
no means proportionate to the vastly superior number of the 
species which there exist. The flowers matured in the dull 
light of our rainy temperate zone are, according to him, 
superior in brilliance to any he has seen during twelve years’ 
experience of tropical life; and in the case of birds, it is a 
fact that whole genera of those inhabiting the Torrid Zone 
are frequently of a dull dusky hue, while their analogues 
in northern climes often exhibit the most gorgeous tints. 
Besides, the gaudy Macaws and Parrots, Toucans, and 
Humming-birds, as a rule, pass their lives in dark um- 
brageous forests, where they are little exposed to the rays 
of the burning sun. Such phenomena must depend, partly 
at least, on other causes, and we know that other causes 
exist. The protective use of colouring, whether as a 
mode of concealment or as a means of attraction, is well 
known; and Bates and Wallace and others have shown to 
how large an extent mimicry has thus assisted in the pro- 
cess of Natural Selection. These causes, it is true, affect 
the birds rather than their eggs, but the essential connec- 
tion which exists between the two must, directly or indirectly, 
