Darwin's Artificial and Natural Selection 159 
Again: “I should be far from’ maintaining that the mark- 
ings arose unconformably to law. Here, as elsewhere, the 
dominance of law is certain. But I take it, that the laws 
involved, that is, the physiological conditions of the variation, 
here are without exception subservient to the ends of a higher 
power — utility; and that it is utility primarily that deter- 
mines the kind of colors, spots, streaks, and bands that shall 
originate, as also their place and mode of disposition. The 
laws come into consideration only to the extent of conditioning 
the quality of the constructive materials — the variations, out 
of which selection fashions the designs in question. And this 
also is subject to important restrictions, as will appear in the 
sequel.” This conclusion contains all that the most ardent 
Darwinian could ask. 
He rejects the idea that internal laws alone could have pro- 
duced the result, because : — 
“Tf internal laws controlled the markings on butterflies’ 
wings, we should expect that some general rule could be es- 
tablished, requiring that the upper and under surfaces 
of the wings should be alike or that they should be 
different, or that the fore wings should be colored the same 
as or differently from the hind wings, etc. But in reality all 
possible kinds of combinations occur simultaneously, and no 
rule holds throughout. Or, it might be supposed that bright 
colors should occur only on the upper surface or only on the 
under surface, or on the fore wings or only on the hind wings. 
But the fact is they occur indiscriminately, now here, now 
there, and no one method of appearance is uniform throughout 
all the species. But the fitness of the various distributions of 
colors is apparent, and the moment we apply the principle of 
utility we know why in the diurnal butterflies the upper sur- 
face alone is usually variegated and the under surface pro- 
tectively colored, or why in the nocturnal butterflies the fore 
wings have the appearance of bark, of old wood, or of a leaf, 
whilst the hind wings, which are covered when resting, alone 
