1875.] Difficulties of Darwinism. 327 
colours in many species, even where not iridescent, shade 
gradually away from one tone to another. 
It is scarcely possible, with any degree of plausibility, to 
harmonise these charatteristic features with the laws of 
Natural or of Sexual Selection. In some cases the colours 
of a species seem exactly calculated to betray it to its 
enemies, or make known its approach to its intended prey. 
Take, for instance, Calosoma sycophanta. You see it running 
about, in the full light of day, on the bare, sandy soil of a 
pine-forest, or scaling the trunks of the trees in search of 
booty. Its broad elytra flash with golden-green, changing 
to an orange-scarlet, to which its blue-black thorax forms a 
striking contrast. It would be difficult to select an arrange- 
ment of colour which, under the circumstances, would be 
more conspicuous. Or, again, if a mass of the dung of the 
horse or cow be turned over, it will generally be found full 
of Aphodii. Some of these have reddish, some brownish, 
and others grey elytra,—all strongly reminding the observer 
of half-digested seeds. These colours must, therefore, 
attract the attention of domestic fowls and other birds 
which love to scratch and peck in dung. Yet these very 
species which thus attract the attention of their enemies 
are the most common. All these facts do not accord well 
with the law of Natural Selection. How, again, are we to 
explain the colours of the Geotrupes and Onthophagi of this 
country, and especially of the Phanai of Mexico and Central 
America? ‘These creatures fly by night, and in the day 
lurk chiefly in dung, or tunnel into the earth beneath it ; 
yet they display a rich array of golden-greens, violets, 
purples, and bronzes. 
We have already referred to the rarity or total absence of 
certain colours among beetles; yet to some of them—as the 
flower-haunting Cetonzas—these very hues would seem de- 
sirable. Pink, lilac, rose, and peach-coloured flowers are 
numerous; why, then, are these colours so rare amongst 
honey-loving insects ? 
The predominant hues among the Hymenoptera are 
yellow, orange, brown, and black, or, on the other hand, 
deep metallic blue and purple. Why this limitation ? 
These colours are scarcely the best adapted for the conceal- 
ment of the insects amongst flowers and leaves. 
But it is not merely in colour and design that animals ex- 
hibit chara¢teristics not readily explained on the principles 
of Natural SeleCtion and Sexual Sele¢tion. There are also 
peculiarities of structure. We must here especially 
call attention to the Dynastide. These huge beetles are 
VOL. V. (N.S.) 20% 
