THEORIES OF LAMARCK AND DARWIN 387 
background. They could be detected chiefly by their 
shadows when the sun was shining. As he walked along 
the coast he came to a wide band of lava which had flowed 
from a crater across the intervening country and plunged 
into the sea, leaving a broad dark band some miles in breadth 
across the white sandy beach. As he passed from the white 
sand to the dark lava, his attention was attracted to a tiger- 
beetle almost identical with the white one except as to color. 
Instead of being white, it was black. He found this broad, 
black band of lava inhabited by the black tiger beetle, and 
found very few, if any, of the white kind. This is a striking 
illustration of what has occurred in nature. These two 
beetles are of the same species, and in examining the condi- 
tions under which they grow, it is discovered that out of the 
eggs laid by the original white forms, there now and then 
appears one of a dusky or black color. Consider how con- 
spicuous this dark object would be against the white back- 
ground of sand. It would be an easy mark for the birds 
of prey that fly about, and therefore on the white surface 
the black beetles would be destroyed, while the white ones 
would be left. But on the black background of lava the 
conditions are reversed. There the white forms would be the 
conspicuous ones; as they wandered upon the black surface, 
they would be picked up by birds of prey and the black ones 
would be left. Thus we see another instance of the operation 
of natural selection. 
Mimicry.---We have, likewise, in nature a great number 
of cases that are designated mimicry. For illustration, cer- 
tain caterpillars assume a stiff position, resembling a twig 
froma branch. We have also leaf-like butterflies. The Kal- 
lima of India is a conspicuous illustration of a butterfly 
having the upper surface of its wings bright-colored, and the 
lower surface dull. When it settles upon a twig the wings 
are closed and the under-sides have a mark across them 
