The Problem of Adaptation ry 
the animal; but if it is true that the same change takes 
place in some of the lizards that live in the tropics, where 
the prevailing color is always green, it would appear that 
the result may have no direct relation with the surroundings. 
It has been shown in a number of well-authenticated cases 
that the pupe of certain butterflies vary in color within 
certain limits in response to the color of the background. 
When the caterpillar fixes itself to some surface, and there 
throws off the outer skin, and acquires a new one, the color 
of the latter is influenced by the background. The result is a 
better protection to the pupa. The change is not brought 
about through the ocelli or eyes, but through the general sur- 
face of the skin, for the same change takes place when the 
eyes have been previously covered with a dark pigment. 
The growth of plants toward:the light may be looked 
upon as an adaptive process, since only in the light can they 
find the conditions necessary for their life. The extraor- 
dinary elongation of shoots and young plants when grown 
in the dark may also be considered an adaptation for finding 
the light, since in this way a plant, deeply embedded in the 
ground, may ultimately reach the surface. Thus while the 
actual process of elongation in the dark is not in itself of any 
use, yet under the ordinary conditions of its life, this response 
may be of great benefit to the plant. 
The closing together of the leaves of some plants has been 
supposed to protect them from too rapid radiation of heat, 
and incidentally this purpose may be fulfilled; but since 
some tropical plants also close their leaves during the night, 
it can hardly be maintained that the closing has been 
acquired for this purpose. It has been suggested that the 
opening of certain flowers under certain conditions of light 
is connected with the visits of insects that bring about cross- _ 
fertilization. 
The preceding examples will suffice to give a general 
idea of what is meant by adaptation in organisms. That 
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