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Page:Popular Science Monthly Volume 57.djvu/61

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Natural selection can not have affected the coloration of the cave forms, for it can be absolutely of no consequence whether a cave species is white or black. It could affect the coloration only indirectly in one of two ways: First, as a matter of economy, but since the individual is in part bleached by the direct effect of the

PSM V57 D061 Three views of amblyopsys.png
Fig. 4 a, b, c.—Three views of Amblyopsis.

darkness there is no reason why natural selection should come into play at all in reducing the pigment as a matter of economy; second, Romanes has supposed that the color decreases through the selection of correlated structures—a supposition he found scarcely conceivable when the variety of animals showing the bleached condition is considered.