The general absence of color in cave animals is conceded. Packard states, “As regards change of color, we do not recall an exception to the general rule that all cave animals are either colorless or nearly white, or, as in the case of Arachnida and insects, much paler than their out-of-door relatives.” Chilton has made the same observation on the underground animals of New Zealand. Similar observations have been recorded by Lönnberg, Carpenter, Schmeil, and Viré. Hamann enumerates a number of species living both in caves and above ground. In such cases the underground individuals are paler than the others. This confirms similar observations by Packard. [Illustration: FIG. 2.--_Chologaster papilliferus_ from Illinois.] Poulton has mentioned that Proteus becomes darker when exposed to the light. This has been verified by others. Typhlotriton larvæ living at the entrance of a cave are dark, while the adult living farther in the cave are much lighter, but with many chromatophores containing a small amount of color. Epigæan fishes found in caves are always lighter in color than their _confrères_ outside. [Illustration: FIG. 3.--_Typhlichthys subterraneus._] We have thus numerous examples of colored epigæan animals bleaching in caves, and also bleached cave animals turning dark when exposed to the light. We have also animals in which the side habitually turned to the dark is colorless, while the side habitually turned to the light is colored. Finally, we have cave animals that are permanently bleached. 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 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. [Illustration: Fig. 4 _a._] [Illustration: Fig. 4 _b._] [Illustration: Fig. 4 _c._ FIG. 4 _a_, _b_, _c_.--Three views of _Amblyopsis_.]