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Page:Popular Science Monthly Volume 57.djvu/60

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to the light takes on color. Loeb has shown that in the yolk sacs of Fundulus embryos more pigment cells are developed if the embryos are kept in the light than when they are kept in the dark. However, in the body, and especially in the eye, the pigmentation was not affected by the absence of light.

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

PSM V57 D060 Chologaster papilliferus from illinois.png
Fig. 2.Chologaster papilliferus from Illinois.

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.

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

PSM V57 D060 Typhlichthys subterraneus.png
Fig. 3.Typhlicthys subterraneus.

fishes found in caves are always lighter in color than their confrères outside.

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.