5 o POPULAR SCIENCE MONTHLY. 



to the light takes on color. Loeb has shown that in the yolk sacs 

 of Fundulus embryos more pigment cells are developed if the em- 

 bryos 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 col- 



2. — GltoLogaster pnpilliferus from Illi 



orless 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 Lonnberg, Carpenter, 

 Schmeil, and Vire. 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 obser- 

 vations by Packard. 



Poulton has mentioned that Proteus becomes darker when ex- 

 posed to the light. This has been verified by others. Typhlo- 

 triton larvae 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. Epigsean 



■ 2 'phUchthy, 



fishes found in caves are always lighter in color than their con- 

 freres outside. 



We have thus numerous examples of colored epigaean 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 habit- 

 ually turned to the light is colored. Finally, we have cave animals 

 that are permanently bleached. 



