THE BLIND-FISHES. 125 



periods exposed to the light takes on color. Loeb has shown 

 that, in the yolk sacks 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 espe- 

 cially in the eye, the pigmentation was not affected by the 

 absence of light. 



The general absence of color in cave animals is conceded. 

 Packard l 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 2 

 has made the same observations on the underground animals 

 of New Zealand. Similar observations have been recorded by 

 Lonnberg, 3 Carpenter, 4 Schmeil, 5 and Vire. 6 



Hamann 7 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 of Packard. 



Poulton 8 has mentioned that Proteus becomes darker when 

 exposed to the light. This has been verified by others. In 

 Typhlotriton, larvae living at the entrance of a cave are dark, 

 while the adult living further in the cave are much lighter, but 

 with many chromatophores containing a small amount of color. 

 Epigsean fishes found in caves are always lighter in color than 

 their confreres 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 

 habitually turned to the light is colored. Finally we have cave 

 animals that are permanently bleached. 



1 Mem. Nat. A cad. Set., vol. iv. 



2 Trans. Linn. Soc. Land., 2d Ser., vol. vi, pp. 163-284. 



3 Zool. Anz., vol. xvii, p. 125. 



4 Irish Naturalist, vol. iv, p. 25. 



5 Zeitsch.f. Natttrw., vol. Ixvi, p. 339. 



6 Bull. Mus. Natur. Hist. Paris, 1895, P- : 43- 



7 Europ. Hohlenfauna, p. 6. 



8 The Colour of Animals, p. 91. 



