68 ANIMAL COLOKATION. 



Adelsberg) in his possession became gradually darker since its 

 removal from the cave; this, however, may only show that the 

 degeneration of the pigment was not complete, and that a few 

 pigment cells still remained which were liable to the influence 

 of light, having been previously in a state of paralysed 

 activity. This explanation, however, is not altogether satis- 

 factory, for light would contract the pigment cells, and so 

 cause, if anything, a more marked bleaching. As has been 

 already pointed out, a frog, or a sole, or any animal with 

 chromatophores supplied by nerves, becomes darker in darkness, 

 owing to the expansion of the chromatophores, and paler when 

 the light is strong and causes their contraction. It seems 

 very likely that Mr. Poulton's Proteus is another example of 

 the production of pigment under the influence of light, such 

 as that which Mr. Cunningham has recently described in the 

 case of flat fish.* 



The colour, or rather the absence of colour, in cave animals 

 has been made use of as an argument for the purposeful- 

 ness of colour in the animal kingdom. It is urged that the 

 colour has disappeared because it is useless; the cave dwellers 

 have no eyes, or imperfect eyes ; and besides, they live in 

 darkness. Hence, there could be no use for warning colours, 

 for protective colours, and so forth. In my opinion these facts 

 not only do not lend such negative support to those theories, 

 but they are to a certain extent opposed to them. 



It has been explained over and over again that the theory 

 of natural selection, as applied to the elucidation of colour 

 phenomena among animals, is concerned only with the dis- 

 tribution and arrangement of colour — with coloration, in 

 fact, and not with the pigments themselves, though it is of 

 course claimed that if pigment is hurtful (e.g. in the Pelagic 



• See p. 64. 



