COLORATION AFFECTED BY THE ENVIRONMENT. 69 



fauna), it may be made to disappear. Mr. Poulton, indeed, 

 says, " Just as the useless eye has become rudimentary in these 

 animals, so has the useless colour gradually disappeared from 

 the skin. The energy necessary for the production and 

 niaintenauce of such structures has been diverted, either wholly 

 or in part, to other and more useful ends." It is trae that 

 these remarks are specially applied to the Proteus, where the 

 pigment corpuscles may be regarded as definite " structures." 

 But as the section which contains these remarks is headed 

 " Loss of Colour in Cave-dwelling.Animals," the observation is 

 probably intended to apply to insects, Crustacea, etc., also. 



Now, in these animals, however much it may be modified in 

 arrangement by natural selection, we must regard the pig- 

 ment as a normal product of their organisation ; this is Mr. 

 Wallace's view of pigment, and it is the only reasonable one. 

 Accordingly, we should expect to find in animals, which, like 

 the cave dwellers, can reap no advantage from protective colora- 

 tion and other such modifications, an irregularly arranged, 

 but not diminished deposition of pigment, perhaps even an 

 increased brilliancy on account of the absence of any check. 

 What we do find is a i^niform absence of pigment, which is 

 highly suggestive of a direct action of the environment — and 

 an environment obviously different from that which has caused 

 or permitted the bright and varied coloration of deep-sea 

 animals. 



Nor can it be urged that the cave-dwelling animals have 

 lost their colour through what Professor Weismann terms 

 " Panmixis " or the " Cessation of natural selection " alone ; 

 for this would also imply that the pigment itself had been 

 called into existence by natural selection. 



If the pigment were to gradually diminish to the very verge 

 of disappearance, because, its presence having become useless, 



