136 ACQUIRED CHARACTERS sec. 



calls forth lighter coloration, can only be explained by a 

 peculiarity in the composition of the pigment. 



More frequently light causes paleness. Indeed, in animals 

 after death, light causes bleaching of the same colours which, 

 united with warmth, it helped to produce during life. The 

 care with which collections of insects have to be shielded from 

 the light is sufficient proof of this ; during the life of the 

 animals the brilliant and dark colour was called forth by 

 active metabolism under the iniluence of warmth and light, 

 after death this colouring matter undergoes changes in the 

 light which cause it to bleach. 



But there are also colours which are bleached by the effect 

 of light during life. In birds this bleaching appears to 

 play a great part in the change of colours. It is clear also that 

 in life both processes may compete together, and I have entered 

 upon these questions once more in order to show with what 

 caution they must be handled, and how little can be inferred 

 from single examples. 



Exactly the same antagonism exists, as has been previously 

 mentioned, in the influences of moisture and other agencies. 

 I may be allowed to make here some additional remarks on 

 this subject also. 



If moisture generally produced darkness of colour, all 

 aquatic animals would be necessarily dark-coloured, which is 

 notoriously not the case. Proteus anguineus, which lives in 

 the caves of the Karst mountains about Adelsberg, is like other 

 cave animals perfectly colourless. That the absence of colour 

 is in this case due to the absence of light is shown by the fact 

 that when the animal is kept in the light it becomes dark. 

 And this fact alone proves the correctness of my view con- 

 cerning the direct action of light, and shows that pammixis is 

 not required in order to explain the colourlessness of cave- 

 dwelling^ animals. 



The view that the darker colour of Arion empiricorum on 



