152 



ANIMAL LIFE 



askers, which are coloured on the back, these cave 

 newts are without any trace of pigment. That they 

 have lost their original colouring subsequently to 

 adopting cave life is a conclusion rendered highly 

 probable owing to the discovery of still another 

 colourless species in South America which is related 

 to quite a distinct family of darkly coloured newts, 

 and is borne out by the occurrence in the same caves 



Fig. 28. —The Cave Newt of Europe {Proteus anguineus). 

 (From specimens in the .Manchester Museum.) 



of white shrimps and bleached insects, whose relatives 

 lead a free life and possess a coloured skin. But this 

 bleaching is only permanent so long as light is excluded, 

 and if these cave newts are brought into daylight they 

 develop in the course of time a dark skin, and after 

 a few months become almost black, the change being 

 most marked on the back of the animal. Experiment 

 thus confirms the power of light rapidly to excite 

 the formation of colour or pigment, and the. power of 



