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absolute necessity is not known. Anyhow, the white skin is 

 almost as susceptible to light as is a photographic plate. If 

 light is not absolutely excluded the white skin becomes in time 

 cloudy, with grey patches, and if kept exposed to stronger light, 

 the whole animal turns ultimately jet-black. Mr. Bles has 

 succeeded in producing several totally black specimens, having 

 kept them for several months in a white basin under ordinary 

 conditions of light. No experiments have yet been made to 

 find out if the black pigment deposited is lost again in darkness. 

 Those which are kept in a tank in an absolutely dark cellar of 

 the Cambridge Museum, with permanent water-supply, are doing 

 very well. When approached with a candle they become rest- 



FIG. 26. Proteus anguinus. x . Front view of the mouth in the left upper corner. 



less or remain partly hidden in all sorts of seemingly most un- 

 comfortable attitudes, squeezed in between the sharp-edged tiles 

 and drain-pipes with which their lodgings are furnished. But 

 the introduction of a wriggling worm, a little crustacean or 

 other live bait draws them from their hiding-places, and, guided 

 by the motions of the prey in the water, possibly also by the 

 sense of smell, they snap it up and devour it. 



If the water is not sufficiently well aerated, they rise to the 

 surface, emit a bubble of air, and take a new supply into their 

 lungs. As a rule they remain motionless under water, but the" 

 gills contract spasmodically and become paler, whereupon they 

 fill again with blood and darken ; the contrast between the pure 

 white body and the carmine-red feathery gills is very beautiful. 



Until recently the mode of propagation was quite unknown. 

 Several Proteus, kept by E. Zeller, laid, in the middle of April, 



