MELANIC VARIATION IN LEPIDOPTERA. 1 29 



that a considerable increase and superabundance of motor 

 energy through the accession of warmth, causes a surplus of 

 oxygenated protoplasm to be applied to the deposition of pig- 

 mentary molecules in the tissues of their fur and feathers ? 



Mr. Harting informs me that ptarmigan assume summer 

 plumage even on mountains where snow remains during the 

 summer months. 



A black hare, one of two killed at Merton, in Norfolk, 

 some years ago, was mounted in a glass case for my collection. 

 Moths got into the case, and the skin was taken out and soaked 

 in benzine ; when the benzine had evaporated the fur was found 

 to be losing its rich colour, and to have a tendency towards the 

 natural brown. If the black was owing to an excess of any 

 greasy pigmentary deposit, the benzine by detaching it would 

 facilitate its bleaching. 



Dr. Sorby * found reason to believe that the development 

 of black colouring matter in hair as in human skin increased by 

 the action of light, and that the amount of colouring matters 

 in living organisms exposed to light were increased even when 

 the same matters were rapidly decomposed by light when ex- 

 tracted from the living tissue. He found that ' some of his 

 pale-coloured solutions of hair in diluted sulphuric acid do 

 really turn very much darker when kept in direct sunlight, 

 though most solutions of organic colouring matters fade more 

 or less rapidly.' 



We might naturally suppose that this observation would 

 rightly account for the blackness of the human skin in the 

 African and Indian races. But Lieutenant-Colonel A. F. 

 Fraser * writes that ' the experience of Europeans in India is 

 that the sun does not burn ; if anything it rather whitens them 

 and pales the complexion. It is only on certain conditions 

 when the sun is obscured by rain clouds, it is cool and the 



* Journal of Anthropological Institute, August, 1878, p. 11. 

 t ' Nature,' Nov. 6, 1884. 



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