IV PRODUCTION OF PIGMENT 87 



tion to generation. The same holds for all organs atrophied 

 through disuse — the degree of atrophy is acquired and 

 inherited. In the first class we see especially the action of 

 direct adaptation, in the second the results of the cessation of 

 this action. A third class of acquired characters are to be 

 traced simply to the immediate action of the environment on 

 the organism, and originally, at the commencement of their 

 appearance, all characters must have belonged to this class. 

 Let us take first an example of the last class. 



Acquired Characters due to Direct External Actiox 



The formation of pigment is universally subject to the 

 influence of light and warmth. N'umerous species of animals 

 living in the dark have become completely colourless ; the 

 deficiency of pigment due to external influences has been 

 inherited and becomes at length a constant character. Every- 

 one who like myself has undertaken, with his eyes open on 

 such questions, a journey from Germany directly to the vSouth, 

 to Africa, as far as the tropics, will acknowledge the gradually 

 increased darkness of colouring even in one and the same 

 race of men, and must ascribe it to the gradual increase in 

 the power of the sun. The result of this action of the sun, 

 however, has been inherited and has become a constant 

 character. We meet near and in the tropical regions of 

 Africa tribes of men who are almost as black as ebony, and 

 who, as for instance the nomadic Bischari, have features, 

 skulls, and general form of body of perfectly Caucasian type ; 

 and the ne^^resses grive birth to lioiit skinned children — a 

 proof, for those who take their stand upon the biogenetic law, 

 that their forefathers were lig^ht-skinned. 



That I allow special importance to sexual admixture in 

 relation to the distribution of dark colouring of the skin, hair, and 

 eyes, I have already shown, since I pointed out that dark hair 



