400 THE GERM-PLASM 



Many butterflies were thus obtained which were not so black as 

 those which had emerged from pupae kept at a higher tempera- 

 ture, hut none were so light-coloured as the ordinary German 

 form. The difference between the Neapolitan specimens which 

 had become light-coloured from exposure to cold, and the normal 

 German form, on the one hand ; and that between the German 

 specimens artificially darkened by warmth, and the normal 

 Neapolitan form, on the other, is too great to be attributable to 

 the incompleteness of the experiments. The German and the 

 Neapolitan forms are therefore constitutionally distinct, the 

 former tending much more strongly towards a pure reddish-gold, 

 and the latter towards a black coloration. 



Both experiments, however, prove the correctness of the old 

 assumption of Lepidopterists that the action of heat on a single 

 generation is capable of giving the German form of a blackish tint ; 

 and since, moreover, it is clear that the development a single 

 generation at a lower temperature can render the colour of the 

 Neapolitan butterfly less black, it appears that the two varieties 

 may have originated owing to a gradual cumulative influence of 

 the climate, the slight effects of one summer or winter having 

 been transmitted and added to from generation to generation. 

 This would then seem to be an instance of the transmission of 

 acquired characters. 



I do not believe, however, that this is the correct interpreta- 

 tion of the facts. If it were, there could be no region in which 

 the species is seasonally dimorphic, as I have myself ascertained 

 it to be on the Ligurian coast. The germ-plasm would then 

 contain either the primary constituents of the red variety, if 

 the colony had been exposed for many generations to a low 

 temperature ; or those of the black one, if a high temperature 

 had influenced it for the same length of time. It would then 

 make no difference to what degree of temperature a single 

 generation were exposed at the present day inartificial breeding, 

 for the colour would have already been determined in the 

 germ-plasm, which would contain, to use my own phraseology, 

 either 'reddish-gold* or 'black' determinants for the wing- 

 scales in question. Hence it would be quite impossible for the 

 spring generation to develop reddish-gold, and the summer one 



assistance he has given me in my efforts. Without his help I should have 

 been unable to obtain the necessary living specimens. 



