SUPPOSED TRANSMISSION OF ACQUIRED CHARACTERS 403 



possessed pure reddish-gold wings, and that it inhabited high 

 northern latitudes, — an assumption which alone enables us to 

 understand the present distribution of the species, and which 

 has been adopted by Hofmann * in his splendid researches on 

 the origin of European butterflies. This, however, is of no 

 great importance in the present question, but we must assume 

 that either the reddish-golden tint, or the deep black dusting is 

 the primary colour. The seasonal dimorphism and the occur- 

 rence of blackish specimens in Germany in hot summers are 

 easily acounted for on the former assumption. 



In consequence of the increase in temperature of the habitat 

 of the species, many scale-determinants in the germ-plasm 

 would gradually become so modified that the action of only a 

 slight further increase on the rudiments of the pupal wings 

 would lead to the production of black scales. In Germany the 

 species has attained this point in its phyletic modification ; and 

 if the weather happens to be hot when the second annual brood 

 enter upon the pupal stage, some butterflies of a blackish tint 

 will be produced. This will be more likely to happen as the 

 internal transformation of the determinants in question advances 

 further, and the blackish tint will become more conspicuous as 

 the scale-determinants which have reached this stage of modi- 

 fication in the germ-plasm become more numerous. These 

 two conditions will obtain most often in districts where the 

 summer is usually tolerably warm ; and the fact is thus ac- 

 counted for that dark specimens of P. phlceas are rarely caught 

 in northern Germany, and in the far north not at all, although 

 very dark forms occur comparatively often in the warm valleys 

 of Valais. 



In still warmer districts, like the Riviera, the summer brood 

 of P. phlcBas is almost always exposed to a high temperature, 

 and hence the transformation of the determinants for the scales 

 has become so great, that with the help of the usual summer 

 heat at the time when the caterpillar enters the pupal stage, the 

 variety eleus has been produced. This variety does not appear 

 in the spring brood, because the additional heat required for the 

 complete transformation of the determinants for the scales is 

 absent during the pupal stage. 



* Ernst Hofmann, ' Isoporien der europaischen Tagfalter, ' Stuttgart, 

 1873. 



