362 THE EVOLUTION THEORY 



This suggestion seems justifiable if we confine ourselves to 

 superficial considerations. We read in every handbook of entomology 

 that the wings only arise during the life of the caterpillar, and in 

 a certain sense this is true, for the primary constituents or primordia 

 of wings only develop into the fully formed wing during the larval 

 period. But even if these primordia were only formed during the 

 caterpillar-stage, what could they develop from'? Only out of the 

 material parts of the caterpillar, that is, from some of its living cells 

 or cell-groups. The constitution of the wings would therefore be 

 dependent on that of the cells of the caterpillar from which they 

 arose, so that if these varied transmissibly through the variation 

 of their determinants contained in the germ, the determinants of 

 the butterfly which were just developing would vary with them ; 

 every transmissible variation of the caterpillar would necessarily 

 cause a similar variation in the butterfly, and this does not happen. 

 If any one hazarded the assumption that the determinants of the 

 butterfly develop only in the caterpillar, but quite independently 

 of its constitution, he would either be making an absurd statement, 

 namely, that the characters of the butterfly were not transmissible 

 at all, or he would be unconsciously admitting that the determinants 

 of the butterfly were already contained in the parts of the caterpillar, 

 and come direct from the germ-plasm. 



That the characters of the butterfly do vary independently of 

 those of the caterpillar I demonstrated many years ago, when 

 we were still very far away from the idea of the germ-plasm or 

 of determinants. I demonstrated then that the constancy of the 

 markings of a species can be quite different in the two chief stages ; 

 that the caterpillar may be very variable, while the butterfly or 

 the moth may be very constant in all its markings, or conversely. 

 I called attention to the dimorphic caterpillars which are green or 

 brown, and yet become the same moth (for instance, Deilephila 

 elpenor and Sphinx convolvuli) ; I cited the case of the spurge 

 hawk-moth (Deilephila euphorbias) ^ whose dark but at the same time 

 motley caterpillars occur in the Riviera at Nice as a local variety 

 (JSHccea), and there wear quite a different dress — pale clay-yellow, with 

 a double row of large conspicuous dark yellow eye-spots — while the 

 moth does not differ from our variety in a single definite character, 

 except in its larger size. At that time, too, I instituted experiments 

 with the caterpillars of the smallest of our indigenous Vanessa species 

 (Vanessa levana), of which the majority are black with black thorns, 

 while a minority are yellowish-brown with yellow thorns ; reared 

 separately, both yielded the same butterfly, though in this case one 



