36 THE ENTOMOLOGIST. 



(according to Zeller), as well as in Sardinia, the spring brood, 

 even in captured specimens, is quite as pure red-gold as with us, 

 while the summer brood is more or less dark. If we might 

 assume that both forms of colour were adaptations, and possibly 

 afforded protection to the insects, then it might be explained by 

 the supposition of two kinds of determinants in the germ-plasm 

 of the insects. But nothing can be adduced to support this ; I 

 at least cannot see what protection the darker colour of the 

 summer form could in any way guarantee. This will not, indeed, 

 say much for the slight insight which we have into the biological 

 relations of the Lepidoptera ; but first we shall be compelled to 

 regard the blackening of phloeas by heat, as the direct effect of 

 the latter, and not as the mere elimination of a second scheme of 

 colour. But, if we do this, the pure fire-colour of the first brood 

 in Sicily and Sardinia appears to prove, that the black powdering 

 of the summer form has in no way impressed itself on the germ 

 hereditarily. 



I should, however, consider this a hasty conclusion. If we 

 look at Experiment II. a little closer there can be no question, 

 but that the brood of Neapolitan butterflies reared and kept as 

 pupae at Freiburg at an ordinary temperature generally produced 

 much darker specimens, than the brood of German butterflies 

 would have done under similar conditions, to be sure much more 

 numerous dark specimens, than the brood of North German 

 butterflies produced, when their pupae were subjected to a high 

 temperature for some time. Out of 28 butterflies only 2 were 

 of the eleus form, i. e. about 8 per cent. ; whilst out of the 35 

 butterflies of the Neapolitan brood, 8 possessed decided eleus 

 colouring, i. e. 22 per cent. ; and it must also be taken into con- 

 sideration, that the latter passed their pupal existence at an 

 ordinary room temperature, but the former at a higher tempera- 

 ture. There can be no other explanation, than that of the 

 greater hereditary tendency towards black colouring of the 

 Neapolitan brood, and the far slighter tendency thereto of the 

 German brood. 



As the direct darkening influence of heat is undeniable, so 

 the idea is suggested, that the greater tendency of the Neapolitan 

 brood towards blackness depends upon a permanent alteration 

 of the germ-plasm by the heat working afresh each summer, the 

 lesser tendency towards blackness of the German brood, on the 

 lower summer temperature operating on numerous generations 

 in the course of time. This is in no way a case of the inheritance 

 of acquired characters, at least, there is no necessity, to so regard 

 it. We need not imagine, that the black colouring of the wings 

 produced by summer heat has been transferred from the wings 

 through the body to the reproductive cells of the insects in 

 question, an idea which can scarcely be thought of; but we may 

 assume, that the heat affected at the same time the rudiments of 



