The adaptation of the butterfly to its protected model has thus exercised no influence upon the caterpillar. Nor has it affected the pupa, which in both cases exhibits the very different and quite characteristic form of the _Danais_ pupa and the _Limenitis_ pupa respectively (Pl. I, Fig. 10_b_, and 11_b_). But even in the butterfly itself nothing is altered, except what increases the resemblance to the model. All else has remained unchanged, above all, the venation of the wings. Since the painstaking and valuable work of Herrich-Schäfer the venation has been made the basis of the whole systematic arrangement of butterflies, and it enables us, in point of fact, to distinguish with precision, not the families alone, but often even the genera, for the course of the veins in the different species of a single genus is the same, and that is true for the mimetic species as well as for others. Thus the Danaid-like _Limenitis_ has the usual _Limenitis_ venation, of the kind seen in our own indigenous species of _Limenitis_, and the already described _Elymnias_ species of the African and Indian forests and grassy plains have always the venation characteristic of this genus, whether they be protected only by sympathetic colouring or imitate an immune _Euplœa_, a _Danais_, an _Acræa_, or a _Tenaris_. However much the contour of the wing may vary, the venation is unaffected, and we can distinguish model from copy by this means alone, so that, even when there is the closest resemblance, no doubt is possible. In its theoretical aspect this constancy of venation is obviously important, for as nothing about the organism is incapable of variation, the veining of the wings might have varied, as indeed it has varied from genus to genus in the course of the phylogenetic history; but as changes in venation could not be detected by the butterflies' enemies, however sharp-sighted, there has been no reason in these cases for variation in this respect.