The emperor-butterflies (_Apatura_), by the ocelli of their fore-wings certainly put us somewhat in mind of the _Satyrinæ_, in which such spots are always present; but this character does not occur in the genus _Nymphalis_, and is likewise absent in most of the other genera of this group. The genus _Apatura_ shows in addition a most striking similarity in the markings of the wings to the purely Nymphalideous genus _Limenitis_, and it is therefore placed, by those systematists who leave this genus in the same family, in the closest proximity to _Limenitis_. This resemblance cannot depend upon mimicry, since not only one or another but _all_ the species of the two genera possess a similar marking; and further, because similarity of marking alone does not constitute mimicry, but a resemblance in colour must also be added. The genus _Limenitis_ actually contains a case of imitation, but in quite another direction; this will be treated of subsequently. It cannot therefore be well denied that in this case the larvæ show different relationships to the imagines. If the “natural” system is the expression of the genetic relationship of living forms, the question arises in this and in similar cases as to whether the more credence is to be attached to the larvæ or to the imagines--or, in more scientific phraseology, which of the two inherited classes of characters have been the most distinctly and completely preserved, and which of these, through its form-relationship, admits of the most distinct recognition of the blood-relationship, or, inversely, which has diverged the most widely from the ancestral form? The decision in single instances cannot but be difficult, and appears indeed at first sight impossible; nevertheless this will be arrived at in most cases as soon as the ontogeny of the larvæ, and therewith a portion of the phylogeny of this stage, can be accurately ascertained. As in the _Rhopalocera_ most of the families show a complete congruence in the form-relationship of the caterpillars and perfect insects, so a similar congruence is also found in the majority of the families belonging to other groups. Thus, the two allied families of the group _Sphingina_ can also be very well characterized by their larvæ;[183] both the _Sphingidæ_ and the _Sesiidæ_ possess throughout a characteristic form of larva. Of the group _Bombycina_ the family of the _Saturniidæ_ possess thick cylindrical caterpillars, of which the segments are beset with a certain number of knob-like warts. It is true that two genera of this family (_Endromis_ and _Aglia_) are without these characteristic warts, but the imagines of these genera also show extensive and common differences from those of the other genera. A distinct family has in fact already been based on these genera (_Endromidæ_, Boisd.). Thus the congruence is not thereby disturbed.