Note 32 — Chapter III · CAUSES OF VARIATION.

Considering that the true Vanessa Atalanta, of more northern latitudes, does occasionally occur around Funchal, it may be reasonably contended that the fact of its coexistence (on the same spot) with the V. Callirhoë is strong presumptive proof that the latter is a true species, and no climatal or insular modification of the former. And so, judging from a distance, and without local evidence to explain this phænomenon, I should have concluded myself: nevertheless, recollecting how easy of transport the larvæ and pupæ of Lepidoptera necessarily are (of which we have the plainest assurance in the almost certain introduction of the Pontia Brassicæ, Sphinx Convolvuli, Acherontia Atropos, &c. into those islands), especially in a region which for more than a century has been receiving a constant supply of vegetables and ornamental plants from western Europe; I am induced to believe that the appearance of the Atalanta is a comparatively recent one, whilst that of the Callirhoë (which, unlike the typical Red Admiral, has naturalized itself in nearly all portions of the group) must be referred to the remote period when migrations over a long-lost continuous land were in regular operation. The slowness of the change, in external aspect, which the isolation of insects from geological causes would seem to bring about (and which follows, as a corollary, if the above conclusion be true), I propose to discuss in a subsequent chapter of this work.