Page:The naturalist on the River Amazons 1863 v1.djvu/37

 the European Nemeobius Lucina. The Pará insect, however, belongs to a genus far removed in all essential points of structure from Nemeobius; namely, to Lemonias, being the L. epulus. It is worthy of note that all the old-world representatives, both tropical and temperate, of this beautiful family of butterflies belong to the same group as the English Nemeobius Lucina; whilst the few species inhabiting North America belong wholly to South American types.

Facts of this kind, and there are many of them, would seem to show that it is not wholly the external conditions of light, heat, moisture, and so forth, which determine the general aspect of the animals of a country. It is a notion generally entertained that the superior size and beauty of tropical insects and birds are immediately due to the physical conditions of a tropical climate, or are in some way directly connected with them. I think this notion is an incorrect one, and that there are other causes more powerful than climatal conditions which affect the dress of species. To test this we ought to compare the members of those genera which are common to two regions; say, to Northern Europe and equinoctial America, and ascertain which climate produces the largest and most beautifully-coloured species. We should thus see the supposed effects of climate on nearly-allied congeners, that is, creatures very similarly organised. In the first family of the order Coleoptera, for instance, the tiger-beetles (Cicindelidæ), there is one genus, Cicindela, common to the two regions. The species found in the Amazons Valley have precisely the same