The distribution of few groups of animals is now better known than that of the larger butterflies and moths (_Macro-lepidoptera_); even those of Siberia have been fairly well investigated. The interesting facts obtainable from their distribution are therefore of special value. No less than 243 species of _Lepidoptera_ are mentioned by Möschler as being common to North America and Europe. It is extremely probable that a fair number of these have either migrated direct from America to Europe or _vice versâ_, though many may be of Asiatic origin, and have wandered east and west from their original home. The following twelve species are mentioned by Petersen (p. 38) as occurring in Arctic Europe and also in Arctic North America, but not in Asia:--_Colias nastes_, _Colias hecla_, _Syrichthus centaureæ_, _Pachnobia carnea_, _Plusia parilis_, _Anarta Richardsoni_, _Anarta Schönherri_, _Anarta lapponica_, _Anarta Zetterstedti_, _Cidaria frigidaria_, _Cidaria polata_, _Eupithecia hyperboreata_; and these, as he remarks, point to the possibility of a former direct land-connection between Europe and North America. Mr. Petersen believes that the chief immigration into the Arctic area of Europe is post-glacial and took place from Siberia, since the majority of the species are still to be found in that country at the present day (p. 57). He also draws particular attention to a fact,--which I shall discuss more fully in the next chapter,--namely, that the most characteristically Arctic forms of Northern Europe, which also partly occur in the Alps, are entirely absent from the Caucasus. Adopting the glacial views of some of our leading geologists, Petersen comes to the logical conclusion that Central Europe could not have possessed any butterflies during the height of the Glacial period, but since all evidences seem to point to the chief migration from Siberia having taken place after the Glacial period, he concludes that they must have survived the severe cold of that time in Central Asia. He leaves us, however, to imagine under what possible geographical conditions the climate in Europe could be too severe for a lepidopterous fauna, while at the same time Central Asia could maintain an abundant one. In a suggestive note on the origin of European and North American Ants, Professor Emery states (p. 399) that a great number of North American ants are specifically identical with European ones; whilst Dr. Hamilton tells us (p. 89), as an instance, that specimens of the beetle _Loricera cœrulescens_ from Lake Superior and from Scotland do not seem to vary to the extent of a hair on the antennæ. He enumerates 487 species of _Coleoptera_ as being common to North America, Northern Asia, and Europe, many of which no doubt have migrated by the Americo-European land-connection.