ca to
Europe or _vice versa_, 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 centaureae_, _Pachnobia carnea_, _Plusia
parilis_, _Anarta Richardsoni_, _Anarta Schoenherri_, _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
coerulescens_ from Lake Superior and from Scotland do not seem to vary
to the extent of a hair on the antennae. 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.

Arctic Scandinavia or Lapland, according to Sir Joseph Hooker, contains
three-fourths of the entire number of species of plants kn