386 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
but this is, perhaps, a matter of minor importance. Both Adams and 
Scharff recognize another center of species formation and dispersal 
in the southeastern states, but none of our Formicae seems to have 
arisen in this region, although this does not apply to other ant-genera. 
F. pallidefulva is the only species of the genus that might be supposed 
to have originated in such a center, but the occurrence of some of the 
subspecies of pallidefulua as far west as Texas, New Mexico, and 
Colorado and the existence of an allied species, F. moki, in Utah and 
Arizona are by no means inconsistent with a southwestern origin. 
There seems to have been some obstacle to the spread of many forms 
westward from Colorado and New Mexico, for no forms of rufa or 
sanguinea, or of the microgyna and _ pallidefulva series are known to 
occur in California. 
If we assume that the genus Formica had its origin in a southwestern 
center, we must conclude that the emigration of species from this 
region to other parts of North America and especially to Asia over a 
Bering Sea land-bridge and to Europe across Scharff’s Greenland- 
Iceland land-bridge, has extended over a very long period of time. 
The first emigrants must have reached the Old World before Oligo- 
cene and probably as early as late Mesozoic times, because we find 
F, flori as a common ant in the Baltic amber. Precursors of the rufa, 
sanguinea, and exsecta groups must have reached the Old World at 
the same time or somewhat later. That these various species have 
since occupied the territory which they invaded, without being dis- 
lodged during the glacial epoch is very probable. Both Kolbe? 
and Scharff have recently given good reasons for maintaining that 
the biogeographical conclusions so generally accepted as following 
from the statements of those geologists who have asserted the exis- 
tence of a very extensive and severe glaciation of the northern por- 
tions of all the great land masses in the northern hemisphere during 
the Pleistocene, must be, to a considerable extent, erroneous. These 
investigators hold that glaciation could not have been so extensive 
as to have “sterilized” the greater part of North America and Eurasia, 
but that temperature and other conditions during the Pleistocene must 
have been sufficiently favorable to admit of the survival of a rather 
considerable fauna and flora in the immediate neighborhood of the 
glaciers. Hence many species were able to maintain the station 
which they had occupied since early Tertiary or Mesozoic times. As 
it is probable that these views will before long cause a revolution in 
1 Glazialzeitliche reliktenfauna ete. Loc. cit. 
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