188 NEW YORK *ZOOLOGICAE SOCIETY. 
relates to mammals, adduced by the advocates of this theory, 
lies in the singular and simultaneous appearance in Europe and 
in America of the same types of animals, the hypothesis being 
that these animals came from a common boreal home. 
As will appear below in the detailed consideration of our va- 
rious animals, the place of origin of each group, based on positive 
and not on negative evidence, can be found in practically all 
cases. There can be no serious doubt, for instance, that the bear 
originated and developed in Eurasia. The same is true of the 
cats comprising the type genus Felis, and of the great deer 
genus Cervus. 
In fact the only American animals about the origin of which 
there is much doubt, are the moose and the caribou. These two 
undoubtedly originated and attained their development in some 
far northern land. It is not necessary, however, to assume a 
polar continent for these two genera, as the existing land areas 
to the north of the American continent, or that portion of Siberia 
lying within the Arctic Circle with the recently submerged and 
adjacent coast, would supply boreal land areas quite sufficient 
in extent for the development of these types. 
TYPE DIVERGENCE. 
In carefully considering the various types of North American 
mammals a very important clew to their origin can be found in 
the degree of differentiation which each one of these animals has 
achieved. It would appear that this degree of radiation and of 
departure in structure from their Old World kindred would in 
some measure correspond to the amount of time which has elapsed 
since the first appearance of these animals in North America. 
The deductions in this article are based on these lines of reason- 
ing, and the conclusions are in most instances confirmed by the 
fossil record. 
When we find, as in the case of the genus Cervus, of which our 
sole American representative is the wapiti, that the Old World 
has about twenty species belonging to this genus and to closely 
allied genera; that is, one species as an inhabitant of the New 
World, against about twenty in the Old World (and some of 
these Old World species, like the Altai wapiti from Mongolia, 
are very closely akin to the American wapiti) ; when we can go 
from England eastward through Germany, Hungary, the Cau- 
casus and the mountains of Central Asia, and find the red deer 
growing larger and finer, and fading imperceptibly through one 
