414 GEOGRAPHIC DISTRIBUTION OF LIFE IN NORTH AMERICA. 
ning not merely through the genera, but even through the respective 
species of which they are composed.” (Lake Superior, 1850, 239, 240.) 
W. F. Kirby, in a paper “On the Geographical Distribution of the 
Diurnal Lepidoptera as compared with that of Birds,” states: “Had I 
been dealing with Lepidoptera only, | would certainly have united Dr. 
Selater’s ‘ Palearctic region’ and ‘ Nearetic region;’ for although the 
species of North American Rhopalocera are seldom identical with those 
of northern Asia and Europe, still the genera are the same with scarcely 
an exception, except a few representatives of South American genera, 
which have no more right to be considered Nearctic species than the 
similar chance representatives of African forms in north Afriea or 
southwest Europe, or of Indian forms in southeast Europe have to be 
considered Palearctic species.” (Journ. Linnean Soc., London, Zool., 
1873, 432.) 
It now becomes evident that the so-called Palearctic and Nearctie 
regions are the result, in each case, of confounding and combining two 
wholly distinct regions—the Boreal with the Sonoran in America and the 
Boreal with the analogue of the Sonoran in Eurasia. Eliminating these 
austral elements as wholly foreign to the region to which they have been 
so persistently attached, there remains a single great circum-polar 
Boreal region characterized by a remarkably homogeneous fauna, cover- 
ing the northern parts of America and Eurasia. 
Cope has shown that the chief differences between Boreal America 
and Boreal Eurasia are found among the fishes and batrachians,—ani- 
mals living wholly or in part in water. Now, it can not be insisted too 
strongly that while the chief factor in the distribution of aquatic animals 
and plants is temperature, as has been long acknowledged, yet from 
the very nature of the case the resulting life regions must be different, 
the one supplementing or being the complement of the other; for, water 
being the medium in which the species live, the bodies of water with 
their prolongations and extensions, as bays, rivers, and lakes, must be 
studied as entities, just as we study a continent with its peninsulas and 
outlying islands, the means of access to a given body of water being 
the principal factor in determining the water area to which its aquatic 
life belongs. And it should be remarked that aquatic mammals (as 
seals and cetaceans), and aquatic birds (as ducks and gulls), conform 
in the main to the laws and areas of aquatic distribution, and should 
not be taken into account in studying the distribution of terrestrial 
forms of life. 
Gill has said with much truth: ‘“‘ There appears to be a total want of 
correlation between the inland and marine faunas, and a positive in- 
congruity, andeven contrast, between the two.” (Proc. Biol. Soc. Wash., 
1884, 11, 32.) 
