25 



it would not be at all surprising to find them in tlie others, for there is no broad 

 ocean to stop their migration, and climate would be the chief obstacle. As a 

 matter of fact, however, species are much more local than this. When we look 

 at the Continent of America, however, the case is very different, for the broad 

 Atlantic and Pacific oceans separate it on either side fron the Old World. These 

 oceans, are, of course, quite impassable by terrestrial animals, and at first sight 

 it would appear as if by no possibility could any interchange of species take place 

 between the Old and New Worlds. 



It is found, however, as a matter of fact, that about twelve genera of 

 mammals have species in both hemispheres, among the chief of which are, Felis, 

 Canis, Lutra, Mustela, Gulo, Ursus, Cervus, Lepus, Mus, Sciurus, Vespertilio, and 

 Bos. Of this genera nearly all are found in North America, except the feline 

 animals, and are animals such as bear, otter, elk, and dog, which can support great 

 cold, therefore, it is not improbable that these animals, at some remote period, 

 found their way from the Old to the New World, or vice versa, by the chain of 

 the Aleutian Isles, or, perhaps, by some more northerly passage about the poles. 



With regard to the tropical forms belonging to the genus feUs, namely, the 

 Jaguar, Panther, and Ocelot, the explanation given above of the means of transit 

 from the Old to New World will be objected to, because it will be said that these 

 animals could not support the cold of the journey round by the Aleutian isles. 

 Without granting the truth of thisi)bjection, which can be contradicted, I think, 

 by the fact that these animals can exist through an English winter, and also by 

 the fact that tigers have been met with far north in Siberia, yet it must be owned 

 that there is some weight in it, and that had this been the course taken by feline 

 animals it would be a matter of great surprise. There is, I think, another way 

 of accoimting for their distribution, which gets rid of the difficulty of climate and 

 calls in to its aid the facts given us by geologists. 



These are, that prior te the cold or glacial period which overspread the 

 temperate zone, there seems to be some good reason for thinking that the climate 

 of the earth was considerably warmer than at present. This is borne out by the 

 evidence of the remains of animals which now only inhabit tropical regions being 

 found in the northern latitudes. 



This fact, if true, would of itself account for tropical animals finding their way 

 80 far north as Kamtschatka and Behring straits ; but geologists tell us not only 

 of changes of climate, but of changes of land and sea, and it is not at all beyond 

 the bounds of geological possibility to believe that the Atlantic and Pacific oceans 

 were at one time, even since the recent fauna came into existence, more thickly 

 studded with islands so as to form a bridge between the Old and New Worlds, 

 and to allow some of the tropical forms to pass across. 



The subsequent Glacial period, of which there can be no doubt, quite explains 

 how some of the northern and temperate forms have become common to the two 

 hemispheres, being borne by icebergs, or the northern seas being bridged over by 

 ice .so as to form a continuous tract. These considerations of the dissimilarity of 



