42 GEOGRAPHICAL DISTRIBUTION. 



torial process but an insignificant journey, and, therefore, it would 

 necessitate the interposition of but a very moderate expanse of 

 water to effectually bar its progress in any given direction. Several 

 members of the cat family are expert swimmers, the jaguar being 

 known to cross the broadest of the South American rivers, the La 

 Plata, as observed by Lieutenant Page. The tiger and elephant are 

 both good swimmers. Deer are likewise prone to take to water, 

 but it may be questioned whether animals of this kind would be 

 apt to trust themselves beyond the sight of land. The domestic 

 pig, even at a very young age, has been known to swim five or six 

 miles, and it is not exactly impossible that the wild-hog, in cases of 

 absolute necessity, might successfully attempt a passage of three or 

 four times this distance. Probably the most remarkable exhibition 

 of the natatorial powers of a land animal is that shown in the case 

 of a polar bear, which was observed by Captain Parry vigourously 

 paddling away in Barrow's Strait at a nearest distance of twenty miles 

 from the shore, with no ice in sight on which it could have secured 

 needed repose. It may safely be conceded, from our present knowl- 

 edge on the subject, that while many of the land Mammalia can 

 effect with safety, and even readiness, such water passages as are 

 most generally to be met with on continental areas, none, probably, 

 would be prompted to undertake a journey across an arm of the sea 

 whose width measured fifty or more miles, or even one much ex- 

 ceeding half that extent.* To these difficulties or impossibilities 

 in the way of dispersion must be attributed the circumstance that 

 the vast number of oceanic islands are deficient, except where man 

 has effected an introduction, in representatives of this particular 

 class of animals. The fact that certain allied, 'or even identical, 

 forms of mammals are found in regions widely removed from each 

 other, and which at the present time are separated by impassable 

 bodies of water of greater or less extent, is practically conclusive evi- 



* In the case of the polar bear above cited, the absence from view of any 

 ice need not necessarily, or even probably, indicate that there was no ice pres- 

 ent nearer to the swimming subject than the ice of the land- border. From the 

 mast of a vessel, elevated one hundred and fifty feet above the surface of the 

 water, an icebenr rising to the same height could not, owing to the curvature 

 of the earth, be distinguished at a greater distance than thirty-four miles ; flat 

 masses of pack-ice, rising but a few feet above the Avater, at only about half 

 that distance. 



