CHAP. I 



INTRODUCTORY 



5 



is none the less remarkable — as proving that mere distance 

 is one of the least important of the causes which have 

 determined the likeness or unlikeness in the animals of 

 different countries. 



In the western hemisphere we find equally striking 

 examples. The Eastern United States possess very 

 peculiar and interesting plants and animals, the vegetation 

 becoming more luxuriant as we go south but not altering 

 in essential character, so that when we reach Alabama or 

 Florida we still find ourselves in the midst of pines, oaks, 

 sumachs, magnolias, vines, and other characteristic forms 

 of the temperate flora; while the birds, insects, and land- 

 shells are of the same general character with those found 

 further north.^ But if we now cross over the narrow strait, 

 about fifty miles wide, which separates Florida from the 

 Bahama Islands, we find ourselves in a totally different 

 country, surrounded by a vegetation which is essentially 

 tropical and generally identical with that of Cuba. The 

 change is most striking, because there is little difference 

 of climate, of soil, or apparently of position, to account for 

 it ; and when we find that the birds, the insects, and 

 especially the land- shells of the Bahamas are almost all 

 West Indian, while the North American types of plants 

 and animals have almost all completely disappeared, we 

 shall be convinced that such differences and resemblances 

 cannot be due to existing conditions, but must depend 

 upon laws and causes to which mere proximity of position 

 offers no clue. 



Hardly less uncertain and irregular are the effects of 

 climate. Hot countries usually differ widely from cold 

 ones in all their organic forms ; but the difference is by no 

 means constant, nor does it bear any proportion to 

 difference of temperature. Between frigid Canada and 

 sub-tropical Florida there are less marked differences in the 

 animal productions than between Florida and Cuba or 

 Yucatan, so much more alike in climate and so much 

 nearer together. So the differences between the birds and 

 quadrupeds of temperate Tasmania and tropical North 



^ A small number of species belonging to the West Indies are found in 

 the extreme southern portion of the Florida Peninsula. 



