OF ANIMALS AND PLANTS. 



5 



CHAPTEll II. 



THE DIFFUSION OF SPECIES. 



The Coral Islands being excepted, Creative power has been exer- 

 cised upon every part of the Earth's surface. Each separate island 

 of the Hawaiian Group contains land-shells, species of Helicido;, that 

 are not found on the neighboring islands, nor in any other part of 

 the whole globe ; species, whose generations during the whole period 

 of human history have never wandered beyond the area of a few 

 square leagues. 



If we search for the cause of restriction, we shall find it in these 

 animals and their ova perishing in sea-water. On the other hand, 

 tlie marine shells inhabiting the same Hawaiian Group, in conformity 

 with their aquatic ova, that can be safely transported by the currents 

 of the ocean, are in general very widely diffused : I have myself met 

 with live specimens of the C/jpycea tigris from the Hawaiian through- 

 out the Southern Polynesian Groups and the East India Islands, to 

 the Eastern coast of Africa; over an area thirteen thousand miles in 

 length, and including one-fifth of the surface of the globe. At the 

 present day, it may not be possible to ascertain the original home of 

 the Cyprcea tigris; but may we not conclude, that the species was 

 called into exstence by the same means and in the same manner as 

 the Hawaiian land-shells, and in all probability, in geographical limits 

 equally restricted. 



The Lecidea geographica, a lichen incrusting the surface of rocks 

 towards the limit of perpetual congelation, occurs except towards tlie 

 poles only on the summits of the very loftiest mountains. I first 

 met with this lichen on our own White Mountains, next on the 

 far-off Fuegian mountain-peaks in sight of Cope Horn, and for the 

 third time, on the lofty mountains on Hawaii: on examining the 

 spores or seeds, these are found to be exceedingly minute, capable of 



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