MEANS OF DISPERSAL. I45 



tains, may, when aided accidentally by the current of 

 rivers, be very rapidly diffused through the country on 

 the other side." ^ 



Rivers, with their occasional floods, it can hardly be 

 doubted, have largely helped to bring about the wide 

 distribution now enjoyed by many organisms, or groups 

 of organisms ; for ages, it will be remembered, they have 

 been constantly carrying objects of all kinds out to sea, 

 thus bringing them under the influence of the oceanic 

 currents. 



Wind. 



Mr. Wallace has suggested that the smaller land- 

 shells, and others in a young state, attached to leaves 

 and twigs, may be carried long distances by storms and 

 hurricanes, and doubtless their eggs, even those of large 

 kinds, may occasionally be transported by these means," 

 but here again, as might be expected, nothing approach- 

 ing actual proof can be given. The hurricanes of 

 tropical regions, Sir C. Lyell observes, sweep along at 

 the rate of ninety miles an hour, rooting up trees and 

 throwing down buildings in their course, possibly 

 carrying, as he remarks, " even the heavier fruits and 

 seeds over friths and seas of considerable width," ^ and 



^ A. Binney, " Terrestrial air-breathing Mollusks," i. (1851), p. 



131- 



- See " Geographical Distribution," ii. p. 525 ; " Island Life," 

 p. 76, ed. 2, p. 78. 



•' " Principles," ii. p. 392. 



L 



