INTRODUCTION. 1 5 



experiments have been made to demonstrate the pos- 

 sibility of a passive transportal of species over wide 

 distances. It was especially Darwin who gave a great 

 stimulus by setting the example to those interested 

 in natural history in the conduct of such researches. 

 He was struck by the fact that, though land- 

 shells and their eggs are easily killed by sea-water, 

 almost all oceanic islands, even the smallest and most 

 isolated, are inhabited by them, and felt that there 

 must be some unknown but occasionally efficient 

 means for their transportal (p. 353). To quote his 

 words: "It occurred to me that land-shells, when 

 hibernating and having a membranous diaphragm 

 over the mouth of the shell, might be floated in chinks 

 of drifted timber across moderately wide arms of the 

 sea. And I find that several species in this state 

 withstand uninjured an immersion in sea-water during 

 seven days: one shell, the HelLr pomatia, after having 

 been thus treated and again hibernating, was put into 

 sea-water for twenty days, and perfectly recovered. 

 During this length of time the shell might have been 

 carried by a marine current of average swiftness to a 

 distance of 660 geographical miles. As this Helix 

 has a thick calcareous operculum, I removed it, and 

 when it had formed a new membranous one, I again 

 immersed it for fourteen days in sea-water, and again 

 it recovered and crawled away. Baron Aucapitaine 

 has since tried similar experiments : he placed one 

 hundred land-shells, belonging to ten species, in a 

 box pierced with holes, and immersed it for a 



