MEANS OF DISPERSAL. 12 [ 



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 cal- 

 careous operculum [or epiphragm], 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 100 land- 

 shells, belonging to ten species, in a box pierced with 

 holes, and immersed it for a fortnight in the sea. Out 

 of the hundred shells, twenty-seven recovered. The 

 presence of an operculum seems to have been of im- 

 portance, as out of twelve specimens of Cyclostoma 

 elegans, which is thus furnished, eleven revived. It is 

 remarkable, seeing how well the Helix pomatia resisted 

 with me the salt-water, that not one of fifty-four 

 specimens belonging to four other species of Helix 

 tried by Aucapitaine, recovered." ^ 



It is suggested that the creatures are likely to be 

 carried by currents while hiding in chinks of drift-timber, 

 and more rarely with icebergs, in the interstices of floating 

 pumice, etc. ; thus situated they may sometimes be pro- 

 tected, or partially protected, for a time from contact with 

 sea- water, and may possibly be safely carried during calm 

 weather to great distances, so that the arrival of shells, 

 still alive, on the shores of a foreign country or distant 



^ " Origin," p. 353. 



