196 THE ORIGIN OF SPECIES 



unknown but occasionally efticient means for their trans- 

 portal. Would the just-hatched young sometimes adhere 

 to the feet of birds roosting on the ground, and thus 

 get transported? 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 tlie sea. 

 And I find that several species in this state withstand 

 uninjured an immersion in sea- water during seven days: 

 one shell, the Helix 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 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 re- 

 covered. The presence of an operculum seems to have 

 been of importance, as out of twelve specimens of Cyclo- 

 stoma elegans, which is thus furnished, eleven revived. 

 It is remarkable, seeing how well the Helix pomatia re- 

 sisted 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, however, not at all 

 probable that land-shells have often been thus trans- 

 ported; the feet of birds offer a more probable method. 



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