MAMMALS ON OOEANIG ISLANDS. 417 



nating 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 im- 

 mersion in sea-water during seven days. One shelly the Helix 

 pomatia, after having been thus treated, and again hyber- 

 nating, 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 recovered. The presence of an operculum seems to 

 have been of importance, as out of twelve specimens of 

 Oyclostoma elegans, which is thus furnished, eleven re- 

 vived. 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, however, not at all probable 

 that land-shells have often been thus transported; the 

 feet of birds offer a more probable method. 



OS THE RELATIONS OF THE INHABITANTS OF ISLANDS TO 

 THOSE OF THE NEAEEST MAINLAND. 



The most striking and important fact for us is the 

 affinity of the species which inhabit islands to those of the 

 nearest mainland, without being actually the same. 

 Numerous instances could be given. The Galapagos Arch- 

 ipelago, situated under the equator, lies at the distance of 

 between 500 and 600 miles from the shores of South 

 America. Here almost every product of the land and 

 of the water bears the unmistakable stamp of the Amer- 

 ican continent. There are twenty-six land birds. Of 

 these twenty-one, or perhaps twenty-three, are ranked as 

 distinct species, and would commonly be assumed to have 

 been here created; yet the close affinity of most of these 



