Yet there must be some unknown, but occasionally efficient means for their transportal.

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 hybernating 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.