WATER SNAILS. 189 
pearance, even in localities, such as a reservoir 
on the top of a hill, where the ordinary agencies 
will not account for its presence. Setting aside 
the wonderful tales of ‘“ showers of snails,’ the 
occurrence of shells in such localities is evidently 
due to transportation by birds, the young snails 
or capsules adhering to their feet. In elucida- 
tion, here follows an experiment performed by 
Mr. Darwin, and extracted from his ‘ Origin of 
Species”? :— 
““T suspended a duck’s feet, which might re 
present those of a bird sleeping in a natural 
pond, in an aquarium, where many ova of fresh- 
water shells were hatching; and I found that 
numbers of the extremely minute and just-hatched 
shells crawled on the feet, and clung to them so 
firmly, that when taken out of the water they 
could not be jarred off, though at a somewhat 
more advanced age they would voluntarily drop 
off. These just-hatched mollusks, though aquatic 
in their nature, survived on the duck’s feet, in 
damp air, from twelve to twenty hours; and 
in this length of time a duck or heron might fly 
at least six or seven hundred. miles, and would 
be sure to alight on a pool or rivulet, if blown 
across sea to an oceanic island, or to any other 
distant point. Sir Charles Lyell also informs 
me that a Dytiscus has been caught with an 
Ancylus firmly adhering to it.” 
