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
molluscs, 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 Dyticus has been caught with an Ancylus (a fresh-water
shell like a limpet) firmly adhering to it; and a water-beetle of
the same family, a Colymbetes, once flew on board the 'Beagle,' when
forty-five miles distant from the nearest land: how much farther it
might have flown with a favouring gale no one can tell.

With respect to plants, it has long been known what enormous ranges many
fresh-water and even marsh-species have, both over continents and to the
most remote oceanic islands. This is strikingly shown, as remarked by
Alph. de Candolle, in large groups of terrestrial plants, which have
only a very few aquatic members; for these latter seem immediately to
acquire, as if in consequence, a very wide range. I think favourable
means of dispersal explain this fact. I have before mentioned that earth
occasionally, though rarely, adheres in some quantity to the feet and
beaks of birds. Wading birds, which frequent the muddy edges of ponds,
if suddenly flushed, would be the most likely to have muddy feet.
Birds of this order I can show are the greatest wanderers, and are
occasionally found on the most remote and barren islands in the open
ocean; they would not be likely to alight on the surface of the sea, so
that the dirt would not be washed off their feet; when making land,
they would be sure to fly to their natural fresh-water haunts. I do not
believe that botanists are aware how charged the mud of ponds is with
seeds: I have tried several little experiments, but will here give only
the most striking case: I took in February three table-spoonfuls of
mud from three different points, beneath water, on the edge of a little
pond; this mud when dry weighed only 6 3/4 ounces; I kept it covered
up in my study for six months, pulling up and counting each plant as it
grew; the plants were of many kinds, and were altogether