537 in number;
and yet the viscid mud was all contained in a breakfast cup! Considering
these facts, I think it would be an inexplicable circumstance if
water-birds did not transport the seeds of fresh-water plants to vast
distances, and if consequently the range of these plants was not very
great. The same agency may have come into play with the eggs of some of
the smaller fresh-water animals.

Other and unknown agencies probably have also played a part. I have
stated that fresh-water fish eat some kinds of seeds, though they reject
many other kinds after having swallowed them; even small fish swallow
seeds of moderate size, as of the yellow water-lily and Potamogeton.
Herons and other birds, century after century, have gone on daily
devouring fish; they then take flight and go to other waters, or are
blown across the sea; and we have seen that seeds retain their power
of germination, when rejected in pellets or in excrement, many hours
afterwards. When I saw the great size of the seeds of that fine
water-lily, the Nelumbium, and remembered Alph. de Candolle's remarks
on this plant, I thought that its distribution must remain quite
inexplicable; but Audubon states that he found the seeds of the great
southern water-lily (probably, according to Dr. Hooker, the Nelumbium
luteum) in a heron's stomach; although I do not know the fact, yet
analogy makes me believe that a heron flying to another pond and getting
a hearty meal of fish, would probably reject from its stomach a pellet
containing the seeds of the Nelumbium undigested; or the seeds might be
dropped by the bird whilst feeding its young, in the same way as fish
are known sometimes to be dropped.

In considering these several means of distribution, it should be
remembered that when a pond or stream is first formed, for instance,
on a rising islet, it will be unoccupied; and a single seed or egg
will have a good chance of succeeding. Although there will always be a
struggle for life between the individuals of the species, however
few, already occupying any pond, yet as the number of kinds is small,
compared with those on the land, the competition will probably be less
severe between aquatic than between terrestrial species; consequently
an intruder from the waters of a foreign country, would have a better
chance of seizing on a place, than in the case of terrestrial colonists.
We should, also, remember that some, perhaps many, fresh-water
productions are low in the