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, {388} 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, freshwater productions are low in the scale of nature, and
that we have reason to believe that such low beings change or become
modified less quickly than the high; and this will give longer time than
the average for the migration of the same aquatic species. We should not
forget the probability of many species having formerly ranged as
continuously as fresh-water productions ever can range, over immense areas,
and having subsequently become extinct in intermediate regions. But the
wide distribution of fresh-water plants and of the lower animals, whether
retaining the same identical form or in some degree modified, I believe
mainly depends on the wide dispersal of their seeds and eggs by animals,
more especially by fresh-water birds, which have large powers of flight,
and naturally travel from one to another and often distant piece of water.
Nature, like a careful gardener, thus takes her seeds from a bed of a
particular nature, and drops them in another equally well fitted for them.

_On the Inhabitants of Oceanic Islands._--We now come to the last of the
three classes of facts, which I {389} have selected as presenting the
greatest amount of difficulty, on the view that all the individua