s,
and will consequently have been little liable to modification. Any tendency
to modification will, also, have been checked by intercrossing with the
unmodified immigrants from the mother-country. Madeira, again, is inhabited
by a wonderful number of peculiar land-shells, whereas not one species of
sea-shell is confined to its shores: now, though we do not know how
sea-shells are dispersed, yet we can see that their eggs or larvae, perhaps
attached to seaweed or floating timber, or to the feet of wading-birds,
might be transported far more easily than {392} land-shells, across three
or four hundred miles of open sea. The different orders of insects in
Madeira apparently present analogous facts.

Oceanic islands are sometimes deficient in certain classes, and their
places are apparently occupied by the other inhabitants; in the Galapagos
Islands reptiles, and in New Zealand gigantic wingless birds, take the
place of mammals. In the plants of the Galapagos Islands, Dr. Hooker has
shown that the proportional numbers of the different orders are very
different from what they are elsewhere. Such cases are generally accounted
for by the physical conditions of the islands; but this explanation seems
to me not a little doubtful. Facility of immigration, I believe, has been
at least as important as the nature of the conditions.

Many remarkable little facts could be given with respect to the inhabitants
of remote islands. For instance, in certain islands not tenanted by
mammals, some of the endemic plants have beautifully hooked seeds; yet few
relations are more striking than the adaptation of hooked seeds for
transportal by the wool and fur of quadrupeds. This case presents no
difficulty on my view, for a hooked seed might be transported to an island
by some other means; and the plant then becoming slightly modified, but
still retaining its hooked seeds, would form an endemic species, having as
useless an appendage as any rudimentary organ,--for instance, as the
shrivelled wings under the soldered elytra of many insular beetles. Again,
islands often possess trees or bushes belonging to orders which elsewhere
include only herbaceous species; now trees, as Alph. de Candolle has shown,
generally have, whatever the cause may be, confined ranges. Hence trees
would be little likely to reach distant oceanic islands; and an herbaceous
plant, though it would have no chance of {393} successfully competing in
stature with a fully develope