quite impossible for rats, mice, or squirrels to cross the intervening
belt of three hundred leagues of sea, their little winged relation, the
flitter-mouse, made the journey across quite safely on his own leathery
vans, and with no greater difficulty than a swallow or a wood-pigeon.

The insects of my archipelago tell very much the same story as the
birds and the plants. Here, too, winged species have stood at a great
advantage. To be sure, the earliest butterflies and bees that arrived
in the fern-clad period were starved for want of honey; but as soon as
the valleys began to be thickly tangled with composites, harebells, and
sweet-scented myrtle bushes, these nectar-eating insects established
themselves successfully, and kept their breed true by occasional
crosses with fresh arrivals blown to sea afterwards. The development of
the beetles I watched with far greater interest, as they assumed fresh
forms much more rapidly under their new conditions of restricted food
and limited enemies. Many kinds I observed which came originally from
Europe, sometimes in the larval state, sometimes in the egg, and
sometimes flying as full-grown insects before the blast of the angry
tempest. Several of these changed their features rapidly after their
arrival in the islands, producing at first divergent varieties, and
finally, by dint of selection, acting in various ways, through climate,
food, or enemies, on these nascent forms, evolving into stable and
well-adapted species. But I noticed three cases where bits of driftwood
thrown up from South America on the western coasts contained the eggs
or larvae of American beetles, while several others were driven ashore
from the Canaries or Madeira; and in one instance even a small insect,
belonging to a type now confined to Madagascar, found its way safely by
sea to this remote spot, where, being a female with eggs, it succeeded
in establishing a flourishing colony. I believe, however, that at the
time of its arrival it still existed on the African continent, but