ded from three or four
original types which reached the islands at some remote period, probably
by means of intervening islets that have since disappeared. In St.
Helena we have a degree of permanent isolation which has prevented any
land-birds from reaching the island; for although its distance from the
continent, 1100 miles, is not so great as in the case of the Sandwich
Islands, it is situated in an ocean almost entirely destitute of small
islands, while its position within the tropics renders it free from
violent storms. Neither is there, on the nearest part of the coast of
Africa, a perpetual stream of migrating birds like that which supplies
the innumerable stragglers which every year reach Bermuda and the
Azores.

_Insects._

Winged insects have been mainly dispersed in the same way as birds, by
their power of flight, aided by violent or long-continued winds. Being
so small, and of such low specific gravity, they are occasionally
carried to still greater distances; and thus no islands, however remote,
are altogether without them. The eggs of insects, being often deposited
in borings or in crevices of timber, may have been conveyed long
distances by floating trees, as may the larvae of those species which
feed on wood. Several cases have been published of insects coming on
board ships at great distances from land; and Darwin records having
caught a large grasshopper when the ship was 370 miles from the coast of
Africa, whence the insect had probably come.

In the _Entomologists' Monthly Magazine_ for June 1885, Mr. MacLachlan
has recorded the occurrence of a swarm of moths in the Atlantic ocean,
from the log of the ship _Pleione_. The vessel was homeward bound from
New Zealand, and in Lat. 6 deg. 47' N., Long. 32 deg. 50' W., hundreds of moths
appeared about the ship, settling in numbers on the spars and rigging.
The wind for four days previously had been very light from north,
north-west, or north-east, and sometimes calm. The north-east trade wind
occasionally extends to the ship's position at that time of year. The
captain adds that "frequently, in that part of the ocean, he has had
moths and butterflies come on board." The position is 960 miles
south-west of the Cape Verde Islands, and about 440 north-east of the
South American coast. The specimen preserved is Deiopeia pulchella, a
very common species in dry localities in the Eastern tropics, and rarely
found in Britain, but, Mr. MacLachlan thinks, not fo