that an enormous change must have been produced in the winds. Instead of a
great difference of temperature between each pole and the equator, the
difference would be mainly between one hemisphere and the other, and this
might so disturb the trade winds as to bring St. Helena within the south
temperate region of storms--a position corresponding to that of the Azores
and Madeira in the North Atlantic, and thus subject it to violent gales
from all points of the compass. At this remote epoch the mountains of
equatorial Africa may have been more extensive than they are now, and may
have served as intermediate stations by which some northern insects may
have migrated to the southern hemisphere.

We must remember also that these peculiar forms are said to be northern
only because their nearest allies are {303} now found in the North Atlantic
islands and Southern Europe; but it is not at all improbable that they are
really widespread Miocene types, which have been preserved mainly in
favourable insular stations. They may therefore have originally reached St.
Helena from Southern Africa, or from some of the Atlantic islands, and may
have been conveyed by oceanic currents as well as by winds.[70] This is the
more probable, as a large proportion of the St. Helena beetles live even in
the perfect state within the stems of plants or trunks of trees, while the
eggs and larvae of a still larger number are likely to inhabit similar
stations. Drift-wood might therefore be one of the most important agencies
by which these insects reached the island.

Let us now see how far the distribution of other groups support the
conclusions derived from a consideration of the beetles. The Hemiptera have
been studied by Dr. F. Buchanan White, and though far less known than the
beetles, indicate somewhat similar relations. Eight out of twenty-one
genera are peculiar, and the thirteen other genera are for the most part
widely distributed, while one of the peculiar genera is of African type.
The other orders of insects have not been collected or studied with {304}
sufficient care to make it worth while to refer to them in detail; but the
land-shells have been carefully collected and minutely described by Mr.
Wollaston himself, and it is interesting to see how far they agree with the
insects in their peculiarities and affinities.

_Land-shells of St. Helena._--The total number of species is only
twenty-nine, of which seven are common in Europe or the ot