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CHAP. XIV.] THE NEOTROPICAL REGION. 33
reptile is a land tortoise ( Testudo nigra) of immense size, and also
abundant in all the islands. Its nearest ally is the equally large
species of the Mascarene Islands ;
an unusual development due,
in both cases, to the absence of enemies permitting these slow
but continually growing animals to attain an immense age. It
is believed that each island has a distinct variety or species of
tortoise.
Insects.—Almost the only insects known from these islands
are some Coleoptera, chiefly collected by Mr. Darwin. They
consist of a few peculiar species of American or wide ranging
genera, the most important being, a Calosoma, Foecilus, Solenophorus,
and Notaphus, among the Carabidse ; an Oryctes among
the LameUicornes ; two new genera of obscure Heteromera ; two
Curculionidse of wide-spread genera ; a Longicorn of the South
American genusi Ehuria ; and two small Phytophaga,—a set of
species highly suggestive of accidental immigrations at rare and
distant intervals.
Land-Shells.—These consist of small and obscure species,
forming two peculiar sub-genera of Bulimulus, a genus greatly
developed on the whole West coast of America ; and a single
species of Buliminus, a genus which ranges over all the world
except America. As in the case of the birds, most of the islands
have two or three peculiar species.
General Conclusions.—These islands are wholly volcanic and
surrounded by very deep sea ; and Mr. Darwin is of opinion,
not only that the islands have never been more nearly con-
nected with the mainland than at present, but that they have
never been connected among themselves. They are situated
on the Equator, in a sea where gales and storms are almost
unknown. The main currents are from the south-west, an ex-
tension of the Peruvian drift along the west coast of South
America. From their great extent, and their volcanoes being
now almost extinct, we may assume that they are of consider-
able antiquity. These facts exactly harmonize with the theory,
that they have been peopled by rare accidental immigrations
at very remote intervals. The only peculiar genera consist of
birds and lizards, which must therefore have been the earliest