y favourable, or
where they were saved from the attacks of enemies or the competition of
higher forms.

_Fresh-water Fishes._--The only other vertebrates in the Seychelles are two
fresh-water fishes abounding in the streams and rivulets. One, _Haplochilus
playfairii_ is peculiar to the islands, but there are allied species in
Madagascar. It is a pretty little fish about four inches long, of an olive
colour, with rows of red spots, and is very abundant in some of the
mountain streams. The fishes of this genus, as I am informed by Dr.
Guenther, often inhabit both sea and fresh water, so that their migration
from {434} Madagascar to the Seychelles and subsequent modification, offers
no difficulty. The other species is _Fundulus orthonotus_, found also on
the east coast of Africa; and as both belong to the same
family--Cyprinodontidae--this may possibly have migrated in a similar
manner.

_Land-shells._--The only other group of animals inhabiting the Seychelles
which we know with any approach to completeness, are the land and
fresh-water mollusca, but they do not furnish any facts of special
interest. About forty species are known, and Mr. Geoffrey Nevill, who has
studied them, thinks their meagre number is chiefly owing to the
destruction of so much of the forests which once covered the islands. Seven
of the species--and among them one of the most conspicuous, _Achatina
fulica_--have almost certainly been introduced; and the remainder show a
mixture of Madagascar and Indian forms, with a preponderance of the latter.
Five genera--Streptaxis, Cyathoponea, Onchidium, Helicina and Paludomus,
are mentioned as being especially Indian, while only two--Tropidophora and
Gibbus, are found in Madagascar but not in India.[108] About two-thirds of
the species appear to be peculiar to the islands.

_Mauritius, Bourbon and Rodriguez._--These three islands are somewhat out
of place in this chapter, because they really belong to the oceanic group,
being of volcanic formation, surrounded by deep sea, and possessing no
indigenous mammals or amphibia. Yet their productions are so closely
related to those of Madagascar, to which they may be considered as
attendant satellites, that it is absolutely necessary to associate them
together if we wish to comprehend and explain their many interesting
features.

Mauritius and Bourbon are lofty volcanic islands, evidently of great
antiquity. They are about 100 miles apart, and the sea between them i