remarks on the involuntary aid which man lends
to the dissemination of species.

In the mammiferous class our influence is chiefly displayed in
increasing the number of quadrupeds which are serviceable to us, and in
exterminating or reducing the number of those which are noxious.

Sometimes, however, we unintentionally promote the multiplication of
inimical species, as when we introduced the rat, which was not
indigenous in the new world, into all parts of America. They have been
conveyed over in ships, and now infest a great multitude of islands and
parts of that continent. In like manner the Norway rat (_Mus decumanus_)
has been imported into England, where it plunders our property in ships
and houses.

Among birds, the house sparrow may be cited as a species known to have
extended its range with the tillage of the soil. During the last century
it has spread gradually over Asiatic Russia towards the north and east,
always following the progress of cultivation. It made its first
appearance on the Irtisch in Tobolsk, soon after the Russians had
ploughed the land. It came in 1735 up the Obi to Beresow, and four years
after to Naryn, about fifteen degrees of longitude farther east. In
1710, it had been seen in the higher parts of the coast of the Lena, in
the government of Irkutzk. In all these places it is now common, but is
not yet found in the uncultivated regions of Kamtschatka.[946]

The great viper (_Fer de lance_), a species no less venomous than the
rattlesnake, which now ravages Martinique and St. Lucia, was
accidentally introduced by man, and exists in no other part of the West
Indies.

Many parasitic insects which attack our persons, and some of which are
supposed to be peculiar to our species, have been carried into all parts
of the earth, and have as high a claim as man to a _universal_
geographical distribution.

A great variety of insects have been transported in ships from one
country to another, especially in warmer latitudes. The European
house-fly has been introduced in this way into all the South Sea
Islands. Notwithstanding the coldness of our climate in England we have
been unable to prevent the cockroach (_Blatta orientalis_) from entering
and diffusing itself in our ovens and kneading troughs, and availing
itself of the artificial warmth which we afford. It is well known also,
that beetles, and many other kinds of ligniperdous insects, have been
introduced into Great Britain in timber; espe