s indigenous to our island. As the
insects are much more numerous in hot countries than in our temperate
latitudes, it seems difficult to avoid the conclusion that there are
more than half a million species in the world.

The number of known mammifers, when Temminck wrote, exceeded 800, and
Mr. Waterhouse informs me that more than 1200 are now (1850) ascertained
to exist. Baron Cuvier estimated the amount of known fishes at 6000; and
Mr. G. Gray, in his "Genera of Birds," enumerates 8000 species. We have
still to add the reptiles, and all the invertebrated animals, exclusive
of insects. It remains, in a great degree, mere matter of conjecture
what proportion the aquatic tribes may bear to the denizens of the land;
but the habitable surface beneath the waters can hardly be estimated at
less than double that of the continents and islands, even admitting that
a very considerable area is destitute of life, in consequence of great
depth, cold, darkness, and other circumstances. In the late polar
expedition it was found that, in some regions, as in Baffin's Bay, there
were marine animals inhabiting the bottom at great depths, where the
temperature of the water was below the freezing point. That there is
life at much greater profundities in warmer regions may be confidently
inferred.

The ocean teems with life--the class of _Polyps_ alone are conjectured
by Lamarck to be as strong in individuals as insects. Every tropical
reef is described as covered with Corals and Sponges, and swarming with
Crustacea, Echini, and Testacea; while almost every tide-washed rock in
the world is carpeted with Fuci, and supports some Corallines, Actiniae,
and Mollusca. There are innumerable forms in the seas of the warmer
zones, which have scarcely begun to attract the attention of the
naturalist; and there are parasitic animals without number, three or
four of which are sometimes appropriated to one genus, as to the whale
(_Balaena_), for example. Even though we concede, therefore, that the
geographical range of marine species is more extensive in general than
that of the terrestrial (the temperature of the sea being more uniform,
and the land impeding less the migrations of the oceanic than the ocean
those of the terrestrial species), yet it seems probable that the
aquatic tribes far exceed in number the inhabitants of the land.

Without insisting on this point, it may be safe to assume, that,
exclusive of microscopic beings, there are between