ound the
abode of _Pyrosoma Atlantica_ to be confined to one particular region of
the Atlantic Ocean.[925]

Let us now inquire how the transportation of zoophytes from one part of
the globe to another is effected. Many of them, as in the families
Flustra and Sertularia, attach themselves to sea-weed, and are
occasionally drifted along with it. Many fix themselves to the shells of
Mollusca, and are thus borne along by them to short distances. Others,
like some species of sea-pens, float about in the ocean, and are usually
believed to possess powers of spontaneous motion. But the most frequent
mode of transportation consists in the buoyancy of their eggs, or
certain small vesicles, which are detached, and are capable of becoming
the foundation of a new colony. These gems, as they are called, have, in
many instances, a locomotive power of their own, by which they proceed
in a determinate direction for several days after separation from the
parent. They are propelled by means of numerous short threads or
_ciliae_, which are in constant and rapid vibration; and, when thus
supported in the water, they may be borne along by currents to a great
distance.

That some zoophytes adhere to floating bodies, is proved by their being
found attached to the bottoms of ships, like certain Testacea before
alluded to.

_Geographical Distribution and Migrations of Insects._

Before I conclude this sketch of the manner in which the habitable parts
of the earth are shared out among particular assemblages of organic
beings, I must offer a few remarks on insects, which, by their numbers
and the variety of their powers and instincts, exert a prodigious
influence in the economy of animate nature. As a large portion of these
minute creatures are strictly dependent for their subsistence on certain
species of vegetables, the entomological provinces must coincide in
considerable degree with the botanical.

All the insects, says Latreille, brought from the eastern parts of Asia
and China, whatever be their latitude and temperature, are distinct from
those of Europe and of Africa. The insects of the United States,
although often approaching very close to our own, are, with very few
exceptions, specifically distinguishable by some characters. In South
America, the equinoctial lands of New Granada and Peru on the one side,
and of Guiana on the other, contain for the most part distinct groups;
the Andes forming the division, and interposing a narro