from St. Helena, in the same manner as
the wild plants of Campania have diffused themselves over Monte Nuovo.
Whenever the first botanist investigated the new archipelago, he would,
in all probability, find a different assemblage of plants in each of the
islands of recent formation; but in St. Helena itself, he would meet
with individuals of every species, belonging to all parts of the
archipelago, and some, in addition, peculiar to itself, viz., those
which had not been able to obtain a passage into any one of the
surrounding new-formed lands. In this case it might be truly said that
the original island was the primitive focus, or centre, of a certain
type of vegetation; whereas, in the surrounding islands, there would be
a smaller number of species, yet all belonging to the same group.

But this peculiar distribution of plants would not warrant the
conclusion that, in the space occupied by St. Helena, there had been a
greater exertion of creative power than in the spaces of equal area
occupied by the new adjacent lands; because, within the period in which
St. Helena had acquired its peculiar vegetation, each of the spots
supposed to be subsequently converted into land may have been the
birth-place of a great number of _marine_ animals and plants, which may
have had time to scatter themselves far and wide over the southern
Atlantic.

_Why distinct provinces not more blended._--Perhaps it may be objected
to some parts of the foregoing train of reasoning, that during the lapse
of past ages, especially during many partial revolutions of the globe of
comparatively modern date, different zoological and botanical provinces
ought to have become more confounded and blended together--that the
distribution of species approaches too nearly to what might have been
expected, if animals and plants had been introduced into the globe when
its physical geography had already assumed the features which it now
wears; whereas we know that, in certain districts, considerable
geographical changes have taken place since species identical with those
now in being were created.

_Brocchi's speculations on loss of species._--These and many kindred
topics cannot be fully discussed until we have considered, not merely
the general laws which may regulate the first introduction of species,
but those which may limit their _duration_ on the earth. Brocchi
remarked, when hazarding some interesting conjectures respecting "the
loss of species," that a