onveyed they would find fit food. It is true that
Cirrhipeds and Lamellibranchs, subsisting on the minute creatures which
everywhere people the sea, would also find fit food. But the chances of
early colonization are in favour of species which, multiplying by
agamogenesis, can people a whole shore from a single germ; and against
species which, multiplying only by gamogenesis, must be introduced in
considerable numbers that some may propagate. Thus we infer that the
earliest traces of life left in the sedimentary deposits near these new
shores, will be traces of life as humble as that indicated in the most
ancient rocks of Great Britain and Ireland. Imagine now that the
processes above indicated, continue--that the emerging lands become
wider in extent, and fringed by higher and more varied shores; and that
there still go on those ocean-currents which, at long intervals, convey
from far distant shores immigrant forms of life. What will result? Lapse
of time will of course favour the introduction of such new forms:
admitting, as it must, of those combinations of fit conditions, which
can occur only after long intervals. Moreover, the increasing area of
the islands, individually and as a group, implies increasing length of
coast, and therefore a longer line of contact with the streams and waves
which bring drifting masses bearing germs of fresh life. And once more,
the comparatively-varied shores, presenting physical conditions which
change from mile to mile, will furnish suitable habitats for more
numerous species. So that as the elevation proceeds, three causes
conspire to introduce additional marine plants and animals. To what
classes will the increasing Fauna be for a long period confined? Of
course, to classes of which individuals, or their germs, are most liable
to be carried far away from their native shores by floating sea-weed or
drift-wood; to classes which are also least likely to perish in transit,
or from change of climate; and to those which can best subsist around
coasts comparatively bare of life. Evidently then, corals, annelids,
inferior molluscs, and crustaceans of low grade, will chiefly constitute
the early Fauna. The large predatory members of these classes, will be
later in establishing themselves; both because the new shores must first
become well peopled by the creatures they prey on, and because, being
more complex, they, or their ova, must be less likely to survive the
journey, and the change of co