ied Cambrian
skeletons. With it, swimming in the water, are smaller members of the
same family, which come nearer to our familiar small Crustacea.

Shell-fish are the next most conspicuous inhabitants. Molluscs are
already well represented, but the more numerous are the more elementary
Brachiopods ("lampshells"), which come next to the Trilobites in number
and variety. Worms (or Annelids) wind in and out of the mud, leaving
their tracks and tubes for later ages. Strange ball or cup-shaped little
animals, with a hard frame, mounted on stony stalks and waving irregular
arms to draw in the food-bearing water, are the earliest representatives
of the Echinoderms. Some of these Cystids will presently blossom into
the wonderful sea-lily population of the next age, some are already
quitting their stalks, to become the free-moving star-fish, of which
a primitive specimen has been found in the later Cambrian. Large
jelly-fishes (of which casts are preserved) swim in the water;
coral-animals lay their rocky foundations, but do not as yet form reefs;
coarse sponges rise from the floor; and myriads of tiny Radiolaria and
Thalamophores, with shells of flint and lime, float at the surface or at
various depths.

This slight sketch of the Cambrian population shows us that living
things had already reached a high level of development. Their story
evidently goes back, for millions of years, deep into those mists of the
Archaean age which we were unable to penetrate. We turn therefore to
the zoologist to learn what he can tell us of the origin and
family-relations of these Cambrian animals, and will afterwards see how
they are climbing to higher levels under the eye of the geologist.

At the basis of the living world of to-day is a vast population of
minute, generally microscopic, animals and plants, which are popularly
known as "microbes." Each consists, in scientific language, of one cell.
It is now well known that the bodies of the larger animals and plants
are made up of millions of these units of living matter, or cells--the
atoms of the organic world--and I need not enlarge on it. But even a
single cell lends itself to infinite variety of shape, and we have to
penetrate to the very lowest level of this luxuriant world of one-celled
organisms to obtain some idea of the most primitive living things.
Properly speaking, there were no "first living things." It cannot be
doubted by any student of nature that the microbe developed so grad