tage in its
development.

The next important stage is also very clearly exhibited in nature, and
is more or less clearly reproduced in the embryonic development of all
animals. We may imagine that the age of microbes was succeeded by an age
of these many-celled larger bodies, and the struggle for life entered
upon a new phase. The great principle we have already recognised came
into play once more. Large numbers of the many-celled bodies shrank from
the field of battle, and adopted the method of the plant. They rooted
themselves to the floor of the ocean, and developed long arms or lashes
for creating a whirlpool movement in the water, and thus bringing the
food into their open mouths. Forfeiting mobility, they have, like the
plant, forfeited the greater possibilities of progress, and they remain
flowering to-day on the floors of our waters, recalling the next phase
in the evolution of early life. Such are the hydra, the polyp, the
coral, and the sea-anemone. It is not singular that earlier observers
could not detect that they were animals, and they were long known in
science as "animal-plants" (Zoophytes).

When we look to the common structure of these animals, to find the
ancestral type, we must ignore the nerve and muscle-cells which they
have developed in some degree. Fundamentally, their body consists of a
pouch, with an open mouth, the sides of the pouch consisting of a double
layer of cells. In this we have a clue to the next stage of animal
development. Take a soft india-rubber ball to represent the first
many-celled animal. Press in one half of the ball close upon the other,
narrow the mouth, and you have something like the body-structure of the
coral and hydra. As this is the course of embryonic development, and as
it is so well retained in the lowest groups of the many-celled animals,
we take it to be the next stage. The reason for it will become clear on
reflection. Division of labour naturally takes place in a colony, and in
that way certain cells in the primitive body were confined to the work
of digestion. It would be an obvious advantage for these to retire into
the interior, leaving the whole external surface free for the adjustment
of the animal's relations to the outer world.

Again we must refrain from following in detail the development of
this new world of life which branches off in the Archaean ocean. The
evolution of the Corals alone would be a lengthy and interesting
story. But a word must be